Hi - i road race my 85 IROC, the rearend bounces a lot if i get hard on the brakes (straight line braking, i'm scared to trail-brake right now). I have Toyo Proxes RR tires (new) and a stiffer suspension all around (all in perfect shape), lowered 1", it has rear LCA relocation brackets and aftermarket spherical rod ends in them. I have a complete 1LE swap in the car and the brakes are fantastic - when I can use them - because I get severe, violent rear wheel hop when I start to use them hard. I have a rear bias valve installed and it seemed to help a bit, I have to run with 3/4 full tank and that also settles it a bit, so did softening the rear shock valving. Any ideas would be just great - thanks!

 

Decoupled torque arm from Unbalanced Engineering or trak-link by Global West are supposed to be the best designs for eliminating brake hop and provide traction for forward bite.

 

Thanks for the reply. I have a global west bar to replace the orig diagonal link. Is there a procedure to setting it up?

 

I've been searching to see a Global West track-link install but haven't come up with anything. You can see the Unbalanced Engineering decoupled torque arm over at frrax.com.

If you are talking about the panhard bar when you say diagonal link, it isn't going to fix the brake hop. Panhard bars locate the rear laterally in the chassis.

 

ok - wasn't sure of the terminology, ya i got a panhard bar. looking into the other options you mentioned - thanks for the info!

 

Have you tried dialing in less rear brake as a temporary fix?

What shocks are you using and what is the angle of your lower control arm at rest? I wonder if this is like axle hop when accelerating, only in reverse. In other words, it comes down to a core problem where traction is making and breaking rapidly causing the wheel hop.

I know nearly nothing about chassis/suspension so don't take me too serious. Just trying to spawn some brainstorming.

 

Thank for the reply - much appreciated. a major part of the set up is the track - and my local track surface is not good, and when I say not good, I mean imagine that decorative river stone for landscaping all glued down and racing on that, almost a 17th century cobblestone street, but flatter. Rubber doesn't stick to it. I have to add a "click" of rear brake bias when I lose a 1/4 tank of fuel to keep the bounce in control with normal lapping, that doesn't work if I start pushing hard. I have 8 position rear shocks now at p4 (down from 8 at the first session) and I kept dropping the tire pressure 2psi each session and it was getting better. The front struts are 4 position set at p4, I was only making one change at a time in the name of scientific process and ran out of sessions to get to the fronts. The battery is behind the pass seat and I was thinking of putting it back; but before I start I want to get more info and move forward from research done.

 

What is the angle of the rear lower control arm at rest?
Sorry, I did a ninja edit on my post while you were responding to my first reply.

 

lol - i dont know the angle, but i have the GW anti-squat brackets welded on

 

That angle has a lot to do with wheel hop when accelerating. Might have something to do with wheel hop when braking too.

 

The arms should be close to level to the ground or the axle end slightly lower, right QwkTrip?

 

should i run a rear sway bar?? there is none on the car currently

 

This might sound strange on this board, but have you tried calling the suspension companies you are using on the car to ask them? If you're using Global West, have you run the question past them? They do some racing of their own and might have suggestions or answers.

We run our car hard across a lot of different quality surfaces and have never experienced what you are describing so I don't have any suggestions for you.

 

A rear sway bar will not affect wheel hop. You may or may not need a rear sway bar depending on weight distribution and more importantly front vs rear spring rate. BUT that has nothing to do with wheel hop.

A de-coupled torque arm is like finding hen's teeth. Unless you have significant fabrication skills, forget it. You need a long torque arm. i.e mounted to the transmission cross member. You can get away with transmission mounted if you don't have much power i.e. stock engine.

LCA is the real issue here. Your LCA should be level to slightly lower at the axle. Level to slightly higher at the axle will improve traction and induce wheel hop under braking. Lower at the axle will eliminate wheel hop, reduce understeer, improve turning in the roll-through zone but reduce traction on corner exit.

Hope that is clear.

 

^They make the decoupled torque arms in batches 1-2 times a year. You have to reserve them ahead of time. Information is in the FRRAX thread on them.