Just swapped an entire brake system (master cyl, proportioning valve, front calipers, entire rear end, all the brake lines) from a 87 GTA w/rear discs into my rear drum 82 Z28.
Got everything rebuilt, bled, and adjusted as best I could.
Then experienced the same weak rear disc brake issue most everyone has.
Read through all the discussions and had a brainstorm.
If the spring inside the proportioning valve (for the rear brakes) is acting as a regulator, then MORE spring tension would be needed to increase rear brake press. Found some s/s washers that had the right inside and outside diameter and placed them between the spring and end-cap to preload the regulator spring.
Started with 6 washers, that was too much rear brake press. Started taking them out one at a time. Got to 3 washers and the fronts were locking first. Went back to 4 washers and it's nearly perfect; rears are locking just before the fronts. Still need to test them out in the rain, but looks promising so far.

What's really cool, was I didn't have to bleed the system
between swapping washers and test driving. If ya pull the rod/piston out you may have to bleed system.

A word of caution, the end cap will strip the alum threads in the housing if ya mess with it too much.

 

Nice work man. I was told that putting a tighter spring would make the rear brakes work less but it appears that it is the other way arround.

 

intresting...... i am always looking for ways to improve rear braking on ROC. what size washers did you use? keep us informed...

 

I was thinking, if the spring held the piston/rod in a position that would prevent flow until a certian brake press was obtained, that would not explain how the rear wheels would only slow to a crawl no matter how much brake peddle press was applied with car on jackstands and in drive.

If the spring/piston/rod assy actually made up a press regulator, that would explain the rears slowing but not stopping since only so much press could reach the rear discs.
On every press regulator I've ever seen, the more spring press, the more output press.

The washer sizes are 9/16" OD and 5/16 ID.
The first two washers that rest aginst the end cap need their ID reamed/filed slightly to fit over a nipple on the end cap. The other 2 washers were un-modified.
I forgot to measure the washer thicknesses, but I'm sure it's close to 1/16".

If anyone else tries this, I would be anxious to hear the results.

 

Last night it rained just enough to wet the roads.
Perfect time for a test drive!
In straight line braking, the fronts locked just before the rears.
(rears lock first on dry pavement)
Visited a local unpopulated freeway cloverleaf and tested the brakes going abt 40 mph around the long curves.
Both inside brakes (front and rear) locked at abt the same time.
Car drifted a little, but stayed controllable and pointed in the right direction.
I think I'll leave it just like it is.

 

Heya, i got a '91Z with the same rear brake problem and went to try out the washer method last weekend. I searched 4 hardware stores but the only s/s washers i could find with 9/16 OD and 5/16 ID were lockwashers. All of the normal 5/16 flat washers i saw had an OD much larger than 9/16. The closest one i could find in s/s was a 1/4 ID, 9/16 OD that I ground the inner diameter to be slightly bigger than 5/16. Unfortunately after all the labor I found it was in fact slightly larger than 9/16 on the OD and it didn't fit. Do you think maybe the washers you found were metric? If they were, i've not seen a s/s metric washer around.. Where did you find them?

 

Good job...
(tennis clapping in the backround) :-)

 

The washers I used came from the bottom of my toolbox. I think they may have been left over from my old job working on planes. Might try a local general aviation repair shop. They usually have a good selection of s/s fasteners. If they don't have them, they could tell you where to look.

 

:hail:

Wow, I am going through this same thing, and someone from the F-Body.Org 3rd Gen list posted this thread for me to see. My next step is to have the system pressure bled to make sure there is no air in the lines. If that does not work, then I will try this trick.

Watching the rears spin with the pedal to the floor is a disheartening feeling, especially with all brand new parts in the rear...

Thanks,
Brent
'88 GTA

 

to add a spin to this (pun intended), i took my spring and plunger out and made it better. now my theory on this is both ways are correct. depends on where the brake lines are connected to the valve. if the rear lines are connected to the rear part of the valve, then adding washers would be theing to do. if the rear lines are connected to the front of the valve, then removing the spring and plunger is the thing to do.

 

When you say remove the spring and plunger, are you talking about from the front of the housing or the rear? On the front, the cap is vented. Did you seal it with something? Or did you do this to the rear?

If you are referring to the front cap for these changes (add washers or remove spring/plunger), then it sounds like you disagree with ZZ28ZZ on the theory that more preload on the spring means more pressure. Am I reading that correctly?

 

Yes I posted the origional post on modifying the pv and I will be trying the washer way on my 88 formula but I removed the plunger and spring from my 89gta The way I found this mod was on www.gtasourcepage.com a guy moded his brakes by removing the plunger and spring from the pv and it worked so I tried it on my gta and it worked so I posted it over here. I will find the link and post it for you.

 

Here is the link for my fix but I will be trying the washer fix to see which I like more.

Edit I forgot to post the link

https://www.thirdgen.org/techbb2/sho...threadid=96449

 

ttt