Mazda MX-5 Miata banner

The Used Parts Gamble... Lsd Repair?

10K views 14 replies 5 participants last post by  playtime 
#1 ·
Evening all,

Been a bit of a crap few weeks if i'm honest.

Clutch started slipping within a few miles of turbo install, new competition clutch put that to rest.

now my LSD i got from an ebayer has shit itself with no prior warning after 400 miles, not blaming anyone as the diff worked perfectly fine up until yesterday so its just one of those things i guess.

i drained the diff and there were a few chunks of metal stuck to the drain plug, so i've refitted the original open diff to get her moving again in the meantime.]

With regard to the diff, is it a bin job or can it be saved?

The trouble with buying used diff's on ebay is every single one is "perfect working conition" but really its a bit of a gamble..

So is it worth looking into getting the diff looked at by a pro? the main crown wheel and pinion both look fine, but without further stripping i cant say where the bits of metal have actually come from....

I'm just a bit reluctant to go down the road of ponying up another £250 for an unknown diff.
 
See less See more
#2 · (Edited by Moderator)
Chunks of metal like these?

Image0620.jpg

If so then you have a Tochigi Fuji Super diff, and if (with a little luck) the ring and pinion gears aren't damaged then you can just pick the bits out and carry on. That's what I did a year or two ago and mine's been fine.

There should be 8 of those metal tabs in all. If you can find all of them, then there's no need to strip the diff down. If you can't find them then you may need to take it apart, in which case it needs setting up properly on reassembly which needs the right tools. At the top of the pic below you can see one of the two tapered friction cones and four locating tabs which have snapped off it.

Image0614.jpg
 
#3 ·
haha, yes those are the exact same bits of metal!

it does sound like they are rattling round inside still, so far only 1 1/2 bits have been recovered!

I spilt the diff and the housing last night, was pretty manky inside so i left it until today to have a proper look, fingers crossed!
 
#4 ·
Chunks of metal like these?
Image0620.jpg

If so then you have a Tochigi Fuji Super diff, and if (with a little luck) the ring and pinion gears aren't damaged then you can just pick the bits out and carry on. That's what I did a year or two ago and mine's been fine.

There should be 8 of those metal tabs in all. If you can find all of them, then there's no need to strip the diff down. If you can't find them then you may need to take it apart, in which case it needs setting up properly on reassembly which needs the right tools. At the top of the pic below you can see one of the two tapered friction cones and four locating tabs which have snapped off it.
Image0614.jpg
Impressed with your diagnostic skills, very helpful!
 
#5 ·
It's a shame these diffs are so fragile. It's a really clever, simple design let down by what appears to be a manufacturing error.

You can probably see how the four broken tabs were part of the friction cone and that they pointed inward, and then that sat in the large casting with the tabs located in the four indents, to lock the cone in place and stopped it spinning. Unfortunately you can also see the raised lands between the indents are highly polished, which shows how many times the cone has slid around, forcing the tabs to bend and ride up over the lands until eventually they snapped off.

A properly machined casting which presented a flat face to the sides of the tabs would have prevented them riding up like that. <shrug>
 
#6 ·
I'm slightly miffed now as this was sold to me a torsen 2 from a 6 speed, i just did the usual checks to make sure it behaved like a LSD on the car and assumed it was a torsen.

I got it from a MX5 specialist breaker too so really they should have known what diff it was.
 
#8 · (Edited by Moderator)
well no point dwelling on it, onward and upwards.

had a quick look at the diff, found a few more bits of metal in the casing, but they quite are bit smaller than the bits in martins picture (ninja diagnostic skills BTW)

otherwise there is no 'major' damage as far as i can see, crown wheel and pinion both look fine, but i dont really dare take it apart any further without reading up a bit more first to find out if its worthwhile.

Just to confirm, there are 2 spring loaded plates in the centre of the diff pushing outwards on to some smaller gears, but cant see much more without stripping it....does this sound like a Fuji super?
 
#9 ·
Yes. That sounds exactly like a Fuji diff. The spring loaded plates preload the two "sun" gears, pressing them outwards against the two friction cones.

There's also the distinctive hexagonal shaft between the planet gears, which you can see by looking through the halfshaft holes. A torsen would have a clear hole straight through the middle with no shaft visible. A type 1 torsen has a wide open hole straight through while a type 2 is narrower in the middle but you can still look straight through the centre unlike an open diff or a Fuji).

Below is a pic of that hexagonal shaft and the planet gears, below it is one of the two plates and behind that is a sun gear. The two springs stand either side of the hex shaft.
Image0618.jpg

Flip that over and you can see one of the holes in the casting which the broken tabs fall out of. You can see the smooth back of the sun gear through the hole and, if you look carefully, you can see the edge of the taper cone too, with a missing bit where a tab has snapped off.
Image0617.jpg

The trick is to try to find all the broken bits by looking into those holes and somehow wriggle them out without taking the diff out of its carrier as you can see I did.

If you do eventually find you need to take it apart then reassembly will involve setting up preload and backlash. It can be done DIY with the right tools and the right info (see here: http://www.miata.net/garage/diff_rr.html) or given to a specialist.

As you're just up the road from me I ought to volunteer that I have an 8" micrometer and dial gauge you can borrow if you feel like giving it a go.
 
#10 ·
Thanks for the offer and the advice Martin, your a legend!

Sadly it is not to be, A broken bit of metal has gone through the gears and snapped a chunk off the end of a pinion tooth....i think this explains the sudden failure and extremely alarming metallic knocking sound i was hearing!

I've done a bit of reading on the 'other' forum and it seems the plates are not available to fully repair the Fuji so its not really worth spending time/money on a diff which will still not be 100% even with a replacement pinion.

I've refitted the old open diff for now while i ponder my next move, I think my fuji unit is ready for the bin which is a shame as it was looking like a may have been salvageable after finding all the tabs rattling round inside....then i noticed the snapped tooth!

At least i didn't waste more time refitting it to find out it was still buggered, I forgot to fit the knuckle duster spacer that sits between the top of the diff and the PPF when i refitted my open diff, had a bit of a wobbly when i realised...just as i was bleeding the brakes and getting ready to clear up as it was getting dark-i wont be making that mistake again.

Many thanks for all the help and advice, great bunch of people on here.
 
#12 ·
I did drop a note to the seller explaining the problem, but its a tricky one as i got the diff in feb, but the car has only been on the road since july so a fair bit of time has lapsed.

he did offer me a VSLD which had a snapped arm but otherwise sound internals for free, but he got a bit mixed up and thought i had a 1.6, so you can't knock him for his efforts....he could have told me to poke it.

he says he doesn't have 1 at the moment so i've asked him to keep a look out and hopefully he'll do me a little deal in the future.

He seems like a decent guy, works out of a unit about an hour away from me so hopefully he'll sort something out.
 
#13 ·
Hi. I've also had the same problem. Had a tochigi lsd rebuilt into my spare 4.1 case, and all tabs were present last week. No more lsd last night, and after strip down this morning, all, yes all the tabs broken off and a tooth mangled on both the crown and pinion. Thank god I have a spare crown and pinion, but 2 questions, if anyone can help?

1. Does anyone know where I can get the replacement tab plates?

2. Or preferably, anyone any suggestions on how I can strengthen the actual locking function? I am aware other cars with clutch plate diffs have multiple plates, so the tabs are stronger due to the larger number of tabs ie. each plate has 6 tabs and 2 plates per side, 4 in total = 24 tabs. Think the lack of plates / tabs in these diffs is the problem here, as i also want to shim the 2 preload springs for stronger lock.

It's prob more hassle than it's worth, but I don't want to run a welded diff on the road, and I don't like the way the torsen unlocks when sliding one way to the other, if that makes sense? My previous car with a clutch plate lsd, stayed locked (1.5 way), and thought if I could strengthen / tighten the tochigi, I would have a good compromise until I manage to find a clutch plate cusco diff eventually. As I said, any advice gratefully accepted.

PS. Before anyone says stop being a girl and just run a welded diff, I have 1 already, will use in the track car, just want a nicer option for the road car.

Cheers, Mike.
 
#14 · (Edited by Moderator)
1. Does anyone know where I can get the replacement tab plates?
Not available as spare part, I'm afraid.

Tochigi Fuji are now owned by GKN. I emailed both enquiring about replacement "taper rings" as they call them, but GKN said "this is not a part that we have available or are able to supply" and Tochigi Fuji said "as service parts, the change only for Taper-ring is not possible. Because clearance adjustment is necessary for LSD assembling".

2. Or preferably, anyone any suggestions on how I can strengthen the actual locking function? I am aware other cars with clutch plate diffs have multiple plates, so the tabs are stronger due to the larger number of tabs ie. each plate has 6 tabs and 2 plates per side, 4 in total = 24 tabs. Think the lack of plates / tabs in these diffs is the problem here, as i also want to shim the 2 preload springs for stronger lock.
<edit 'cos I already said all this further up this page> My belief is that the weakness is not the locating tabs themselves, it's the indents in the casting which the tabs locate in. The sides of the indents ought to be completely flat or even slightly undercut to stop the tabs trying to bend up and climb out, but I believe they were never machined so, under heavy load, the tabs do indeed bend, flip up out of their indent and slide around to the next one. Eventually the repeated bending fractures them.

See the 2nd pic I posted, of the inside of mine, showing the four highly polished lands between the indents in the casting, where the tabs have slid around until the repeated bending eventually fractured them.
 
#15 ·
Thanks Martin for the info. Just back from my mechanic who had my tochigi apart for me to see. I see what you mean about the tabs. Thought when i saw the bits in person, I could get the diff casing drilled and tapped and screw in 4 bolts into the back of the broken taper ring to locate in place instead of the broken tabs, but back surface of it is not parellel to the diff casing.

Although thinking of welding around the top edge of the taper ring to the diff casing, the whole way round may locate it securely. Looks like the diff is junk now anyways, so if the welding takes to the hardened taper ring, might give the diff a temp reprieve.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top