57 truck brake issue

[lowrodderchev]

Ok here’s the skinny I have a 1979 Camaro clip on my 57 chevy truck under floor master cylinder kit drums in the back. So after driving my truck all day around town I notice the front brakes getting real tight. Not all the time just here and there. Tight enough were you can smell the brakes smoking sometimes so tight it wont move in gear. I adjusted the push rod to where it feels comfortable and not getting tight. So yesterday jump on the freeway after about 35 minutes I use my brakes to find them really low. Scary low. But after pumping them a few times the pressure builds back up I’m good to go. Only happens after driving on the freeway a bit or it sits. I’m running residual valves my front brakes are 14 inches off the ground middle of master cylinder is 11. Any suggestions? Thank you in advance guys

[47 Fasttoys]

What are the pressure ratings of your valves? For disc they should be 2 PSI. Are you sure they are pointed in the right direction? Is this a new set up? Are you sure you have no pinching or folding points on your brake lines during suspension compression? Is your pedal returning all the way to the top after you use the brakes? What is the condition on the calipers? Are they clean and have free movement of the piston, meaning no chance of jamming in the out position?
Just some things to check.
Rob

[Speedbumpauto]

I'm fighting the same problem with the same set up. I've narrowed it down to header heat on the brake pedal pivot. Made a heat shield for the booster/MC and that solved some of the problem but I discovered that after some run time where heat soak can be a problem, the pedal will stick down about 1/2 inch, almost unnoticeable, which keeps some pressure on the brakes, especially the fronts and gets them hot, truck doesn't roll free, etc. Easy test is when it starts to happen, hook your foot under the pedal and pull up. If it moves up slightly and it moves easier at the stop light, you've found part of your problem. I'm working on a fix but nothing that meets my satisfaction yet. The frustration is I worked very hard to have a clean firewall and now I'm facing an unintended payback for all my work. I do have lots of engine under the hood and the under hood heat is a problem in AZ summer at times.

[OrrieG]

In 85 I also had the same issue when I converted to 4wd with discs up front, turned out the pushrod did not have the proper clearance (about the thickness of a paper clip) to let the mc release all the way. Also check to make sure your calipers have the bleed screw on the top to get all of the air out of the caliper.

[lowrodderchev]

Thanx for the responses guys a have a return spring on my pedal all new stuff tho has been a ongoing problem but first time on a long freeway drive I'm going to check to make sure my valves are going the correct direction other than that not sure

[Speedbumpauto]

I have a return spring also and have adjusted it multiple times. The down side of return springs is they operate from the short side of the leverage stick and it doesn't take much to overcome them. Just saying.

[ChuckDriver]

Are both of the fronts doing it at the same time or just one? You mentioned the residual valve, but do you have a proportioning valve in the system too?

[lowrodderchev]

I was just thinking that the other day I usually only check the drivers side. I tighten it up yesterday so far the brakes are good. tomorrow I'm off i'll try it again

[lowrodderchev]

so its back and worst than ever. yesterday I drove for 45 minutes to fresno and coming off the freeway the pedal was really tight but it did brake. well coming back on 198 I realized I got no brakes YIKES!!! I coasted into a turn off. master cylinder full, no leaks. the pedal goes down to the floor and barely slows down the truck. 6 hours later I go outside to move it into the garage and still same issue but this morning I go outside to check it underneath and the brakes are working fine. no issues. so air in the line? bad booster? I'm lost here.

[dwcsr]

Take out the residual valves. Most people think that the residual valve is for under floor masters but they are only needed IF and only IF the master is physically below the Caliper or wheel cylinder, not even with or close to or anything but below the master. They prevent drain back so if your lines are getting hot and you use a residual valve the fluid now has no place to go but into the caliper tightening the brake pad until it hits the 5 or 7 lbs and releases.

[OrrieG]

Look at your calipers and make sure the bleeder is on the top. they can be swapped side to side, if bleeder in on the bottom you will have an air bubble that is next to impossible to get out. Pedal to the floor is either air in the system, blown MC seal or maybe rod to mc adjustment (to long not allowing mc valves to close). Booster will not cause the pedal to go to the floor, when it fails the mechanical rod acts like regular brakes.

read this current thread too. http://67-72chevytrucks.com/vboard/s...d.php?t=679582

[lowrodderchev]

Originally Posted by dwcsr

Take out the residual valves. Most people think that the residual valve is for under floor masters but they are only needed IF and only IF the master is physically below the Caliper or wheel cylinder, not even with or close to or anything but below the master. They prevent drain back so if your lines are getting hot and you use a residual valve the fluid now has no place to go but into the caliper tightening the brake pad until it hits the 5 or 7 lbs and releases.

there's a 1-1.5 inch distance between my height of my caliper and master cylinder.my truck sits pretty low like 4 inches off the ground low when i bleed my brakes i had the wife help me. we went around it twice. I'm going to have a buddy come over tonight and help me bleed the crud out of them. I'm really hoping its a simple thing like that and not pulling out my booster. i had a few shade tree mechanics tell me its the booster figured i better ask the professionals (that's you guys) what you thought. thanx

[tmoble]

I'm with dwcsr. likely your RPVs are holding pressure causing the calipers to get too hot. pedal to the floor issue could have been caused by boiling brake fluid. The deal with something causing the piston in the master to not return completely is popular too.

FWIW I ran a 57 with a stock master and a 2nd gen Camaro clip without issues for years, like 15 or so. Then installed a C4 Vette rear without touching the master. Ran the 4 wheel discs with stock master for several years OK till I stripped it to the bare frame this week. Going back with 12" fronts off a 9C1 Impala, aluminum generic Vette master in stock location and the same Vette rear. No power assist, install it later if I need it.

[tmoble]

BTW, If you find or make a bleeder wrench that you can use without removing the wheel you can verify the pressure issue quickly. drive it till it starts to act up, stop. hop out and crack a front bleeder. If fluid sprays out you're getting close to a solution.

BTW II, when I yanked the brake lines off my frame yesterday I discovered a long forgotten aftermarket RPV in the line to the rears. I've owned/drove this truck since 1984, have no idea when I installed that thing. might have been when I installed the Camaro front in 93. Also no idea why it didn't cause problem with the Vette rear discs. Maybe it's bad. Everybody gets lucky once in a while.

[lowrodderchev]

I'm going to ditch the residual valve today talk to a buddy mine this morning who's a car guru in my eyes he said same thing you guys said the fluid got hot

[dwcsr]

You may while your at it run the line through some heat shield sleeve.
DEI makes some Part# 010403 is a 3/4" x 3 ft for about $14

[OrrieG]

This got be thinking about brake line proximity to exhaust piping, think I will get some header wrap to use next to the mc. At speed probably enough air movement, but I will spend a lot of time off road where temps could build up.

[lowrodderchev]

New problem lol so pulled the check valve to inspect it and the rubber grommet ripped. Easy fix nope can't find one that will fit not even a repop one. I got the kit from American classic truck parts the grommet says mbm 151-19 so assuming its a mbm kit

[lowrodderchev]

So I bleed the heck out of them the rear is shooting fluid no issues soon as i open the valve the pedal went to the ground. The front let fluid out but the pedal didn't move at all after the valve was cracked open so after 6 rounds of bleeding the system its not braking the truck very good so I went under the truck and adjusted the pedal its way better. Tomorrow I'm going to bleed it a few more times see how it goes

[lowrodderchev]

Talk to MBM very nice people. going to send me a few check valves free of charge. besides wrapping the exhaust I'm going to also put a heat shield for the master hopefully its cures it all thanx for all the responses

[yoshi]

My 49 is 2 1/2" from the ground to cross member & I don't have any residual valves fitted, I bought some but didn't need them

[dsraven]

make sure to reroute (thats what i would do) or insulate the brake lines well. brake fluid likes water and will absorb condensation. then the moisture rusts the internals out prematurely. hot/cold allows condensation, too hot allows the fluid to boil, usually poor brakes at that point.
if the fluid is getting too hot and discoloration occurs you should bleed them till you get fresh fluid at all the wheels, then make sure to fix the heat problem.
i am with whoever said "go for a ride (on a back road away from traffic) and wait till you have some tight wheels, then crack a bleeder and see if the fluid is under pressure". if it is then chuck those valves. another thing to check is if the pedal is bouncing while you drive and effectively "pumping up" the system. could be a weak return spring allowing that? seems like a lot of linkage with the underfloor systems.

[lowrodderchev]

I pulled that valve already next I'm going to put a heat shield between the master and the exhaust and most likely buy some wrap off eBay and wrap the pipe that near it

[dsraven]

sometimes, if you have the room, you can just install a simple sheet metal shield between the exhaust and the problem area. that is what new cars use so it HAS to be the cheaper fix, ha ha. take a buddy with you when you go cruisin next time and have him run some phone video of the brake pedal when things get warmed up. maybe the return spring is getting heat soaked as well so the pedal is jumping causing the brakes to pump up. one would think though that it would 'unpump" once you stop moving. when hot it would also be a great time to roll under there and have a look at the linkage for the master, maybe binding up somewhere? how close to the exhaust is the booster? problem? i think a starting point would be the bleeder screw cracking when you have a problem. that way you know if it is a hardware issue-rotors, pads, calipers, mounts etc- or a problem with adjustment or valveing. have you tried driving with the vac line plugged for the booster? that would eliminate a possible booster issue, worse than manual brakes though with it unplugged......

[ChuckDriver]

You may have covered this, but do you have a "combination" or "proportioning" valve in the system?