I have a 91 z28 350 car with a drum brakes rear end .
I assume someone changed this out at one time.....
Question I have......would the master cylinder or proportioning valve have to be changed out also...........?
Thanks

 

No. Yes, for best brake performance (I'm assuming you wish to swap in discs).

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

 

Your car has the original drum brakes from the factory. Parts shortage of rotors resulting in deleting disc brakes from some models in 1990/1991.

Master brake cylinder will be alright but the proportioning valve will need to be replaced for the rear disc swap.

 

It will not "NEED" to be replaced. Many on this forum have done a disc brake swap, and said they see no difference, while on the other end many safety nuts argue it's best.

While I do agree it's best to swap the right proportioning valve in, it's not completely necessary. My advice would to do the rear swap, and test the feel of the car in dry/wet conditions.

I have a disc brake setup out of a 4th gen sitting in my garage that's going to be installed after I install 4.10's in it, and I will not be installing the "correct" proportioning valve until I test the car out.

 

Keep in mind that GM developed a disc/drum, a disc/standard disc, and a disc/1LE valve for those applications.

While any of those valves will function, as I say above, for the best brake performance, the correct valve would be the best bet.

JamesC

 

Why not just put an adjustable prop valve somewhere along the rear lines....like under the drivers seat for instance?
You can change the brake bias to whatever you want....no?

 

Went to look for the RPO code sticker and its missing(glove comp. and rear comp.) .
Is there anyway to go to GM with my vin# to see if they can pull what options my car has.........?

 

NO....GM deleted all the records on cars 10 years or older.

 

I swapped to a disc rear in my 89 RS that had drums originally, and I ran the drum prop valve for quite a while. It didn't work ideal, but it did do the job. If you do decide to install one of the rear disc prop valves, I'd highly recommend the 1LE valve. Lots of guys with the factory J65, 4-wheel disc prop valve have complained that it doesn't give enough line bias to the rear discs. In fact, if you have the rear of the car up on jackstands and put the car in drive, you have to damn near stand on the brake pedal with both feet to get the rear wheels to come to a full stop! The 1LE valve will cure this since it puts quite a bit more line pressure to the rear calipers. Of course as mentioned above, you can always put in an aftermarket, adjustable valve, but that requires cutting and reflaring some of the brake lines to install it. If you want a simple, bolt-in solution, the factory 1LE valve is the easiest and most effective valve to use. I installed the 1LE valve in mine after using the drum valve for a couple of years with the disc rear, and the difference in stopping power to the rear discs was pretty amazing. Btw, there was 2 different 1LE valves since the thread pitch of the brake lines were changed halfway through the 1989 production year. Since you have a 91 car, you'll want the 2nd design 1LE valve. I don't have the part number handy at the moment, but a quick search on this site for "1LE Prop Valve" should turn up plenty of posts with the part numbers for each of them.

 

Both 1LE valves can be found below:

http://www.flynbye.com/catalog/c1_p1.html

JamesC

 

Save alot of money and order from
http://www.gmpartsdirect.com/

Orginal GM PN: 10164112
'90-92 1LE/J65 Proportioning/Combination valve
GM factory 1LE/J65 rear disc brake proportioning/combination valve for 1990-1992 applications.

Just search at gmpartsdirect using the original gm part number, and it's $65.44. Call them first to verify it's the right part though. I ordered a little clutch pedal rod detainer (plastic clip) that was impossible to find, but found it from them and ordered it for like $10 shipped.

 

Perhaps a check at your local dealership might prove beneficial. I purchased my first-design valve there for $67.97, albeit back in Feb. of 03.

EDIT: Sick, put the above part number in GMPartsDirect and see what the shipping/handling charges are--oh, call the paramedics in advance.

JamesC