924Board.org

[Mich924S]

I have an 87 924S. 38,000 miles on it. Just had a recent service. New rear tires, all have proper inflation, no pulling to one side so alignment seems right. But above 70, I can watch the steering wheel shake like crazy and it worsens at higher speeds. What could be the most realistic possibilities? Motor mounts? Help appreciated!

[924RACR]

Obviously you're driving too fast, slow down, behave yourself, or you're gonna kill someone!



#1 tire/rim imbalance, then check for a bent rim, then look to make sure there are no worn front suspension components (bushings, balljoints, tie rod ends, strut mounts, etc.).

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[dwak]

Bad motor mounts are usually noticeable when releasing the clutch. Sounds like a front tyre or rim problem (balance) to me.
PS Try going up to 120MPH and if it goes away then never go below that speed.(NOT!)
_________________
DWAK de bois
78 924NA had argument with racoon
79 924NA in tatters
80 931 syncro in 2nd buggered
81 931 engine in pieces
87 924S she's so fine
and a bunch of other unrelated crap

[ This Message was edited by: dwak on 2002-03-13 06:11 ]

[Mich924S]

Hey I was just performing an Italian "Tune Up". I just hate feeling like I can't go about 60mph due to this shaking. I'm going to check out all my suspension in front and the tires/rims again just to make sure. Aside from that I'm loving this car it's almost showroom new aside from 2 very small cracks in the dash.

[jcope]

Sounds like a great car. I get the impression you just bought it. I have the same car. It had 53K on it when I bought it 2 years ago.

The motor mounts were bad. They caused a lot of vibration at low RPMs (at idle or just above), whether I was moving or not. At higher RPMs there was no vibration.

I also had shaking in the front end at around 60mph. The speed would vary a little bit. It went away when I put new tires on it. The vibration wasn't quite as bad as yours though. I would think if the car sat for a long time, especially if it was outside, you could have problems with the tires. Mine sat for over a year in a garage before I bought it.

[numbers]

Check all of the nuts for mounting the struts, and the bearings at the top of the struts. jack it up and get the weight off of the front wheels and see if you have any play at the top of the struts and rock your wheels top to bottom to see if your wheel bearings are in good shape and ajusted properly. Rotate tires front to back to isolate any wheel or tire problems.

[chrisoc]

I'm putting my money on the front tires/rims. especially a low mile 15 year old car. also have them check for any rot around the bead that could weaken the seal. Nothing worse than getting rid of a high mph shimmy only to lose the rest of the car to a tire failure. And finally, these cars are sensitive, speak in soothing tones and always end with a compliment. Believe it or not it helps.

[wdb]

I think you have a out of round tire , roll the car slowly in reverse ,the steering wheel should turn away from and back toward the bad tire. look for a small pucker in the sidewall that runs from the rim to the tread of the tire. usually caused by hitting rr tracks at speed .that tire is likely to fail soon! replace it or put it on the rear,keep it on the same side ,radials dont like changing direction of travel.

[dwak]

By the way, the local tire shop says their balancing is only good up to 60MPH. Where do you go for better balancing?
dwak

[wdb]

there are new balancing machines that can tell if your rim is bent or tire is unbalanced , I forget what they are clled , but a dedicated tire retailer would/should know thier name and where to find 1
scroll down to click link GSP 9700 vibration control system
http://www.hunter.com/pub/product/product.htm
directions to follow 6 links is a PITA . here's the info






Why the GSP9700?
Eliminate Tire and Wheel Vibration with the GSP9700 Road Force Measurement™
Hunter's GSP9700 is both a balancer and a vibration control system. It is also a Road Force Measurement analyzer for passenger car and light truck tire/wheel assemblies.

Each tire/wheel assembly is tested for the amount of dynamic/static imbalance and Road Force.

The GSP9700 simulates a "road test", with a unique "load roller" which applies up to 1400 lbs of force against the rotating assembly. The roller measures the loaded runout of the assembly (deflection while under load) and automatically recommends corrections when needed. The GSP9700's technology eliminates many of the time consuming, subjective and often non-productive manual measurements previously used to diagnose and repair ride disturbance concerns.

The following image shows an example of a GSP9700 diagnostic screen.




While driving a vehicle, consider all the wheel-related items that can cause vibration


Wheel Imbalance
Runout of the:
Rim
Tire
Rim and tire as an assembly
Force Variation of the Tire
Mounting Error While Balancing
Issues Related To The Vehicle:
Bent hubs
Mounting of the wheel to the vehicle hub off center
Excessive radial runout of the studs
Out of balance rotors and drums
Up until now the wheel service industry could just balance wheels. The GSP9700 fills the gap doing 75% more than wheel balancing.

Let's review some of these issues:

Wheel Balance
Have you ever heard a customer say he is still receiving wheel vibration complaints after he has balanced wheels? Many people do not realize that balancing is only a small portion of wheel vibration. If the wheel never came in contact with the road, then balancing would be sufficient. A square wheel can be balanced, but a square wheel will not give a smooth ride.
Runout
Not usually checked until there is a problem. Bent rims or defective tires might be found "by an experienced eye," but we all know that most operators of this type of equipment have little experience or training. Is it the runout in the rim, tire or a combination? How much is too much? Is it affecting the ride quality? These questions are tough to answer. Runout is usually considered after the customer comes back complaining. This diagnostic time is usually done at the expense of shop labor profits and can be time consuming. What about the customers who have a problem and don't return going to another shop looking for an answer?
Many rim manufacturers measure runout during the assembly of the rim . The valve stem location is sometimes drilled to the request of the OEM at the low or high side of runout or a paint dot or stamp is placed at the identified location.
Many rims on the market today are also purposely designed so that the pilot hole is .002-.004" off-center to allow for adjustment capabilities by the assembly lines when encountering force variation on the tire. It gives the chance to adjust for tire force variation if runout is induced into the rim. But up to this point ONLY BY THE OEM!
Up until now, anyone could measure rim runout at the bead seats with a dial indicator. The drawbacks? It's too time consuming. The GSP9700 will automatically measure the inner and outer bead seat and determine the effects on ride quality.
Force Variation (Tire Uniformity)
Radial force variation is the amount of change in stiffness of the sidewall and footprint when a load is placed against the tire. There are specifications and acceptable limits from tire manufacturers. Up until now, force variation has been measured only by OEM's in an industrial setting using equipment in the range of half a million dollars. For example, a tire and rim could be perfectly round when measured with a dial indicator (free runout) and the wheel will still vibrate when driven due to excessive force variation. Many tires on the market today have a "paint dot" or mark on the tire that indicates either the high side or low side of force variation. Many have attempted to solve vibration problems by blindly '"Lining up the dot" with the valve stem. The operator assumes the "dot" is the high point of radial force of the tire and the wheel valve stem hole is the low point of runout of the rim. Unfortunately, this is not always true. Many tires are not marked and many wheel manufacturers do not use the valve stem as the low point. Other OEM's use the marks to indicate high points instead of low points! The GSP9700 eliminates any guesswork. The locations of runout and tire force are quickly located and measured. The GSP9700 also automatically determines if they can be used to solve an existing non-balance related vibration, before any extra work is performed.
Mounting Error
The wheel, when balanced, must be mounted on the vehicle the same way it came off the balancer. All too often, the technician improperly mounts the wheel on the vehicle off center and the balance is compromised.
Today's vehicle designs are lighter and more sensitive to road feel. It has become more critical to be aware of wheel mounting on vehicles to eliminate vibration during balancing.
The GSP9700 will automatically alert the technician when a mounting error is detected on the balancer, thus preventing improper centering on the balancer from taking place.

In Conclusion:

With the GSP9700, virtually all possible complaints due to Wheel Balance, Tire Runout, Rim Runout, Tire Force Variation, and Mounting Error are all eliminated before the tire and wheel assembly is placed on the vehicle.
100% Seamless Quality Control of all wheels going out the door. It takes no more effort by the operator, no more steps than doing an everyday type of wheel balance.
If there is a vibration coming from the vehicle when it is driven after the wheels are measured on the GSP9700...then the problem IS NOT WHEEL RELATED! No more wasted diagnostic time. No more swapping of tires. No more falsely blamed tires sent back to the manufacturer. No more loss of profits tracking down blind vibration problems that cannot be traced. This is good for the tire dealer, this is good for the tire manufacturer, this is good for the consumer. There is no other piece of equipment available doing such a task.
Now if there is a problem. What can we do to fix it?

1) Grinding the tire? Ugh...Who wants to have their brand new tire ground away? There are numerous serious problems associated with this type of technology.

2) Match the heavy spot of the tire with the light spot of the rim? No. For years, traditional wheel balancers have offered this form of weight optimization. The primary benefit here is reducing weight; however, this does not take into consideration force variation. In some cases, weight optimization can even increase force variation complaints. The vibration becomes worse.
Hunter Engineering chose a better direction.



How to eliminate tire and wheel vibration with the GSP9700
Match the Tire to the Rim
This can be helpful if the first harmonic of the rim can be indexed to cancel the force variation of the tire. As stated previously, this is not the same as the relatively ineffective common practice of most balancers to match imbalance of the tire to rim to minimize weight.
R & R Tire or Rim
Replace the defective rim or defective tire and also be able to locate and quantify the problem.
Record the Value and Reuse the Tire on Another Rim!
If a rim and tire cannot be matched and the tire is not out of spec, the actual value of the force variation can be written on the sidewall of the tire and placed back on the shelf. At a given point in time the entire inventory in that tire size can be "measured." Eventually a "measured" tire can be hand picked to match a given rim. This would be analogous to picking an alignment shim to fix the alignment condition and bring the wheel as a "tire and rim" back into specification. The GSP9700 moves vibration solving in wheels to a new level of professionalism. "Road Force Measurement" against the wheel before the balance has been needed for years!


[ This Message was edited by: wdb on 2002-03-13 15:06 ]

[ This Message was edited by: wdb on 2002-03-13 15:14 ]

[Mich924S]

Well I took it to Belle Tire and the front tires were very out-of-round. The rears had been replaced in the last 200 miles but the fronts weren't as they appeared to have good tread. I replaced the front tires and it's driving 100% better. They also said one of the rims in front may have a slight bend in it but the tires did balance. He said if it persists, to bring it in and they'll move that rim to the rear. So my thanks to all. I had to get this done and I'm glad I just did it. Now I can race up to 100mph no problem. Isn't that wonderful?!!. J/K. Thanks again.

[dwak]

Holy GSP9700, Mich924S, looks like the KISS Rule wins again. Now all you need is a radar detector.
dwak du bois

[Mich924S]

Well my Valentine 1 isn't too shabby Worked wonders on my 200mph Suzuki Hayabusa so it should work fine in the 924S!

[924RACR]

Heck, I didn't realize you are in Clarkston! You've gotta come out this season and see a race at Waterford: http://www.waterfordhills.com

I'll be there starting Race 1, beginning of May. I'm working now on prepping the car for the season. You also should get in on the loop with our region of PCA, for which I'm webmeister also:
http://vista.pca.org//rsp/

The website does need a little updating, but I've been so busy it's no surprise. We've got a spring tech session coming up, as I recall. Gotta update the site tonight with the latest events schedule.

Glad to hear the car's happy now. Give a holler next time you're down in the Plymouth area...

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Mich924S]

Vaughan,
I will plan on coming out this year to see some races. I'll bring my sons. I live about 5 minutes from the waterford hill track..if that. I'm super close. I don't plan on racing my 924S though..I want to keep it street stock for daily nice weather use. I'm going to look at the site and see the schedule. Which day do you recommend coming to see the races with my kids? Thanks for the info and hope to see you there!