My sad suspension
08-29-2006, 02:49 PM
#46
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Originally Posted by Andrew Olson
The thing with suspension is that it's the spring that (mostly) provides the resistance and rebound to the vertical forces that are encountered while driving from bumps and force vectoring when turning. The strut's primary function is to limit the oscillation of the spring. We've all seen a car driving down the road bouncing up and down. In this case the springs are fine, but the strut has lost its ability to dampen the oscilation.
Unfortunately Bill, as you pointed this out, it only happens at high speeds, so it's hard to test for. I think you either have a a bad spring(s) or a poorly sized strut (need something with more damping). Now, the other components that come into play are:
Bushings - you suspect these
Sway bar - I doubt this as this transmits the vertical forces to both wheels, not just one
sway bar links -
Are you running stock links? The rubber inserts can wear out!
Ball joints - Assume this is good.
tie rods/joints - Also assume this is good
hub & bearing - Again, assume this is good.
Tires - I was surprised to hear you were running 16's. The forces you're creating are pretty substantial for a car with that tall of a sidewall - could have been flexing?
control arms - Assume these are good
Eccentrics - I have to assume these are good, but worth checking.
the rigidity of the chassis - Again assume this is good
Did I miss anything?
Unfortunately Bill, as you pointed this out, it only happens at high speeds, so it's hard to test for. I think you either have a a bad spring(s) or a poorly sized strut (need something with more damping). Now, the other components that come into play are:
Bushings - you suspect these
Sway bar - I doubt this as this transmits the vertical forces to both wheels, not just one
sway bar links -
Are you running stock links? The rubber inserts can wear out!Ball joints - Assume this is good.
tie rods/joints - Also assume this is good
hub & bearing - Again, assume this is good.
Tires - I was surprised to hear you were running 16's. The forces you're creating are pretty substantial for a car with that tall of a sidewall - could have been flexing?
control arms - Assume these are good
Eccentrics - I have to assume these are good, but worth checking.
the rigidity of the chassis - Again assume this is good
Did I miss anything?
- front sway bushings are poly...rear are rubber....hmmmm
- tires - yep...but these haven't changed over the last 3 years and I used to be able to corner OK, at least nothing close to as bad as this last weekend.
- Eccentrics could be worn, but these are locked with 88 ft lbs up front and some god awful torque in the rear (140?)
08-29-2006, 02:52 PM
#47
Bill -
170k. The lower A-arm bushings on two of the 3 cars I have disassembled have been suspect or downright toast. The inner and outer sections of the circumphrential (new word) actually SEPARATE. So rubber is rubbing on rubber, and what happens then is an actual wearing away of the each surface. I replaced the arms on the 85 euro I sold because of this, and I will on the 86 I have in surgery right now. My 89 arms were not like this, nor were the 78 arms. But my old 81, and the 85 had this, IIRC.
That would then create WAY more movement down there then you may imagine, and again, it wouldn't happen until higher forces were present.
The upper arms on the rear are also suspect on the higher mileage cars that I have encountered. That would keep the rear tire from positive cambering out in a turn that let the rear get some force. There are rubber bushings in those arms, and they wear over time as well.
My honest opinion, and you can take it with a grain of salt or even a smidgen, is that at 170k, you AT LEAST need to replace almost all of the rubber supporting this car if you are going to be doing 160mph in the desert.
The shocks and springs are already on the table, so I will not mention those. I do believe that you will need to drastically upgrade your spring rates to keep this 3600 pound car from moving around alot at 160mph.
You have to understand that of the many many thousands of 928s that are on the road today, I have been privy to very few, but the gallop poll takes a poll of 1000 for 300,000,000 people in this country for an opinion about George Bush, so if I say that I believe from seeing 6-7 928s up close and personal, that most of them couldn't hold the road properly at 160mph without serious rubber replacement (front/Rear included), Steering rack bushing and tie rod replacement, as well as NEW SHOCKS and NEW SPRINGS (metal wears out), then please allow me to.
The rubber replacement in the rear lower arms is a feat I havn't even wanted to tackle, but I might now that I have relegated my opinion to that idea that unless I have totally rebuilt a 928 from the ground up with all new parts it will not last as my daily driver for more then 8-12 months, and have bought a Honda for that.
Good Luck. I have both Bilstein/Eibachs and Koni/Hypercoil, and I have noticed that the Konis don't really react well to the fender test as Bilsteins do. Bisteins are very very tight, as they should be, as I think they are gas.
170k. The lower A-arm bushings on two of the 3 cars I have disassembled have been suspect or downright toast. The inner and outer sections of the circumphrential (new word) actually SEPARATE. So rubber is rubbing on rubber, and what happens then is an actual wearing away of the each surface. I replaced the arms on the 85 euro I sold because of this, and I will on the 86 I have in surgery right now. My 89 arms were not like this, nor were the 78 arms. But my old 81, and the 85 had this, IIRC.
That would then create WAY more movement down there then you may imagine, and again, it wouldn't happen until higher forces were present.
The upper arms on the rear are also suspect on the higher mileage cars that I have encountered. That would keep the rear tire from positive cambering out in a turn that let the rear get some force. There are rubber bushings in those arms, and they wear over time as well.
My honest opinion, and you can take it with a grain of salt or even a smidgen, is that at 170k, you AT LEAST need to replace almost all of the rubber supporting this car if you are going to be doing 160mph in the desert.
The shocks and springs are already on the table, so I will not mention those. I do believe that you will need to drastically upgrade your spring rates to keep this 3600 pound car from moving around alot at 160mph.
You have to understand that of the many many thousands of 928s that are on the road today, I have been privy to very few, but the gallop poll takes a poll of 1000 for 300,000,000 people in this country for an opinion about George Bush, so if I say that I believe from seeing 6-7 928s up close and personal, that most of them couldn't hold the road properly at 160mph without serious rubber replacement (front/Rear included), Steering rack bushing and tie rod replacement, as well as NEW SHOCKS and NEW SPRINGS (metal wears out), then please allow me to.
The rubber replacement in the rear lower arms is a feat I havn't even wanted to tackle, but I might now that I have relegated my opinion to that idea that unless I have totally rebuilt a 928 from the ground up with all new parts it will not last as my daily driver for more then 8-12 months, and have bought a Honda for that.
Good Luck. I have both Bilstein/Eibachs and Koni/Hypercoil, and I have noticed that the Konis don't really react well to the fender test as Bilsteins do. Bisteins are very very tight, as they should be, as I think they are gas.
08-29-2006, 02:53 PM
#48
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doesnt squating in the rear cause toe in , not toe out? (ie weisache design)
Originally Posted by Bill Ball
I have always had some tramlining. The toe was out prior to the recent alignment. It should be in now, but I will check per Captn Earl's technique.
Rear is stock.
Toe in rear is 0.15 and 0.16 degrees.
Rear is stock.
Toe in rear is 0.15 and 0.16 degrees.
08-29-2006, 02:54 PM
#49
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You might reconsider going back to the stock sway bar with the bilstein/eibachs in there. I have bilstein/eibachs and with the progressive springs in there I do get some body sway in the corners. I ordered DR's sway bars to help with this, even though I already have front and rear Ott drop-links. They give a nice comfortable ride for street driving, and when pushed hard do well with spirited driving, but i would prefer a little less sway then they provide.
08-29-2006, 03:11 PM
#50
Road Warrior
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purely anecdotal info on my part, but I can't imagine 20 year old rubber replacement isn't on the list already. all the rubber on my old gal was toast -but you couldn't tell till you pulled it out and watched it crumble. I did the bushings when I did the springs and shocks, so it's hard to tell which made the most diff, but I'd guess it all helped/wouldn't consider doing just 1 or the other since new stuff will just push old stuff into not working more... ie the weakest link theory. sounds kinda like what might be happening here.
also ck the sway bar mounts - I"ve seen them break loose on 911's when pushed hard. till they are totally gone a partial break can lead to some strange handling.
also, going back to 16's after running 18's will make the car seem pretty loose, imo... are you running the same pressure and are the newer tires the same sidwall ply ratings as before??? sometimes manufacturers mess w/that stuff and it can bite you.
hope you get it resolved
also ck the sway bar mounts - I"ve seen them break loose on 911's when pushed hard. till they are totally gone a partial break can lead to some strange handling.
also, going back to 16's after running 18's will make the car seem pretty loose, imo... are you running the same pressure and are the newer tires the same sidwall ply ratings as before??? sometimes manufacturers mess w/that stuff and it can bite you.
hope you get it resolved
08-29-2006, 03:13 PM
#51
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Brendan: You make good sense. 170K miles is much higher than any other 928 running these races. To do crazy things like this, the suspension should be renewed all over.
Appreciate the sway comments, Shane. I wondered about the progressive springs in that regard.
928ss: Another vote for the doing the bushings. Good. They look fine, so it will be interesting to see what they are like after getting them out.
Appreciate the sway comments, Shane. I wondered about the progressive springs in that regard.
928ss: Another vote for the doing the bushings. Good. They look fine, so it will be interesting to see what they are like after getting them out.
Last edited by Bill Ball; 08-29-2006 at 04:43 PM.
08-29-2006, 03:20 PM
#52
Since this seems to have started to occur pretty suddenly, could it be related to the assembling procedure discussed in this thread?
https://rennlist.com/forums/showthre...hlight=control
With it only seeming to happen at the high speeds, have any changes been made to the car since it was driving well that would affect the aerodynamics in some way? (Different front or rear ride height, belly pan, rear wing change, front spoiler change, etc.) Same tires?
https://rennlist.com/forums/showthre...hlight=control
With it only seeming to happen at the high speeds, have any changes been made to the car since it was driving well that would affect the aerodynamics in some way? (Different front or rear ride height, belly pan, rear wing change, front spoiler change, etc.) Same tires?
08-29-2006, 04:14 PM
#53
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I have an original upper control arm bushing sitting on my desk. It was removed from my car at approximately 160,000 miles. I can rub my fingernail or finger across the surface of the rubber and it simply crumbles and falls off.
Definitely it has exhausted its period of resiliency, and should have been replaced when it was replaced. I would do those before doing anything else.
Definitely it has exhausted its period of resiliency, and should have been replaced when it was replaced. I would do those before doing anything else.
08-29-2006, 04:19 PM
#55
928 Collector
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Originally Posted by Ron_H
I have an original upper control arm bushing sitting on my desk. It was removed from my car at approximately 160,000 miles. I can rub my fingernail or finger across the surface of the rubber and it simply crumbles and falls off.
Definitely it has exhausted its period of resiliency, and should have been replaced when it was replaced. I would do those before doing anything else.
Definitely it has exhausted its period of resiliency, and should have been replaced when it was replaced. I would do those before doing anything else.
08-29-2006, 04:57 PM
#56
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Originally Posted by Larry928GTS
Since this seems to have started to occur pretty suddenly, could it be related to the assembling procedure discussed in this thread?
https://rennlist.com/forums/showthre...hlight=control
With it only seeming to happen at the high speeds, have any changes been made to the car since it was driving well that would affect the aerodynamics in some way? (Different front or rear ride height, belly pan, rear wing change, front spoiler change, etc.) Same tires?
https://rennlist.com/forums/showthre...hlight=control
With it only seeming to happen at the high speeds, have any changes been made to the car since it was driving well that would affect the aerodynamics in some way? (Different front or rear ride height, belly pan, rear wing change, front spoiler change, etc.) Same tires?
- different front swaybar
- lowered ride height 5-10 mm in front and back to 160 rear, 155 front.
- new Konis on same springs replacing a 3 year set of Konis
- fresh alignment - was previously toed out in front (with inside tire wear). Alignment set with me sitting in the car in race configuration. Previous alignment was 3 years prior.
- I followed the front lower A-arm assembly procedure (85 ft lbs rear holder after lowering car to ground and lowered to correct ride height; 62 ft lbs front), whereas before I had the rear holder clamped to 62 ft lbs and done before lowering the car. I had been running that way for years.
08-29-2006, 05:17 PM
#57
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Bill, when you're checking bushings, the upper A-arm bushings should be able to slide axially along the pivot -- rearward IIRC -- so movement there does not necessarily indicate a problem. Excessive radial movement OTOH indicates wear.
HTH
HTH
08-29-2006, 05:20 PM
#58
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Originally Posted by mark kibort
doesnt squating in the rear cause toe in , not toe out? (ie weisache design)
...Our alignment guy (formerly Roger Kraus) agrees that 928 squat increases toe in....and not the opposite...
He also suggested that you could test upper A arm bushing play by using the
weight and momentum of the car to test for noise and movement in those bushings.
While sitting in the car with foot on the brake, slowly drive the car forward with someone on the outside watching the front wheel. tap the brake repeatedly with just enough to load and unload the suspension and look for the wheel to jerk unusually as it rolls forward and listen for noises from the bushings.
Al
Devek fab guy
08-29-2006, 05:22 PM
#59
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Originally Posted by SharkSkin
Bill, when you're checking bushings, the upper A-arm bushings should be able to slide axially along the pivot -- rearward IIRC -- so movement there does not necessarily indicate a problem. Excessive radial movement OTOH indicates wear.
HTH
HTH
Last edited by Bill Ball; 08-29-2006 at 05:58 PM.
08-29-2006, 09:25 PM
#60
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Putting the rear springs on the front was brought up a few times. Is this even possible? The front springs are a bigger circumference. Kind of hard to tell by the pic but the 2 on the left are fronts, wider and shorter.