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Date: Thu, 05 Mar 1998 18:02:32 -0600
From: "D. St. James" <saintJnopsamPC.COM>
Subject: Re: Wheel shudder in Saab 9000


Hi Paschel, What a great name (by the way). Well, I'm glad you solved it. I hope that is not what's wrong with my car and it 's really just tires. I'll do that manneuver you suggested and see what happens. Next step after that is to go to the tire people and get it over with. ( I'm going to save your post, however, for future reference just in case...) Thanks for the trouble shoot! Paschal McEnroe wrote: > Diane > > (My first reply to a new group, so bear with me!) > > Over the last two weekends, I've done quite a bit of investigation > trying various things. I finally solved the problem this weekend. > > I tried changing the wishbone bushes - no effect. > > I changed a wheel bearing (even though the original felt fine while > spinning the wheel, no free play etc.) > > I'd replaced the outer CV boot rubber after I bought the car so I knew > this to be in good condition, in addition there were none of the > symptoms asscoiated with an outer CV joint (knocking on sharp turns etc > etc.) > > I finally pulled out the drive shaft to look at the inner end of the > shaft and there I found a horror story (well almost, it had never > actually let me down). > > For a start there was no clip securing the large, inner diameter of the > CV boot rubber. When I extracted the shaft and joint, there alomost no > sign of grease. The tripod joint was very badly worn and the "cup" of > the CV joint had a depression worn in it. > > I tried greasing the whole thing up, but no difference. > > This last weekend I exchanged the wheel bearing for a complete inner CV > joint and fitted this. Problem solved. > > It's a reasonably straight forward job, if anyones interested in the > details. The CV joint was from a newer car and was a much beefier item > than the original, perhaps it was a problem early on. > > Now that I've seen the problem I understand the symptom more. In case > anyone needs to diagnose a similar problem, the symptoms are as follows; > > Because the CV joint has a depression worn in it, under power the joint > will tend to return to this postion. Any movement of the shaft due to > suspension movement will cause the joint to have to run outside of this > "slot". The shuddering was caused by the angle of the shaft forcing each > of the three rollers out of the slot in turn. > Under power this would require quite a bit of force, hence the > shuddering at, I assume, three times the wheel frequency. > > The other symptoms were; when someone sat in the passenger seat (left, > right hand drive car)the extra suspension movement again tired to move > the shaft with the result that a constant thrumming sound/vibration. > > When driving over undulating roads ( no sharp bumps) when the car > started to rise, again suspension movement caused the joint to vibrate. > > On the problem you mention with your own car, if the noise persists when > driving straight, it sounds like a symptom of a possible wheel bearing > or out of balance wheel. > > The first can be checked by performing gentle sweeps from side to side > on a smooth road. The noise will diminish when the problem wheel in > unloaded. However if it's a distinct thud, it more likely to be at wheel > speed and hence associated with the wheel itself. > > I know from experience that an out balance wheel, even at the back, will > cause a quite severe shudder throughout the car. > > Paschal > > D. St. James wrote: > > > > Hi Paschel, > > > > I seem to be having the same thing. I have a '90 9000CD with 77,000 miles. I > > think my rear tires are wearing badly, but have not checked them out. I > > think I see some cupping on the edges. However, it does seem to be worse > > sometimes after I have turned a corner - a thumping sound and feeling that > > gradually tapers off to a mild thumping. It's very annoying at 65 MPH. > > > > I know you said your tires are new, so I guess I will pay attention to any > > answers from the newsgroup. > > > > Diane > > > > Paschal McEnroe wrote: > > > > > Hi > > > > > > I wonder if anyone can help me with a problem of wheel shudder. > > > > > > I have a 1988 Saab 9000 Turbo Automatic. It has approx 127k miles on the > > > clock and I’ve owned it for the past two and a half years. > > > > > > The problem is as follows: > > > > > > When accelerating in a straight line (normal driving) a shudder can be > > > felt throughout the car. This becomes worse if I am turning right, for > > > instance pulling away from traffic lights and turning right at a > > > junction. > > > > > > When driving at normal speeds a slight vibration can be felt which seems > > > to be part of the same problem. > > > > > > It seems to be worst when the LHS is loaded, either in cornering or when > > > carrying passengers in the car. The frequency of the shudder feels to be > > > higher than wheel frequency. > > > > > > I suspect the LH front wheel bearing, however, I’ve jacked the car up > > > and checked the wheel bearing for play and roughness. I cannot detect > > > any play or roughness. Running the engine and wheels does not indicate > > > any roughness or noise from the wheel bearing. > > > > > > The tyres are relatively new and I’ve tried switching wheels to no > > > effect. Wheel balance is fine. The suspension bushes appear to be fine ( > > > I replaced the front wishbone bush some time ago as it looked well > > > beaten). > > > > > > Before spending money on a wheel bearing/hub kit (£150 from Mr Saab for > > > the kit alone) I’d like to confirm that the wheel bearing is the > > > problem. > > > > > > Are there any other circumstances which may give rise to this problem; > > > CV joint, bushes, anything else? > > > > > > Thanks in advance > > > > > > Paschal McEnroe

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