We just installed a rear on my 91Z. Let me first start by saying yes I over did it with the gears but the price was too good to pass on.

We removed my old rear which was a 2.73 drum and replaced it with a 4.10 EATON POSI Disc. Replaced all brake lines, proportioning valve (OEM), new callipars and rotors. Put it all together and it goes pretty fast... The probem is the rear brakes are not working now.

I had to use the old eBrake cables that was attached they do not really work right now. Ordered new OEM eBrake cables from GM.

Can the fact that the eBrake cables do not wotk be the reason why I am not stoping?
Should I have changed the master cylinder because I added discs to the rear?

HELP please!!!!

So far I have not modified the motor. I know this has nothing to do with the brakes not working but I know someone is going to ask....

 

Which rear brakes do you have now?

 

I have OEM Discs

 

What year rear end?


Jay

 

That's part of the problem. I was told by the guy I got it from that it came off a '91 Z28.


I got the rear from a speed shop that was closing up.

 

what do the brakes look like...LT1 style?

Jay

 

They look the same as the fronts. Not LT1 style

I do not have the car here now or I would send you a picture.

The whole no brakes thing I chose to leave it the shop..

 

this is from a 91...to the right the shitty 10 bolt ...the left is a moser 12 bolt

Jay

 

Yep it looks just like that..
Can you offer any advise?

Does anyone have a thought on this...

 

TTT


HELP!!!!!

 

Is everything bled properly back there?

 

the back doesn't hold at all?

 

Yes everything is bled.

They are gripping a little very little.

I am thinking the proportioning valve I got must be bad.

 

Yeah if you went from drum to disc you should change the prop valve

 

Did change it actually had to add it. Do I need to ugrade the master cylinder?

 

you shouldn't need to, how do they work with the new prop valve?

 

They don't!

 

Does that rear end have rubber lines from the hard line to the calipers? Those get kinked pretty easlily and can cause failure.

 

I would check to make sure you are getting good flow when you hit the brakes (after you bled thme) I've seen those solid brake lines kink up when the rear is lifted.... so i just got new lines

 

I am waiting on the new brake lines to come in.

 

i'm not certain on this, but i think (heard somewhere) that the master cylinders are different from 2w disc to 4w disc cars and the 4w disc master is a higher pressure for the rear and that a prop valve alone won't cut it..i have a similar situation on mine although not as bad.

 

I noticed when I was looking for parts that the master for 4w disc was different. I am sure that is probably it.

I was able to get about 75% brakes out of the rear. Next thing to change is the master.

 

Now that you mentioned it, I do recall reading a thread on another forum over this issue, you should still get basic brakes tho, hopefully those new lines help some

 

please keep us updated as to whether or not the new master cylinder fixes the problem so I can follow your lead and do the same....