what will happen i was to drive with a disc/drum combo valve and i have a 4 wheel disc setup?

 

the rears wont work as well as they could

 

mine actually worked better!

 

Perhaps the rear discs themselves work better than the drums. If so, they'd be better yet with the correct valve, IMO. The following from another post:

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/susp...fferences.html

There are different combination valves (if only one was needed, why would GM design valves for different applications?). For exampe:

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

Using the correct application seems to be the right approach to me, but I'm a bit **** in such matters.

JamesC

 

My 89 IROC had the J65 brake option, so I never had a problem when it was changed to a 93 rear disc setup..

 

The rears are actually worse with the ile valve ?