Load valve in rear brake line

[kipps]

SweetK30 mentioned that this is commonly bypassed. How does this thing work?

My theory is that it's a simple valve that restricts braking force when unloaded. When loaded, it opens the valve, allowing full braking force. If true, a simple removing of the valve will bias the brakes toward the rear, since removal is the same as fully loaded. If it's removed, it seems the proportioning valve should be swapped out for a truck that did not have one of these load valves. Correct or no?

Is this valve even a problem? Why remove it?

Here's another thread discussing the issue, and evidently GM issued a tech bulletin a few years later instructing on how to bypass the valve. Keith Seymore says the valve was intended for passing a specific government test, and wasn't really applicable to the general populace. I have a little hard time believing that.

How does this valve fail? External leak only, or does it ever mysteriously block the rear brake line either on or off?

[sweetk30]

guys swap them out all the time like i said n problems. i have done it my self on one .

yes its a flow restriction when unloaded . but the problem is the older they get the more they freeze up and don't work so then your doing front brakes only .

you dont need to remove it . its just a bit of info i gave incase you ever were going to ask about it .

i am sure others will post up in here on there feedback of them .

[Nodnarb76]

I'm in on this. My Suburban has one, and I would like to remove it. Curious to see what everyone comes up with.

[kipps]

Originally Posted by Nodnarb76

I'm in on this. My Suburban has one, and I would like to remove it. Curious to see what everyone comes up with.

On the contrary, I want to keep mine, unless someone convinces me it's a safety or dependability issue. I'm going to be carrying widely varied loads, though.

[sweetk30]

my 1 k30 i have is 6,300lbs average weight . i have used it for daily driver to loads . years ago i did a few load from the gravel pit with 4,000 on the truck and around 4,500 in the 8ft pickup box trailer with gravel . she stopped just fine with no brakes on the trailer . now i wasn't doing 70mph or long distance but she was just fine.

when i build my trucks i do a tee fitting for the front and adjustable bias valve rear and ditch the stock valve on the frame under the rad . few test drives and she is dialed in better than factory ever felt .

[dieseldawg142]

ditch it, your brakes will feel way better.
mine was rusted up and doing nothing really.
brakes harder now, never had any kind of lock-up probs at all with it gone. i too haul alot on my k30, camper and trailer-16 k
mines been gone for yrs and the only thing i got from removing it was better braking

[kipps]

Has anyone ever opened up one of these to see what's inside? It looks doable, but I don't won't to damage a working one.

[SunSoaked]

I removed mine recently. It makes absolutely no difference. Only reason I took the time to remove it is because it was in the way of my dual exhaust I installed. It's mounted on a bracket that is obnoxiously in the way. I drilled the 2 rivets out and removed the bracket. This will leave about a foot of excess brake line hanging inside the frame at a 90* angle. Instead of cutting and flaring lines to make it all pretty I found an ingenious solution. Carefully straighten the bend in the front line up against the inside of the frame rail. Then buy a 20 inch braided hose from Skyjacker. It's a perfect bolt in without mods! Anything more than a 2" lift will need a longer hose. No extra fittings, line or adapters needed.

[kidatheart]

Originally Posted by sweetk30

my 1 k30 i have is 6,300lbs average weight . i have used it for daily driver to loads . years ago i did a few load from the gravel pit with 4,000 on the truck and around 4,500 in the 8ft pickup box trailer with gravel . she stopped just fine with no brakes on the trailer . now i wasn't doing 70mph or long distance but she was just fine.

when i build my trucks i do a tee fitting for the front and adjustable bias valve rear and ditch the stock valve on the frame under the rad . few test drives and she is dialed in better than factory ever felt .

So, if I understand this correctly, when you build a truck you don't run the front brake lines through a proportioning valve at all? Just the rear through an adjustable, correct?

[sweetk30]

Stock valve is just a tee for front . Rear is a fixed reduced flow with flow pin to trip light if loss of line pressure .

So my way updates the rear to let ME adjust rear bias as I want it to feel .

[SunSoaked]

Exactly. You want 100% pressure to the fronts at ALL times. Adjust the rear so they provide maximum pressure without locking up.

[SunSoaked]

All the factory load sensing valve does is reduce pressure to the rear brakes under NORMAL load. Load it up, the vehicle squats down. This moves the lever and changes (increases) the pressure to the rears. It's a very crude system that produced negligible results. Unless you conduct controlled tests with maximum braking under load, you'll never detect a difference.

[DieselSJ]

There is an ex-GM engineer lurking here. I remember him posting that the valve was added to pass a very specific braking test for the feds and that it wasn't necessary and he bypassed them whenever he reworked the brakes on his trucks.

[Keith Seymore]

Originally Posted by kipps

SweetK30 mentioned that this is commonly bypassed. How does this thing work?

My theory is that it's a simple valve that restricts braking force when unloaded. When loaded, it opens the valve, allowing full braking force. If true, a simple removing of the valve will bias the brakes toward the rear, since removal is the same as fully loaded. If it's removed, it seems the proportioning valve should be swapped out for a truck that did not have one of these load valves. Correct or no?

Is this valve even a problem? Why remove it?

Here's another thread discussing the issue, and evidently GM issued a tech bulletin a few years later instructing on how to bypass the valve. Keith Seymore says the valve was intended for passing a specific government test, and wasn't really applicable to the general populace. I have a little hard time believing that.

How does this valve fail? External leak only, or does it ever mysteriously block the rear brake line either on or off?

I appreciate the vote of confidence.



I did total vehicle development (including brakes) for the C/K/R/V programs at the GM Milford Proving Ground from 1986 - 1989. I did brake and driveline development specifically at the GM Desert Proving Ground from 1990 - 1994.

MVSS brake testing is so specific that some combinations would be borderline pass/fail in portions of the test procedure. We would request certain brake technicians by name to drive those tests during development and validation, just to be sure (if you don't pass the test you are legally blocked from selling trucks). Since we would "self certify" for brakes, noise passby, etc, you could also classify those as "development" tests and keep repeating them until you finally got one to pass, and then reclassify the successful run as your "validation" test. Those portions of the tests don't have any real correlation to actual customer usage, because you personally are probably not going to run a statistically designed experiment to determine if your stopping distance at GVW is "x" number of feet vs "x+1" number of feet at 150 lbs pedal force, and then trade that off for similar data at lightly laden vehicle conditions.

It's a Rube Goldberg device. Usually the failure mode is the linkage corrodes or gets gunked up and binds. If it fails it is probably going to fail in the reduced pressure configuration, and I'd rather have full brakes at LLV than not enough brakes at GVW.

I'd remove it, on top of everything else, for the simple reason I don't like any of that extra claptrap under my trucks.


K