Brakes Tightening While Driving 32 Ford

Newly built 32 Ford Tudor under floor master cylinder pumps up while driving. After about 20 minutes of driving city traffic the brakes are dragging enough that I cannot push the car by hand, but it still drives OK. After sitting a couple of hours+/- the brakes free up but the pedal is lower than normal with barely enough brake to drive safely. The master cylinder rod has been adjusted out twice with no relief. The left side 2 1/2 inch exhaust pipe p***es under the master cylinder with 1 1/2 inches of clearance. The exhaust pipe has been wrapped with DEI wrap, double thickness near the master cylinder. The master cylinder has been wrapped with Kool Mat insulation. Front discs, rear drums, no boost.
Looking for advice please.
Al

 

I had the same problem once...my push rod needed to be shortened....it was causing pressure on master cyl....causing heat build up , with caused brakes to lock up

 

It doesn't have to be just the master cylinder. Any brake line that is to close to a heat source can cause this problem. I do agree with the response about shortening the push rod, and not making it longer or tighter. Cause if your fluid is gettin hot it will expand and the tighter push rod will have no relax area and will act as your foot and activate your brakes...John

 

there are little ports in the MC that allow brake fluid to return to the reservoir. they are uncovered when the piston is all the way out....when you push down on your brake pedal the piston inside covers them up. so either the piston is not coming all the way out because of mis-adjustment of the push rod , or the little holes are plugged with ****

 

Thanks, I was beginning to wonder if the holes might be plugged.

Al

 

IS your wrap around the cylinder closing off the cap vent?

 

Thanks, I'll have another look at the plumbing. The adjustments that we've made have effectively shortened the rod quite a bit. Will take another look into this.
Al

 

We had a brake pedal that wasnt returning all the way and it was doing the same as yours.
There was a brake pedal stop on the return.

 

Good question, but after adding the wrap there seemed to be no change, better or worse.
I'll check this out further.

Al

 

I don't think that's the problem but will check.

Al

 

You need a return spring on the pedal , then you need to set 1/16 to 1/8 freeplay at the push rod when the pedal is returned via the spring. do you have residual pressure valves installed ? if so are they the right way around ? you could be pressurizing the m/c not the wheel cylinders if they are in backwards. My 2c.

 

Hmmm... no spring on the pedal. I'll have to check the residual pressure valves. But the brakes do work good enough to drive.
Thanks, you've given me some things to check. I'm the owner but not the primary builder.

Al

 

Also did you adjust up the rear brakes with a little drag when cold ? often forgotten & must be done to bleed brakes correctly & get a proper pedal .When it is dragging check the front & rear to see which end or both are binding , narrow down the problem that way too .

 

I think we're good there but will check.
Thanks again.

Al

 

Precisely...!

I had the exact same problem

It has to fully release to work and recheck your return spring to see if there's enough "PULL" to return the pedal all the way back.

 

I had this exact same problem too. Turned out it was the wrong pushrod for the master cylinder. Needed a shorter one. Try that, it's an easy fix.

 

Limey Steve hit on it with his lack of freeplay comment.

After you install a return spring you should have 3/8"-1/2" free play.

 

Free play with a return spring. Sometimes the weight of the pedal can apply enough pressure to take up all the free play and keep the piston from returning that last little bit. The return spring takes the weight of the pedal off of the piston. The spring inside the M/cyl. is not enough. All cars have pedal return springs just for this reason. It's critical in an the under the floor M/cyl. system.

 

Residual valves can only be used with drum brakes . If you have a residual valve in the line to the disc brakes it will cause them to drag. Keith

 

I appreciate all of the comments. Now I have several things to check and/or correct.

 

ummm, no. you use a 2lb for disc when the master is lower then the caliper (like under the floor) and a 10lb for drums.

i also agree with needing a pedal return spring and then setting up the free play.

 

I'm sure you mean 3/8 to 1/2 freeplay at the pedal NOT the pushrod !!

 

I'm pretty sure the cap vent is clear, the wire latch is holding the wrap up off most of the cap.

I've added some wrap around the MC to cover the brake lines as they enter the cylinder.

There is a blue color coded residual valve on the disc brakes and a red coded one on the drums. They are clearly marked for directions and are installed correctly.

I'm now working on a return spring and a place to anchor it. The pedal is heavy and the weight takes up all of the slack. I think the slack is about the right amount when I pull the pedal up.

Al

 

Corect.

Thanks

 

Here's one way.






You'll need a pedal stop so there is no possibility of the rod dropping out.


This one is adjustable.


The threaded rod shown is a cut-down standard Ford M/C rod

M/C is a dual chamber Mustang with 7/8" bore.
(Goes to 68-70 Mustang discs - 11" rotor - and 11" 68 Mercury wagon drum brakes in rear.


The one shown is in my 31 on 32 frame roadster project.

I have an identical spring setup in my 32 and its been doing fine for 15 years and 50,000 miles.

 

Nice piece of work. I had not thought of a compression spring.

My pedal is stopped by the lower part of the firewall. I don't think it is possible for the rod to pop out but I'll make sure.

Thanks for the pictures.

 

Nice stuff C9,, this is a quality thread , how the HAMB should be .

 

Regardless of the problem.......................Get rid of the Aluminum residual valves! We have had many discussions here about how bad they are or will be down the road. I prefer the Br*** ECI valves. The old shop I worked at had a small drawer of cracked and beat up anodized Speedways and Wilwoods gathering dust.

 

ECI or one of their dealers. Ralph from ECI is on the HAMB, search my brain addled primate pal

 

It seems the Aluminium ones split out from the pipe thread and rely on a tight seal.Br*** holds up mucho better. Serious, search "residual"