Hello all, I recently Upgraded the rear brakes in my 86 Trans am from Drums to Disc's. I Installed a Pair of Wilwood Dynalite Pro Series Disc Brakes. I upgraded to a Stock GM Disc Brake Prop Valve, Wilwood Master Cylinder, Stainless Steel Brake lines all around and Steel Braided Flex Lines going to the Caliper.

Here my Problem, When I Have to Stop Slowly (say stopping at a stop sign) the brakes respond well. But when I have to stop fast (say a panic stop) Or when heavy pressure is applied the car stops horrible. It almost feels like I have half a pedal or like there is something preventing the pedal from being pressed down. The car doesnt want to stop. My old Drum Brakes worked better than these. The wheels dont lock up either when the pedal is pressed hard and fast.

Any help would be great as I try to figure this one out.
The Front Brakes are all stock.

 

Post a link to the brake kit and the master cylinder.

 

Here are 2 Links

Brake Kit
http://www.summitracing.com/parts/WIL-140-7582-D/

Master
http://www.shop.speedunlimited.com/p...-112-bore.aspx

I am running a Currie ford 9 inch in my Car.

 

So the front are the same? Does it seem like the fronts aren't working as well either?

Did you bench bleed the master cylinder?

Which GM disc/disc prop vavle did you use? there are at least two different ones.

 

The Fronts are stock. No they dont seem to work well either the car as a whole doesnt want to stop.

Yes I bench bled the master.

I cant find the receipt for the Prop. The Numbers I pulled off it are listed below.

10994900 ACH K/H - Off the Black rubber Cap on the Front of the Prop.
NB 14 KH 1479 or 1473 - Stamped number off the LT Side of the Prop
502525757- Engraved number off the LT side of the Prop (Hard to see this one)

 

By going to the larger bore Wilwood M/C (1.2") you decreased the line pressure by approximately 38%. This is why the brakes no longer work as they should.

Need to get a M/C with a bore of about 24 mm to be the same as the brakes originally were.

RBob.

 

Thanks for the input Rob. Is there anyway I could modify mine or do I have to replace the entire Master? Also I think the bore size is only 1.120.

 

I would just put on a stock master cylinder and see how it responds.

 

Yes, 1.120", not 1.2", too early for me to be posting. However, that is still a 29% reduction in line pressure.

The other item is what brakes pads did you use? Although, it appears that you only changed the rear brakes, lines, combo valve, and the M/C. So the front pads are the same as before? If so, we are back to the reduction in line pressure.

Or the combo valve is bad. The best way to troubleshoot this is to get a brake caliper pressure gauge.

If you still have the stock M/C, bolt it on and see what happens.

RBob.