Does my truck have a residual valve for the rear brakes?

[Ataylor]

Hello,

I just finished converting my rear drum brakes to disc. I ended up using brackets from Ruff Stuff Specialities and GM calipers. I bent new brake lines for the axle and used a new braided line for the drop from the frame, and new braided short lines to the calipers. I bled 2 quarts of brake fluid though the system and bled the front calipers.

The pedal feels pretty good, but when I got back from the intial 20 minute test drive I got under the truck to look for any leaks. No leaks at that time, but the rear calipers and discs were warmer than I think they should have been. I shot them with a IR gun and the left side was 120 F and the right was 95 F. I should have gone up front and felt the fronts, but didn't. I didn't do any hard stops for the last 10 minutes of the drive and thought they would have cooled by the time I was home.

The next day I got under the truck and saw brake fluid leaking from under one of the copper washers on the caliper. I didn't double them up, and used one on top and one under each banjo fitting. The other side had some fluid leaking from one of the bleeder screws. I know I got both of these things tight. I will put a wrench on them again and then do another test drive.

I was wondering if anyone knows if these trucks have a residual valve for the rear brake circuit that could be holding a few psi back and causing the brakes to drag while driving. If there is a residual valve, where is it?

Thanks for any advice,

Archie

 

[riotwarrior]

As far as I know a RPV is for when the MC is lower than the wheel cylinders to prevent the cyls from siphon feeding back to the MC.

Perhaps the proportioning valve is sticking or stuck, I cannot think of anything else that would cause a problem.

One thing not clear in your post is if the GM calipers are actually new or used? If used perhaps they had some rust in the bore and when installed with new pads are sticking...I don't know cause there is just not enough clear info on what is new and what is used.

JM2CW

 

[Ataylor]

I bought remaned calipers from Napa that were used on the front of a 1977 Chevy 3/4 ton 4x4.

Archie

 

[riotwarrior]

I bought remaned calipers from Napa that were used on the front of a 1977 Chevy 3/4 ton 4x4.

Archie

If the calipers are a reman...there shouldn't be an issue with the caliper sticking in place because of some rust in the bore of the cyl. However if the bracket that said calipers bolt to are slightly tweaked or causing misalignment then the calipers may just actually stick and cause them to be warm. Just thinking out loud here....without seeing it and being able to play with it I really cannot say what's up.

More n likely the pads are bedding in and it's normal for them to be quite warm doing so.

Again the proportioning valve (WAS) for a drum brake setup so not sure how well it will work with the disk setup. Maybe it's time to get a manually adjustable one?

How do you find the performance of the new setup? Are you satisfied with the performance?

I'll be doing a similar conversion using 76-8 Caddy Eldorado calipers on my 10.25 Sterling...

 

[Black dawg]

do you have the rabs valve still? It is very common for them to hold pressure to the rears when they fail

 

[riotwarrior]

do you have the rabs valve still? It is very common for them to hold pressure to the rears when they fail

I wondered that....but its an older 87...not sure when it came out but good call

 

[franklin2]

Residual valves are usually located in the outlet ports of the master cylinder. More than not letting the fluid drain back, they kept the cup seals pressed out against the bore of the wheel cylinders.

With all that said, I read somewhere that they came out with a more modern design of the cup seals, and the residual valves are rarely used anymore. More than likely the master cylinder on these trucks doesn't have them.

 

[tknomaj]

Residual valves are usually located in the outlet ports of the master cylinder. More than not letting the fluid drain back, they kept the cup seals pressed out against the bore of the wheel cylinders.

With all that said, I read somewhere that they came out with a more modern design of the cup seals, and the residual valves are rarely used anymore. More than likely the master cylinder on these trucks doesn't have them.

Yes these trucks master do have them. Replace master with 4 wheel disc master. Disc brakes require the pull back of fluid to get full release of caliper piston. drums require constant residual pressure for the cylinder cups also get proper proporationing valve . if cannot find local abs brakes orange ca. they will ship

 

[ocnorb]

+1

Getting a 4- disk valve would be the best way.

Guys used to get a welding rod hot on the tip and melt a hole in the residual valve to "convert" it to 4-wheel disk. I wouldn't recommend it, though.