Ak951

Hi guys-

I've recently replaced control arms, bushings, ball joints, struts, tie rod ends, and did an alignment in my 86 turbo.

I started to get a shimmy at 60+ after replacing the struts and still persists after an alignment. I did the repairs in this order....rotors/pads, tie rod ends> control arms, bushings, and ball joints> struts>alignment.

The car physically rides solid and tracks straight.

1) tires could be out of balance?

2)wheel bearing adjustment?

3) ???

Any help would be appreciated

Van

Balance the tires first and check for bent rims. Hit any potholes recently?

911lnv87

Bent wheel +1

odonnell

Cale, my car does the same thing. 250# up front on Bilstein HDs and the same sways as you.

Ak951

Not anything substantial that I remember. Could've knocked wheel weight of or something. I'll go get them balanced this weekend and report back.

Michael, we're almost the same setup up front...I'll let you know what I find after balancing.

Autox is this Saturday and I need to be on point!

thomasmryan

see if you can get a road balance on the newer machines. tip the dude that indexes the heavy part of the tire away from the heavy part of the rim...those yellow and red dots are on the rubber for a reason

did you replace the castor blocks, strut hats and did the bearing races seat square?

Humboldtgrin

I would say either a bent rim or a bad tire. Your tire could be out of ballance or have a flat spot from locking up the brakes once or there old tires and bricked or the tire could have a buble starting in the tread. It's something with the wheels being out of round for sure if you can feel it thru the steering wheel. Most likely one of the front wheels/rims.

marc abrams

Let me ask you how often do you use your car?

Ak951

I daily it every other week.

marc abrams

Hum....do you have any tires that you know that are a100% good that you can try on the front and not let them sit for more then a few hours before you drive it?

Ak951

Yep...I'll throw them on when I go balance the ones on it

Smike

First off, check for bent wheel or tire damage. If the shop says "slipped belt" run away. They're idiots. Belts are cured into the rubber and are a part of the tire. Look to the outside edges of the shoulder for a groove being worn into the blocks. That could be a sign of belt edge separation (centrifugal force is throwing tread and belt package out as you spin the assembly; thus wearing out that section first). Could have been caused by severe impact or improper flat repair (rope plug over plug patch).

Are those Porsche specific wheels? AKA hub pilot is correct with tight fit? If not, could be off-center on the hub pilot. Take off center cap and look for uniform and close tolerance. 944s are hub centric (hub helps center wheel).

If it the vibration increases (gets worse) as you go faster (eg starts at 60 and is worse at 80) -- its imbalance related. Specifically static imbalance. This could be from a counter-weight falling off or the tire is moving/slipping on the bead. Rebalance and witness mark inside wheel and rim (using a pin-plate adapter and rear cone/collet - DO NOT front cone: it will give you a poor balance). You do not need to "road force" the assemblies; just balance correctly.

If it the vibration has a narrow speed window (eg starts at 60, stops at 64, no shake past that) then it is resonance related. The tire and wheel assembly is creating a frequency that is exciting another part in the car (frame, axle, mounts, seat, etc) causing it to shake. Then you need to know the starting "road force" number. This is a calculated number of the assembly (wheel + tire + any tooling error on machine). It is not the R1H (radial first harmonic) of the tire. From there you can index the rim and tire to oppose the rim's radial run out to the tires machine calculated radial force. Result will be a matched pairing and lower calculated number. Result is you move the frequency the tire is "talking" to outside of whatever was being excited.

Dot colors and meaning vary manufacture to manufacture. Some use red as radial 1st high or low and yellow is tire static high or low point. All depends. Consult tire manufacture.

Ak951

Thank you!

Yes it is a Porsche wheel although I'm running an adapter up front without a hubcentric ring built into it....I have them on my rears but my fronts didn't come with them.
It starts at just under 60mph and continues up to 80 and probably more but it's most severe around 60...it's the like frequency increases with speed and becomes more stable for a lack of a better way to put it.

Smike

No problem.

Check that the front wheels are centered when bolted down. Can use a radial run out gauge to center line of tire with car off the ground. Find high RRO point, mark it, set to 1200 position, loosen lugs, re-tighten and check RRO again. If it moves a lot - consider different spacers with the correct hub ring.

Not frequency per se. But how the static imbalance upsets the whole car. Likely static imbalance of multiple assemblies where you are getting phasing - one assembly is cancelling other. Rebalance. There is a way to have the balancing machine to display static values (some call it single plain balancing). You want that to be 0 (or below machines blind 0.34 oz).

The dynamic or dual plain result would be pure couple (equal and opposite imbalance 180* apart though the axis of rotation). Couple imbalance is a low speed phenomenon (wobble left/right feeling // think loose wheel) and rule of thumb is that pure couple value would have to be 5x of the static value to give you a low speed wobble.

What the balance machine is trying to do is use 2 weights (inboard and outboard) to counter-balance static (single point) and couple (2 points) - 3 targets. Where in reality, static is main driver that causes vibration.

Ak951

Again, thanks for the awesome input! I'll check if they're centred then go from there. The issue just started but I've been running the wheels for a month now....very well could be out of center from me taking them off for strut change.

If that isn't I'll check for balance and wheel straightness them find some hub centric adapters if it comes down to it.

Much appreciated!