Juddering on Full Lock
Discussion
When I pulled out of a tight parking space yesterday, with the steering on full lock, there was a nasty juddering as I reversed. Has anyone any idea what this may be? The car has just been serviced so I suspect it might be the tyres catching on the wheel arches. All I know is it isn’t a TVR quirk, ‘cos I used to have a Boxster which did it – never did find out why.
Noticed a similar knocking with my Chimaera, I thought it might be the CV's so I asked Dave Batty to take a look when it went to him to be serviced last week. He couldn't find anything wrong and he reckoned it was the Limited Slip Diff causing the knocking, nothing unusal and nothing to worry about
madhatter said: I get the same problem, but only when I pull the car off the drive in the morning. I haven't investigated further because I'm assuming it because the types are cold and their skipping under a full lock turn.
Thats exactly what my car feels like. Assumed it was a TVR characteristic, but would be interested to know if it's likely to be a fault.
ribol said: Can we assume we are not talking about the power steering pump noise on full lock? Most cars make weird noises from the power steering under full lock when it is working at maximum pressure.
Ivan
I think we're talking about how the rear wheels judder and slip slightly as you turn on full lock at slow speeds. With a Limited slip diff a certain amount of drive is always supplied to both wheels, unlike a normal diff where you can hold one of the drive wheels still and all the drive will go to the other wheel.
I think the cause of the juddering on a LSD is that one of the wheels doesn't 'freewheel' and ends up been dragged along at the speed of the (slower moving) inner wheel.
>> Edited by dannyboyo on Wednesday 5th February 23:47
dannyboyo said:
ribol said: Can we assume we are not talking about the power steering pump noise on full lock? Most cars make weird noises from the power steering under full lock when it is working at maximum pressure.
Ivan
I think we're talking about how the rear wheels judder and slip slightly as you turn on full lock at slow speeds. With a Limited slip diff a certain amount of drive is always supplied to both wheels, unlike a normal diff where you can hold one of the drive wheels still and all the drive will go to the other wheel.
I think the cause of the juddering on a LSD is that one of the wheels doesn't 'freewheel' and ends up been dragged along at the speed of the (slower moving) inner wheel.
>> Edited by dannyboyo on Wednesday 5th February 23:47
You are right to say a certain amount of drive is always supplied to both wheels, that is why a LSD exists. The juddering, if it is coming from the rear is more likely to be due to the LSD "working" than anything to do with tyres scrubbing. If that is how a LSD worked tyres would be scrubbing all the time - I think not.
Ivan
ribol said:
If that is how a LSD worked tyres would be scrubbing all the time - I think not.
when the diff locks both wheels have to move the same distance, so the innerwheel will spin (or scrub) an also the car will try to understeer ( try pushing a kart on full lock and you'll see what i mean)
in normal cornering the differences in distance travelled will be taken up by the limited amount of slip in the diff hence no tyre scrubbing...
does that make sence
G
Hi all,
I have been experiencing a juddering when full-lock cornering at very low speeds, but to me it feels like the front wheels are juddering. It feels like they turn a bit then jump sideways, continue turning then jump etc - happens forwards and reverse. I had thought that it was something to do with the camber of the wheel but not sure really. Checked my wheel nuts were all present and tight which was my first fright!
Any other ideas, as there isn't a LSD in the front axle is there?
Matt
I have been experiencing a juddering when full-lock cornering at very low speeds, but to me it feels like the front wheels are juddering. It feels like they turn a bit then jump sideways, continue turning then jump etc - happens forwards and reverse. I had thought that it was something to do with the camber of the wheel but not sure really. Checked my wheel nuts were all present and tight which was my first fright!
Any other ideas, as there isn't a LSD in the front axle is there?
Matt
taylormj4 said: Hi all,
I have been experiencing a juddering when full-lock cornering at very low speeds, but to me it feels like the front wheels are juddering. It feels like they turn a bit then jump sideways, continue turning then jump etc - happens forwards and reverse. I had thought that it was something to do with the camber of the wheel but not sure really. Checked my wheel nuts were all present and tight which was my first fright!
Any other ideas, as there isn't a LSD in the front axle is there?
Matt
Yeah Thats how it feels!!!!!!
When you turn a corner, the front wheels need to change by different angles, so the inside wheel describes an arc of smaller radius than the outside wheel. As the steering angle increases, this difference also needs to increase - it's known as the Ackerman angle.
Now the geometry needed to accomplish this is pretty fiendish, and it's not easy to set up a car's steering so this difference is correct at all steering angles. If you design the steering for low speeds and large steering angles, then high speed handling becomes scary. Conversely if you set the steering up for high speeds and low angles, it judders at low speed as one wheel is dragged or pushed around a different radius to the one it would naturally describe.
Well, that's my explanation and I'm sticking to it
Pete
Now the geometry needed to accomplish this is pretty fiendish, and it's not easy to set up a car's steering so this difference is correct at all steering angles. If you design the steering for low speeds and large steering angles, then high speed handling becomes scary. Conversely if you set the steering up for high speeds and low angles, it judders at low speed as one wheel is dragged or pushed around a different radius to the one it would naturally describe.
Well, that's my explanation and I'm sticking to it
Pete
Graham said:
ribol said:
If that is how a LSD worked tyres would be scrubbing all the time - I think not.
when the diff locks both wheels have to move the same distance, so the innerwheel will spin (or scrub) an also the car will try to understeer ( try pushing a kart on full lock and you'll see what i mean)
in normal cornering the differences in distance travelled will be taken up by the limited amount of slip in the diff hence no tyre scrubbing...
does that make sence
G
I think the kart example is not valid here, a LSD does not lock the axle it has a limited slip percentage called the “locking factor.” This varies from make to make and even to a point on how it is assembled (pre-load etc) but the bottom line is none lock 100%.
Ivan
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