Handling problems - any advice?
10-05-2010, 01:12 PM
#31
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Thread Starter
I would start by having the alignment checked. If it hasn,t been done for 10 yrs it,s long overdue even if the tires are wearing evenly.A readout without any adjustments will cost less than replacing one rear shock or swapping 2 tires from rim to rim with a new balancing. I suspect corner balance and alignment will be the root cause. Corner balance can be way off on these cars after years of driving. Most shops including some P car dealers don,t even understand what corner balance is. I was visiting a new Pcar dealership last week and the Hunter alignment reps were there and showed me the new $50000 alignment machine just installed. I asked about corner balance as no one in this town has scales. The reps and service mgr. didn,t even know what I was talking about. There is a simple" tripod method" of checking if it is close but real accurate setup requires scales. Simple corner balance check. Measure fenders to floor heigt at 4 corners. Lift car at centre rear engine seam. Measure fronts again if one side is now lower than other the low corner is soft. Repeat from front at centre of ctossmember and check rears .Either a front or rear corner can be soft. The car can still sit level with all on the ground. I have often seen 911s with a premature front one side brake lock issue which is caused by corner balance and on off torque steering can also be the result
10-05-2010, 01:18 PM
#32
I haddah Google dat
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Yup, this is why I look to wheel bearings. Sporadic handling means the wheel is changing it's orientation. It's got to be either bearings or suspension bushings.
10-05-2010, 01:22 PM
#33
I haddah Google dat
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YHaha! Hope you Change $ome part$.
10-05-2010, 03:15 PM
#35
Drifting
start with the simple stuff first. start with tire pressures - with modern tires I like ~30 front and 34 rear.
Then jack up each corner and try and push/pull the top and bottom of the tire/wheel - any play will indicate either a strut issue (at the front) or bearing (both f/r)
If it's been ten years for an alignment/corner balance, I might look at replacing the a-arm bushings at a minimum - maybe even front shock inserts - and THEN going for an alignment/corner balance. If my cabriolet needed them at 56,000 miles - pretty sure most cars of this vintage will too. Chances are the rubber bushings are worn, why not make it count?
Then jack up each corner and try and push/pull the top and bottom of the tire/wheel - any play will indicate either a strut issue (at the front) or bearing (both f/r)
If it's been ten years for an alignment/corner balance, I might look at replacing the a-arm bushings at a minimum - maybe even front shock inserts - and THEN going for an alignment/corner balance. If my cabriolet needed them at 56,000 miles - pretty sure most cars of this vintage will too. Chances are the rubber bushings are worn, why not make it count?
10-05-2010, 05:12 PM
#36
Rennlist Member
DOn't think you're gonna' find tires to be your issue.......dick around with them, if you will (no harm done,..and data points, to boot). Look closely at the suspension related things already suggested by people who "know"........the problem is reay to be discovered!!!!!!!
Just be sure you deal with a shop that KNOWS these cars backwards and forwards,..DO NOT compromise this notion.
Stay tuned, as these boys will stay with you until the end. Just watch.............
Best,
Doyle
Just be sure you deal with a shop that KNOWS these cars backwards and forwards,..DO NOT compromise this notion.
Stay tuned, as these boys will stay with you until the end. Just watch.............
Best,
Doyle
10-05-2010, 07:34 PM
#37
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Thread Starter
I had the tires fitted to loose wheels as I had a bad experience with shops using impact guns to put the wheels back on. When I put them on myself I checked the wheels for free play and they were all good. I appreciate you making me third guess myself though (I'd already second guessed myself!). I'll definately check them again this weekend. I'm inclined to do a check, swap the tires and take it for an alignment. Hopefully a professional set of eyes on it will reveal any point of concern.
10-05-2010, 07:35 PM
#38
Racer
Torque steer could also be caused by a failing motor or transmission mount. The shocks,wheel bearings,and motor mounts and to a lesser degree the suspension bushings are all robust long life parts. Because the ride height and alignment angles are all adjustable at all 4 corners these cars are able to be optimized by correct adjustment. They are also able to be way out of adjustment in many ways at all 4 corners. A simple explanation of Corner balance think of a condition where if 60% of the cars weight is at the back then ideally 30% is on each side.40 % at front,20% each side.A car out of balance can have 60% rear with 40% left 20% right.The 40% front can be 15% left 25% right.The car still sits level and looks OK. When you accelerate the weight transfers rearward and the "soft " corner sinks more and the car steers left or right.Brake and the opposite happens. The tripod check I suggested takes about 15 min and will tell you if balance is the problem. If it is ,you or your mechanic can get it close with a tape and floorjack, then get an alignment. Just checked the 993 manual.The factory spec is no more than 20kg (44lb) difference on the diagonal.
Last edited by johnsjmc; 10-05-2010 at 10:04 PM.
10-05-2010, 09:35 PM
#40
I haddah Google dat
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I had the tires fitted to loose wheels as I had a bad experience with shops using impact guns to put the wheels back on. When I put them on myself I checked the wheels for free play and they were all good. I appreciate you making me third guess myself though (I'd already second guessed myself!). I'll definately check them again this weekend. I'm inclined to do a check, swap the tires and take it for an alignment. Hopefully a professional set of eyes on it will reveal any point of concern.
10-05-2010, 10:16 PM
#41
Quit Smokin'
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That's very good. But if I can offer some more input, it's better to check the wheel bearings with the car on the ground, and the bearings supporting the car's weight. Then, try to move the car side to side as I described before, by pressing with your shin against the rear bumper while staring at the wheel rim for play. Shake the car agressively, and you can also check for sidewall flex as well.
10-06-2010, 11:00 PM
#42
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Thread Starter
That's very good. But if I can offer some more input, it's better to check the wheel bearings with the car on the ground, and the bearings supporting the car's weight. Then, try to move the car side to side as I described before, by pressing with your shin against the rear bumper while staring at the wheel rim for play. Shake the car agressively, and you can also check for sidewall flex as well.
10-07-2010, 12:28 AM
#43
Quit Smokin'
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Sounds like it!... People have asked me why I shake the cars so hard when I'm working tech at autocross events. That's exactly why. It's really hard to say for sure over the web without hearing it. But I would say there is a very good chance you have a bad wheel bearing. Do both sides have the sound, or just one?
10-07-2010, 01:36 AM
#44
I haddah Google dat
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Yes, I think we found it. It can be wheel bearings, or more likely the hub nut has worked it's way loose. It takes some mongo huge torque, like over 200ft lbs. You need to check the exact torque in the Bentley manual or have someone look it up. Best to rent a proper 3/4" socket and wrench, and a large pipe.
10-07-2010, 01:40 AM
#45
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Thread Starter
I'll have to check as I only shook from the drivers side, my garage is only a single car wide and I park it next to the wall so I have walking/door access. It's sitting where I turned it off after 400 miles through heavy rain drying out 
I probably won't get a chance to do anything till the weekend so I've been reading up on the manual.
Another point I'd like to mention. I bought one of the lifting pads that goes into the jacking point. I jack the car one side at a time (I only have one jack). After jacking the left side I placed a stand under the torsion bar in front of the wheel and repeated the process on the other side. I can't remember the exact point during the operation to get all 4 wheels up but I do recall hearing a clunk. It was loud enough at the time for me to think sh*t, what was that. I wonder if the forces of lifting one wheel at a time has placed too much force on something and caused it to shift, altering the alignment. I did read it was ok to rest the car on jackstands at those points. I also read it was ok to jack the rear under the engine where the cases meet but I was reluctant to do so. Is it possible these actions could also have caused the issue as I did nothing but remove the wheels for new tires and refit them?
I probably won't get a chance to do anything till the weekend so I've been reading up on the manual. Another point I'd like to mention. I bought one of the lifting pads that goes into the jacking point. I jack the car one side at a time (I only have one jack). After jacking the left side I placed a stand under the torsion bar in front of the wheel and repeated the process on the other side. I can't remember the exact point during the operation to get all 4 wheels up but I do recall hearing a clunk. It was loud enough at the time for me to think sh*t, what was that. I wonder if the forces of lifting one wheel at a time has placed too much force on something and caused it to shift, altering the alignment. I did read it was ok to rest the car on jackstands at those points. I also read it was ok to jack the rear under the engine where the cases meet but I was reluctant to do so. Is it possible these actions could also have caused the issue as I did nothing but remove the wheels for new tires and refit them?