Reverse, clunk, stop - repeat?

jasst said:
I just told my guys that I've been told about possible problem if they use brake rollers, and they will be liable for Big bill if it goes t**s up, but they said they knew not to use cars with LSD on rollers anyway.
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I agree with the above, the vast majority of testers already know that it is (not advisable) to use the rolling road for 4WD & LSD vehicles. When they get a print out of the VSI, it will advise them that “if in doubt” to utilise a Tapley meter. My local garage / tester told me that he would never consider using a rolling road for a customers car with LSD, but there is no hard and fast law or rule that says he can not do so. Unfortunately that could make it a very grey area if it came down to a claim due to alleged damage arising from such. Always discuss with your garage first, then there should be no problem.
 
Just discussed this with Emblem as they have just done my MOT and they explained how using a rolling road can knacker your limited slip diff. You must go somewhere where they have a decelerometer. It's a pita for the MOT test station as they have to take the car out and find a suitable quiet road to do it, and fo no more money either.
Using the rolling road will wear out the clutch plates as they hold one wheel and roll the other.
Eb
 
So this may be a silly question but how do you know if you have LSD? My mot is overdue but I am aligning it to onoff road times so it will be done late a March.
G.
 
Ebenezer said:
Using the rolling road will wear out the clutch plates as they hold one wheel and roll the other.
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Which is exactly what it is designed to do..!
But the key is in limited, surely ?
There should be no need to run the rolling road at speeds that would rinse the LSD friction plates..even if they hold one wheel ( which they are entitled to do if they fail to get an adequate reading testing both....)
Not all LSDs are made the same. In this case, that is a possibility but only if they have exceeded the diffs capacity to allow transverse axle slip. It shouldnt be assumed that they do as a matter of function, surely?
 
Gazcw said:
So this may be a silly question but how do you know if you have LSD? My mot is overdue but I am aligning it to onoff road times so it will be done late a March.
G.
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I only recently learned that you dont need a car taxed to make the journey on the highway to attend an MOT....In case that was the reason !
 
TimR said:
I only recently learned that you dont need a car taxed to make the journey on the highway to attend an MOT....In case that was the reason !
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That's under threat now though. As you can get your new MOT a month before expiry there is no reason to allow the idea of travelling to a pre-booked MOT. Up to local law enforcement discretion :-(

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TimR said:
Which is exactly what it is designed to do..!
But the key is in limited, surely ?
There should be no need to run the rolling road at speeds that would rinse the LSD friction plates..even if they hold one wheel ( which they are entitled to do if they fail to get an adequate reading testing both....)
Not all LSDs are made the same. In this case, that is a possibility but only if they have exceeded the diffs capacity to allow transverse axle slip. It shouldnt be assumed that they do as a matter of function, surely?
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No. But as you step into the ' it should be ok' area you are also increasing the ' maybe it will break' potential.

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Zep said:
I don’t suppose Marios is able to give a diagnosis of the cause of failure? If, for example, the fault was caused by damage to the friction plates in the diff, this would be a smoking gun for the MOT causing a fault. If it is the planetary gears inside the diff and something has broken this could dispel the “wear and tear” argument. If it is a disintegrating bearing, you might end up wearing it.
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His view was it was a failure not wear and tear. But a difficult to prove issue.
I'm waiting to hear from MOT people in this. They've gone a bit quiet!

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I don't know what people are paying for MOT tests these days but when I finished doing them in 2014 we were charging £35.
Peoples expectations were unbelievable with some leaving the service book and locking wheel but on the passenger seat.
Much prefer Matt's method of Donuts or Sausage Rolls.
Seriously though the responsibilities and people coming back on you is stressful.
So for me if there was potential risk doing this visual test I would pass and advise more on the printout.
Taking a car around the block I always thought was a good idea testing items as you drive.
 
TimR said:
Which is exactly what it is designed to do..!
But the key is in limited, surely ?
There should be no need to run the rolling road at speeds that would rinse the LSD friction plates..even if they hold one wheel ( which they are entitled to do if they fail to get an adequate reading testing both....)
Not all LSDs are made the same. In this case, that is a possibility but only if they have exceeded the diffs capacity to allow transverse axle slip. It shouldnt be assumed that they do as a matter of function, surely?
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I think the issue here is the amount of difference between the two wheels. On a plate type LSD the friction plates at intended to resist the difference in rotational speed between the two wheels. In practice this means that the friction needed to prevent the wheels spinning at different speeds is a function of the grip the tyre has to the road in low grip situations. Once tyre grip (friction) is overwhelmed the required friction to prevent the slip drops off.

What the rolling road does is force the wheels to rotate at completely different speeds overwhelming the frictional forces with no drop off in the required force. This means the wear is massively accelerated. It’s a risk that is just not worth taking when there are other options (like the tapley meter) available.
 
RobinL said:
His view was it was a failure not wear and tear. But a difficult to prove issue.
I'm waiting to hear from MOT people in this. They've gone a bit quiet!

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You need to know exactly who and how the person involved performed the rear brake tests..
If they've gone a bit quite, chances are the tester f*cked up and there keeping stum!

The only reason I say, it happened to me with a fairly new Sierra 4x4 Cossie, in the end it cost them 6k for a new transmission!

Dave
 
TimR said:
I only recently learned that you dont need a car taxed to make the journey on the highway to attend an MOT....In case that was the reason !
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Car was registered October and dealer I purchased from put an mot on her in December. Thought I may as wait until March time purely for weather and naff cold Pirelli purposes.. As long as mot is booked and you go straight there all is good.
 
RobinL said:
His view was it was a failure not wear and tear. But a difficult to prove issue.
I'm waiting to hear from MOT people in this. They've gone a bit quiet!

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I had my 3200 MOTed recently and the first thing I told them was that the car has an LSD and is not suitable for rolling road. They replied that of course they are aware of that and I drove the car with the tester using a device on the passenger mat to check breaks and hand break.
 
Any prudent owner would surely do the same thing. As should the testing station...
What I meant about feeling a bit of a bellend is that you would anticipate a respected AM dealership, with a decent workshop facility attached, probably knows more about the issues of LSDs than the average commuter...
Nevertheless. Gathering up your skirts to patronise the sh1t out of them is the only sensible approach...!

I think I paid less than £60 for my MOT. They had to take the car out on the road and put up with my initial neurosis - it took them just under an hour. They arent geting fat on the back of the testing procedure..!:confused:
 
Exactly no money in MOT testing with initial outlays.
Its a service you can offer your customers.
What used to grind me would be the wanna be mechanic who brings a car in and it fails.
Okay once but several re tests later is a bit vexing.
More money made from Service and Repair work.
 
The Maserati dealership I spoke to weren't aware of any special treatment for LSD. And probably wouldn't be as they outsource their MOT work in any case. It's an interesting 'voyage of discivery' for me.
I'd like to see some compensation but being realistic it can be seen as 'low expectation'.
But I'm learning stuff about MOT!

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RobinL said:
The Maserati dealership I spoke to weren't aware of any special treatment for LSD. And probably wouldn't be as they outsource their MOT work in any case. It's an interesting 'voyage of discivery' for me.
I'd like to see some compensation but being realistic it can be seen as 'low expectation'.
But I'm learning stuff about MOT!

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As an ex Maserati Tech I find that hard to believe.
The Service desk maybe but not the guys in the workshop.
I certainly wouldn't ask Sales as they are a bunch of clowns.
 
RobinL said:
That's under threat now though. As you can get your new MOT a month before expiry there is no reason to allow the idea of travelling to a pre-booked MOT. Up to local law enforcement discretion :-(

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I would have thought there was... people who own numerous vehicles and spread their use across any number at any given time are likely to find they need to MOT a car that is SORN'd. A pre-requisite of road tax is a current MOT. ( & insurance )
 
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