Inliners International Forums General Discussion Drive Train brake system back pressure

i haven't post a question for a while but i haven't been working on the old truck ,either! i rebuilt all the wheel cylinders and the master recently . the truck sat for years and some cylinders were pretty stuck when i dissasembled them . i now have a rear wheel cylinder that doesn't always retracted after stepping on the brakes, making that drum lock up . the lines were flushed out a little and i was thinking maybe i should flush even more . how long should i bleed the system? could ther be something wrong with my master cylinder and how could i check . anybody ever come across this problem?

Hello, is just one of the rear wheel cylinders locking up or is it both rear wheel cylinders? I have on several ocassions had problem with the rear flex hose collapsing internally and it acts as a residual valve. Most of the time the exhaust was a little too close but a few times it was just a old hose. Just a thought---Paul

actually at first i thought it was just the one rear locking . then i was changing the front tire and the brake seemed very tight. i was reading last night that the pedal adjustment needs to have 1/2 inch free play to allow the master cyl piston to return far enough for the vent to be exposed for return pressure. and the other thing i read was that any mineral spirits used in cleaning can warp and distort the rubber cups .i'll try checking these things and then .......who knows

Yes the pedal ajustment can cause the brakes to be slightly applied. If all the brakes are locking up the residual valvein the master cylinder may be bad and if it was cleaned with mineral spirits it maybe toast-- mineral sprits can be used to clean only the metal parts then air dried completely before assembly.I use clean brake fluid to clean any rubber parts and as a lubricate during assembly. Thought I might mention, I have found a hand vacumn pump to be one of the best ways to bleed a system and you can do it by yourself.Paul

well now for an update. adjusted the freeplay first ,then the heck with it pulled the master and inspected it for foriegn matter and honed it ,checked all components and reassembled ,tried it out seemed to be better at first ,then back to the same result .next i'll replace the hose or all of them ,they probably need it anyway . it seems to be only the rear passenger side drum but it in turn makes the rear end growl and rumble by putting strain on the spiders . one other thing to know ,i did add a hydraulic brake light switch off a t fitting directly at the master while i was building this truck. this was to avoid mounting and wiring the stock switch. could this be the cause of my problem?
i think i will put some new return springs in the problem drum ,also.. thanks for your input everybody

I need to tackle something like this on my '39 Chevy 2 door this spring. I parked it in frustration last year, and have been working on other projects, instead ( both of them inlines, of course!).

My brakes (disc front, drums back, small booster/MC under the floor) would start to lock up the rear axle and drag on the front after a few miles of stop & go traffic. I think that my brake pushrod, from the pedal into the booster, is just a little too long, and won't let the brake fluid drain back to the MC. I'm going to take the rod out, and grind about 1/4" off of it, and see if that improves things.

Later, Kinky6.

Kinky 6 , make sure the master cylinder you are using is for dics/drum aplication. Sounds as though you have M/C designed for 4 wheel drum system,which contains a residual in the frt. port.Not to cause confusion but floor mounted M/C's in some cases need a very light residual valve to keep a firm pedal, however the factory residual valve is to strong. After changing to a Dics/Drum M/C you may have to install an aftermarket "2 psi"(blue)inline residual valve on the frt.side. May this will help.... Paul

Dr tile< the pressure type switch will not cause any problems with the system. I do not perfer to use them because they take some line pressure to activate so a light tap of the pedal lots of the time will not bring the brake lights on.Also ckeck to make sure you have the shoe with the shorter linning on the frt. side and then make sure the emergency brake cable is free and not binding... =woooo bring on the WD 40----Paul

thanks paul for the thoughts. i know that the shorter lining is in the front , and i don't have the emergency cable in the drum it is being remade for me. i am going with the hose next because the cylinder releases the pressure immediately when i crack the bleeder fitting . unfortunately i'll be busy til the weekend after next so i'll just rack my brain til then !
by the way get this ! i was reading an older repair manual and it showed a diagram with the shoe with the full lining in the front .Audel's automobile guide (1949) great book but it makes you wonder.

That would be correct if you are dealing with the "Huck" brakes on the 50 and earlier Chevys----I was assuming that you are working on "Bendix" brakes on the 51 and later GM vehicles. Seems I remember you mentioning a few post back that your truck Has a olds rear end??? Did you replace the whl.cyl. cups or just clean them?The fact that the pressure releases when you break the bleeder screw leads me to believe now that the whl.cyl. is binding. This will sound stupid but I had the same problem once and found when I reassembled the whl.cyl causing the trouble, I put one of the pistons in the wrong direction--hehehehe...Paul

on a similar question, I have installed a late model non-power dual piston master cylinder in my 54 chevy truck. I a told I need a proportioning valve, but no one can explain WHY. What i get is "the back brakes will lock up" which doesnt make sense to me.

In the original configuration, all four wheel cylinders were subjected to equal hyd. pressure from the single piston. as the dual pistons are of equal size, and traverse an equal distance when the pedal is depressed, there should be the same pressure at all four wheel cylinders. If weight dist. made the critical difference, than a proportioning valve would have been necessary with the original kit. Anyone?

I thought proportioning valves were most important if you switched to a power brake system
or a front and/or rear disc brake system where the bias would be too much at the front wheels so some balance had to be made to the rear,especially if it was a disc/drum system.I hope a more experienced brake tech can help you on this one.

This is going to be a long post so hang on!!This has become a baffling question because of some misunderstanding of the part functions and imporperly named parts. The function of a proportining valve is to 1: allow the rear brake to apply first,which reduces wear on the frt brakes. Then as pedal force increases so do the line pressures, so 2:the proportioning valve steps in again to limit the pressure been applied the the drum whl.cylinders.The dics brake line pressures greatly exceed the drum brake line pressures so 3:it allows the pressure applied to the disc to continue increase as needed to bring the vehicle to a stop. This function"does" help keep the rear brakes from locking-up but, it's design intention was not anti-lock.This function is more of a safety feature to keep the rear wheel cylinder from "blowing- out"or leaking. I do not intend to make any one mad but in most cases the valve that is beening sold and used on the rear brakes as a proportining valve is actually only a "Pressure Regulator Valve". I am not saying the does not work or help but a brake system which incorporates a "factory" or "true"proportioning valve will function better and have more "brake life". To clearify the use of daul- master cylinders, I believe there is two intentions here--1: safety again as it actually gives you two braking sytems. 2: drum and disc are two differnt sytems and have different valve requirements--more on this later. The drum brakes need a residual valve because they are return to rest position by springs.Rotational force repositions the disc Pads so it does not need a residual valve when the M/C is mounted above or higher than the whl.cylinders & disc. pistons. The factory chose to incorporate the residual valve in to the master cylinder. If you want,I will explain "Residaul valves",thier function and application in another post---I have some work I have to go do right now--paul

thanks paul , you are correct i have a different rear end (cadillac ,actually ) the truck frame is 54 chevy and the rear is 55 cad. i replaced the cups with rebuild kit . i can surely rehone (which i rushed through by hand ) and install a new kit and put a new hose on the rear and then check it out ....they are bendix. i was reading a old book which explains the huck style with the larger shoe on the front! you're sharp!!

final report on this situation.pulled the cylinder , honed and replaced the cups ,they looked ok ,but what the heck . then installed new return springs .that took care of it . thesprings were all i really needed ,i think. thanks all.

for all inliners; Paulweldit will be at the Texas chapters picnic May 29th., Sat.(Memorial Day weekend) allowing those attending two days to recuperate, er, travel. All Inliners are invited. I'm sure Paul will answer every question posed but, more important there will be many good Inliners to make you all welcome and Granbury has some great family entertainment. Points of contact:Jim Killough,ph# 817 626 5019 or Bill Mulholland,ph# 817 326 4949, e-mail:mulhollabi@aol.com. Y'all come.
Bill mulholland#3527

for those that followed this epic . it didn't stop there . brake hoses , no relief still . finally i put a NEW master cylinder in. works like a champ ......gtg ...up and down the street now

This makes me wonder if the residual valve in the the master cylinder got put in backwards after you overhauled it. You might want to pull it apart some time to check it.