Support Team Shaun_E Posted April 5, 2006 Support Team Share Posted April 5, 2006 There are lots of discussions on here about not putting LSD equipped cars on the brake rollers for an MOT and in fact the MOT manual does say don't do it. For the past 2 years my car has gone on the rollers so today at my MOT, I asked the tester why. He surprised me by saying that he hadn't realised that mine had an LSD as it hadn't behaved like one when he was turning the rear wheels during the checks of the rear. He said he usually spots them during that check. Because of the unusual behaviour, it wouldn't affect the brake test - seems the MOT instruction is because of the effect on the test rather than any likelihood of damage. He wondered if the diff behaves differently at different speeds and maybe the roller speed wasn't enough to activate it. So the question is: what is it about an AP Suretrak that makes it behave differently from, say, a ZF? Its definitely an AP diff as a)I have the original purchase docs for the car b) the diff is stamped with an AP part number and c)it does rather excellent donuts. Yellow SL #32 Link to comment Share on other sites More sharing options...
shn7 Posted April 5, 2006 Share Posted April 5, 2006 Good question. I've wondered this too as when my car was MOT'd last year the tester suggested that it didn't have a LSD for exactly the same reason. Steve. Link to comment Share on other sites More sharing options...
martinwhitcher Posted April 5, 2006 Share Posted April 5, 2006 I believe that the AP diff behaves like a "normal diff" ie. when turning one wheel the other wheel turns the the other way, whereas an ZF turns the same way as per typical LSD Martin MW 51 CAT Superlight No.171 now known as:Superlight DVA 207 Link to comment Share on other sites More sharing options...
shn7 Posted April 5, 2006 Share Posted April 5, 2006 Ah but the question I was wondering is, Why? Steve. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted April 5, 2006 Share Posted April 5, 2006 The AP design gives a torque-biasing effect. The diff is more locked up when there is lots of load going through it. In the MOT test, at least one shaft is always free to move, so the diff behaves as an open diff would. Link to comment Share on other sites More sharing options...
Support Team Shaun_E Posted April 5, 2006 Author Support Team Share Posted April 5, 2006 OK that makes sense. Just to be sure, does that mean that mean it is fine to put on the rollers for a brake test? Does the Quaife diff behave in the same way then? Yellow SL #32 Link to comment Share on other sites More sharing options...
caterhamnut Posted April 5, 2006 Share Posted April 5, 2006 More importantly Shaun, they look really cool inside - see here www.mycaterham.com here 91,000 miles -1st 1.6k Supersport, '95 Motor Show car Link to comment Share on other sites More sharing options...
caterhamnut Posted April 5, 2006 Share Posted April 5, 2006 Oh yes, and if you ask an expert how it works, they kind of think, and then say - 'well, its sort of magic......' I think, briefly, I understood how it worked when I was looking at the constituant parts, but I soon lost it, and its a b*gger to explain!! 😬 www.mycaterham.com here 91,000 miles -1st 1.6k Supersport, '95 Motor Show car Link to comment Share on other sites More sharing options...
Support Team Shaun_E Posted April 6, 2006 Author Support Team Share Posted April 6, 2006 Angus - I looked at your site again to remind me of what it looked like but, as you say, trying to understand how it works is a different matter 😳. They do look kind of funky inside though. Yellow SL #32 Link to comment Share on other sites More sharing options...
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