OK,this topic may have been beat to death, but I am so happy I must post!! I have a 85z that came with drum rears. I went to a pick and pull and grabbed a 87 rear disc. After the install, I was not real happy. Last weekend, I did the bolt mod(very easy!!) and you wont believe how much better the car stops now!! I did auto cross the car today and I was able to point and slow down SO much better then this car has ever done since I have had it! Man, what can I say!! I am so happy with this cheap ($$) upgrade!!

 

Ok. I'm lost. What bolt mod? Please explain.

 

ditto.

 

im thinking the bolt in the stock combination valve when you take out the plunger and all that maybe? I did it to mine but it's still restrictive. but i do have the pre-pbr disks also.

 

Ok, here is what I did. On the portioning valve, there is a bolt on the bottom, remove it and take out the spring and valve. Then, I drilled out the bolt with a size 8 and tapped it (it's a real smaal one) I installed a small allen set screw and put thread lock on it. Reinstall the bolt and bleed brakes.

This is what I got. I autocross the car all the time and the rear disc's have always looked rusty and I just installed 900lb front springs and before the mod, the front brakes locked up real bad. Now, no lock up and I have shiny rear disc! The car stop's very fast.

This mod was done on 85z that came with factory disc/drum setup and I installed a disc rear myself. Cost was the best part. I think I spent $12 bucks for the drill bit, tap and allen set screw.

 

im interested in this project, but after reading your post several times, i still dont understand what you mean by drilling the bolt,

 

you dont need to drill anything, find a spare combination valve and take it with you to a bolt/nut specialty place or lowes had one that worked for a friend of mine that did it.

 

Any of you happen to have pictures? If not don't worry. Ill just pick up a 1LE valve. My rear breaks are weak. And its all new and 89 pbr's

 

What exactly does this mod do or what is the indended purpose of this?

TIA

 

it allows more pressure to go through the line unrestricted. That's why you use a adjustable proportioning valve. If it quits raining I'll snap a picture of ow I did mine. I don't know what that guy did. Now that i've been thinking about it though. I would have rather just skipped the combination valve all together.

 

i wounder if running full pressure to the rear will make it perform better......i suppose if you had some nice wilwoods in front (the 4 pot kind) it might work. (lock the front before the rears i mean)

but no tuning....

 

http://www.cardomain.com/memberpage/205049/10
not my car but maybe help
did it to my car befor i put c4 hd's on the front, 98 ls1 rear end in and a adjustable pv and it did help alot but the back brakes do lock up first whith the mod so take care brakeing hard in the corners

 

I feel like a moron, i understand completly now.

Anyone happen to know what is the correct hex nut to use as a replacement plug?

 

the thred size is 5/8" - 18