Brake bias problem - help needed

[GeoffP]

Hi guys,

While at RTTH this past weekend, I found out with the help of Michael Tucker that my car's brake bias is messed up. I can't lock the rear wheels no matter how hard I push the brake pedal. The car in question is my 68 Camaro. It has Prodigy Customs whole car brake kit (bought several years ago). The system is all Wilwood. It has 12.19" drilled and slotted rotors front and rear, DynaPro 6 calipers in the front and the standard Dynalite 4's on the rear. Braided brake lines for all the flex lines. Dual diaphragm brake booster with a old style Corvette 4 wheel disc master cylinder and a generic brand adjustable proportioning valve. The prop valve is turned all the way in for the highest rear line pressure and I removed the OE prop valve when I installed everything so that's not an issue. Dutch from Baer suggested that I had a few options to try to fix it: 1. bigger rotors 2. swap brake pad compounds until I find one that works 3. replace the calipers for ones that have a larger piston diameter. I think I prefer option 3 but I'm honestly not sure where to start as far as figuring out what caliper in Wilwood's line I already have vs what I should look at for replacement. I really think I'm to the point that I really need to work on tuning my car to get any faster on the autocross so I would love to figure this out before GG Charlotte since I'm thinking about going.

Thanks in advance for any help y'all have for me!

[rchaskin]

Brakes are over-rated......it is way more fun sliding off the course under power!!!!!!!
HAHAHAHAHA!!!!! What a fun day!!

Good luck with the brakes.

You might want to try another Adj prop valve.....maybe the wilwood unit.

Randy

[GeoffP]

No doubt sliding through the cones at the top of the straight was exciting!! Thanks - I didn't think to try another prop valve. That would be cheaper to try than calipers.

[Apogee]

What pads are you running now? Have you scuffed them and the rotors to make sure they're not glazed?

Otherwise, if you have access to a caliper pressure gauge(s), I would check to see that you're getting the same pressure front and rear first. If the rear caliper pressure is lower, I would check the line pressures at the outlet pot to the rear brakes, which should tell you if you're having an issue with the proportioning valve or not.

While you're digging into the rear brakes, measure your caliper piston diamters and calculate your piston area. Odds are it will have either 1.12" or 1.38" pistons for equivalent piston areas of 1.98 or 3.00 square inches. Similarly, the Dynapro 6-piston caliper is available with several areas as well, 3.08, 4.04, 5.06 square inches, so knowing that could help with troubleshooting as well.

Tobin
KORE3

[GeoffP]

All I know is that the pads are poly matrix pads. It's whatever came in the kit since I took it for granted that Prodigy was providing matched components. I didn't know enough to log exactly what part numbers I got. Now that I've reviewed Wilwood's website I've found out that I should've logged the part numbers for reference. Oh well - you know what they say about hindsight being 20/20. I think I'll probably need to buy a brake pressure gauge and I'll have to pull the system apart to check the piston sizes unless there's a number on the calipers somewhere that will tell me?

Thanks for the input Tobin! The system I have on my car is my first aftermarket system so I had no clue where to start with trying to troubleshoot it.

[jpgolf14]

Wilwood prints part numbers on the calipers. Find the part numbers and post them up. For location, you can see where the number is printed on my FSL's. See bottom inside face of caliper.

Right click - view image for larger version.