I have a 95 3/4 ton Suburban that I have been fighting with a weak rear brake problem for about two years now. Everything is new by now, I tryed everything possible from sensors to bearings. It seems the problem started when I went in the engine to change the cam and polish the heads among a few other little things. Does any body else have this problem or is it the engine work that has caused this problem. I should give a little more info such as engine size: 454, when problem occurs: when ever truck is not in park or neutral, and pedal feel: good and firm throughout travel. Thank you and I hope I can be of help to someone else someday.

What all have you replaced?

Without hearing more details or knowing what you know about cars, I have the following guesses:

The load valve (not the real name, can't think of it now) on the rear axle. It's there to provide more braking when there is weight on the back. If it is disconnected you would have little to no brakes.

Swolen rear brake hose(s). Have you bled the brakes? Fluid should come out the same as on the front.

Star wheel. Make sure the rear is adjusted right. If they are working properly, you can back up and hit the brakes to adjust them. Keep doing this until they feel right.

Would I be correct to assume that you have a hydraboost system on your vehicle?If so ,are you getting the required amount of hydralic boost to your master cylinder?This may be another area to investigate.
chuck's

OK guys thanks for the advice so far. I was unaware of a "load valve" being on my vehicle. And the brakes are bled the same as the front, and are adjusted to the point that I'd say is too tight.(too much drag). Also what is hydraboost? I checked vaccum and its fine. Where should this "load valve" be? Thanks again!!

From your last post it appears that you don't have a hydraboost system.It uses fluid from the power steering pump to create the boost instead of engine vaccum.The load valve should be located along the frame connected to the rear brake flex line.You should also see linkage connecting the valve to the rear diff.The linkage is what controls brake pressure in relation to the weight on the rear axle.I hope this clariffies things for you.
chuck's

OK I just checked engine vaccum. Hydraboost would be a few lines comming off the power steering pump. I do have this then. As for the load valve I must have it cause this truck has everything that was available then. I must not have noticed it before though. Hope this helps a bit more.

Hi, the load valve is the rear proportioning valve that will let more brake fluid through when the rear is loaded down.
It is a normal part of the basic braking system. Nothing fancy or optional.
Take care, Eggert :bananasmi

OK guys, I checked the load valve apeers to be fine. Now about this hydraboost?????? what should I be looking for? I did find that the brake line was zip tied to the axle(apeers that who ever I had do the exhaust thought that it might hit the exhaust) and it had a sharp bend to it but it wasn't kinked. I cut the tie and it was no where the exhaust. I haven't got to try it yet but I don't think this was the problem.

You changed the cam so that changed the engine vacuum used by the brake booster

Hydraboost simple check is with the power steering pump.With the steering wheel turned all the way against the stop in one direction listen to the sound of the pump.Then, with the wheel still turned all the way against the stop,press the brake pedal.If the sound stays the same,the pump should be good.You shouldn't hear a loud growling coming from the pump.The belt should not slip at any time testing the pump.Hydraboost lines go from the pump to the brake booster, down to the steering box, then return to the reservoir of the steering pump.Did you ever change the rear wheel cylinders during the two year problem period?If you did ,was the proper size cylinders given to you?Has the master cylinder ever been changed?The master cylinder may be leaking internally and not generating enough pressure in the rear system.You could also visually observe the rear flex line as someone depresses the brake pedal.You should see the line swell as the pressure in the line increases.You can compare it to the front lines,but remember that the rear should swell more because the pressure divides after the line(don't forget about load valve) whereas the front pressue is split before reaching the flex lines in the front.I hope this helps.
chuck's

Changing the cam didn't change the vaccum at all. It is a mild cam. Also the master cylinder has never been changed and has been checked thoughrolly and is not leaking. The wheel cylinders have been changed 3 times. And I am sure they are correct. Power steering pump could use a flush when I checked the hydraboost. Could this cause something?

I don't think that the fluid in the power steering reservoir will affect the brakes.My final suggestion would be to disconnect the rear link from the proportioning valve and move the valve maually to a different position,lock the link in that position,(maybe with mechanic's wire) and then try the brakes.See if there is a difference in how the rear brakes preform.
chuck's

On the Hydraboost system p/s fluid is VERY important

Ok how does this sound, I just get rid of the ABS system totally and put in an equalizer block and switch back to the "old" style of no ABS system. I just realized that I forgot to mention that the ABS system is not working, and has never been since I bought the truck.(sorry if this clouds things from earlier.)

I found that M75 said this in another thread concerning the Suburban's brakes:

"A TSB was published from GM addressing this issue. I own a 95 1/2 ton 2WD with 5.7 engine. Disc/drum brakes.

The TSB indicates replacing the rear brake shoes with kit # 18029651, the front disc pads with kit# 12471685, and most importantly, replacing the brake proportioning valve with Valve Kit # 125448265. Seems the trucks and Subs were classified as being of similar design/dimensions for braking purposes, when in fact the increased body weight of the Sub versus the pickups have always placed a heavier than normal load on the brakes of the Subs. The brakes of the series were designed for a truck much lighter than a normal Sub,,,it only took a few years (and many worries from owners!0 to realize the vast difference between the models!"

I own a '99 and I don't like the brakes either. I'm trying to figure out if I have this proportioning valve installed in my truck or not. I hope this information helps...