Vibrations after 85 MPH

[deftom]

Hi guys,

Quick question, I feel vribrations when i'm driving the old lady.

It starts around 85 PMH getting worse at 100 MPH et getting a little bit better after.

I feel it in the seat but not in the steering, so it came from the rear.

I already changed shock absorber, bushing, bearings, tires etc etc etc...

It does not seems to be related to the engine as the vibrations are quit the same in 4th gear or neutral.

So where do you think it came from???

Have a nice day.

Cheers

[GH85Carrera]

I would guess it is a tire or wheel issue.

The first and easiest test, find a local friend with a similar or same size front tires, and do a quick swap. Drive on his tires, and see if the problem goes away.

My 85 911 is super sensitive to tire balance issues. It was a challenge to find a shop that was willing to balance the tires down to dang near perfect, and not within just a 1/4 ounce or so. I found a shop that does "roadforce" balance. The machine presses on the tread during spin-up and and they will dismount the tire from the wheel, and rotate the tire on the rim to find the best balance, and then start adding weights.

After that, I had no vibration at all.

[sedouglas72]

100% agree with Glen. I worked in tire shops in college. A rear wheel separated tire or balance issue feels weird, usually mostly in your seat. It could have thrown a weight, which is pretty easy to check for. If you don't have someone to swap tires with, you can have Discount Tire (or whoever) throw them on the balancer and it should be pretty obvious.

[Duc Hunter]

My experience mirrors above, and typically feeling it in the seat and not steering wheel is a rear wheel. Feeling it in the steering wheel is the front. Also, wheels out of balance often change. Meaning the vibration changes as you go around a corner, as the left/right wheels change their speed. So the vibrations can get slower, then stop, then start to come back, and get faster..... as you go around a corner, even freeway corners.

bottomline, get your wheels balances on a good machine and go from there.

[deftom]

Ok guys, you all seems to have the same opinion, so I will deeg in taht direction.

Thanks a lot for your time.

Have a nice day

[pampadori]

I wasn't sure this was SFW when i read the first sentence!

I've had vibration issues caused by the items below on different cars. Usually though, it was the tires or a bent wheel.

Tire/wheel balance
CV axle shafts
worn tie rod ends

[wrxnofx]

I had vibrations at 70-75 mph. Brought the wheels in and had them rebalanced, gone.

[spoke]

Originally Posted by GH85Carrera

I found a shop that does "roadforce" balance.

Absolutely agree with roadforce balancing. I won't go to a shop which doesn't have it.

[Jgordon]

What everyone else said. That speed, it's almost definitely a tire out of round or off-weight.

[deftom]

Perfect

Thanks a lot )

[porsche930dude]

maybe try some tire beads instead. Wheel balancers certainly dont spin up to 100mph so even a tiny bit off gets amplified. put a micrometer on the wheel lip and across the tire tread maybe itll give you a clue as to where the problem is. New tires doesnt mean good tires.

[manbridge 74]

I’ve had some weird ones over the years. Remember ru-glyde? It’s still around and is really slippery. So much so that a high powered car can easily spin the rim inside the tire the first time out. Also, tires that are out of round or wheels that have too much axial or radial run out. Maybe ask to see a short video of wheel being spun up. I mention all this because while you can balance a stop sign perfectly it will never be smooth turning along a surface...

[Jgordon]

Originally Posted by porsche930dude

maybe try some tire beads instead. Wheel balancers certainly dont spin up to 100mph so even a tiny bit off gets amplified. put a micrometer on the wheel lip and across the tire tread maybe itll give you a clue as to where the problem is. New tires doesnt mean good tires.

You need a new shop. I had shops chasing a vibration that came on like a light switch at 80 mph for years. Finally took it to Wheel Dr. in Yonkers, and he told me a rear tire was out of round. Balanced it 7 times before he was satisfied. He definitely took it to 100 on the machine.

Crazy Wobble... Looking for Advice

[deftom]

I will, I just have to find out which one

Thanks

[LIRS6]

I pushed my 7's up front, and put 9's in the rear. Mounted Pirelli's that were allegedly road force balanced. Getting steering wheel vibration 65 mph +/-. In conversation with another 911 owner, he told me that getting the wheels perfectly balanced was difficult to do when placing weights only in the inside of a wheel (for cosmetic purposes).

Any comments to that?

Thanks

Jason

[SL8R]

Finally have salt off the roads in Wisconsin and was ready for some spirited driving in my newly acquired 1987 911 3.2 G50 coupe. (While waiting for spring to arrive, I had front brakes redone.)
As soon as I approached 80mph the steering wheel began vibrating to the point of safety concerns. Backing off to 75 and below, all solid.
Could this be caused by wheels out of balance, or???
Thanks for your input.

[ClickClickBoom]

Most tire shops are just guys who were never trained to manufacturer standards.
The colored dots on the sidewall have distinctive meaning:
Red dot: High point for uniformity mounting process
Yellow dot: Light point for valve stem alignment.
I was watching a tech with a nationally known chain try to balance my tires and wheels, he was chasing the lead application to crazy lengths. I asked him if the yellow dot was aligned with the stem and he said "I don't know". Went back to the tire machine and checked the yellow dot was 1/3 out of place. I said pop the bead and rotate and align. One spin and 1/8th oz of weight got it spot on.
I spent too many hours as a an aircraft mechanic sitting in annual training classes. Even simple things have their own procedures.