Hot Rods Residual valves

I have a TCI 40 Ford chassis that came plumbed 4 wheel disc brakes, GM calipers, proportioning valve and residual valves ,2psi. Came back from a little drive yesterday and back brakes were dragging after 40 miles, had to downshift to get up a hill. Are these residual valves really required for an under floor master? rear rotors were 400 degrees and coudn't roll the car, waited 15 minutes and it was fine, any suggestions?

 

make sure the MC pushrod length is adjusted properly, so the compensator port in the master cylinder is not covered when your foot is off the pedal. It needs some free play.

 

Does the rear have parking brake, type calipers?

 

These have never done that before, all wilwood with internal park brake, I did have problems adjusting mc to booster pin, if you set the clearance before touching brakes, its good, but as soon as you break, the residual valves kick ,than I have instant brake drag just sitting and have to back off the pin a bit. Then when you go the next day the residual valves seem to bleed off and the pedal goes way down to the floor till you pump it once then all is good.

 

Here’s a thought , apparently some prop valves incorporate residual valves …. If that is the case could having double residual valves be the problem . I’m no expert just spit balling .

 

Are you sure they are 2lb valves? I’m with @squirrel that I would suspect pushrod adjustment

 

Also from your description of the brakes sticking when you step on the brakes and readjusting the pedal, it’s not the valves, they simply are a one way check valve, they have zero affect on the pedal adjustment. Is all the pedal linkage free?

 

Is the master cylinder higher then the caliper bleed holes? Pull the residules off and see how it acts or pull the guts out of them.

 

https://www.speedwaymotors.com/the-...valves-and-what-your-brake-system-needs/31069

 

They are 2 psi valves, everything moves freely, it just started doing this after 4500 miles, I may just replace them.

 

sounded like a new build, from the first post

the more info you provide, the more pertinent the advice might be

 

It is a fairly new build I got from a good friend, he had health issues, 1940 ford pickup, all brake lines installed by TCI at the factory, my friend had removed them all to paint the frame and they sat on the shelf for ten years before I got it. I'm thinking there may be some debri possibly came thru the lines, I will remove it and check and probably still replace it and give it a try, thanks.

 

You can replace them but the residual valves will not affect pedal adjustment so it would seem to be a waste of your time to replace them

 

Silly me, I never run residual valves with disc brake calipers....just drums
but then again, I have mechanical brakes too

 

I am going to measure height of bleed screws and height of top of master ,if they are within an inch I may pull out the guts and see how it all works.

 

I had my own shop for over 30 years. I never had any Wilwood 2 psi valves that worked correctly. I have a box full of them. Use anyone else's valves.

 

And this is why I stay away from brake threads, someone explain to me how a residual valve of any type can affect the pedal adjustment. All they do is retain press In the line after the valve. The master cylinder returns to the same spot with or without them.

 

Did some measuring today, rear bleed screws are same height as mc fluid level, fronts are 1 1/2 inch higher, I think I will remove guts from the rear and give it a try.

 

I’ve had ECI residual valves (made of brass, not aluminum) on my car for almost two decades and never had a problem with them.

 

While I understand the theory of why residual pressure valve, here is an example of not having them and works fine. My 52 Chevy Ute I converted to disc brakes on front, with a 56 Chevy car open rearend in back. Removed the stock RPV built into the underfloor master cyl. Then just straight lines to each corner. It DOES NOT LEAK BACK into the master cyl or leak air into the calipers or wheel cylinders. Even after sitting over winter. Don't ask me the theory, it just works. It is the single master cyl, not dual. It stops straight and true, much better brakes than stock drums.

 

It isn’t a guarantee that they will bleed back. And most even remotely modern wheel cylinders have cub expanders in them so if it works good without them then life is good.

As far as the question that started this thread, either we don’t have information or he is dead set on changing residual valves, in which case I’m not sure why he asked.

 

The only way fluid should bleed back out of a caliper is if air enters the caliper or the fluid can pull the piston with it.

 

Thank you for the link. I’ve been watching brake threads for awhile, I will be replacing a 7-1/4 Chrysler rear differential with 9 x 2 drum brakes with a Ford 8.8 rear differential with I believe 10 x 2.5 drum brakes, also down the road I’ll probably install disks up front. Anyhow I usually leave most brake threads involving proportioning and residual valves more confused than before I read the thread.
The speedway motors article makes sense to me.
Dan

 

Except for the blatantly wrong information it’s great.

 

Id be most concerned about the pedal going to the floor on first depression after sitting overnight. That shouldn't happen, ever.
Freeplay at the pedal has been mentioned, but not addressed. It's not the same as the clearance between the booster and master, it's a separate consideration.

Chris

Chris

 

What info is wrong?
Dan

 

Totally agree.

 

For starters the part about 10lb residual valves being used because of spring pressure in the drums. Nope, they are to prevent air entering the wheel cylinders on brake release, or to prevent fluid running back to the master if it’s lower than the wheels.

 

Have you ever yanked on those shoe springs? No way ten pounds would overcome those. Fargo is right.