Brake help

[3dracer]

Embarrassed. Brake question I cannot figure out on my own. All new stuff on a new modified chassis. Afco pedals, steel brake lines, Afco calipers, Afco high temp brake fluid, Afco brake pads, Wilwood Rotors and hubs, quick car electronic RF brake shut off. They are semi spongy from the get go. No more air can be found in the system. Then all of the sudden there was no brakes. I could pump pressure into them and then the next corner no brakes again. We have looked for a misalignment, and everything clamps good. No leaks can be found. In the pits the brakes are there, on the track they are not. There is no wobble or runout in the rotors either. Any ideas or questions?

[stock car driver]

loose hub.

knocks the piston back in on the track

[72Dubya]

I agree with SCD on the hub deal. Had a night at FC in a car you are very familiar with that I lost brakes in heat race every time I came off the corner and they needed pumped up. All lines were good but the hub had a nice wobble when we jacked up the car. Quick turn with the spanner and never had an issue again. That was mid last year.

If it isn't the hub though, when we had non stop sponginess on the Diamond car we found out it was improper adjustment of the stud/nut that come out of the boots on the master cylinder. The guy that put the car together had it set so it was only letting the piston barely move so proper pressure wouldn't build up and when you pumped it up it wouldn't seem to stay. When you checked clamping power in the shop it seemed fine but on the track, nope. Set them properly and it was a whole new car.

[z40chief]

Make sure your bleeders are at the highest point when bleeding or they will keep air trapped. If you are using the AFCO calipers that work on left or right by changing the bleeder around I would almost bet that is the problem.

[ace1]

Probably not your case with a new car but I reworked the rear suspension on a old 3 link car once and got the rr spring to close to the caliper. When in the turns the spring would contact the caliper and push it in. No rear brakes in next turn. Hit the wall and tore the rt ft off 3 times before I found it. Something to check.

[3dracer]

Thanks everyone. We will take a look at all. We are running the preload spacers on all 4 corners. It might be causing a little hub shake.