MOT & LSD
- Thread starter John Sims
- Start date
My understanding is that you can't. MOT testing stations have the hand held brake meters. I always tell them in advance that the car's got an LSD and tell them that I want to drive it whilst they do the brake test.
ORIGINAL: Diver944
.......so thats why Tony can corner faster than me [] [
Oh yes I'm sure that must be the case..............NOT!!! [
]My understanding was you shouldn't put LSD's on the brake rollers but my MOT station didn't seem to know if this was the case or not. We did road test the brakes ......I'm still finding particles of the testers bodily fluids on the inside of the windscreen. [
]
I believe it can lash up the LSD.
I assume the rollers apply torque to each wheel individually and separately. Under test the LSD thinks one wheel is spinning (because the wheel has more torque applied to it than the other side and so doesn't stop) and tries to lock up. If it locks up the previously stationary wheel then has to instantly spin the stationary rollers up to the same speed as the torqued roller. []
I don't know this to be the case and would be most grateful if someone could tell me if I am right or wrong.
I assume the rollers apply torque to each wheel individually and separately. Under test the LSD thinks one wheel is spinning (because the wheel has more torque applied to it than the other side and so doesn't stop) and tries to lock up. If it locks up the previously stationary wheel then has to instantly spin the stationary rollers up to the same speed as the torqued roller. [
]I don't know this to be the case and would be most grateful if someone could tell me if I am right or wrong.
sawood12
New member
Well the purpose of the rollers is to test each corner individually so I always throught you couldn't use an LSD equipped car on the rollers but maybe there are some roller types that can cope with an LSD. But maybe if you've got an LSD that doesn't lock on overrun then it would (should) be OK as the wheels are being driven and are not driving. Torsen diffs can either be open or locking so I guess the same rules apply.
George Elliott
New member
The Rollers "check" each wheel separately and measure the braking force.
It is irrelevant that what the other wheel on the axle is doing.
In a car with an open diff, it will be doing nothing IF the wheel being tested is on the same side as the Crown-wheel.
If the wheel being tested is NOT on the same side as the Crown-wheel, then both wheels have to be turning - as its (the wheel being tested that is on the opposite side to the Crown-wheel) drive comes thru the diff - via the Crown-wheel).
If the Car has a LSD, then both wheels on the Axle WILL be turning, - but the Brake Tester Unit only looks at them one at a time for its measurements, and what the opposite one is doing - ie: turning or static does not matter.
I know this because I sat in 3 different cars with LSD being tested on an Automated MOT Test.
I know the diffs are working because of the Cars behaviour[].
George
964rs
944T
It is irrelevant that what the other wheel on the axle is doing.
In a car with an open diff, it will be doing nothing IF the wheel being tested is on the same side as the Crown-wheel.
If the wheel being tested is NOT on the same side as the Crown-wheel, then both wheels have to be turning - as its (the wheel being tested that is on the opposite side to the Crown-wheel) drive comes thru the diff - via the Crown-wheel).
If the Car has a LSD, then both wheels on the Axle WILL be turning, - but the Brake Tester Unit only looks at them one at a time for its measurements, and what the opposite one is doing - ie: turning or static does not matter.
I know this because I sat in 3 different cars with LSD being tested on an Automated MOT Test.
I know the diffs are working because of the Cars behaviour[
].George
964rs
944T
George Elliott
New member
John,
definitely no damage or potential damage either, nor even any wear - basically the wheels are free to do what they naturally do as influenced by the open diff (no drag side to side) or Ltd Slip (drags side to side).
The torque plots on some of the engines on this forum - now they could damage the diff [8|]
George
definitely no damage or potential damage either, nor even any wear - basically the wheels are free to do what they naturally do as influenced by the open diff (no drag side to side) or Ltd Slip (drags side to side).
The torque plots on some of the engines on this forum - now they could damage the diff [8|]
George
sawood12
New member
OK so here is the process as far as i've observed. Both rear wheels are driven by the rollers. The brake is applied and the measurement made. The process is repeated for the other wheel. What I havn't observed is if the rollers are rotating in the same or opposite direction. If the non-driven side roller is freewheeling i'd expect it to be rotating in the opposite direction for a conventional open diff and the same direction for an LSD. I've not actually made this observation.
Paul it is highly likely that your LSD is not working especially if it is original. Easy enough to check next time it's on the hoist and definitely why someone can outcorner you if they have one and you effectively don't. Big difference on the track.
ORIGINAL: Diver944
I've heard this mentioned before but don't know if it's just hearsay [&:]
Anyway mine has been tested fine on the MOT for the last five years that I've owned the car.
Maybe my LSD is bust (so thats why Tony can corner faster than me [
Or not at all. Spin one wheel and nothing happens to the other. When working, repaired or replaced they make so much difference. I had my stock 40% rebuilt in the interim and even on the crap kumho ecstas that I use on the road, it gripped way better than before. It's a must on any performance car in my opinion and a forgone conclusion if you ever go to the track.ORIGINAL: Hilux
I have cos when I buy a car that SAYS it has an LSD I want to know[
If you have an LSD and jack the car up when one wheel is rotated the other will rotate the same way. A non LSD will have the wheels rotate opposite ways.
George Elliott
New member
333
Agree that LSD should be in all performance cars, once you get to 200bhp with 2 wheel drive , its basically 1 wheel drive without limited slip.
Just admiring the spec of your car, whats the mph / 1000 in top, and the 0 to 100mph time - brisk I imagine[8D]
Oh, - and with a LSD do the wheels turn the opposite direction to us over here compared to Oz[]
George
944T
964rs
Agree that LSD should be in all performance cars, once you get to 200bhp with 2 wheel drive , its basically 1 wheel drive without limited slip.
Just admiring the spec of your car, whats the mph / 1000 in top, and the 0 to 100mph time - brisk I imagine[8D]
Oh, - and with a LSD do the wheels turn the opposite direction to us over here compared to Oz[
]George
944T
964rs
sawood12
New member
It's not even one wheel drive with an open diff because all your power is wasted through the spinning wheel leaving your remaining wheel with grip with no power at all. In fact strictly speaing you only really have one wheel drive with an LSD as all an LSD does is to limit the amount of power that goes to the wheel that has lost grip. The wheel that has lost grip - usually the unloaded inside wheel, will be spinning (because it's lost grip) therefore not effectively drivng the car (just like when you are wheelspinning from a standard start - you get some drive but not the optimum drive), but the LSD also ensures that some power (40% max in the std 944 LSD) goes to the outside wheel that is not spinning and still has grip therefore driving you out of the hairpin.
Posts made and opinions expressed are those of the individual forum members
Use of the Forum is subject to the Terms and Conditions
