Andy Lef Posted May 25, 2017 Share Posted May 25, 2017 Sorry for the numpty question.I need to top up the diif (Sierra) oil but don't know if it's an LSD or not. How do I tell?In haste. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 25, 2017 Member Share Posted May 25, 2017 I usually get criticised for this, but try jacking up the car and turning one wheel. If the prop shaft turns stop it (Edited: This is wrong: see below.). Which way does the other wheel turn?What's the history of the car?Jonathan Link to comment Share on other sites More sharing options...
Andy Lef Posted May 25, 2017 Author Share Posted May 25, 2017 OK done that and it looks LSD. 1992 S3 ford running gear. What oil do you recommend for the top up? Link to comment Share on other sites More sharing options...
revilla Posted May 25, 2017 Share Posted May 25, 2017 I usually get criticised for this, but try jacking up the car and turning one wheel. If the prop shaft turns stop it. Which way does the other wheel turn?Jonathan, that can't be right!If you keep the propshaft still and turn one wheel, the other one must turn in the opposite direction unless the gears are broken.I think the idea is that with an open diff the propshaft tends not turn and so the other wheel moves in the opposite direction (but this assumes that there is less overall friction to turn the other wheel than the propshaft and gearbox, so isn't foolproof), with an LSD the mechanism tends to want to lock the wheels together, which tends to make the two wheels turn in the same direction and force the propshaft to turn. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 25, 2017 Member Share Posted May 25, 2017 You're right. My prop shaft doesn't turn. I was misremembering a previous response.JonathanPS: The criticism was that there's a type of LSD where the test is misleading. Link to comment Share on other sites More sharing options...
Mark Durrant Posted May 25, 2017 Share Posted May 25, 2017 Go to a quiet car park or road, dial in 6k revs and dump the clutch. If you have made two tyre marks you have an LSD Link to comment Share on other sites More sharing options...
Ian Mackenzie Posted May 25, 2017 Share Posted May 25, 2017 Car park test No2....donuts....1/2 donut = no LSD*Full donut = LSD* Note even some torque biasing diffs can still spin the inside wheel if the traction is lost completely on the inside wheel. So an AP Suretrac as fitted to some Caterhams will behave like an open diff with the car jacked up... Link to comment Share on other sites More sharing options...
revilla Posted May 25, 2017 Share Posted May 25, 2017 @Mark Durrant - Also depends on what tyres you are running. If you are running hard T1Rs like me you can spin them as much as you like and when you get out there aren't any marks at all Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 25, 2017 Member Share Posted May 25, 2017 Perhaps I was thinking of measuring the final drive ratio...;-(Jonathan Link to comment Share on other sites More sharing options...
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