Cascade Crew

blue89 · Posted: Thu Nov 02, 2006 10:15 am Post subject: Engine braking wheel hop

Been trying to figure this out. The car is 26.5" to the fender lip in the rear, LCA relocators set so the LCA is just past level. 175lb/in springs, OEM bilstein rear shocks, urethane everywhere except the torque arm mount.

When I down shift to 2nd or 1st and let the engine brake the car, the rear wheels will hop badly. Just like a power brake wheel hop, but backwards. I noticed it recently after I put in the 1-2 gear syncro in my 700r4 (harder shifts up and down).

Any idea's?

If the rear axle is being pulled rearward, should I get a solid torque arm mount or decrease my LCA angle to control axle twist?

Dewey316 · Posted: Thu Nov 02, 2006 10:28 am Post subject:

Brake hop is pretty common on F-bodies, more so with the later cars, that have better brakes (LS1 specificly). The more extreme the angle of the LCA's get, the more pronouched it is. You can also try to eleminate some nose dive under braking. If you have an adjustable prop-valve, you could also dial out a little rear braking power. YOu might try putting the LCA's up one more hole in the LCA brackets, and see how that effects thing.

The IC location is the major player in the problem, without going crazy with torque arm fabriction, you don't have a lot of things to play with, beyond the LCA angle.

A search on FRRAX for brake hop might be good, a lot of the LS1 guys have a lot more information on the subject, as it is much more common.

blue89 · Posted: Thu Nov 02, 2006 10:56 am Post subject:

I do have an adjustable prop valve. But the problem is not with braking, its with engine braking. When the rear wheels are locked or sliding it is solid. Its just under a rolling/sliding decel that it does it.

Where should the IC's be? Or better yet, where does it need to stay away from? Doesn't the torque arm mount define the IC? Or is it where the LCA's line up with the torque arm? Thanks for your help Dew, don't know why I just don't call you when I have suspension questions!

Tech Support: 1(800) Dew-y316 Very Happy

Twilightoptics · Posted: Thu Nov 02, 2006 10:58 am Post subject:

Sounds more like the tune is causing a bucking event to occur.

blue89 · Posted: Thu Nov 02, 2006 11:28 am Post subject:

At least it doesn't wheel hop on launch. That was getting old and embarrassing. I'll try to change the LCA angle, and then check on my torque arm mount. Maybe its toasted.

Dewey316 · Posted: Thu Nov 02, 2006 12:53 pm Post subject:

If it is only doing it when engine braking, and not when you are on the brakes, it sounds mechanical with the engine, or tranny. I would have suspected it would do it under heavy braking, with the engine also doing braking.

As for the IC location.

The construction line is based on the directon of force, so moving the TA mount up or down has almost zero effect on the IC location, moving it for/aft has a HUGE effect. Changing the angle of your LCA's has the effect of moving the IC higher or lower.

But the more you descibe things though, it sounds like something other than suspension.

blue89 · Posted: Thu Nov 02, 2006 2:20 pm Post subject:

Is the above diagram an ideal condition for suspension alignments? Makes me think that the torque arm is potentially letting the rear end twist counterclockwise. With an automatic, i just don't see how the hopping could be due to the powertrain. I could see that the LCA relocator brackets give the axle more leverage for bending the torque arm or squishing the torque arm slide mount.

I think for an immediate solution, I'll quit engine braking so hard...

Dewey316 · Posted: Thu Nov 02, 2006 2:25 pm Post subject:

Engine braking, or rear brakes, same thing. Its the torquing of the rear housing that is the issue, this is a for/aft force issue, not a left/right issue. Heavy engine braking, is the same adding a bunch of rear brake bias. If you drivetrain is putting a TON of engine braking to the rear wheels, the car is going ot behave like it would if you had a ton a brake bias dialed in back.

I would bump the LCA's up a notch in the rear, and then take out a hair of rear brake pressure, and see how it does. If you engine brake all the time, tune the car that way. I myself don't like to engine brake much when I'm racing. I like the control that the brake pedal gives you.

blue89 · Posted: Mon Nov 13, 2006 12:02 pm Post subject:

Just learned that it does the hop when you loose traction in reverse! Eek! I'm going to have to try some things now. I'm going to start by leveling the LCA's. I'll keep this up to date.

rjmcgee · The Hammer Joined: 08 Jan 2004 Posts: 2328

I don't get any wheel hop accelerating or decelerating, but I think any of these will hop if you spin the tires in reverse. I know I only made that mistake once, thought the whole car was coming apart.