Looking for someone to give me a sanity check and provide any applicable tribal knowledge.

I have a 1938 Chevrolet that has a full 1984/1985 suspension and brake system. I purchased the vehicle already built but it has significant mechanical issues and I have been working on it for about a year. This will be a long post as I want to outline what I have done. I truly appreciate any help you all can provide.

I disassembled and rebuilt each caliper. There is no pitting on any of the pistons and they went together as they should.
I installed a dual diaphraghm 7 inch booster, I cannot go larger because of the chassis space limitations. The booster and MC are under the car.

I set the push rod on the booster to just touching the MC and then just over half a turn in (.025 to .035 inch gap). The linkage is adjusted properly so that there is about 1/8 inch of play before moving the booster.

I replaced all the brake lines and hoses, no kinks that I can find.

The brakes work well and stop the car. When they are cold they work perfectly however as they heat up the rears will drag for a while after use. If I am on the road for a while they will loosen up but then will drag as soon as I hit the brakes. The drag is not significant but can be felt when idling in gear (car does not roll as easy).

I have checked brake temps after a run, fronts were both 180 to 185 and rears were both 250 to 255.

I think there is an issue with the master cylinder (have not replaced it and it did have debris in it when first removed.)

Any ideas from the forum? I know this is not a Vette, but it's a pretty cool car (my other car is a 2012 GS).

Thanks in advance, Chris

 

Since your master cylinder and booster are mounted low in the car, did you run a residual pressure valve?

 

The early C4s used a two brake System a Drum for parking inside the Rotors, are they possibly dragging?

since it appears the calipers are New/Rebuilt I wouldn't dwell on them first. could you have a collapsed Brake line, one that allows fluid into the Caliper under high brake pressure but meets Resistance under low release pressure. I know you already chased it but I would give a second look, when the brakes are dragging do you have pressure still remaining in the calipers, if you crack the bleeders do they Squirt a lot of fluid?

 

Warm it up, get the brakes dragging, then open the rear bleeders. Do they still drag?

If yes, it's a mechanical issue at the brake. If no, it's a hydraulic issue. For me, this would be "step 1".

 

Thanks for the replies,

Yes I verified the parking brake was not dragging by disconnecting and adjusting the brake.

I do not think I have a collapsed brake hose because both brakes are dragging equally as evidenced by the equal temps. by the time I jacked it up and got a wheel off the pressure had dissipated and I did not get a "squirt".

The MC is under the car but the reservoir is in the trunk and about 9-12 inches above the calipers. No residual pressure valves are installed due to reservoir position.

Thanks, Chris

 

could there be a problem at the block where the two rears meet or the line to the Master, I almost wonder if the problem is having the remote reservoir it's not grossly higher than the system, But the stock system had the reservoir rite on top in two small chambers. Just a quick after thought the brake system was a home design Retrofit so it would be safe to say that many of the brake lines were Custom built by hand in the double crimp faired ends could there be a restriction Closed up crimp? and something is keeping the rears applied equally

Is the master your using is it the type that would be called for the Original car, because that car Didn't know the pleasure of disk brakes at Birth and had 4 wheel drum brake with nice large brake return springs to release. and as one of the posts said crack the bleeders does it release. Mechanical or Hydraulic problem.

 

The brake system is completely C4. Master cylinder is from a 1984 or 85. All the lines are new and flow tested with proper metric bubble flaring. I blew air through all of the lines when the MC and calipers were off, no issues. The brake hoses are new.
The MC is connected to the reservoir by a custom machined aluminum block. Brakes bled fine, but the rears were slower than the fronts. Bled them with a pressure bleeder at 5 psi.

I will not have time this weekend to jack it up, but I think my next step is to get them hot, jack the car up and see how they act when the brake is pressed (measure time to releasing drag).

I will also crack the bleeder to verify it is hydraulic but I am 99% sure it is.

My concern right now is that the booster sits differently with vacuum than it did without, which is how I set the gap.

Thanks again for the help, Chris

 

MC front/rear lines may be switched @ the MC, verify correct plumbing.

Quick booster to MC pushrod length check:

Loosen the master, install an alignment shim between master & booster on each bolt, tighten MC then road test.

Nice street rod, Buddy in IL had a similar ride in C3 Vette yellow the sweat bees loved landing on it.

Luck with the binders.

 

Thanks Churchkey, shimming the MC is my plan, will get it done this week and update.

The lines are correct, two smaller to the front and a single larger to the back. (MC is backward in the car but the lines go to the right spot.

Thanks again all!

 

Ok,

I see many posts where people have a problem and you never hear the solution. I don't want to be that guy.

So I shimmed the master cylinder, seemed to do a bit better on a much cooler morning, thought I had it licked. Then drove it home in the afternoon and when backing in the garage the car would not move, brakes dragging again.

Drove it the next day, just a short drive maybe 6 miles. Back in the driveway car would not roll in reverse. Got a dumb idea and pulled the pedal up with my foot, pedal came up an inch and the car started moving....

The car has a custom linkage on the original pedal, the push rod is about 3 feet long and is supported in two locations with rubber bushings to prevent bowing. The pedal return spring has almost zero leverage when the pedal is up, the drag on the linkage was preventing the return of the pedal. I made a new spring bracket giving the spring more leverage and the problem is gone.

I would like to thank everyone on the forum for the help, and am more than willing to be the poster child for missing the simple stuff.

Thanks, Chris

 

Very cool glad you have the fix, I hate it when you know it's a little Something and you just don't see it and when found you go Dam. well done !!!