Hi guys, I'm having a problem with my brakes on my 1938 Plymouth sedan and I would love to get input of you to help fix my carproblem. The car has all original parts, so no difference with all brake parts. What happened: 2 weeks ago my brakes were gone just before a 90 degrees bend so that wasn't very nice. We've looked for leaks but there were not and the brake fluid in the master cilinder was still at maximum so we had to look further. After searching we came to the conclusion thatit had to be my master brake cilinder so I removed it and the cup was damaged and the cilinder lining had been sanded with probably 80 sandpaper by the previous owner a couple of years ago. We were amazed that it had been working for the 2 years that I have been driving it. I ordered a new master brake cilinder and mounted the part. Now I have all main parts changed by new parts because last year I had already changed the wheel brake cilinders for brand new ones. I filled the brake system with fluid and started bleeding the system. The problem: Somehow, after all the air is out I still get brake pressure after the third time I press the brake pedal... There are no leaks in the system, All the cilinders are new and moving, Pipes are copper ones except for the 2 hoses to the front drums. These are good, original rubber ones who do not expand or something because of a wrak spot, Bleeding the traditional way, with 1 guy pressurising the system with the brake pedal and the other one bleeding doesnt give the result we want. Even bleeding under slight pressure so the air is all out doesn't help. So: what are we doing wrong?? Or where do we have to look? Or what do we oversee? Please help me out here. I can't be the only one who has had this problem I believe. Thanks already for thinking with me!! Kind regards André (the Netherlands)
Are your brakes adjusted correctly? Also, is there an adjustment on the master cylinder rod that may have to be adjusted due to a nice new master cylinder that is working? Sounds like a nice car, good luck!
Make certain your shoes are adjusted properly prior to bleeding. I cannot stress this enough. Here is a home made tool to use as an adjustment tool....it should work on your brakes, too.
Did you bench bleed the master cylinder before you installed it in the car? I am thinking you still have air in the system. Matt
Make sure the MC piston is returning ALL the way. It is possible that the pushrod is a bit too long for the new MC.
Thanks a lot guys for the suggestions. I've been buzy with it all day trying them out. The pushrod adjustment had been done yesterday, screwed it back to zero what was a bit too much so today I adjusted it again to the point that the piston has returned completely. The brakes have been adjusted also. Made me a tool as discribed and went to work with it. Then started bleeding the entire system again but no result whatsoever... The only thing I hadn't done is remove it to benchbleed but I think that with bleeding it under 1.5 bar pressure should push all the air out. It has always worked well so far. But there's always a first time for everything.. So But I'm starting to loose it after all this.. I'm starting to think it's the new mastercilinder that isn't right... I hope it isn't because it hadn't been easy to get one and it has cost a bunch of money. So I really hope there's someone who can point me in a direction that can solve the problem. So please help me again Thanks already!!r André
You can 100% test the master cylinder if you can find the correct fittings that will block the hole where the line is attached. You would bleed any air in it, at the plug you just installed. If you get it blocked off, the pedal will be way up and rock solid, if the master is OK.
Also found a cap to seal the mc so I could try to check the mc and it was rock solid so that isn't the problem either... Been bleeding the daylight out of it the 2 person way, still air mainly at the right front. Bleed it till there's no air And next time: air again. Been bleeding it under pressure, everything air free but still normal pressure after the third push.. The only time it feels like it's supposed to is when the pressure (1.5bar) is still on the mc. And also kept the entire system pressurised for 32 hours so I had to see something leaking (even the smallest leak) And guess: no leaks what so ever. The only thing we can think of is that one of the rubbers in the mc (the middle one) is a bit awkward and only seals entirely off after being pressurised after 3 kicks.. All suggestions are still welcome because it's still one big mistery.. I'm going to get the mc out next saturday to look at that seal. And I'm thinking about a brand new (modern) Wilwood mc with an adapter plate to mount it if it still isn't working.. The need to brake is now more important than originallity
Does this brake system use any residual valves or check valves, either in the brake lines or possibly in the master cylinder?
@ClayMart No it's the simplest system you can imagine. Mc, 1 out then a deviding block with 3 outs, one to the rear and 2 to the brake cilinders on the front. At the rear axle a devider to the 2 back wheel cilinders, that's just it..
Having to pump the pedal to get a solid system is usually the result a displacement problem, caused by air, and/or improper adjustment on a drum system. You didn't mention a rear hose (only the front two). Is it in good condition? Your master should have an internal residual, like all drum masters had up to the '70s. With the pedal firmly returned by it's own spring, 1/16"-1/8" max push rod clearance is all that's needed. You mentioned using 1.5 bar (about 22 psi) bleeding pressure. For many years I also used fairly high bleed bladder pressures, until the two-piece masters with plastic reservoirs came along in the '80s, and a couple of them blew off during bleeding! Found that just 5-10 psi or about 1/2 bar is all that's needed to perform a good pressure bleed. Bleeding technique is sometimes the problem. The pedal should be slowly and fully stroked, during manual and pressure bleeding. Start at one corner and make at least three laps around the system. As soon as you have a pedal, check for leaks by "standing" on the pedal (100-150 lbs force) for a few seconds. Use isopropyl (denatured) alcohol for general cleanup, especially all the brake fittings, for easier leak detection.
O/k, firstly do you have the correct master cylinder, they use the same 1936 to 1941, you say you have a new M/c......have you a workshop manual that shows the correct orientation of the pushrod, piston, valves etc and are you 100% certain yours is correct?......it sounds like one of the small holes or ports at the bottom inside the M/c is blocked or covered by an incorrectly assembled piston etc.......I'm no expert but as you say they are a very simple system........btw those 2 rubber hoses...you say they are original rubber...do you mean they are 76yrs old?.......or NOS original style hoses recently installed.....if the former I'd replace them...............lol.............andyd
I would have guessed this to be the case with drums in all four corners, but I sure don't have any real experience with this brake system. The only other thing that came to mind, since brake adjustment seems to be critical, is if there was an adjustment for how far the brake shoes can retract when the pedal is released. But looking at the service info posted above I don't see any mention of such an adjustment.
Hi guys Thanks for all the help & suggestions! Unfortunately there is still no progress.. Yes there is a residual in the mc but further no valves whatsoever. Yes it is the correct mc, it's exactly the same as the one that came off. Yes we do bleed it the 2 person way by slowly pushing the brakepedal down all the way, yes we bled the systen 3 times in a row. Yes I did benchbleed it, yes I corrected all the brakes correctly. We checked everything for leaks, no leaks whatsoever, no strange or odd things are wrong with the 3 rubber brakelines (not the 76 year old originals but repro's, maybe 4 years old now) Still no result than what we had.. First push nothing, second push a little pressure, 3 time pressure. Yes I adjusted the pushrod to very little clearance and now I adjusted it so that I turned it so far that the brakes started working And then turned it back a little so the brakes are free. Result: still the same for one small difference: when applied the brakes 3 times to come to a halt and then go again the next time braking there is a reasonable chance it works the first time (not always..) Any other suggestions? Or preferably that one brilliant idea? I've also tried to change the original mc for a brand new Wilwood one while I thought it could only be the mc but that doesn't work for 2 reasons: the "axle" where the pushrod is attached to doesnt have the foreward action to push the wilwood all the way in and second the "axle" has a bit of a downward movement so it makes the pushrod angle awkward with a chance to damage the inner cilinder. After finding that out I checked the original mc And it works as it should (I know it's strange to go for a Wilwood without checking the mc but desperation struck..)
Sorry that you haven't found the problem yet, but happy to see that you're still approaching this methodically and logically. I'm pretty sure you'll get this sorted out. You said that you found a cap to seal off the m/c and got a solid pedal. I'm going to assume that means that you sealed the output port at the m/c so that no fluid was entering the brake lines. And I'm also assuming that you plugged the m/c downstream from the residual valve. All this makes me suspicious again of the residual valve. When working properly, this valve holds a few pounds of pressure on the volume of fluid between the wheel cylinders and the output side of the residual valve. The shoe return springs can only retract a small amount before the valve closes and traps the fluid, under slight pressure, in the brake lines. If the valve has failed then the brake shoes can continue to retract and push an additional volume of brake fluid back into the m/c. When this condition occurs, the next time you apply the brakes that additional lost volume of fluid in the brake lines and wheel cylinders must be replaced before the brake the brake shoes can move far enough to contact the drums. Pumping the pedal a couple of times serves to replace this lost fluid volume and your brakes feel like they're working properly. By plugging the output at the m/c I'd guess that there's not enough fluid volume under pressure to properly test the working of the residual valve.
Drum brake return springs, by design, return the shoes fully to their anchor(s). No way can a 10-20 lb. residual overcome the much more powerful shoe return springs, in spite of what you'll read on some brake supplier's web sites. The drum brake residual's only function is to prevent air from entering past the wheel cylinder seals during brake release. A side benefit is a firmer pedal because of a slightly charged fluid line. A failed residual can cause a partial loss of pedal because of air entering the system.
Hi guys, The feeling in the brake pedal is the same as the first time I kicked thrue the old MC. totally nothing the first time, the second time a bit of pressure and the 3 push the brakes worked. The residual is also brand new so how big is the chance that it is defected? I've also checked the old residual and it doesn't seen to be broken so I think this isn't the problem. The first time I put in a new mc kit, including a new residual there wasn't an improvement either. Checked that one too, same result as the old one. But please correct me if I'm wrong!! What I've done now is the following: I've made the pushrod as long that the brakes blocked. Then I turned it even so slightly back that my frontbrakes didn't completely blocked but were still braking. After that I adjusted my brakeshoes on the front (had to adjust the left one back to zero) so they were free. The first time I pushed the pedal it went to the bottom and the second time I had good pressure. I rolled around the block to try the brakes and there was still pressure. So they work now but after standing all night I tried the next morning and same: first push no pressure then they worked. I've been for a bigger round. The pressure faded a bit but pressurising by pumping twice make it seriously good. Btw, after the time I found out the old mc was rubbish and ruined another seal from the new mc kit, I ordered another mc kit by RayBestos and when it came in I noticed that the piston that was with it was significant longer than the one I had. Maybe the guys from RayBestos had noticed that to make this mc needed to be adjusted so much with elongating the pushrod that they made the piston longer so you don't need to adjust it that much. Does that make any sence? The idea now is to drive it a couple of days to see how it goes, then again bleed them n see what happens. In the meantime I would love to hear more suggestions from you guys.
OK. Well now I'm just grabbing at straws here. Where's the m/c mounted on this thing? I'm guessing it's mounted below the floor, lower than the wheel cylinders. Which might make things more difficult to bleed. Here's a couple of different methods you might try. http://www.how-to-build-hotrods.com/how-to-bleed-brakes.html Your bleeder screws are at the top of your wheel cylinders, aren't they?
The mc is below the floot and the bleeder screws are higher indeed. I've tried all these bleeding methods exept the one that works from the bleeder screws back. The brakes stopped working like they did at the beginning of the week and I had to pump again like before. Today I'm going to get the mc out again and replace the residual valve. See what the result will be.. Because maybe I was stupid to believe that a new residual valve is supposed to be ok..
Then again, I thought what the heck, the first part of my brakeline isn't original anymore, Lets go for an residual valve that I can fit on the first part, just behind the mc. So I want to the nearest autosport shop and bought me a Wilwood one. Going to put it on to see what's gonna happen.
I've put in the wilwood residual valve just behind the mc, bled the system 3 times, adjusted the pushrod again to blocking brakes minus 1/6th. Then liftend the car and adjusted all brakeshoes with the wheels on it and it seems to be working. I sprayed all the cups of the wheelcilinders as well with bardahl superspray. Only, most of the time in the morning it needs one pump and then the brakesystem works. So it looks good and I'm starting to get more confident. Still crossing my fingers that it stays that way.. Thanks guys for the support! Appreciate it very much!!
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