Imperial Home Page -> Repair -> Brakes -> Brake Bleeding
How to Bench Bleed your Master Cylinder:
After successfully rebuilding a master cylinder (or when fitting a new one) it is a good idea to bench bleed the MC before installing it in the car. This will fill the master cylinder with fresh air-free fluid and in effect "prime" it for integration with your car's hydraulic brake system, making your on-the-car brake bleeding a little easier.
The basic idea is to create mini hydraulic system on your bench. You can use old brake line fittings if you have them but I didn't so I purchased a master cylinder bleed kit from my local auto parts store. A new master cylinder may include the necessary parts already. The kit should consist of a number of plastic fittings which are designed to fit in the outlets (usually two, front and rear) of your master cylinder. One end of the fittings will be threaded and the other will have a round smooth hose adapter. Thread the appropriate fittings into the outlets on your master cylinder. The kit will also contain a length of plastic hose. My kit had black hose but I found some spare clear hose and used it instead - this will allow viewing of the air bubbles passing through the hose. My kit also had a plastic clip used to hold the two pieces of hose together and clamping to the edge of the fluid reservoir.
Clamp the cylinder firmly in a bench vise so that the cylinder area is level. If it is pointing upwards the air will remain in the cylinder. Slide the hoses onto the fittings. Cut the hoses just long enough to reach into the reservoirs and remain submerged - the shorter the length of hose the better. Place the other ends of the hoses into the fluid reservoirs (you'll probably have hold them in place somehow because once you start pumping they'll want to flail around in the air and spray brake fluid everywhere). If you can get a helper that is ideal.
Fill the reservoirs with new brake fluid, and pump the piston slowly and evenly, full strokes. I used a big Phillips screwdriver because its tip doesn't damage the piston and the handle gives you something to lean against. I would not worry about the fluid getting recirculated because it is brand new and you are creating a temporary hydraulic circuit with the hoses which will not become contaminated with dirt. The air which is still in the system at this point will be bled out. Pump the cylinder until the tubing contains no more air bubbles and no new ones emerge from the master cylinder on the down stroke. On my master cylinder this took about 15 strokes some may require more, some less. Keep going until the air stops as this will make the task of bleeding the brakes in the car much simpler. When all the air is out, mount the cylinder in the car. Here you have to be careful to prevent the fluid still in the hoses from spaying your car and any other painted objects nearby - brake fluid is a great paint remover! If you decide to remove the hoses before installing on the car, make sure to plug up the fittings - I just held the hoses up while transferring from bench to car. Once the master cylinder is mounted in the car, remove the fittings and connect the brake lines. You'll lose a little fluid but the check valves in the cylinder should stop any major leakage. Now you are ready to bleed the brakes in your car and it should be a lot easier than if this step was avoided.
Tip from Mikey:
In a word about Mity Vacs, as far as brake bleeding: THEY SUCK! And no pun intended either. They are great for checking vacuum advances, heater controls or actuators, lots of vacuum operated or controlled devices. We never had the degree of success with Mity Vac bleeding that we did with pressure bleeding.
This was over the course of several years, bleeding brakes on cars, trucks, industrial equipment....anything with hydraulic brakes. One problem is that with a Mity Vac, you have the potential problem of pulling air into the system as well as pulling brake fluid from the master cylinder. Another difficulty is getting some of the mity vacs to work as well if you inadvertently get brake fluid into it.
We used a pressure bleeder that was nearly identical to the garden sprayer type that was mentioned earlier. It was a commercial pump and canister, and a 0 - 15 psi gauge on it, a shut off valve, and a length of hose and adapter that was made up to attach to the fittings that were installed on the various master cylinder covers we had for the different master cylinders we worked with.
The one caveat with these , or any pressure bleeder - don't let the fluid level get too low or you just went from pressure bleeding to pressure aerating in a very short time.
Addition from Dick:
A fundamental problem with the vacuum extraction type of brake bleeder such as the Mity Vac is that they rely on an air tight seal around the threads of the bleeder screw to achieve a vacuum seal. My experience with these is that this is very hard to get, most of the time, so that the vacuum jar gets bubbles on every stroke, and you never know when the lines are clear of air.
I have an expensive (Snap-on) commercially made brake pressure bleeder, but I've found it just as convenient to supply pressure to the reservoir directly from my air compressor, with the regulator set to 30 PSI to overcome the check valve in the master cylinder, and just bleed off fluid until I see clear new fluid coming down into the jar. I have to stop and top up the master cylinder each two wheels or so to avoid drawing in air, but that is a small price to pay for a perfect bleed every time. I have one spare master cylinder cap for each of the types I have worked on, with the vent holes plugged and a motorcycle type (metal screw in) tire valve installed. My air hose chuck has a latch-on type tire chuck, so I just clip it on the cap, set the pressure, and off I go, merrily riding around on my creeper!
Question from Gary (concerning which fluid to use after you bleed your brakes):
Any adverse reaction to using dot5 in place of dot 3? I recently replaced the entire brake system including master cylinder, brake lines, calipers and rebuilt rear brake assembly. The system was "sterile" before adding dot5. After about two months (maybe sooner) I developed a leak in both the front brake calipers (BUDD). In the seam that joins both sides of the caliper together on both calipers. Hence, the fluid leaked and completely ruined the pads as they are soaked through. Could this be caused by the use of dot5? In that time the car has only been driven about 75 miles. Napa is replacing the front calipers and the pads. I don't want to introduce them to dot5 if that is the reason the seals failed in the calipers. If the replies come back negative in dot5 I will first have to flush out the existing dot5 and replace with dot3 or 4.
Replies:
From Jack:
I rebuilt the complete brake system on my 61 five years ago, using silicone brake fluid. I noticed a slow, constant loss of brake fluid (filled up master twice a year) with no signs of a leak. I lost my stop light switch (mounted on the master cylinder) I replaced it with a brake pedal mounted stoplight switch rerouting the two stoplight wires. The ability of silicone brake fluid to retain air was taken care of by slowly heating the silicone brake fluid on my stove to release the air before putting it into the system. (make sure your wife or girlfriend is not around) My brake pedal is high and firm. Now, five years later I wouldn't do it any other way. Putting brake fluid in my 61 is a pain the a** because of the location of the master and booster. Not worrying about spilling brake fluid on my paint is one problem I don't need. Silicone brake fluid will not harm paint.
From John:
I have converted a couple of my cars (a '60 and a '63) over to D0T5 when I rebuilt the brake systems. Based on my experience, I agree that DOT5 is the way to go and would never go back to the glycol fluids. I've noticed that DOT5 is prone to formation of tiny air bubbles if you agitate it or pour it fast from the bottle. This is why it is difficult to get hard pedal (especially in the pre-'63 cars with the dual front wheel cylinders that are cocked off vertical -- can be a b*tch to bleed no matter what fluid you are using). After a while the tiny bubbles combine to form larger ones and you get more pedal travel. I hadn't thought of trying to de-gas the fluid by heating it up so will have to try this on the '60 since it's due for a re-bleed (the pedal is about 3/4 the way to the floor on a hard stop). I've, also found with DOT 5 that pressure bleeding works better than manual bleeding (if you manual bleed it has to been done s-l-o-w-l-y) but have had lousy results with vacuum bleeding. I have had no problems with leaks and the hydraulic brake light switch is still working fine after 2 years. The '63 was a slam dunk needing no special bleeding technique and I had firm, high pedal on the 1st try with manual bleeding. About 5-6 years now and the master cylinder looks brand new.
From Bill:
I have always been told that to use the Silicone brake fluid, the system must be entirely new including the master cylinder. Seems like you did that so I would think you may have had a pair of faulty calipers. Myself, I would stick with DOT 3 and not take the chance. Not sure what you should do to switch back short of replacing all components again.
From Bill:
DOT 5 will is unforgiving, it will find every way to leak out of a system. To the extent that some car manufacturers do not recommend it any more. This stuff is used also in hydraulic clutch mechanisms. It also has been know to destroy brake light switches and to boil at lower temperature levels than other fluids. Today I have 5 cars with it and am wondering if I shouldn't go back and change it. Some of my cars have had it for 10 years with only two problems. 1. I had to reroute a brake line because it was to close to the exhaust and I would get a soft pedal after long driving. Moving it solved the problem, I guess it was boiling in the line. 2. I have had brake switches fail in my older cars which I understand is a common problem with DOT 5. Now I preload the switches with DOT 3 or 4. No more problem there.
From Brett:
When converting to Silicon DOT 5 brake fluid, ALL RUBBER parts need to be replaced as the DOT 5 & DOT 3 fluids react to each other. I have heard this issue mentioned before, but "How to Restore Your Collector Car" by Tom Brownell (©1984, ISBN 0-87938-174-4) tells a different story... The book explains that DOT5 was developed by Dow Corning as a solution to polyglycol (DOT3). After all, the military was an immediate customer with many vehicles that sit for long periods of time... even the DOT3 in trucks parked in Arizona absorbed 8.4% water over two years. Direct from the book: "... it is possible to gain most of the water-free advantage of silicone brake fluid by flush-filling the brake system with silicone. Since silicone fluid is compatible, though not miscible (i.e. will not mix), with standard polyglycol brake fluid, the glycol residue that remains in the system will not affect the performance of silicone fluid." "...siphon or scoop all the old brake fluid from the master cylinder and wipe the chamber or chambers with a clean, dry cloth. Next, refill the master cylinder with DOT5 silicone brake fluid. Allow several minutes for the fluid to settle so that air bubbles can escape, then purge the system of its remaining polyglycol fluid and bleed any air that is trapped in the lines." Bleed the system according to your shop manual. You'll see a change of color when the fresh DOT5 comes through. "Although flush-filling a car's brake system with silicone fluid reduces corrosion, it is impossible to remove all the glycol fluid by this method. A better approach, especially if the brake system need maintenance anyway, is to dismantle and rebuild the wheel and master cylinders, replace the brake shoes and corroded lines, then refill the reconditioned system with fresh silicone fluid." I doubt the publishers of this popular book or their attorneys would allow the instructions above if there was any chance DOT3 & DOT5 in the same system may cause a brake failure. In addition, I have converted at least four of my own cars (in the 1957-61 range) to DOT5 using the method listed here without any problems. In fact I haven't had to replace any wheel cylinders once silicone was in the system... six years. The only issue DOT5 has caused me is the premature failure of hydraulic stop light switches.
Question from Mike (about replacement bleeder screws):
In one of the various magazines, perhaps one of the Mopar car magazines, I have seen an advertisement for a replacement for the standard type bleeder screw that has a check valve built into it. when tightened it acts like any other bleeder screw, when loosened the check valve keeps air from going back into the system when the pedal is released but allows fluid to escape when the pedal is depressed. Has anyone else heard of these or used them, sounds like a viable alternative to me, sort of like the old method of the tubing into the jar of brake fluid.
Reply from Dan:
They're called Russell speed bleeders. They are about $7 apiece, but they really do work! To bleed one of them, you just loosen it up and pump the brakes until you are happy. There is a plunger inside that lets fluid out on the down stroke, and seals back up on the upstroke. I don't know if there is any longevity issues with them, but there are people on the Firebird/Camaro list that have had them for at least a year with no problems. You can get them from summit or jegs.
Question from Tim (1956):
Stupid question to all you pros out there. Should the car be running to bleed the brakes?? I bled them yesterday after replacing front brake cylinders but I had the car running. I still don't have the pedal I should. The petal goes quite far down and I did adjust the brake lining like the manual says.
Replies:
From Paul:
Brake bleeding is usually done with the engine off. I can't think of any benefit there would be to having the engine running. I do not know what the effect of having power assist would be during the bleeding operation, but I do know that while bleeding the brakes, all that you are doing is expelling the air from the system. Done correctly, you should have pedal with the engine running or not. With the engine running it might create exhaust fumes for the person who is under the car opening the bleeders.
Fill the master cylinder, press the pedal, WHILE IT IS DOWN open the bleeder, expel the fluid, close the bleeder, release the pedal. Following this procedure several times at each wheel cylinder, and doing the them in the order outlined in the shop manual will eliminate the air from the system.
While bleeding the wheel cylinder, it is best to use a bleeder hose in a jar with some clean brake fluid in the bottom so that you can watch the bubbles leave the system. Once the bubbles are no longer visible, the air is gone from the system. Check the level in the master cylinder often. Do not pour fluid from the jar into the master cylinder. Always use new fluid from the fluid container.
Some shops recommend pumping the brake pedal with the bleeder open as long as the bleeder hose is in the jar of fluid to expel the air more efficiently. I have not tried this.
Another option is the use of a pressure bleeder, which I think would be one of the best ways to do this job.
Center Plane Brakes (1956 through 1962) they must be absolutely free of air in the system, adjusted 100% correctly, and in good condition in order to function right. There is little room for error here, so be sure to read the shop manual thoroughly.
From Steve:
Having the car running is not necessary to bleed the brakes. You may have to bleed the rear wheels too to get all the air out of the system. Bleed them in this order-RR-LR-RF-LF.
Question from Tom (1956):
I will have to bleed the brakes on my '56 very soon and I was wondering what the difference is between "modern" brake fluid and the older silicone type. When I did the first brake job, I sent away for the silicone brake fluid from a specialty shop (Andy Bernbaum, I think) and it cost about $16.00 per quart, plus shipping. Is that the right way to do it, or can I use the DOT 3 fluid available from the local supply store?
Replies:
From Tony:
I can't pretend to be anybody's authority, but I switched my '61 convertible to silicone brake fluid specifically because of its non-corrosiveness (NEVER let older-style brake fluid get on your paint!) and its indifference to water (older-style fluid absorbs water, encouraging rust and reducing brake-effectiveness) - My '61 coupe's brakes always needed something or another to keep them from getting spongy - I've had zero problems with my convertible. It strikes me as a no-brainer - swap it out properly and you'll never look back!
From George:
Yes I did too. More stability. A little more pressure needed when applying the brake. But better for the car. No water, therefore, less corrosion. Go ahead and do it. Never mix the silicone with anything else!! I did mine after a total replacement of the braking system.
From Brett:
I agree with Tony. Regular DOT3 fluid can absorb tremendous amounts of moisture. This moisture will rust out the wheel cylinders on any car that sits for a period of time. This is a real problem here in Florida because of the humidity. DOT5, or silicone fluid, was developed by the military for vehicles that go through periods of disuse. It's also non-corrosive as a bonus. If you drive your car frequently (several miles, a few times per week), then the heat build-up from regular use will dissipate moisture in your brake lines. There is also DOT4 fluid that is supposed to absorb less moisture than the DOT3 does. Some people don't like the "feel" of DOT5. They say it's a bit spongy. DOT5 can also cause connection problems with the hydraulic brake-light switches that are on 50's and early 60's Imperials. But, these problems are rather minor when compared to the cost of a full set of shoes and wheel cylinders.
Question from Tony (1957)
How do you bleed the master cylinder ? On mine (57) there's no bleeder screw...
Replies:
From Leo:
Usually you get the bleeder tubes with the rebuilt master-cylinder. Put the master-cylinder in a vise, attach a tube from the outlet port or ports into the reservoir. Fill the reservoir with brake fluid and keep depressing the piston all of the way with a dowel until no more bubbles appear in the fluid. This only applies to a new or rebuilt master-cylinder. On used ones, only depress the piston part way, otherwise the corrosion in the un-traveled portion of the cylinder will damage the piston cups.
From Steve:
You attach a plastic tube from the brake line connection and route it back into the brake fluid reservoir. There are kits available in most part stores for about $5 with all the different connectors and the plastic tube. These kits are made by a company called "Help". Once attached use something like a wooden dowel to cycle the master cylinder. Do this with the master cylinder clamped down to a table and as close to level as you can get. Cycle the master cylinder until all the bubbles have disappeared (I usually do this for about five minutes even though the bubbles cease around one minute. Leave the hoses in place and install the master cylinder in the car then quickly switch over to the regular brake line. Start bleeding the wheel cylinders from the furthest to the closest (passenger rear, driver rear, passenger front, driver front). Be very careful not to let the master cylinder run dry! If your 57 is like my 59 then it is very hard to tell how much fluid is in there because the power brake booster blocks the view. If the master cylinder does go dry you have to start all over again. I usually repeat the bleed process for the wheel cylinders three or four times to make sure I have gotten all the bubbles.
From Jack:
Before you adjust the brakes try stepping on the brake pedal a few times to center the brake shoes. Sounds also like you still have air in the system. I had a rough time getting my brake pedal up after the last brake job. It was a total brake job, lines, wheel cylinders, master, and hoses. I bench bled the master before I installed it. I went through the whole cycle of bleeding all wheel cylinders to no avail. Finally in disgust I re bled the master at the line going in and to my surprise I got a hiss of air. The pedal came right up to the top. To bleed a master on a car you must have someone pump up, then hold the brake pedal down while you loosen and tighten the fitting holding the brake line going into the master cylinder. The same way you would bleed a wheel cylinder by cracking open then shutting the bleeder valve.
From Marc:
If you want, you can also run a line into a can/jar of brake fluid, and then when you step on the pedal, you can watch the air bubbles come out( place the hose and can/jar where you can see it) and as you let off the pedal it sucks fluid back into the system, therefore you don't need another person, and there is no chance of air getting back into the system . This usually creates the hardest pedal I've found.
Question from Timothy (1960):
I've been busy over the last three weeks puttering away on a brake job on the sixty in my "spare" time (I have none hence 3 weeks for a 1.5 day job...). Here's the situation... No pedal! no matter how many time you pump it. We have replaced the front shoes and hoses, rebuild the front wheel cylinders, took apart the back drums and realized that the have already been done in the not to distant past and left it at that for the moment and adjusted everything, then gave it a try. When that didn't work we checked for leaks and air and decided that the master cylinder was leaking out the back. Yanked it and rebuilt it, reinstalled, re-bled, readjusted, and still nothing. The car slows down and will sort of stop if it's not on high idle or pointed downhill. I have a new rear hose which I am still meaning to install but both BJ and I can't see how a hose that's not leaking could cause the problem. I am rather frustrated and having trouble coming up repair ideas that don't include a stick of dynamite. Anybody got any less volatile ideas???
Replies:
From Bill:
Are these power brakes? Did you bench bleed the master cylinder properly before reinstalling? With every thing else you have done, I would have to think your problem is in the master cylinder or power booster area.
From Dietmar:
You will have a master cylinder defect or a leak. First check if you loose brake fluid, if yes find where (front junction, wheel cylinders) If not check the master cylinder piston. Mostly while ventilating the system people push the pedal too far. The old piston goes through the corroded area of the cylinder and get damaged. Then you need a rebuild kit for that or a new complete system with a NEW OUTLET since the sixties are made of very week metal. They will only fit once.
From Scavenger:
One sure way of telling if you are getting any action from the hydraulic system would be to remove a drum and have a partner observe at the brake cylinder while you GENTLY apply the brake pedal. I overhauled the brakes on my '57, and it took several trips around the car bleeding the brakes before I got a substantial "pedal". I would also suggest adjusting the brakes so they are just barely dragging, then bleed them Thoroughly. This whole process requires a lot of patience. It also helps if you have an assistant helping you. One person inside operating the brake pedal, another at the wheel being bled opening and closing the bleeder valve on wheel cylinder. Also, as someone else suggested, check the adjustment at brake pedal.
Question from Luke (1960):
I'm reconditioning my rear brakes at the moment and was wondering if any one has had any experience with the 'bleeding' part. I haven't got to that bit yet but I'm not looking forward to dealing with that pesky brake fluid reservoir, it looks hard to top up as you're bleeding the system. Is there a cheat to this one? Also what's best to clean all the years of old fluid and grime off the brake parts?
Replies:
From Elijah:
A really good cleaner is "Brake Parts Cleaner." It's available at any parts store, Wal-Mart, K-Mart, etc. here in the U.S. I'm sure you can find it in your part of the world too. I've found it very useful for many other things besides cleaning brake parts.
From Bob:
You didn't ask, but seriously think of using silicone fluid when you're done. My research indicates there's no downside to this and many advantages - Somebody said that there is supposed to be a "mushy" feel to silicone brake-fluid, but _I've_ never experienced it. It's really, really good. No downside.
From Frank:
Silicone is good, but not compatible with standard brake fluid. ALL of the old fluid must be removed. The best way to do that is to rebuild the wheel cylinders / calipers and the master cylinder. Then bleed the lines thoroughly. Silicone is more stable and does not have an affinity for water like regular fluid, so it is much better.
From Brett:
You'll need to bleed the brakes in sequence to avoid trapping air... right rear, left rear, right front lower, right front upper, left front lower, left front upper. As far as the reservoir, I use a plastic cone-like nipple that screws to the top of the brake fluid can. (Sort of like what's on top of a plastic catsup squirt bottle) Then I attach an 8" piece of rubber hose and fit and small "L" shaped piece of metal brake line on the opposite end of the hose. This allows me to get the "L" shaped brake line piece under the booster and into the reservoir... I can then tip the brake fluid can so the liquid flows through the hose, brake line part and into the master cylinder.
Tip and Question from John (1960):
I've been having trouble getting the air out of the braking system in my '60 Crown convertible -- fresh rebuild (all new, cylinders and hoses) using DOT 5 silicone fluid. Silicone doesn't absorb water like the glycol based fluids but it loves to retain air bubbles which makes thorough bleeding difficult. The cockeyed dual front cylinders with the coupling tube make matters worse. Started with my "Vacula" vacuum bleeder with no luck -- pedal to the floor with not even enough pressure to keep the hydraulic brake light switch on. Kept sucking an endless trail of bubbles (even with the sloppy bleeder screw threads sealed with silicone grease). A couple tries at manual bleeding with a tube in a catch jar seemed to improve things a bit. Having my wife pump the brake pedal while I was under the car opening and closing (on the up stroke to prevent air bubbles from sucking back) the bleeder screws helped a bit more but still too spongy. Keeping the master cylinder topped off (with medicine dropper) is a real joy with the cruise control servo and the booster blocking access and line of sight. God help you if you let her run dry and have to start all over again! So, out of desperation, I bought a KD shop quality pressure bleeder tank (about $200). I have enough cars (actually, way too many) and do all my own brake jobs so I figured in the long run it would be worth it -- if it really worked! It's a pressure vessel with a bladder in the middle. In one end you pour in fluid, in the other end you pump in 15 lbs of air. I had to rig up a spare master cylinder cover with an inlet tube to connect with the bleeder tank -- the standard master cylinder adapters will not clear the power brake booster (nor will they plug the 2.75 inch reservoir diameter!). With the tank connected to the master cylinder you just crawl under the car and open one screw at a time, letting the fluid squirt into a catch jar. After one pass around the car...AMAZING...it really worked great. Good pedal in about 20 minutes of effort.
Replies:
From Ed:
Well, that's one tool I lucked out on. A man I know who always goes to auctions bought a bunch of them that were old army models from the 60's -- for scrap aluminum! He gave me two; I gave one to my brother and kept one. I had to buy us each new bladders, for about twenty or thirty bucks each, and I was feeling like I spent too much on the deal until now. I'll definitely tell my mom to keep her old master cylinder cap from her '65 when she gets the new cylinder, so I can make a bleeder cap from it. I do have trouble with that technique with those silly plastic MC lids of some of the later model cars....
From John:
I have a K-D pressure bleeder tank that is similar to if not the same as the Snap-0n tank. The tanks are a great tool and if used correctly do a much better job than vacuum bleeders, check valve bleeders, etc (I've tried them all). I have a few cars with the master cylinder (single round 2-3/4" bowl) mounted under the power brake booster and none of the commercially available adapters I have would fit. I made my own MC adapter by soldering a length of 1/4" copper tubing through a scrap MC cap. A short length of clear plastic hose connects the tube to the bleeder tank. To get a good seal between the cap and the master cylinder bowl, I use a gasket that was made to seal a toilet tank to a toilet bowl and clamp the cap down with a rubber washer under the cap bolt. I tested this at 25 PSI with no leaks so nominal bleeding at 15 PSI is no problem. You don't say what kind of master cylinder you have so I'm not sure if my solution for the round MCs will work for your car. Don't run with any more pressure than 15 lbs and dial down to 10 or 5 lbs if you needed to stop leaks. The lower pressure will just slow down the bleeding time a bit. Regarding corrosion, DOT 3 glycol based fluids will eat through anything given enough time and they suck water so will pit MC and WC bores on cars that sit or fluid not changed often. I've seen some nasty looking used bleeder tanks for sale on E-Bay and elsewhere. The bleeder tank is a pressure vessel so the tank is heavy gauge metal (stainless?). A plastic or composite tank that could withstand up to 45 PSI (at which point the pressure relief valve goes) without blowing up like a balloon would be bulky and/or expensive. To get away from the corrosion problems I use DOT 5 silicone in my bleeder tank and I'm switching all my cars over to DOT 5 as they need brake system rebuilds. I've had DOT 5 in one of my '63s for over 5 years and the MC both inside and outside show no signs of rust or other crud.
Follow-up question from Jim:
Can you tell me how you modify the m/c cover to work? I have a bleeder that I can rarely use because of fitment issues.
Replies:
From Ed:
I didn't see anybody else answer this, so I'll try (I don't always have good luck with it, that's why I was waiting.). I take the old master cylinder cap, find a fitting...lessee, it's like a hose fitting with a threaded end; sometimes I use old brake bleeder screws... and drill a hole in the cap just smaller than the fitting I'll be using. If it's thick steel, I might have to borrow a tap, but so far I've always been able to get the fitting threaded in with brute force. Sometimes I use JB Weld for a combination sealer and strengthener. Then, so long as the cap fits securely [which is the problem with the later model plastic mc's] I just clamp the hose from the pressure bleeder to the fitting, install the cap on the master cylinder like normal, and turn on the flow of pressurized brake fluid. I bleed all the air I can out of the bleeder and it's line first. I've mentioned to my mom to make sure she keeps the cap from her master cylinder when she gets the new cylinder so I can get her set up this way. Do the other "pressure brake bleeders" do it any differently? I should go to a brake shop and ask them, I suppose.
From Paul:
Pressure bleeding brakes is out. Vacuum sucking brakes is in. Get a vacuum brake bleeder for about $25 from any parts store, stick it on the bleeder of your choice and start squeezing the handle. It is so much easier.
Question from Mark (1966):
What is the proper brake bleeding sequence for a '66 crown 4 door? My Imperial's brake system is just about totally rebuilt with only the master left to replace and it is sitting on the work bench. All units are new, not rebuilt (all other brake cylinders and hoses have already been replaced).
Replies:
From Demetrios:
Start from the drum furthest from the master cylinder (rear right) and continue with the next furthest (left rear), then front right.
From Dick:
But: Bench bleed the master cylinder first!
Question from Don (1966):
I just put new brake shoes, good drums and rebuilt the wheel cylinders on my 66 Crown Coupe. The original problem was very low brake pedal-almost on the floor. I power bled the system after all the work and with the car sitting there the pedal was rock hard and very high. When I started the car and stepper on the brake pedal it went almost to the floor-as in before the brakes were done. One thing I found when I was doing the brakes was that the rear wheel cylinders were seized solid-I could not free them up even with a hammer and punch. I ended up replacing them both. When I bled the brakes using a pressure bleeder, the front wheel cylinders squirted out a healthy flow of brake fluid while the rears just dribbled a small steady amount. Is this normal? Or is it indicative of a restriction in the system as in the single brake hose at the rear axle?
Replies:
From Phil:
I'd check the rubber brake line that goes to the rear axle. I've had the rubber lines go bad in internally before on different cars. Once I had one go so bad, it would lock the wheel temporarily, after applying the brakes. To look at it on the outside, you couldn't tell anything was wrong on the outside. But the inside of the line had somehow with age, managed to swell shut and also, become clogged with small bits of corrosion. You should have the same amount of flow out of the rear as you do the front when bleeding. If changing the rubber line doesn't help, check all the lines going to the rear of the car for dents or bends, anything that could cause a restriction.
From Bill:
The flow of brake fluid should be pretty much the same front & rear. Also, too many times the brake hoses are ignored when repairing the brake system. I never assume they are OK just because they "look" good on the outside. If in doubt as to how long they have been on the car, replace them. In addition, when opening a brake system for repairs I always bleed out all the brake fluid, then fill the system with denatured alcohol and continue to bleed that out until the fluid coming out at each wheel is clear or clean looking. Then proceed to do your usual rebuild or replacing of wheel cylinders, master cylinder, and brake hoses.
From John:
If the rear cylinders were seized for some time, you may find that the rear lines are full of rust also. Either take off & clean or replace them as well as the rear hose. If the pedal still goes to the floor after this, most likely the master cylinder is bad.
Question from Don (1967):
I have got a frustrating situation with the brakes on my '67 LeBaron. Firstly, she has a re-built (her own-no exchange parts) booster, master cylinder and left front caliper. I had a problem with fluid leaking our of the master, so back it went and they quickly re-did it - turned out that the actual casing wasn't flat where the lid touches, so a file and a few moments solved that problem (I hope!!!) Now I've got absolutely no leaks but still have a very low pedal. They've been bleed with the master being bench-bleed prior to installation. FYI: pads, shoes, rear cylinders, rotors and drums have been inspected by two different mechanics and reported to be all good.
Replies:
From Mike:
Seems like everything has been checked, and I will assume the rear drum to shoe clearance is ok, so by any chance did the pushrod that comes out of the booster into the master cylinder get changed or adjusted - I don't know if yours has an adjustment but my 62 does and it is very important. It affects how far the pedal and booster travel until they start to move the m cylinder piston.
From Bill:
As simple as it may seem but have the mechanics adjusted the star wheels on the rear brakes? This usually will tighten up the shoes and give you a better pedal. Even though they are self adjusting, sometimes they are not working the best and only adjust when braking in reverse. The bench bleed on the master cylinder is critical, hopefully they did it right.
Question from Allen (1969):
I had the power brake booster on my 69 replaced for the same reasons - hissing sound and loss of braking power. After a caliper rebuild and turning of the disks on front, and adjustment of the rear brakes, my pedal travel seems too long also, and they are VERY grabby. My gray haired mechanic says that's how those all were in that day. True? I find when I take out my new car, I have to use considerable force in comparison to stop it. Once you are used to the Imp's brakes, though, but for the pedal travel, they are wonderful when you consider the heft of the car.
Reply from Steve:
It's a situation worth monitoring/investigating. My power booster died in 95. So I converted to dual circuit at the same time. I believe in opening through the brake system up as little as possible. I just don't think you want that pedal travel to be too long. My 64s brakes are no longer "self adjusting", so I have to lift it and turn the clockwork every so often. That's the usual reason for long pedal travel, along with air in the system. If there's air in the lines or the MC you'll have long travel, and perhaps grabbiness. If the shoes/and or linings are new, you'll have grabbiness for a while. So My (gray haired) experience basically agrees. Also, it's a great time to consider switching to silicon brake fluid IMHO. I did three years ago, no problems since.
Question from Elijah (1971):
I have a question regarding the braking system on my '71 Imperial. Over the past month or so, I've been experiencing a slow loss of brake fluid. When I first noticed this phenomenon, I took the car to a recommended shop, where they replaced one front brake hose and the two rear wheel cylinders. However, since that time, the fluid loss has continued. It looks to me at this point like the fluid is actually being pushed over the top of the master cylinder -- the outside of the master cylinder is damp, and there are obvious drip spots beneath it. What are possible causes and solutions here?
Reply from Dick:
Sounds to me like you have a combination of pressure buildup in your reservoir plus a poor seal at the lid gasket. Perhaps the system was not completely bled of all air when the work was done. Is the pedal soft and spongy, or high and firm? If the former, I would take it back to the brake shop and have them power bleed it. In any case, they should be concerned enough to help you figure it out. Another place to look for mysteriously missing brake fluid (defined as fluid missing from reservoir but no sign of leakage anywhere) is the vacuum line to the intake manifold. Pull it off and sniff for the characteristic alcohol smell of brake fluid (assuming you are running dot-3 or dot-4 fluid.) If you are running dot-5 (silicon) fluid, you are out of luck here, it is odorless. In any case, fluid in the vacuum line always means its power brake booster time, sorry.
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