MOT test of cars with Limited Slip Diff

[Davidonly]

Anyone shed any light on whether or not the roller based tests carried out during MoT (brake test?) might damage the M-Diff?

Just something I heard recently.........

[arfur daley]

Yes it might get damaged however, the mot tester will have this printed out on his special notice during the mot, and he may well roadtest the vehicle to test the brakes.

[2stis]

How fast is the brake roller spinning?!?! I've had a car done with the 'road test' method a couple of times but only because the tester guy thought it was so low that it would catch the underside when it dropped down onto the roller if he did it that way. The rollers I have been on the speed differential between the wheel being tested and the stopped one doesn't seem any different from having the car on full lock and reversing, in which case you can feel the diff at work (so I guess you could say it is subject to some wear) but its hardly 'damaging' it.

[shibby!]

Mine has always been roadtested, same with previous cars too. If Lsd.

I have gone with them once to see what they do.

I trust them so dont mind them driving it, might be different if I took it to kwikfit though!

[E30M3SE]

Mine doesn't go in the rollers on the rear.

Why allow them to increase the wear when there is a way of testing without exposing the diff to unnecessary wear, and it not the same a reversing on full lock as one wheel isn't being held stationary while the other is turned.

[stevesingo]

On a plate diff it won't make any significant difference in wear. Under the condition the brakes are being tested there is no tengine torque being transmitted through the diff to the pressure loadings on the clutch plates are at the lowest they could be whilst having a speed difference accross the axle.

It would be far more stressful on th LDS clutch pach accelerating hard out of a tight corner in a low gear, an I don't worry about doing that.

The brake rollers operate at something like 5kph for 10 seconds per side, or about 14 metres, or about 6-7revolutions of the wheel.

The fact that one wheel is stationary is immaterial, it is the speed difference,the torque difference and the duration that will generate heat in the lSD clutch pack. The torque difference is NIL the speed difference is medium at 43rpm and the duration is short at 10secs.

Edited by stevesingo on Monday 10th December 15:56

[shibby!]

Mine has always been roadtested, same with previous cars too. If Lsd.

I have gone with them once to see what they do.

I trust them so dont mind them driving it, might be different if I took it to kwikfit though!

[b16a2_VTi]

When my track car was road legal i was running a plate lsd, sounded like broken driveshafts when cold but the mot station knew his car and the car has been known to the garage for many years so he made sure it passed.

if its a garage you trust road test, or just say you want to sit in as a passenger in the car?

[Mr Wolf]

It won't make any difference at all

As long as they are efficient and dont mess about and allow the clutches to overheat - this would take a lot longer than you would think - then it will be fine.

Each test is done with slow rotation and lasts a couple of seconds. No issues to worry about imho

[Beedub]

i have no issue with my car being brake tested on those rollers.... i can gaurantee its being stressed more on my local sprint circuit coming out of the hairpin trying to manage the 500+ Hp i put through it.....

id rather them do it that way then do a road test in my pride and joy.

[phelix]

They road test the car not because of potential damage to the LSD on the rollers (basically not possible) but because the LSD can make the left versus right balance test of the brakes meaningless.