Possible diff trouble. Advice welcome.

[gforceg]

Afternoon, my GF reported a strange noise to me yesterday when she got back from a trip in her MX5 Mk2.5 (Torsen diff).

I think I've traced it to the diff or drive shafts but can't get much further.

The symptoms are a fairly obvious vibration when the car is on the over run but not when drive is applied.

The vibration is less if I de-clutch but doesn't disappear completely.

It seems worse at lowish speeds but that might be expected if higher frequency didn't cause greater oscillation, if you see what I mean.

At low revs in a high gear (2000rpm in fifth) a press on the accelerator does create some harshnss from the diff (again, maybe not surprising?)

I've been underneath and nothing is obviously loose or leaking. How much play would you expect in the drive shafts if you give them a good push and pull?

Any ideas or questions to clarify, I'll do what I can.

Thanks,

[MX-5 Lazza]

Is the rattle rev related or speed related?

[gforceg]

Hi Lazza, I nipped out again this morning for a longer test. The noise is road speed related and is most noticeable coasting or off drive at speeds up to about 40. It can be heard slowing to nothing as the car is brought to a halt.

Above 40 mph the frequency rises enough for it to become all but indistinguisable from other road and mechanical noise.

The noise changes slightly between clutched and de-clutched and is noticeable on gearchanges when drive is removed from the drive train.

My focus is on the diff but is there much else it could be? I'm planning a diff oil change at the weekend so I'll see what's stuck to the plug when I take it out!

Thanks.

[MX-5 Lazza]

Without hearing it for myself, the options are prop-shaft, dif or a drive-shafts. Get the back end off the ground and see if you can feel anything when turning a wheel by hand (try both wheels - being a TorSen it might only be felt from one wheel). After that, see if you can see or more likely, feel any play in a UJ on a drive-shaft. Any play at all, any slight clunk or knock felt by hand will identify the problem.

[gforceg]

Thanks, that helps to answer one of my earlier questions. There was definitely a very small amount of play in the drive shafts when I was under it on Sunday. It didn't feel like much at all but I suppose it magnifies.

I'll give it another rattle this evening and take it from there.

Cheers
Greg

[seany87]

What year is her mk2.5? Can you be certain it is a Torsen?

The 1.8's had a Torsen diff up until 2003 I believe then went to a clutch type diff after that. My 2004 diff shat itself so it was replaced with a much better Torsen diff

[gforceg]

Hi, it's a January 03 registered 52 plate, so built in '02. I didn't know there was a change of type tbh.

[MX-5 Lazza]

They all had TorSen but there are different types of TorSen and the later ones are more fragile than the earlier ones. Not sure of the change over date.

[seany87]

Google 'tochigi fuji diff MX5' - that will tell you all you need to know. If yours has this diff then when the oil is drained expect a couple of 'tabs' to pop out, like mine did. Hopefully you won't have this issue though

[gforceg]

Thanks for that lead Seany, I've read through those threads, very interesting. I'll go ahead with a diff oil change at the weekend and see what I see. More next week...

By the way, what was your course of action when the tabs appeared? New diff or a rebuild?

Edited by gforceg on Wednesday 19th August 19:57

[seany87]

Swapped it for a proper Torsen diff, not one with fragile clutch plate tabs like on the Tochigi

[gforceg]

Ha! I should have guessed. Rough cost if you don't mind saying? I see there's a helical LSD available on MX5 Parts. Any views on that, guys?

[seany87]

The Torsen I fitted was a 2nd hand one from a 1994 car. Straight fit. Cost me about 250

[gforceg]

I drained the diff this morning and found these on the plug magnet.



It would appear they are the tabs visible in this image I got from another link Seany pointed me to.



I also noticed that when turning one wheel with the back jacked up the other wheel spun in the same direction. I think that means I have a non functioning LSD.

I guess I'm in the market for a new / secondhand Torsen diff. I don't think I'd trust myself to replace it so does anyone know a good indy or MX speialist in the South West who could help?

[MegaMinion]

I don't really know of any MX5 specialists in the south west. But to be honest it's not a major job any decent garage will be able to do it. Your more difficult task is finding another diff. Is your car a 5 or 6 speed. Most earlier LSD were only fitted to 6 speeds and have a different final drive ratio which makes them a bit long on a 5 speed (I found that out the hard way).

[gforceg]

Hi, it's a 6 speed sport model. I guess I have a few options so I need to decide which way to jump.