Twitchy during braking..

[pitts64]

My car has been aligned 3/3.2 positive caster, 1/4 degree camber, 1/32 toe in.. Rear steering linkage in excellent condition..

I'm experiencing some side to side movement during braking..

I hate to mess with the Caster/ Camber because I have almost 0 bump steer now.. Thought I do have a light steering wheel feel..

Would adding a little toe in help?

Thanks....

[David Pozzi]

I would suspect either bottoming on the bumpstops if the car is braking hard, or toe out condition. Also check your front anti roll bar for binding. Don't over tighten the end links and are the bar ends close to level with car on it's wheels?
David

[JRouche]

Im with David. It sounds like she is toeing out on heavy braking.

On heavy braking the steering is fully loaded. And if there is any movement in the control arm bushings they will allow the wheels to toe out even more than during a normal driving sitch.

The heavy load on the tires during braking will pull the tie rods out (or in your case in, rear steer). And if you have rubber bushings they will start to flex and allow the lower control arm to move ever so slightly with the toed out tire. So you get more toe out from one wheel until it grabs, and all the slack is taken out of that side. But then the other side is toed in slightly now. Because the steering linkage is a firm linkage. Once the one side has bottomed out the excess bushing movement it will bounce back (the steering) because the other side is fighting to center the steering. So it grabs and the cycle is started again with the other side. And you get a cyclic back and forth of loading.

And Im not talking about very large movements and increases in toe. If you have a 1/32" for toe all it takes is a 32nd in bushing deflection to create the cyclic bouncing back and forth during braking. With wore out bushing the shimmy can be even larger.

And really, even with tight control arm bushings, with that tight of a toe setting you can get some cyclic action with the spring of the tires. Yes, tires are part of the springs on cars.

And not to mention a sloppy steering. Like wore out bearing surfaces. But I dont think thats it. You would notice that during normal non-braking driving.

You said light steering. And just the number (1/32") leads me to believe you need a lil more toe in.

And Im not all that sure but for a rear steer thats gonna be a lil too small. Front steer can handle very small toe in numbers. You are dragging the steering arm and its always loaded. Rear steering arms can get into a "void". Meaning they can get unloaded because they are trailing the load. They are a lil slow to correct for the changes. So some dwell time is there.

Im not sure about the 1/32" toe. You got to that number for a reason. I just think its a lil short for a rear steer. I would increase it to 1/16" and see if that helps. That will keep a positive load on the steering parts and the control arms. Keep everything slightly loaded so it wont slack out. And it may improve the light feel you have too. Dunno?? Just a thought. JR

[pitts64]

You guys described the problem perfectly.

I made the mistake of installing my Addco bars poly bushings like the old rubber bushings and tightened them until they even with the washer..

Thanks!

[David Pozzi]

Glad you got it!