AndyK

Anyone know what would cause the above condition? When I step on the brakes at 70, I feel the wheel shudder back and forth very slightly--but it's there. Let off the brakes, and the wheel is steady as a rock. The pads and rotors are new (Zimmerman rotors, Metal Master pads), as are the A-Arms, and shocks (all within the last 8k miles).

I hate to think what else could be loose or going at this point? Add this mystery to my exhaust rattle, and I really start to get that "For Sale, Best Offer" feeling, yet again!

Any ideas??

duncs

i notice this on my 944 and a guy i know who has an '83 944 has the same. i have heard from a few different sources and mechanics that it's a pretty common trait on these cars. i've had new wheels, steering rack, new brakes, 4 x wheel balances and also 2 x tracking all in the past 8 months, and it's still there. it's more like a front wheel shimmy than a steering wheel shimmy though, i'd say.

Stan944

The obvious culprit would have been warped rotors, but you have new ones...
I wonder if excessive play in the wheel bearings could cause this?

AndyK

Wheel bearings are original...

Would I be able to jack up the car, and pull on the tires, to see if there is play to test the wheel bearings?

Geo

Could be wheel bearings.

More likely it's bushings. What happens is the sudden change in forces on the suspension causes some movement in the suspension. That will translate to wheel shake.

It's still possible it's the rotors though. Did it do this with the old pads and rotors? If not, you may have have picked up some resin from the pads on the rotors which would glaze them slightly as well as increase the local thickness.

Is the shimmy accompanied by any pulsing in the brake pedal? If not, I'd suspect bushings first.

AndyK

The suspension seems "loose" to me lately. Like it's not 100% glued to the road...hard to describe. Could be I need rear bearings and front bushings?

Would new bushings in front mean an alignment, or no? Is this a major job, or an easy one?

Z-man

Simple enough to test:

Jack car up. Leave wheel on.

1. Check for play in the wheel - hold wheel top and bottom and see how much play there is - how much wobble you have. Note that the strut tower has some play in it, and that is normal. Now, do the same wobble test going left to right. If there is wobble present, you could have loose wheel bearings.

2. Check for vibration - put your finger on the spring (the strut assembly spring). With other hand, spin the wheel. If you feel a high frequency vibration, your wheel bearing is toast.

Now, back to the brakes - Could be the rotors having a high spot on them, or being out of balance. (Side note: Porsche OEM rotors, though more $$ than the Zimmermans, are better, IMHO). You can have a shop test the rotors to see if they are smooth and have a flat surface. My mechanic (Bob @ Powertech) put on a fresh set of rotors on his 951, and they were 'warped' - not due to cooking the brakes, but they were flawed. It happens.

That said, I suspect your culprit will be the rotors.

But before you put a For Sale sign on the window, give me a call, will ya!?!?!

-Z.

Stan944

yes, you can do it this way, and the adjustment procedure for the front bearings is described in Clarks.

... what George says about the bushings makes sense to me too.

I was wondering if you replaced all 4 rotors, or just 2 ?

AndyK

Z--I am gonna call your guys at Powertech and have the car looked at by people that KNOW the 944 line. My mechanic is a "if it's not broken, wait till it breaks" kinda guy. Saves me money, but I don't feel like he's checking everything he should. I need a suspension and exhaust "PPI" done, so I know what I am in for!

I'll try your wobble test too. These rotors only have a few hundred miles on em (all 4 replaced at once). And I think this shimmy has been a very recent developement, leading me to think it's the bearings, or bushings, rather than the rotors.

RMills944

have you done ball joints?

Stan944

In addition to bushings, the tie rods (not just the ends) and the ball joints at the control arms are a suspect. Try to feel for excessive play when you lift the front end up.

It is advisable to do the alignment after changing the bushings. It's not easy to change the bushings without a press (but possible ).
Incidentally, I noticed a considerable improvement of the car stability after putting new front bushings (one side only, but still)...

Z-man

Andy - stop by this Saturday at the Meadowlands -- NNJR PCA autox. I can take a quick look at your wheels / wheel bearings between the runs. I'll bring my tools.

-Z.

ibkevin

Andy, to be honest I think shimmy is just an 83'/84' thing. Dad noticed this on my 83' in his early days of the car (original owner), replaced the A-arm and it was still there. Since then I've done 225/245's and a four wheel align by Mind Over Motorsports and they couldn't find a cause either.

The four wheel align did bring the speed that it flattens out down to 47-49 mph.

AndyK

Good idea Z! Between you, and Adrial, there is an infinate racing knowledge I can tap! What time is a good time for me to show up?

I have rebuilt A-Arms from 944 Racing. Looked solid and new when I had them installed last year. Since the bearings, or bushings have 107k, I am guessing that's what I'll be replacing in the future.

Z-man

Andy - anytime from 9-sh to 3-ish. When I'm running is hard to determine before the day of the event. Dave A. will most likely be there as well, but I'm not sure if Adrial will be there or not. Regardless, we'll help ya out!

Just come on down, and hopefully we can at least eliminate some possible causes, maybe eliminate the exhaust rattle. And - I'll give ya a ride or two out on the course - perhaps I'll even drive well enough to show you the potential our cars have!

-Z.