2nd Gen Non-Engine/Transmission Rear brakes giving up

[AggieJustin]

I've got a early model 2001 with the drum brakes on the rear. As everyone knows, the rear braking performance isn't up to par. I keep the rears adjusted by hand after oil changes, and I've got a set of GM wheel cylinders waiting to go in. But I think I might have some other issues in play with the rear brakes.



Occasionally when coming to a hard stop, it feels like the rear brakes just completely release and only the fronts are doing any work. You can feel the rears grab at the beginning, but they just suddenly let go and you can feel the rear of the truck raise up as all of the braking force shifts to the fronts are. It doesn't do it all the time, but it does seem to be getting more often. It's not too noticeable on a slow stop, but you can really feel it on the highway when dropping from 70 to make a turn onto a side road.



According to the service manual, there is no adjustment to the proportioning valve. The metering valve, proportioning valve and pressure switch are all in one unit (which I imagine will be pricey), so I'm hesitant to just starting blindly replacing parts.



Has anyone else experienced this? Any input anyone can provide? I'd like to get some idea what might be wrong because I'll be out of town next week, so it's the perfect time for my truck to go into the shop to get this resolved.



TIA,



JM

 

[rkressg]

What is happening is, as you apply the brakes, the rear of the truck comes up in the air, which releases pressure on the rear porportioning valve (I. E. if you had a lighter load in the truck) and causes the rear brakes to loose braking power.



Just get rid of the rear load sensing valve, install the 1-ton wheel cylinders, and you should be fine.

 

[AggieJustin]

Do the '01s have a load sensing valve in the rear? I've looked around under the truck and haven't seen anything that resembles one. And I can't find anything about one in the service manual.

 

[AggieJustin]

BTTT



Anyone have any ideas on the load sensing valve? Or other input as to the problem if there isn't one??

 

[budctdca]

Just a thought, but if the release is pretty severe, it could be the master cylinder, but I doubt it, when you do the GM cylinders, I would flush the fluid out, as it loses it heat exchanging and lubricity capabilities over time. my . 02 cents worth

 

[ekonruff]

I have the same rear brake total release on my 99. Is there a load sensing device on it and if so will the same change work on it?



I looked in my shop manual and don't find anything and my "dealer service" doesn't seem to know anything about any problem or sensing device. (not really suprising as they couldn't service the automatic either).