Rear control arm question - lateral axle movement

[67 goat]

Hey guys,

I did a search but couldn't find anything on this. Last spring I installed a Stage 1 plus from Marcus on my '67 GTO along with SPC lowering springs, Bilstein shocks all around and a basic Hellwig rear sway bar that bolts to the lower control arms. The rear upper and lower control arms are still stock. I'm extremely happy with how the car handles and rides. My only issue is with a very minor tire rub in the rear but only under very, very aggresive cornering.......like just to the point of oversteer. The tire (285/40 on 17x9.5s) is just barely kissing the inside fendor well. I've "massaged" it a little, but there's still a minor rub and I don't want totally beat it senseless. The tire does not rub on the outside fender lip since I have slighter more clearance there but I'd rather not run a wheel spacer, plus the clearances are almost symmetric, so that would probably just move the problem to the other side of the fender well anyway.

I have about 3/8" clearance but obviously I'm getting:
1. tire deflection
2. lateral axle deflection
3. maybe some lateral body deflection?

Does this sound about right? If so, then I think decreasing the axle movement is probably the easiest, cheapest solution. I think a minor improvement is all I need to eliminate the rub.

OK, here's my questions.

1. I'm assuming the upper control arms are mostly responsible for controlling lateral axle movement?
2. Would a boxed upper control arm be my best bet to improve this?
3. Any other suggestions?

Thanks,
Jeff

[JRouche]

I think you are getting roll induced deflection. As the body is rolled during hard turns the rear end is keeping with the road and the top of the tire will get closer to the inside fender.

Imagine a straight vertical line drawn on the face of the wheel looking from the back of the car. Then have a parallel line that is attached to the inner fender. During vertical suspension travel the two lines stay parallel and spaced apart evenly if there is a decent lateral locating device.

Now picture it again, from the back of the car during a turn. As you tilt the body over the lines can intersect due to roll of the body. The only way to keep the vertical lines (the wheel and fender) from intersecting is to increase the amount of space between them or limit body roll. No amount of lateral locating is gonna stop roll interference. JR

[67 goat]

Good point JR. I hadn't thought of that, but it makes perfect sense. Unfortunately, I don't think limiting body roll is an option without increasing spring rate, which I'd rather not do since the car corners well enough for my taste and still rides nice.

Everything deflects under load though (at least a little), so in addition to body roll, I have to think there's some amount of lateral axle movement relative to the body.

If so, can we agree that improved upper control arms and/or bushings might give me the tiny bit of improvement that I need to eliminate the problem?

[bochnak]

Stock rubber bushings? How old?

[monteboy84]

It's impossible to know exactly how much the new upper arms and bushings will cut down on lateral movement, but yes they should help. If you really want to keep her centered without a Panhard or Watts link, run solid spherical bushings in your UCA's. :)

-matt

[JRouche]

If so, can we agree that improved upper control arms and/or bushings might give me the tiny bit of improvement that I need to eliminate the problem?

YES.. Definitely Ill agree with that. Say for example, on the extreme, that the control arms are very flimsy, along with the mounting brackets you could see some addition twisting that is uncontrolled suspension travel. Same with washed out bushings. Every lil bit of flex in the suspension converts into unwanted (un-controlled) suspension travel. JR

[JRouche]

It's impossible to know exactly how much the new upper arms and bushings will cut down on lateral movement, but yes they should help. If you really want to keep her centered without a Panhard or Watts link, run solid spherical bushings in your UCA's. :)

-matt

I think the interference he is seeing might be due to close tolerances between the tire and quarter. Maybe some flex in the suspension also.

I have a pretty solid 4-link with metal spherical rod ends and a solid watts link.

That takes care of lateral movement during vertical suspension travel. But when I rotate my axle housing in relation to the body, like during a turn my upper section of the tire still closes distance to the quarter. In my case I have contact when I rotate the rear end at 7 degrees. And 7 degrees of roll is pretty high. Im shooting to keep it at 5 degrees max. I also have a tight tire to quarter fitment, about 5/8". JR

[bochnak]

Can you pinpoint the exact location of the rubbing? If it’s at the very top of the inner fender (12 o clock) then it’s safe to say it due to roll. If you also see rubbing between 9-3 o clock then maybe it’s lateral play?

I lightly sprayed some white paint in my wheel well to find rubbing.

[67 goat]

I'll have to take a look at the bushings, I can't remember if I put poly bushings in there when I did the frame-off 15 years ago or just new rubber bushings. Either way, they haven't been touched since. I have about 35,000 miles on the car since then, so they should be in decent shape, but I'll certainly take a closer look before spending money on control arms.

If I do new arms, I'll definitely go with spherical bushings. These are also referred to as "Johnny joints" correct? I think most companies are offering these now with their control arms.

As far as rubbing location, it's only in one spot, right around the 10 'o clock location if looking straight in from the wheel side. This has mostly to do with the shape of the wheel well and that this happens to be where the well is closest to the tire, but this also could indicate lateral movement I suppose.

Thanks for the input guys. I think I'll do a close inspection of everything under there first....mostly at bushings, then make a decision. I may also call Marcus too.....I'm sure he'll have some good input as usual.

-Jeff

[bochnak]

I have stock arms at the moment, but would consider these:

http://scandc.com/spohn_delsphere.htm

I like the fact that the bearing is adjustable (adjust out any play). Not a bad price either.

[67 goat]

I have stock arms at the moment, but would consider these:

http://scandc.com/spohn_delsphere.htm

I like the fact that the bearing is adjustable (adjust out any play). Not a bad price either.


Wow, I like those. Definitely a good price too compared to most upper (and lower) arms.

[monteboy84]

Those arms are a steal. I was trying to decide on rear arms for a build, looks like those win! The fact that they're spherical is huge, stock bushings are far from ideal when it comes to axle articulation.