This past weekend I did the front ls1 brake swap.Stops better then before I must say lol.But can be better if the rears work.Working on a 87 iroc so I have the pos iron calibers.I planned on doing the ls1 rear swap as well.But if I can "bolt on" different calibers without changing the backing plate are change the spring in the valve.Just tell me what should I do.

 

Changing the prop valve spring is cheeeeeep and eeeeeeezy. Won't substitute for better brakes period, but might at least make them detectable on occasion. I'd say, go for it, while looking for something that actually works.

 

For those with rear brakes that won't hold when the rear is supported on jack stands, what is the correct OEM fix if skipping the spring trick? My stock 88 disks and my upgrade to 89 PBRs are just along for the ride.

Is the true root cause a faulty prop valve or master cylinder?

 

I've been trying to get the early 4th gen PBRs that PO swapped on to the car to work better for a long time. Tried the stiffer spring, replace master with a NEW unit, replaced all brake lines, bled everything really well, and it still will barely hold the rear wheels if at all. For me the solution will be to bypass the stock prop-valve and go to an adjustable prop-valve for the rear. I haven't found the time to do that yet, but just wanted to share my experience with the PBR brakes.

 

That sure is frustrating. I want to avoid adding an aftermarket valve if possible. I hope the spring works for me, but I also don't like the idea of just putting a bandaid on it.