Rear brakes locking up information for you

[Ricko1966]

There's been a lot of posts lately about rear brakes locking up after you've done xy and z. I did a little digging,just in one year gm used 4 different combination valves in these trucks. They all have different bias. If you look at the bottom of the chart that @Keith Seymore posted and @legopnuematic reposted, the numbers and settings for the valves are listed at the bottom. Just for fun I tried to find some new real deal GM ones found 3 and all discontinued. The moral of the story is if aftermarket is selling just 1 for disc drum applications for any year,but GM had 4 for just 1 year,the aftermarket combination valves must be a compromise of what works on most common setups. I'd be grabbing original combination valves out of any trucks I was robbing brake parts off of.

 

[Keith Seymore]

Exactly.

It's like buying a generic carburetor and setting it on and expecting it to work.

K

 

[xm20k]

There is also this option. But requires you do some fiddling/testing.

Wilwood Disc Brakes 260-8419 Wilwood Brake Proportioning Valves | Summit Racing

Free Shipping - Wilwood Brake Proportioning Valves with qualifying orders of $109. Shop Brake Proportioning Valves and Distribution Blocks at Summit Racing.

www.summitracing.com

 

[bucket]

Or an adjustable combo valve.

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[Ricko1966]

Remember boys and girls even if you go with an adjustable proportioning valve,you still need your original combination valve,it has the brake standoff valve in it. Looks like @bucket has found an adjustable combination valve. That's sweet. Dam It no shuttle valve in it,still pretty sweet.

 

[squaredeal91]

Remember boys and girls even if you go with an adjustable proportioning valve,you still need your original combination valve,it has the brake standoff valve in it. Looks like @bucket has found an adjustable combination valve. That's sweet.

What does the standoff valve do?

 

[Keith Seymore]

It holds the front brakes off until the rear shoes can take up the clearance and contact the drum.

On the brake chart is is called "metering" (the characteristics of the proportioning are called "metering", "split" and "slope").

K

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[squaredeal91]

I guess this is why they say you don't need a proportioning valve with 4 wheel disk. Is that true?

 

[Ricko1966]

I guess this is why they say you don't need a proportioning valve with 4 wheel disk. Is that true?

There's more to it than that,but that is part of it. Disc's and drums also operate at different pressures so that needs regulated,also most drums are self energizing,so that also has to be taken into account so the car will stop in all situations without the back end coming around like an Ebrake turn

 

[xm20k]

It holds the front brakes off until the rear shoes can take up the clearance and contact the drum.

On the brake chart is is called "metering" (the characteristics of the proportioning are called "metering", "split" and "slope").

K

They do have an adjustable combo valve as well but its twice as much.

Pardon Our Interruption

 

[Ricko1966]

They do have an adjustable combo valve as well but its twice as much.

Pardon Our Interruption

You're late to the party post #4. Just giving you grief,thanks for the link.

 

[xm20k]

You're late to the party post #4. Just giving you grief,thanks for the link.

Ya well mine has a pressure switch for brake lights so mehh.

 

[squaredeal91]

There's more to it than that,but that is part of it. Disc's and drums also operate at different pressures so that needs regulated,also most drums are self energizing,so that also has to be taken into account so the car will stop in all situations without the back end coming around like an Ebrake turn

Thanks Yoda lol

 

[Sgt Gus]

Yes, quite a few posts. My daughter said the truck locked up on her twice yesterday. Once when backing out of the garage and once at school parking lot to go forward.
She said she went back and forth from R to D with foot on brake and that seems to resolve for now.
I do know it seems to be with the combo valve (PV2), front disc & back drum. I've heard the valve pop and release the back drums sitting in garage more than once.
Just fyi...

 

[Ricko1966]

It holds the front brakes off until the rear shoes can take up the clearance and contact the drum.

On the brake chart is is called "metering" (the characteristics of the proportioning are called "metering", "split" and "slope").

K

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Okay guys look at the gm factory combination valve that @Keith Seymore posted for us,that most of you call a proportioning valve. Look at the labeling it's called a combination valve because it does proportioning,hydraulic failure warning and brake stand off. So in a previous post I mentioned if you go with an aftermarket proportioning valve keep your combination valve in place so you would still have the brake stand off valve, and I think still having the shuttle valve is nice. Anyways @bucket And @xm20k both posted what I thought were combination valves with adjustable proportioning section. I couldn't find any info on the one bucket posted but the wildwood one is a distribution block with a proportioning valve in it. So I contacted Wilwood and asked about this. According to Wilwood install a 10psi residual pressure valve in the rear line if using this on a disc drum vehicle since you are losing the standoff valve. So even if running an seperate proportioning valve and distribution block I'd run a 10psi residual pressure valve. This makes my life easy because I already have everything except the residual pressure valve. I hope this helps soneone,it helped me.