JetSepter Posted May 15, 2018 Share Posted May 15, 2018 I've now moved from Kent to Cornwall. Cornwall Sevens are a pleasant bunch, who have made Mari and me welcome.Funny day today - the JetSept went in for a service and MoT this morning. According to the factory build sheet when I ordered it (and my detailed bill for the car!) my Seven has a limited slip diff. But the mechanic, wanting to check it before ordering appropriate oil, applied the ordinary test - hold the prop shaft and rotate one wheel. An open diff normally has the wheels going in opposite directions, an LSD in the same direction, I believe. I was expecting the latter. It did the former. So no LSD? Or does the unit the factory put into the BMW casing in 2011 not react in the usual way? Can anyone enlighten me? And assuming nobody knows - short of taking it all apart - which is the better way to err - put LSD-preferred oil in an open diff, or open diff oil in an LSD? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 15, 2018 Member Share Posted May 15, 2018 Some types of LSD are detected by that trick, but others not. Apparently.Jonathan Link to comment Share on other sites More sharing options...
revilla Posted May 15, 2018 Share Posted May 15, 2018 If you prevent the propshaft from rotating then the wheels MUST turn in opposite directions. This is fixed by the gearing inside the diff irrespective of the limited slip-ness of it. I think the idea is that with (some types of) LSD the preload causes the opposite wheel AND THE PROPSHAFT to turn, with an open diff the path of least resistance is for the other wheel to rotate the other wheel rather than the propshaft turning. If that makes sense? Link to comment Share on other sites More sharing options...
Area Representative gileshudson Posted May 15, 2018 Area Representative Share Posted May 15, 2018 Everything you need to know on one handy page... Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 15, 2018 Member Share Posted May 15, 2018 Except for laying rubber, although not necessarily in all four gears?:-)Jonathan Link to comment Share on other sites More sharing options...
JetSepter Posted May 16, 2018 Author Share Posted May 16, 2018 Thanks for these offerings. I had looked at Angus and Tessa's diff page. Unfortunately, it does not include a 'from the halfshaft' pic of Titan LSD innards, which is what I think was being fitted in the BMW casing in 2011. But in any event, at this stage I was hoping for a way of establishing the likely situation without taking things to bits. My mechanic may be doing that today. Carefully, on a smooth garage floor, he is going to lift one rear wheel off the ground with a trolley Jack and then see whether gentle application of engine power will cause that wheel to spin or the other to move the car forward. After all, that is the essence of what an LSD should do, right? Or is somebody going to tell me that they only take effect above a certain speed? Anybody got any info on the oil question I posed? Link to comment Share on other sites More sharing options...
Tazio Posted May 16, 2018 Share Posted May 16, 2018 Or you could simply try some standing starts and leave some 11s on the road, if both tyres leave rubber.... Link to comment Share on other sites More sharing options...
Ian Mackenzie Posted May 16, 2018 Share Posted May 16, 2018 If it is a Titan, which it should be for that year it would be a plate diff, so if you lock the prop shaft and try and spin one wheel, the other will go in the opposite direction as previously started, however....- If is is an LSD there will be resistance in spinning the wheel (unless the LSD is in bad need of a service and there is no pre load....)- If it is open then there will be very little / no resistance in turning the wheel.RE oil, here are the details here for Titan diffs: http://www.titan.uk.net/products/details/bmw-limited-slip-diff I hope this helpsCheersIanP.S Looking through the casing the view will be the same as the ZF. Here is a pic of my Ford Titan, though you can't see through bearing...... Link to comment Share on other sites More sharing options...
7 wonders of the world Posted May 16, 2018 Share Posted May 16, 2018 - If is is an LSD there will be resistance in spinning the wheel (unless the LSD is in bad need of a service and there is no pre load....)Not always the case ...... my ZF is set very light, perfectly set up however the drag in the driveshafts, bearings and brakes is enough to overcome the preload so mine does not exhibit the normal plate characteristic of both wheels turning in the same direction when spinning one road wheel. Link to comment Share on other sites More sharing options...
Roadsport06 Posted May 16, 2018 Share Posted May 16, 2018 Just try to donut in an empty car park. Link to comment Share on other sites More sharing options...
DougBaker Posted May 16, 2018 Share Posted May 16, 2018 Needs to be multiple donuts for a valid test as it is possible to get do at least one donut with an open diff.I tested this last saturday at Dunsfold after spinning at the far end of the slalom course Link to comment Share on other sites More sharing options...
sjl1 Posted May 16, 2018 Share Posted May 16, 2018 Simply jack the rear of the car under the de dion and turn one of the rear wheels, if the other rotates the other way its an open diff, the same way, its an LSD. When I did this on my 2016 sigma with BMW LSD (written in pen on the diff) the wheel turned the other way indicating an open diff. Caterham acknowledged they had a known problem with the carbon plates on the titan LSD fitted and repaired it (although I had to pay for the removal and refitting). Link to comment Share on other sites More sharing options...
7 wonders of the world Posted May 16, 2018 Share Posted May 16, 2018 As I mentioned in post #9 - this is not always the case...... Link to comment Share on other sites More sharing options...
Toby S Posted May 16, 2018 Share Posted May 16, 2018 I love the suggestions made - definately 2 camps of owners here - the technical based argument, and the "give is a lash" and see what the car does - Must say I fall into the latter !! Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 16, 2018 Member Share Posted May 16, 2018 As I mentioned in post #9 - this is not always the case......And in #2.But the question I asked on a previous occasion was whether the following was true:If you do the rotation test properly (see #3) and the other wheel rotates the same way then there's an LSD, but if it rotates the opposite way then it could be either.Jonathan Link to comment Share on other sites More sharing options...
JetSepter Posted May 21, 2018 Author Share Posted May 21, 2018 All interesting stuff, for which I’m grateful. Thanks, chaps. Final update - Titan innards in BMW casing; carbon plate, with lots of carbon in the oil drained from the diff. Attempting to drive the car forward on a trolley jack holding up one wheel caused the lifted wheel to rotate backwards but the other wheel to start inching the car forward, though without much success. So conclusion - yes, an LSD, but one which now needs maintenance if it is to continue to function as such. But I don’t track the car so I’ll probably not pursue that for the time being... Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now