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Discussion Starter #1
Hi All. I have a series four spider. I have put a chassis stiffener on it and the IAP shorter, stiffer springs and koni reds. I recently (several months ago) got Yokohama Avid T4 tires on the original 14 inch wheels. Ever since, there has been a fairly violent shaking at around 50 mph (regardless of engine rpm). Above and below 50 are fine but there is a window of a few mph where it is not comfortable. Also, during hard acceleration (in 1st, or 2nd, not 3rd as much) the entire car pulls to the left. If I hold the wheel straight, the car will just drift to the left enough to make me correct after a few seconds to keep from switching lanes. At high rpm engine braking, the car drifts the other way.

So that's a problem. Since I have noticed this, I have had the alignment done, no problems there, and the bushings on the trailing arms replaced. I took the car back to the tire place and they took a look at the tires and concluded (not sure how) that they were fine. The guy did mention that my left rear wheel had a small dent in it but it was small enough to counter with weights.

I jacked the car up and spun the rear wheels and I can see the edge pulse a bit, like it is out of round by a few mm.

The car drives and brakes straight otherwise....

My next step will be to put the old tires back on and see if I still have the symptoms. If I'm lucky I might be able to borrow the wheels and tires off another alfa in town.

I'd appreciate any advice you have!
Thanks!

Happy motoring,

-H
 

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1966-2013
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Shake at 'X' speed usually indicates a bent wheel, damaged/mismounted/out of balance/flatspotted tire, possibly a driveshaft harmonic or bent axleshaft.

Pulling one way or the other (or both as you decribe) is usually something far more sinister in the suspension or alignment.

You say the trailing arm bushes were replaced and alignment were checked as good. How about the mount points on the chassis proper? (dogbones, and all bushes up front, the yokes at the rear that anchor to the floorpan) How're the trunion bushes and mounting? (if it's sloppy, the diff will twist up pretty fairly regardless of hownew and improved the rest is)

Of course it could be one or more roached out ARB mounts letting things get up a good bind when you're on and off the throttle regardless of the chassis stiffener. (it stiffens the chassis, not the suspension)
 

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Try swapping tires/wheels F -> R and see if the symptoms change. If so, then it is likely the problem is with the tires/wheels. If not, then it is more likely a suspension/chassis problem.

IME, a shaking at a specific speed is usually a balance/out of round issue. Keep in mind that one can 'balance' a square tire but it wouldn't ride very well...

The bulging you mention makes me wonder about a broken belt in the tire. Or the dent in the rim isn't as 'insignificant' as your tire guy says. I have no idea what they mean by 'counter it with weights'. That doesn't make sense to me.

Pulling to one side on acceleration and the other on deceleration (engine braking not 'the brakes') usually indicates the rear axle is twisting on its mounts. This is common on the MG with its leaf springs & loose axle/spring bolts. I am not sure if there similar situation on the Alfa rear axle.

You said you replaced the trailing arm bushes - rubber bushes or polyurethane? There is some controversy about using bushes there that are too stiff. The trailing arm bushes do have to allow some angular motion.

Anyway, I'd start by consulting a new 'tire guy'...
 

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My two cents.

How're the trunion bushes and mounting? (if it's sloppy, the diff will twist up pretty fairly regardless of hownew and improved the rest is)
Trunion ? is this the 't' bar from the diff to the body?
The mounts on the body side have shims between the rubber of the mount and the body. They can dissintergrate.
If lucky you wont have to replace the mounts, just the shims.
I just had somewhat the same problems sorted out on my Spider.
I also had a bent extra wide steel rim that I took to a wheel repairer and he re-rounded/or re-rolled it for about 40 bucks. Good as new now.
I was told "trailing arm bushes, rubber is ok for street otherwise you lose some flex and your liable to start lifting a rear wheel and lose traction. The 'T' bar, dont think hard bushes are available for the mount to the body but definately put a nylothane or hard bush in where the bar is attached to the diff.
This will true up you rear end and stop it steering the car."
Hope some of this helps.
Cheers:cool:
 

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Discussion Starter #7
Great! Thanks for all of the suggestions! I have swapped the rear tires left to right and there was no change. The trunion bushing has been replaced.

The trailing arm mounts all looked okay. Nothing seemed out of the ordinary to me. Tifosi, what do you mean by ARB mount?

The trailing arms are suspended with rubber.

Spider4Me: Thank you for your offer! I am in Eugene for the summer. Hopefully I can find a car and willing person in this town.

Thanks again and I'll keep the board posted.


-H
 

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ARB: Anti Roll Bar

If the bushes in the little arms that connect the bars to the differential or front suspension are torn up, displaced, or outright disconnected you'll have all sorts of strange problems, particularly if it's only one that's messed up.

Same goes for the strap mounts and bushes that hold the ARBs to the chassis. If the bar isn't properly anchored, goofy stuff can happen.
 

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Discussion Starter #9 (Edited)
Ha ha! Right. Yep, those are all fine, I replaced the rubber and the bar (with the slightly bigger one (15mm I think) from IAP. The metal straps that go over the bushes looked fine as well. I didn't even think of all that but those kind of things would definately mess things up.

I found some wheels and tires in town; I'll try them out and hopefully that solves the problem. While it's up I'll check out the little bits that hold the wheels on per the board's suggestions.

Thanks!

Edit: I found some tires on old ('80s) wheels. They are nice, black stars with polished lips and star pattern. I might see if I can buy them. The black on black looks nice. Anyway, the shuddering at ~50mph was gone but the pulling was still there. All the little bits under the car look like they are in good shape. Thinking about it, the axle would want to rotate kind of back/counter clockwise. With the support on the diff on the left side, if things flexed, the axle would shift, bring the right wheel back and the left forward, making the car track left a bit. But things shouldn't flex because of the big trailing arms.

I measured the distance from rim to rim on each side and the left side was a quarter inch longer. I'll be taking the car to the alignment guy so he can check out the alignment of all four wheels. We'll see how that goes. In the mean time, I need to take those tires back to the store....
 
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