Bent De-dion tube?
Discussion
During my last trackday we noticed the rear wheel alignment of my car looked a little odd. After getting some straight edges out, it seems the rear wheels have adopted a toe out of about 2 degrees, all of which seems to be on the left side with the right maybe about 1/2 degree toe in (with respect to chassis centre line). Visual inspections shows nothing amiss but wondered what the correct toe angle should be. The car seems to drive OK.
Clearly this is fixed by the De-dion tube and ears -can these bend with track use? I do use the curbs quite hard. The other possibility is the the watts linkage is set up wrong but it seems a big amount for this.
The car did have a thump from another car on the drivers side rear wheel last year but was checked and found to be aligned OK at that time - could this have weakened the De-dion tube?
Anyone with similar experiences out there?
Thanks
David
Clearly this is fixed by the De-dion tube and ears -can these bend with track use? I do use the curbs quite hard. The other possibility is the the watts linkage is set up wrong but it seems a big amount for this.
The car did have a thump from another car on the drivers side rear wheel last year but was checked and found to be aligned OK at that time - could this have weakened the De-dion tube?
Anyone with similar experiences out there?
Thanks
David
Edited by DCL on Saturday 1st October 12:16
Yep, I did wonder about that thread. I suppose the reason I posted was that it is a 2008 car (and a bit late for these failures). There are no visible cracks. I was just wondering what the correct toe angle is, and whether it is possible to bend them in 'normal' use (not jacking on the tube).
David
David
DCL said:
The car did have a thump from another car on the drivers side rear wheel last year but was checked and found to be aligned OK at that time
Have you checked if the wheel is straight? If the suspension has been distorted by the knock, and the wheel has bent slightly, you could find that the measurements are Ok with the wheel in one position, but look out when the wheel is rotated half a turn.downsman said:
Have you checked if the wheel is straight? If the suspension has been distorted by the knock, and the wheel has bent slightly, you could find that the measurements are Ok with the wheel in one position, but look out when the wheel is rotated half a turn.
^this. I learned to check how straight rims were tha hard way after we really struggled to set up a GT3 for 2 meetings. Turned out the wheel was bent about 2 degrees, so we had a 4 drgree error margin - and the car handles utterly horribly!Of course, your issue might not be, but it's deffo worth checking the wheel. We used a camber gague witht eh car in the air to test the wheel on 1/8th turns.
The wheel was new, but you put enough doubt in my mine for me to checked it. It's running pretty true and is certainly not enough to account for the problem.
I suppose it'll be a strip down job to try and work out what's gone wrong. I'd put my money on the bump being the cause. I'm just surprised it has taken a year for it to come to light. The strange thing is the car has never felt better or gone quicker!
I suppose it'll be a strip down job to try and work out what's gone wrong. I'd put my money on the bump being the cause. I'm just surprised it has taken a year for it to come to light. The strange thing is the car has never felt better or gone quicker!
Just an update on this:
Stripped it down today and checked the tube carefully with straight edges and triangulation. It was fine where it mattered, but was surprised buy the amount of distortion the welding seems to introduce. Toe-in seemed a touch high at just under 2 degrees - anyone know what it should be?
The only thing that may have caused the misalignment was driver's side rear watts linkage was unscrewing itself from the chassis and probably allowed 5 mm movement. The bolt had't fallen out but was close to it. The threads showed signs of wear too. This is the second time this has happened even though it had been put in with loctite.
Stripped it down today and checked the tube carefully with straight edges and triangulation. It was fine where it mattered, but was surprised buy the amount of distortion the welding seems to introduce. Toe-in seemed a touch high at just under 2 degrees - anyone know what it should be?
The only thing that may have caused the misalignment was driver's side rear watts linkage was unscrewing itself from the chassis and probably allowed 5 mm movement. The bolt had't fallen out but was close to it. The threads showed signs of wear too. This is the second time this has happened even though it had been put in with loctite.
2° of toe in is way too much!
I think that "standard" is 30' toe in. With 2° toe in on the rear, you'll be scrubbing speed off, and it will be resisting change of direction.
Zero toe feels a little vague when driving in a straight line, but is good in the corners.
If you've had a rear bump, it's also worth checking the chassis rails where the trailing arms fix. My own car has a bent trailing arm retaining boss, but the dedion ears are shimmed so that the rear tracks in a straight line.
I think that "standard" is 30' toe in. With 2° toe in on the rear, you'll be scrubbing speed off, and it will be resisting change of direction.
Zero toe feels a little vague when driving in a straight line, but is good in the corners.
If you've had a rear bump, it's also worth checking the chassis rails where the trailing arms fix. My own car has a bent trailing arm retaining boss, but the dedion ears are shimmed so that the rear tracks in a straight line.
Standard rear toe is "in 5 minutes", as Charles says that's a couple of mm across the wheel (obviously wheel size dependant)
While you're checking stuff, the camber should be 1.5 degrees on standard ears, it may be worth putting a new ear on and re-checking first. The ears tend to bend first if you've had a side impact, the tube is more likely to go if the impact is longitudinal
Also worth checking the drive shafts after this sort of incident as the retaining cup has a habit of jumping out of the centralising spring
HTH
While you're checking stuff, the camber should be 1.5 degrees on standard ears, it may be worth putting a new ear on and re-checking first. The ears tend to bend first if you've had a side impact, the tube is more likely to go if the impact is longitudinal
Also worth checking the drive shafts after this sort of incident as the retaining cup has a habit of jumping out of the centralising spring
HTH
OK it is back together and I'm now more puzzled than ever! Once rebuilt it tracked with about 17 minutes toe-in. I'll shim it to a little less.
My assumption was that the tracking was 'fixed' by the tube but I've come to the conclusion that it is more complex than that. I guess what was happening was the loose watts linkage was allowing one end of the tube to move around with the A frame, shocks, and other watts linage providing enough stiffness to flex the tube and give various toe readings depending on the loads on the wheel. Also the camber on the ears can transfer to the tracking with rotation of the tube (depending on the watts linkage lengths).
Thanks everyone for their help.
David
My assumption was that the tracking was 'fixed' by the tube but I've come to the conclusion that it is more complex than that. I guess what was happening was the loose watts linkage was allowing one end of the tube to move around with the A frame, shocks, and other watts linage providing enough stiffness to flex the tube and give various toe readings depending on the loads on the wheel. Also the camber on the ears can transfer to the tracking with rotation of the tube (depending on the watts linkage lengths).
Thanks everyone for their help.
David
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