View Single Post
Old 07-29-2014, 06:59 PM
67Rally's Avatar
67Rally 67Rally is offline
Senior Member
Join Date: Oct 2010
Posts: 137
Thanks: 0
Thanked 1 Time in 1 Post

Originally Posted by dontlifttoshift View Post
Knock back is caused by the rotor pushing the pistons back in the caliper. Eliminate the movement of the rotor or allow the caliper to move with the rotor.

Wilwood's bearing retainers aren't exactly superstrong pieces, they usually bend slightly on installation and after that it doesn't take much for them to flex resulting in bearing end play and consequently knockback. Stronger retainer plates can be fabricated and careful machine work to maintain the proper bearing preload can go a long way in minimizing knockback.

Floating hub eliminates the rotor movement. You don't like that option, I get it. It's not inexpensive or easy at this point. It is the only surefire way that I am aware of to eliminate rotor movement.

The floating caliper sounds like a perfect solution. Late model Mustangs use a single piston floating caliper with a rotor diameter as large as 13.8" and have no issues with knockback. This is on a clip rear end with ridiculous amounts of axle end play. The key to a floating caliper working is that the force required to move the piston back must be greater than the force required to move the caliper on it's slides. If the piston pushes back before the caliper slides, you still have knockback. Even with a floating caliper, a residual valve may still be required.

What size wheels and backspace are on your car? Front and rear please.

Have you confirmed that the knock back is definitely coming from the rear? Misadjusted front bearings or spindle flex can cause this as well.
Thanks Donny, you also replied over on PT. I had posted the following question about ruling out the front pad knockback:

Let's say I take it to a vacant parking lot and make some hard turns and can replicate the knockback. Then pump the brakes back up, crank the proportioning valve all the way to the front (so there are no rear brakes) and perform the same manuevers.

Is it safe to assume that if I don't have knockback (with the rears blocked off), that the fronts are not the culprit, and if I do still have knockback that the fronts are part of the issue, but the rears may also be involved?
Fronts are 18x8 w/5" bs, rears are 18x9 w/5.25" bs. 245/40/18 and 275/40/18 Nitto 555's.

I the bearing retainers are thicker than standard. The came from Strange, when I had the new rear built.
Reply With Quote