Thinking that my proportioning valve is bad I replaced it with one that had rear drums, mine has 4 wheel disc. What is the difference between the two, and will i notice a difference?

Thanks in advance!

 

Depends on what your car is and what brakes are on it.

If it has the 82-88 cast-iron calipers, a drum valve will render them even more useless than the dead unsprung weight they already were. Not only will they merely not do any braking and just add weight in the worst possible place, but the wrong valve will even prevent the fronts from living up to THEIR already limited potential.

If it has the 89-up aluminum calipers, those won't be quite as adversely affected; their hydraulic requirements (fluid flow, pressure, etc.) are more similar to drums. In fact for a couple of years, maybe 91-92 or so, the drum & disc systems used the same prop valve.

Of course, since this is already a done deal and not "research" of a "potential" "future" purchase, you could just drive the car, and come back and tell US how it acts, so we don't make the same mistake (or, so we know what we can successfully do if we need to, as th ecase may be).

 

In searching I've found that 89-91 shows the same Cylinder, Brk Master GM 18014286. Earlier years show different masters for J50 and J65. GM, however, pretty much made them interchangeable (All have the 'quick take up' master):

https://www.thirdgen.org/forums/su...fferences.html (Master Cylinder Differences)

There are different combination valves for 89-91:

Valve, Brk Combo (1989 2nd Des) (J50) (1990 [and also 91]) (J41, J42) GM 10136839
J41 - BRAKE SYSTEM, POWER, FRONT DISK, REAR DRUM, CAST IRON
J42 - BRAKE SYSTEM, POWER, FRONT DISK, REAR DRUM, ALUMINUM

Valve, Brk Combo (1989 1st Des) (J65, 1LE, Y82) GM 14089496
J65- BRAKE SYSTEM, POWER, FRONT & REAR DISK
1LE - PERFORMANCE PACKAGE, SHOWROOM STOCK RACING
Y82 - MERCHANDISED PACKAGE, FORMULA

At any rate, for best performance, use the correct valve for the braking system you're running.

JamesC