Twitchy rear end, 996 Turbo
Discussion
OK here goes. Doing about 60 mph, sweeping curve, at what feels like 8/10ths i.e. plenty more to spare, but some side gee's to be sure. Anywhere between every half to one second - did not time - I got a sideways twitch from the rear, which did not inspire confidence to push harder, quite the opposite in fact. Now I get this on a particular road only - but then each road is different - so I do not exclude the possibility that it's due to imperfections in the road surface. However, I don't feel any bumps, etc only the rear apparently just letting go for a millisecond. I must add - on a neutral throttle.
So I may have nothing wrong with the car, or I may.
Does anyone have any first hand experience of this, and any advice?
Thanks and M.C. and A.T.B. you know the drill...
So I may have nothing wrong with the car, or I may.
Does anyone have any first hand experience of this, and any advice?
Thanks and M.C. and A.T.B. you know the drill...
Edited by 996TT02 on Sunday 25th December 13:39
mikep240 said:
Classic 996 'heave' by the sound of it. Constant radius long corners do it to mine and it has had the kitchen sink thrown at it at Center Gravity, including RSS engine mounts etc. Chris just described it as I did above.
Hmmmm, interesting. If disappointing! Yes the curves are just as you describe, pretty much constant radius, and fast.I got undertaken by a Fiat 500 this morning when I feared giving it any more!
What happens beyond that 8/10ths? - Something that I should not want to discover for myself?
Interesting, if slightly concerning problem! We need to press further on a runway or the like. I do find it hard to believe the Fiat has more grip, though. Will it do it on a tighter constant radius turn? Slower speed, likely, and so safer to test.
Perhaps CG could do some more dramatic interventions (not quite sure they do do) such as widening front or rear track a bit. I presume they soften or stiffen the damper and spring settings, ride height and angle of attack of the wheels f&r. They can also stiffen / adjust tie rods, perhaps. I remember a separate problem of a chap complaining about axel tramp and how to resolve it. I don't think 997T suffer, but 996T do.
Perhaps CG could do some more dramatic interventions (not quite sure they do do) such as widening front or rear track a bit. I presume they soften or stiffen the damper and spring settings, ride height and angle of attack of the wheels f&r. They can also stiffen / adjust tie rods, perhaps. I remember a separate problem of a chap complaining about axel tramp and how to resolve it. I don't think 997T suffer, but 996T do.
Yes indeed I wish I had the space to replicate, safely. No I don't think the Fiat had more grip - but I just did not chance giving it any more when it was doing what it was doing, and was certainly not out to prove a point, possibly very expensively!
If indeed all is well with the car and nothing wrong with the road - could it be the engine's weight, being where it is, playing wobblies with the front and rear suspension bushes? Under certain conditions? At those instants, it felt like momentary weight transfer.
If indeed all is well with the car and nothing wrong with the road - could it be the engine's weight, being where it is, playing wobblies with the front and rear suspension bushes? Under certain conditions? At those instants, it felt like momentary weight transfer.
There are so many rubber bushes in the 996 suspension that are only "tested" when cornering.
If the car is an 02 model (14 years old) I would suspect a majority of the bushings are less than perfect - even if the geo is correct.
From my own experience the Front Strut Top Mounts can be at the point of break up by 60K.
I pretty much changed all the arms with rubber bushings plus shock absorbers and the car was transformed to be very taught and pointable.
I did this d.i.y as the the total book cost would have been prohibitive. Obviously, I didnt do the geo, that was done by JAZ.
For me it was totally worth the effort.
If the car is an 02 model (14 years old) I would suspect a majority of the bushings are less than perfect - even if the geo is correct.
From my own experience the Front Strut Top Mounts can be at the point of break up by 60K.
I pretty much changed all the arms with rubber bushings plus shock absorbers and the car was transformed to be very taught and pointable.
I did this d.i.y as the the total book cost would have been prohibitive. Obviously, I didnt do the geo, that was done by JAZ.
For me it was totally worth the effort.
Pugley said:
There are so many rubber bushes in the 996 suspension that are only "tested" when cornering.
If the car is an 02 model (14 years old) I would suspect a majority of the bushings are less than perfect - even if the geo is correct.
From my own experience the Front Strut Top Mounts can be at the point of break up by 60K.
I pretty much changed all the arms with rubber bushings plus shock absorbers and the car was transformed to be very taught and pointable.
I did this d.i.y as the the total book cost would have been prohibitive. Obviously, I didnt do the geo, that was done by JAZ.
For me it was totally worth the effort.
Agree. It's the kind of suspension system that will hide a multitude of sins, also. You'll be shocked and amazed if you do a full 're-arm' and re-geo of the suspension.If the car is an 02 model (14 years old) I would suspect a majority of the bushings are less than perfect - even if the geo is correct.
From my own experience the Front Strut Top Mounts can be at the point of break up by 60K.
I pretty much changed all the arms with rubber bushings plus shock absorbers and the car was transformed to be very taught and pointable.
I did this d.i.y as the the total book cost would have been prohibitive. Obviously, I didnt do the geo, that was done by JAZ.
For me it was totally worth the effort.
996TT02 said:
Hmmmm, interesting. If disappointing! Yes the curves are just as you describe, pretty much constant radius, and fast.
I got undertaken by a Fiat 500 this morning when I feared giving it any more!
What happens beyond that 8/10ths? - Something that I should not want to discover for myself?
Nail it! It is fine when pushed further as the tyres start to slide rather than 'wind up'. CG explained it to me that with nearly a foot of rubber on both rear tyres, the inside of the tyre (closest to the corner generated radius), is travelling slower than the other side of the tyre, or rather wanting to! However they are linked by the tyre carcass, which winds up and releases, leading to the sensation. This is not my explanation but Chris's by the way. I got undertaken by a Fiat 500 this morning when I feared giving it any more!
What happens beyond that 8/10ths? - Something that I should not want to discover for myself?
The sensation is odd, but it only does it on one long radius corner near my house, especially at 70 mph. If I increase the speed to 90 the sensation goes away, odd but true.... I presume this is because less tyre is presented to the road by the inner wheel due to roll/sliding. Equally odd, if I drive the car in the opposite direction on the same bend It exhibits no issue whatsoever, so this kind of confirms his theory, as by driving in the opposite direction I am on a greater radius by dint of being on the other side of the road and therefore on a larger radius corner.
To echo others, sounds exactly like the rear end settle on the 996.
Load up and a moment later the rear end settles with what feels like a very distinct step across and down. I always found motorway speed sweepers, especially with a little bit of off camber were perfect for displaying it as the combination allows individual motions to become a little more stretched out. They are always there in reality but usually come all together so are more tricky to pick out.
Load up and a moment later the rear end settles with what feels like a very distinct step across and down. I always found motorway speed sweepers, especially with a little bit of off camber were perfect for displaying it as the combination allows individual motions to become a little more stretched out. They are always there in reality but usually come all together so are more tricky to pick out.
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