Just picked up (finally!) my Eunos Roadster. It's 1990 April car with 47k km's. Trader in Japan told me there was a problem with the rear LSD when I bought it so was expecting trouble. We'll it needs to be fixed... As far as I know you can have 3 scenarios (as I do not know what is fitted to the car):

1) Standard Diff
2) Plate (clutch) type LSD
3) Helical (torque Biasing)

LSD Symptoms: When cornering under power you can feel the diff jerking/clunking. Like a gear that's missing a tooth for example. No accelerator, no problem. So, this makes me think that it is an LSD of some description. How can I tell if it is a Plate or Helical type LSD? (6/01)

Hmm...it's most likely to have had a viscous diff as standard. But the symptoms are of a sick clutch type, which were not fitted to Roadsters as standard, but were available on the aftermarket, particularly in Japan. The other type fitted to MX-5's as standard is a Torsen, but only to later cars.

Be careful - there are drive shaft implications - esp the Torsen used different drive shafts, but the Viscous and Open diffs used the same ones. If a clutch type replacement was fitted, it may or may not have the original drive shafts.

Plenty of diffs about - try Ka Yu. Doesn't really matter if you get an open or viscous - the viscous ones lose most of their limited slip capability over time. But be prepared to have to change the drive shafts too. You can't tell the difference between open and viscous by looking. It is possible that it's a clutch type with the wrong lubricant - might be worth consulting a local expert, if you can find one. But if it is sick (eg broken teeth), it's not likely to be economically repairable. (6/01)

You'll probably have replies to this already but just in case:

1. Sounds like a Clutch type going off or maybe it's just in need of "juice" - likely to be Japanese aftermarket one on a '90. I understand there were some very useful makes installed - Japanese don't seem to stint on diffs, clutches etc.Top gear preferred - Mazdaspeed even Quaife diffs have appeared on imports!

2. On the assumption it could be a "top notch" jobbie it might even be a serious racing model like a Katz. Jim Rotter has one of these which sounds as though the back end is about to fall off but that's just the clutch mech. doing it's job - very well. Apparently they are "Drag" clutches so you can drop 'em at 6K and the clutch just smiles and politely says "thankyou" ....your wheels fall off and the clutch bursts into flame but the diff's OK ;)

3.Doubtful this is std. "open" diff as they quickly go "bang" (spectacularly) once they start making a noise - no mistaking a diff about the go - believe me.

4. If it's a clutch type that's really had it you can:
A. Replace it with same thing
B. Replace with standard "open" diff from another 1.6
C. Upgrade to 1.8 size "open" diff altho' you will have to get 1.8 propshaft and drive shafts i.e. whole 1.8 rear end.
D. As C. but source a Torsen - much, much more difficult to find. Most scrappies don't know about them and if they do (usually when you have to describe exactly what you want) then they up the ante big time. ** If you want to got his route I'd not muck about (unless man of leisure) and get on blower to Powerdrift or Kay Yu Autos. They most definitely know what a Torsen looks like and what they are worth BUT they are both good and won't waste your time sending you std. spec. 1.8 units like most of the cretins in the business - I've been there. Finding one could also take a long time.

So unless ready and waiting I'd get a std.1.8 open diff and wait for a torsen which you can bolt into the 1.8 diff carrier when it comes available.Std. 1.6 diffs are weaker and do eventually go. If you are turbo'd or drive really hard then a 1.8 conversion makes sense short and long term.

Oh yes - only way to tell a Torsen diff is by talking off the drive shafts and looking thru' the hole - if there is a bar about 2 cm diameter thru' the hole it's a std. open or clutch type diff. If it's completely open then it's a Torsen. Yes, I know that contradicts their descriptions but life is full of such inconsistencies. (6/01)

Okay, I have driven the car a little bit more (no tax or registration!) today and gained some more exact experience. Under no throttle the rear diff is a smooth as silk, under any acceleration not carried out in a straight line it will jerk, feels like you are taking the corner in small movements. I think the diff is locking up??? Even manoeuvring parking the car can make big clunking noise, even real slow... The more lock applied (i.e. more difference in rotation between the rear wheels) the worse it becomes. Once moving (20mph+) it is not noticeable, but coming out of junctions full throttle is a scary prospect, as you don't know if the car will get to the other side!

I think the diff is a Plate type, and hopefully a CUSCO one, as you can get repair kits for these! (6/01)