Guest Ash-IV Posted June 3, 2015 Share Posted June 3, 2015 Just a quick question. When I bought my Supra the bloke said "Yeah it has an LSD fitted but also comes with the standard diff that you can fit after if you want." When I took it for a test drive, at low speed cornering it was bucking a bit from the back wheels and making a loud banging noise. He said that was "the piston in the LSD engaging to lock it". There was the familiar smell of BS creeping into the car... however I didnt care as I was buying it for potential not what it actually was (i'm sure a lot of you will understand this) so wasn't bothered by any issues. Anyway, im dubious to what that noise is, so far I think i've figured out it is one of the tyres jumping across the tarmac where they are both trying to rotate at the same rate but can't. Also when I changed the clutch the test driver said "You wanna get rid of that welded diff, i span it on the first roundabout i came to". So lets put the obvious aside that he was clearly ragging my car around *deep breath*, he used the words "welded diff". Is it likely the last owner didn't have a clue and i dont have an LSD, just a bodge? And would it be a good idea to chuck it? Quote Link to comment Share on other sites More sharing options...
Shane Posted June 3, 2015 Share Posted June 3, 2015 Certainly sounds like its welded, or if it is really a LSD then its got a problem that sounds pretty terminal. The danger is that you will break a drive shaft or coupling. Can be good fun until then though Quote Link to comment Share on other sites More sharing options...
Guest Ash-IV Posted June 3, 2015 Share Posted June 3, 2015 Oh Christ! Cool man, thanks. Quote Link to comment Share on other sites More sharing options...
binfieldx Posted June 3, 2015 Share Posted June 3, 2015 (edited) My import does the same thing, when I took it to Lee @ SRD he said it had an aftermarket diff. It sounds like the same thing yours does, when you turn corners it makes like a clunking sound where both tyres are turning, apparently its normal for an aftermarket diff? Well at least for mine anyway. No idea what diff it is though Edited June 3, 2015 by binfieldx (see edit history) Quote Link to comment Share on other sites More sharing options...
pedrosixfour Posted June 3, 2015 Share Posted June 3, 2015 At very slow speeds with no load on the car/engine/transmission at full lock in either direction is there still banging and hopping coming from the rear? A proper LSD should work without noise under these conditions, but touch the throttle and the LSD mechanism engages giving all sorts of rachets & clanks. Quote Link to comment Share on other sites More sharing options...
Guest Ash-IV Posted June 3, 2015 Share Posted June 3, 2015 Under those conditions it doesn't bang but you can hear the wheel skidding. Basically the drive shafts are locked in sync. I'll double check at lunchtime. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 4, 2015 Share Posted June 4, 2015 Kaaz and Cusco LSD's without special lubricants, (and often even WITH special lubricants), are very uncivilised and grab and clunk at low speeds. The TRD and all none special order Giken ones do not do this. It may be welded, easiest way is to pull the cover off and have a look, unless you have access to an endoscope. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 4, 2015 Share Posted June 4, 2015 At very slow speeds with no load on the car/engine/transmission at full lock in either direction is there still banging and hopping coming from the rear? A proper LSD should work without noise under these conditions, but touch the throttle and the LSD mechanism engages giving all sorts of rachets & clanks. That is correct for cam and pawl types, Weissman, and Torsen type LSD's but totally incorrect for preloaded diffs like plate types. The plate preload friction needs breaking before independent rear axle shaft speeds can be attained. Whther this slippage is smooth or not is in the design and materials used in the device. Quote Link to comment Share on other sites More sharing options...
Scooter Posted June 4, 2015 Share Posted June 4, 2015 I had (I think from looking inside the diff and at online pics) a Cusco in my NA that was noisy/juddery/grabby and I've now got a TRD in it which is very quiet as Chris has said. The Cusco had 'in & out' play in one side flange which I'm not sure would have contributed to the noise? Quote Link to comment Share on other sites More sharing options...
pedrosixfour Posted June 4, 2015 Share Posted June 4, 2015 (edited) That is correct for cam and pawl types, Weissman, and Torsen type LSD's but totally incorrect for preloaded diffs like plate types. The plate preload friction needs breaking before independent rear axle shaft speeds can be attained. Whther this slippage is smooth or not is in the design and materials used in the device. I understand what you are saying Chris, but the Cusco Type RS I just fitted to the track car would fall into the plate type category, wouldn't it? My original comment was based on my findings with the new diff as I was doing the figure eight method of breaking it in. Let the car coast through the turn and the diff was quiet & compliant. Have any kind of load on the drivetrain through the turn or during the straightening period and I could hear gears whirring & tyres hopping. The more time I spent driving around in circles the quieter it got and by the time I arrived at the track with fresh oil in the diff it was pretty well behaved to be honest. Now that is based on just a single, brand new diff, and my first ever experience with an aftermarket LSD, you've probably seen more of them than I've had hot dinners! What I'm trying to say is that, going on my own diff's behaviour, I could certainly tell the difference between it and a welded unit. But as you say some units might be designed to utilise the friction reducing additives better than others. Edited June 4, 2015 by pedrosixfour (see edit history) Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 4, 2015 Share Posted June 4, 2015 Hi Damien, the noise you heard was the plates, breaking apart and being pushed together again. In a straight line there's justr the pre load pressure pushing the plates together, and breaking the bond is solely down to the sping pack pressure. In cornering there are wedge shaped ends on the planetary unit, that bear in wedge shaped holes. As you put torque through the unit, either in a straight line, or cornering the angle machined on these mating surfaces moves the pack of plates tighter together, adding to the pre-load. The Japs use one way, 1.5 way and 2 way to describe how the unit behaves. One way means there's a single angle, and preload only increases in forward motion, with power put through the unit. 1.5 way means there are two angles, and deceleration torque puts half the preload into the plates for any given DEceleration torque. 2 way means deceleration and acceleration both add equal pre-load to the pack. Usually a RWD car will have a 1.5 way diff. 2 way diffs cause corner entry understeer, and are more used in specialised forms of motorsport. Some clever units allow you to turn the assembly around to have either 1 way and 1.5 way or 1.5 and two way, depending on how you assemble it. Specialised diffs are available with a range of ramp angles so you can tune the diff. Things like Skylines with the active rear diff option have hydraulic rams in the rear diff, computer controlled, so they are infinitely and actively (real time) variable. All 4WD Skylines have an active centre diff, too. Chrysler had shocking issues with their Jap rear LSD units making noises and often cracking the plates, to boot. They developed a friction modifier to add to the oil. Available from any Chrysler dealer in small bottles. Add 2 to your diff oil if it continues to make cracking noises, it can make a big difference in the wet, and to longevity. The (mega expensive) "special" Giken LSD oil has friction modifiers already in it. OK, enough already..... Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 4, 2015 Share Posted June 4, 2015 (edited) Well not quite, Porsche raced a Le Mans car (the 962) with a locked "spool" rear diff, but suspension geo and set up negated the understeer these would normally cause. The danger of a spool, (or a welded up), LSD is if one driveshaft or C/V joint fails. With a normal LSD only relatively low drive torque would be applied to the still driven wheel, and in a straight line the car might pull a bit to one side, under torque. A tight plate diff might allow one to drive slowly back to the pits for repair, albeit the LSD plates and diff oil may be goosed through the massive heat build up. With a spool, failure of one drive shaft makes the car turn hard and sharp, to one side, depending which shaft or C/V joint fails. Too fast to catch, and into the barriers or whatever. This is because ALL the torque is now applied to one rear wheel. Nasty in a near 1000BHP car of light weight! There has been a vast amount of development and designs in LSD's over the years, some good, some abject failures. NOW, enough already! Edited June 4, 2015 by Chris Wilson (see edit history) Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.