Can a worn out rack & pinion cause shimmy?

[bkreigsr]

New tires all around, with a good balance from my tire guy, whom I really trust.
The fronts start to shimmy at 65 then the shimmy will fade away above 75.
Could this be due to the rack and pinion needing a rebuild?
Steering wheel has always had a lot of back-and-forth play, but no vibration.
Car is 77 Turbo Carrera with 110,000 miles.

Thanks in advance.

Bill K

[proporsche]

how about your front shocks are they ok? Is there a play when you lift the front of the car and try to move the wheel side to side?
Ivan

[jjeffries]

My feedback: before you do anything to the car, try another set of front wheels/tires, as in, borrowed from a p-car friend. This will help you rule out the tires, although - assumimg the car was OK until now/rexently - I'd put 90% odds on it being the tires, which can balance perfectly, even on a good Hunter RoadForce machine, and still have a wobble that causes what you're experiencing. I'd avoid replacing any parts before you do this. Best of luck, John/CT

[Trackrash]

^ +1

The rack won't cause shimmy, but can allow it if the tires are off.

FWIW, most of the time when I have had new tires mounted I have had a vibration in the front of my 911, UNTIL I re-balance them myself with my old fashion bubble balancer.

I'm not sure why those spin balancers don't do Fuchs right. YMMV

[proporsche]

trackrash..i am with you i just had to redo my Fuchs at another shop..In the good old days we left them on car and used the strobe light and spin the wheel with this tool set up.You put a glass of water on fender and it would not move after i was done balancing.

This is the tool i used to have

[faapgar]

When I first worked at a Porsche dealer 50 years ago the shop foreman would have us mount the tires with no weights.He would road test the car for 20-30 miles to seat the tire to the wheel.Then we would balance them.I still do this today.It was very effective and reduced the issue of tire tramp.Fred

[Autoban]

Originally Posted by bkreigsr

New tires all around, with a good balance from my tire guy, whom I really trust.
The fronts start to shimmy at 65 then the shimmy will fade away above 75.
Could this be due to the rack and pinion needing a rebuild?
Steering wheel has always had a lot of back-and-forth play, but no vibration.
Car is 77 Turbo Carrera with 110,000 miles.

Thanks in advance.

Bill K

What do you mean with “the steering wheel always had a lot of back-and-forth play”? There should not be any play in the system. Can you post a video?

Juergen

[bkreigsr]

Thanks all.
I did test the run-out of both fronts.
One of the 43 year-old Fuchs had about a 1/8th inch wobble, but it never effected driving. Maybe the new tires (Pirelli- P Zero Rosso) have less forgiveness in the sidewalls then the Khomos I removed.

Fred - Precision in Eatontown?
No wonder they charged so much !

Bill K

[jjeffries]

Originally Posted by faapgar

When I first worked at a Porsche dealer 50 years ago the shop foreman would have us mount the tires with no weights.He would road test the car for 20-30 miles to seat the tire to the wheel.Then we would balance them.I still do this today.It was very effective and reduced the issue of tire tramp.Fred

Fred, that makes sense. Of course nowadays the question would be, "Who pays me the 1.0 flat rate hours for the road-test?"

When I was a service manager, I learned the "first, install a known good set of wheels" ishould be standard protocol, or else you have technicians rebuilding front ends to no avail.

Last fall I bought a new set of Conti Sport Contacts from Tire Rack for my SC...stock wheels, stock sizes. the old tires were shagged/worn out but didn't cause any wobbles. I had a meticulous dealership tech, working off hours, mount and balance them using the nicest Hunter RoadForce machines and following directions as to where the colored dot was located vis a vis the valve stem, BUT on installation I had a front end wobble around 70mph. Frustrating! I knew it was the tires because the car didn't do that with the old tires. I drove it 200 miles and it was still there. Rebalanced, no change. One of these two fronts had required more weight, so (listening to a smart older tech) rotated that tire 180 degrees on the rim and rebalanced. That solved the problem to an extent where I would have been happy if it felt that way when the new tires were first installed, but I called Tire Rack, explained where I was at and they (hassle-free) sent me a replacement Conti which balanced nicely right out of the box. Point being, even a good brand tire can have manufacturing-related issues that aren't revealed on the balancer.

Those on-car "finish balancers" like ProPorsche showed were cool. I remember seeing Hoffman branded units up until the early 90's, but haven't spied one in years. John

[proporsche]

hmm Jeff...good point i will take the 911 next week for a spin i hope there is no more shaking..if it is i do what you said remount them..and see...
Yup, old timers good machines, hard to find probably nowadays?

Ivan

[faapgar]

I worked for Gardner P/A in Bernardsvlille NJ back then.The balancing method was done as a customer courtesy and there was no charge for the road test.We had issues with Dunlops being out of round back then.Fred

[RedCoupe]

Even if the front wheels are perfectly balanced, if there is wear or play in the steering or suspension (tie rods, ball joints, strut mounts, control arm bushings, loose wheel bearings) shimmey can occur. If you have both out of balance front wheels and loose steering, the out of balance shaking can turn into dangerous "death wobble" that can only be stopped by slowing way down. Best have it examined by someone who knows these cars well.

[DanielDudley]

https://www.hunter.com/wheel-balancers/road-force-elite