SM2 GSL-SE wheel hop on hard braking - suggestions?
 

While running Victoracers, I get fairly violent (rear axle) wheelhop during hard braking.

Setup:
85 GSL w/ GSL-SE suspension front/rear.
ST springs all around
Tokico blue front, Tokico stock rear
RB front bar, no rear bar
20 year old bushings on all rear links
205-55-14 Victoracers on 14x5.5 GSL-SE wheels

I feel the rear does fine on acceleration and corners. Don't have time to do the tri-link setup right now. I'm considering urethane bushings in the lower links and in the Watts. I don't want to spend an afternoon doing this and making things worse!

I have some in car video but nowhere to host. If you want to see/hear the ugliness pm me your email address and I'll send the approx 1mb mpg.
Thanks!

It's a common problem with live axle cars under braking on race rubber. Basically it's an oscillation that gets setup between the tire and the spring. If you have adjustable shocks many times it can be cured with a slight change in the shock or in the tire pressure. Normally the conditions that lead to the hop are narrow so just a slight change to the shock or tire pressure will often fix it.

There may be an FB specific suspension problem as well. Hopefully one of those guys will chime in.

I was thinking of putting Tokico adjustables on the back. I did get wheelhop with the Tokico 'blues' but had a lot more trouble getting into the power on corners. The stock Tokicos seemed to do better for me (heavy right foot) for autocross and the the 1/4mi.

Anyone else with this trouble? Or a fix?

Do the rear brakes lockup? I used to get axel hop with rear brake lockup under hard braking. Brake proportioning valve on the rear brakes fixed that.

I'm sure the proportioning valve would stop the wheel hop but it doesn't address the root cause of the problem. But, that may be the easiest way to get rid of the symptom.

On video it looks like front lockup happens first.

I have a feeling it's hopping because the lightness of the rear plus race rubber.