1995 Chevy suburban c2500 7.4 combination valve modification.

[superchevysb]

I have read a lot of posts about the Suburbans having very poor rear brakes and mine as well. I finally pulled the proportioning valve apart and removed the spring and rubber plunger that actuated the pressure limit and it stops so much better. Also by removing the spring the valve no longer has the cushion of the spring to push against and is just bottomed out now so that greatly improved the peddle feel also. Finally getting some use out of them huge 13x3.5 Inch drum brakes! Another thing I noticed on my 1998 k1500 pickup it has the same ABS unit and combination valve except the rear section on the valve is cast solid and has no pressure limiting proportion valve so it gets full master cylinder pressure just like the one I modified does now.

 

[Spareparts]

My brakes seem to work fine, No complaints. I did need to replace the hydroboost though not long after i got the truck maybe that why?

 

[Schurkey]

I have read a lot of posts about the Suburbans having very poor rear brakes and mine as well. I finally pulled the proportioning valve apart and removed the spring and rubber plunger that actuated the pressure limit and it stops so much better. Also by removing the spring the valve no longer has the cushion of the spring to push against and is just bottomed out now so that greatly improved the peddle feel also. Finally getting some use out of them huge 13x3.5 Inch drum brakes! Another thing I noticed on my 1998 k1500 pickup it has the same ABS unit and combination valve except the rear section on the valve is cast solid and has no pressure limiting proportion valve so it gets full master cylinder pressure just like the one I modified does now.

The whole point of the proportioning valve is to prevent the rear brakes from locking before the front brakes.

The reason is that when the front brakes lock first, the vehicle will skid in a straight line. When the rear brakes lock first, the vehicle becomes uncontrollable, the ass-end will slide around whatever way it wants to.

What you did is NOT a good idea. You should have fixed whatever was wrong, instead of defeating a device designed to keep the vehicle controllable. Perhaps having functional ABS will help. Maybe...maybe not.

 

[someotherguy]

The reason is that when the front brakes lock first, the vehicle will skid in a straight line. When the rear brakes lock first, the vehicle becomes uncontrollable, the ass-end will slide around whatever way it wants to.

What, you mean the front and rear swapping ends during hard braking is an undesirable outcome?? Who knew?

Richard

 

[superchevysb]

The whole point of the proportioning valve is to prevent the rear brakes from locking before the front brakes.

The reason is that when the front brakes lock first, the vehicle will skid in a straight line. When the rear brakes lock first, the vehicle becomes uncontrollable, the ass-end will slide around whatever way it wants to.

What you did is NOT a good idea. You should have fixed whatever was wrong, instead of defeating a device designed to keep the vehicle controllable. Perhaps having functional ABS will help. Maybe...maybe not

 

[superchevysb]

The whole point of the proportioning valve is to prevent the rear brakes from locking before the front brakes.

The reason is that when the front brakes lock first, the vehicle will skid in a straight line. When the rear brakes lock first, the vehicle becomes uncontrollable, the ass-end will slide around whatever way it wants to.

What you did is NOT a good idea. You should have fixed whatever was wrong, instead of defeating a device designed to keep the vehicle controllable. Perhaps having functional ABS will help. Maybe...maybe not.

What ever is wrong? There is a TSB out for that rear combination valve not applying enough rear hydraulic pressure and the rear shoes are useless. My abs is completely functional and the modification I did does not change the the sequence that the brakes apply in. Front still apply first. The combination valves found on the 1500's have no rear brake pressure limiting built in to the valve it is cast solid and has straight fluid passages through it and those light back ends of those truck do not skid out either. The abs has complete control of that and the fluid apply sequence. So I can either have completely none functioning rear brake that increases my chances of never being able to stop in a panic or I can now have good working balanced brakes that I can predict with the assistance of the abs as well. IV tested the brakes in many situations and they still will not lock up the rear in the wet. Also before with having limited rear brake fluid pressure due to the factory limiting device it would lock up the front brake and skid very easily. Just idling around a stone driveway the 454 has so much torque it would just skid the front everywhere. The safety function and sequence function of the valve is still the same as it was. I don't just make changes for no reason I spend a lot of time researching and evaluating the possible outcomes of my planned modification.