Sounds like a brake pad issue.. If you are not having problems on the street but then comes race time and you are losing some pedal.. What is the part # on the pad you have right now? You need to find pads that have a higher coefficient of friction when you get them hot when autocrossing or open tracking.. More than likely you have a BP10 or 20 which will fade after a couple of laps.. street pads..

What brake fluid are you running? I hope you are not running dot 5 silcone..

I have a car in the shop that is set up for open tracking with smaller rotors, calipers & tapper bearings & have never had the customer complain about losing pedal or pad knock back

Hey Gonzo,
I read your PM and was going to look into the pads before I replied. I'm pretty sure they are BP10's. I looked recently and checked them on Wilwoods site. They are street mild track pads. It's not the pads even though braking improves with heat. I can replicate it easily on the street by doing a slalom. The pedal engagment point drops 2-3 inches. I'm running Wilwood Dot 3 fluid.

I would try some 15E or 15B pads.. I would not run BP10s for agressive street driving or autocrossing.. I have tested all of Wilwood pads & these are the ones that have worked the best for me!

Don't rule out pads!

This has been going on too long! How much could the excessive body roll be contributing to the lateral load on the caliper?

How much would 1" smaller rotors reduce the knockback vs how much performance would you sacrifice?

Is front spindle deflection a contributing factor?

You've probably done numerous hours of searching and reading on the subject and already seen this but:
http://www.stoptech.com/tech_info/wp_knockback.shtml

One way to possibly isolate the issue would be to test with active knickback springs in the suspect calipers.

This has to be very frustrating after a couple years, numerous hours and dollars. :mad:

Todd check your set20 bearings, my play increased after mileage and abuse. I now consider them a racing wear item. And it was not bearing wear is was the axle sideloads that put wear on the bearing seal cup.

I think Todd has thrown just about everything at this issue....

Yep, the rear bearings have loosened up. I've even thrown some shims behind the races with no noticable change. I want to go floater but hear a certain someone may have a solution in the works. :lol: (not me)

I adapted these to work on my car, it’s not a kit but just some parts that I made work, I had to make my own brackets, knockback is gone and the car stops amazingly well.

Rick, thanks for sharing your idea. I'm just not sold on a smaller rear caliper as hard as we run these cars.

Todd I agree with you but this did eliminate the problem and overall my brake performance is way better then when i had the 4 piston rears, another problem with this small calliper is they dont make an aggresive pad for it.

I will continue to work on another setup involving a 6 piston caliper that i can convert to a floater, more like a floating bracket.

Todd, you've been dealing with this problem for what seems like forever. When I started having knock back issues this thread was a wealth of knowledge on the situation. I read this whole thing over carefully, and went back and forth on how I was going to try to address it. Having seen all of the work that you did to try and find an adequate solution, I decided to go with a floater. I wasn't sure whether or not it would be overkill. Yes, tapered bearings and a 1" master cylinder have worked, Bad Penny being an example, but I didn't want to run the risk of having it not work, leaving me having to put up with the problem, or throw more money at it.

From the four autocross runs I did before I had to retire my car, I can tell you I didn't have any problems with the floater under the car. Hopefully nothing pops up after more track miles! I know you're tired of spending money on the car, but IMO the presence of mind in knowing that you wouldn't have to screw around later would be worth the 1500-2000 for the floater.

... You probably didn't need my little testimonial though :lol:
Feel free to give me a call if you are seriously contemplating the change, or give the guys over at Wilwood and Speedway a call. They worked together every step of the way, and came up with a solution that was very reasonably priced considering I replaced everything except the third member.

Matt

Matt, I appreciate your insight. I did speak with Dustin at Wilwood at the event and he mentioned they could adapt a floater to my caliper. Put some more miles on your set up so I know it's a sorted out fix. :D

I drove my old 69 @ RTTC.. Here are the specs on te brake system that I set up 7 yrs ago..

12 bolt rear with stock c-clips
12 inch disc with bridgebolt Dynalites, 1.38 bores, 1/2 thick non-vented rotors
Front- bridgebolt Dynalites, 1.75 bores, 12 inch disc/.810 thick rotors
1.00 bore cast iron 69 Corvette Master cylinder.
I can't even remember what pads I put on it.. but I think they were the old tan pads.. I had brake fade on the first day .. but by the 2nd day pads were gripping & no brake fade.. but was using less brake as I got used to the car & the track..

Never experienced knock back issues!! but was only running 255-18 in the rear & 225-18 in the front..

Quick solution to your problem Todd.. Change to floating calipers in the rear!
Expensive solution.. Full blown floating rear end!!

Apples and oranges buddy...:D

Todd, I forget to tell you I tried the floating caliper thing out. We put the brakes on at BOS, however, it was on the test drive immediately afterward that I got hit by the lady running the red light. so I couldn't tell you whether or not they solved the problem. The C6 Z51 brakes literally have maybe a mile on them. They're just sitting on a shelf full of parts right now. If you want to "try" them out I'll send them your way. If you put a track day on them and they don't work, just send them back, if you want to keep them then we can figure out a price. They are for a 9" though so you would need different retainers, but that is about it.

I'm not trying to sell you anything, just figured it would be a good opportunity to do some more informative trouble shooting to help everyone out that is currently building a car. Then again, if you don't feel like testing out another product, which may or may not solve the problem, I completely understand.

Matt

Matt, you're the man. Let me think on that and I'll be in touch.

Todd,
Just an observation, but it seems to me that you have spent a lot of time and effort patching the symptoms but you have not addressed the root cause. Here's what I suggest, loose the conventional axles and go with a NASCAR or SCORE Off-Road type floating hub. This will give you two taper bearings in place of the one you currently have and the axle no longer has to carry any weight it's only job is to transfer power. This company sells all the floating hub parts and kits you need to either convert an existing rear or a complete 9" floater housing.

http://9inchfloater.com/index.htm

Hope this helps!
Steve

I agree that a single tapered bearing is not ideal and not engineered for this application at the end of the day. I'll be collecting info and making a decision on a direction soon.

Just an update, Moser sells a complete 9" rear housing with floating hubs and axles in any length you specify for $879. Here is my rear end during installation.

http://hayes-ent.com/steve/images/ca...maro%20034.jpg

http://hayes-ent.com/steve/images/ca...maro%20035.jpg

Moser also sells floating hub kits that allow you to adapt floating hubs to your existing rear end housing for $450. Check out Moser's Circle Track Rear end section.
http://www.moserengineering.com/circ...and-parts.html

Speedway Engineering also supplies a lot of NASCAR teams with rearends and floating hubs parts.
http://www.1speedway.com/

Lots of good info here.

Did you get it all sorted?

I went with a floating caliper and it resolved the problem. It was the most economical fix on a street/mild track car.