Should I be saving for a new diff?
 

I did the oil in the diff yesterday and found the attached piece of gear sitting on the magnetic drain plug. It is about the height of my average fingernail.
I suspect it is from the previous owner but don't know. Certainly I have not done any clutch dropping redline launches but with 360hp at the rears it does lay the odd skid easily. I have only had it a few months.
Anyone else had this type of thing occur but in the mean time the diff still appear to work ok?
Is it only a matter of time before it grenades? (given 360hp)

Looks like a piece of one of the spider gears, if there is one piece there are most likely more. I would stop pushing it hard and start shopping for a replacement. Far after market LSD units I have found the ATS Carbon to be fantastically strong while remaining virtually silent. ATS LSD (93+ RX-7)


Example of complete failure, much more expensive since the ring and pinion gears need to be replaced also.

https://www.rx7club.com/attachments/...royed_diff-jpg

I found 3-4 chunks like that on the drain plug's magnet once. Drove it for another 3-4 years and finally replaced it when a local guy was getting rid of his diff after his car was wrecked.

YMMV

Found a chip like that on my drain plug too. Diff doesn't make any strange noises or perform poorly. I plan to replace it eventually, but I'm not freaking out about it yet :]

I think I will change the oil soon again and check for other metal chips. There were no flakes as such so it could have been hiding from a previous diff grenading for all I know.

However, I was surprised that when I had it on the jackstands and spun one wheel that the other did not spin at all - for clutch LSDs I have had in the past the other would rotate the same way and for opens the other would spin in reverse.

I have read online but most people say for a torsen the other would spin in reverse but mine did not spin at all?

It sure lays both tyres though...

Can't argue with that logic, it is always better to drive around on broken/failing parts for years instead of replacing them before the failure becomes much more expensive. :scratch: :dunno:

Same logic can be applied for chipped apex seals, no need to bother rebuilding the engine, it still runs. :icon_tdow :lol:

BTW, time is not a measure of mileage, we have customers that put little to no miles on each year, so 4 years could amount to 4 or 40K miles.

Pop the diff cover and inspect, then make the determination if you are on the verge of being stuck on the side of the road with a broken diff.

All good advice.

I put about 15k miles on mine fwiw. Rolled the dice knowing it could go bad. Thankfully, it didn't.

Without opening mine up yet, I have about 22.5 degrees of play. I'm pretty sure my ring and pinion are shot. Time to go 4.30?

It seems odd that if I jack it up and spin one wheel the other doesnt move at all?

was the tranny in gear when you tried to spin one wheel?

If the diff fails completely you will likely damage the ring and pinion or crack the case, making a rebuild more expensive in the long run. I'd fix it asap.

Nah not in gear

Definitely part of the diff carrier Torsen helical gears.

Stop driving the car. There are loose pieces in there and when they finally get caught in the main gears you will lunch the diff completely and possibly split the diff housing. It will break down and not need dragged onto a rollback.

I split one of the helical gears down the center along the shaft they ride on. It wedged between the R&P and split the housing in two. Get the cover off and inspect it. Sitting on the side of the road with your car peeing diff fluid sucks.

Opinions seem divided. No harm in me pulling the cover and having a look etc see what I find. If no more bits then maybe keep driving it. Is it normal for one wheel not to move when on stands in neutral and one wheel spun?

Pull cover. Have a look. Say hmmmm. Pack diff with banana peels forget about it for 100k km's till diff falls out on side of road in the middle of butthole nowhere.....

No. This would mean the Torsen components are blown and not engaging - ie. you have an open diff.

I fully expect you'll find more metal fragments in there.

Thanks for all the advice. I will pull the cover and report back with pics if I can get some suitable. The piece of metal is definitely from the helical cogs in the torsen unit now that I look at the curve on it.
I have priced up a FD LSD (full head/housing) second hand (must prove no chipped teeth), but I can get a second hand S4/5 LSD cheaper (full head/housing, housing will go to waste), which from what I read on some threads in the 'useful links' section will fit into the FD housing and probably be less prone to breaking with 363rwhp.
The saving by using the FC diff guts over the FD in price will be spent paying someone set it up i.e backlash and probably shimming it up as I assume it will be worn (had this done on another vehicle for the exact difference in price).
Can someone just confirm that the FC LSD will fit in the FD housing?
If it does I will go the FC route and do a swap. If not, I will buy the FD full head/housing and keep it as a spare. I have free towing if I break down so the main hassle is taking the bumper off and getting the car back into the garage :)
Sorry if my diff terminology is a bit off.
Thanks again.

S4 TII is a clutch style LSD and pretty robust, the S5 is a Viscous LSD and not worth installing.

If you go with an S4 I would not bother installing it without rebuilding the LSD with new clutch discs. Some people have had issues finding carrier spacers thick enough to shim the TII LSD in the FD housing. The TII does not use shims.

Well today I picked up a S4 clutch LSD (yep opened it and verified), and the guy was a fellow FD owner and threw in a broken S6 diff also (nice guy as they all seem to be). I was going to turn it down as never plan to install a welded diff etc, but glad I took it anyway now as it is a free housing at the very least but useful for other parts i.e. I could grenade my diff and have a spare now made up from necessary S4 and S6 parts.

I just popped the S6 diff cover and was surprised to see it already had a S4 clutch LSD in it. I don't think he knew this but anyway I was expecting torsen chunks and it was just the usual filings. All appears ok inside ring and pinion, but I havent pulled the centre yet. Struggling to get the axle stubs out of it. On the S4 diff I popped them with a crowbar but given this 'broken' diff has been sitting outside maybe that has made them somewhat seal in a bit too much if you get what I mean. Any other ways to pop them out? Or maybe this is related to the diff being broken.

I guess one of the gears inside the centre might have gone and I have heard about clutch plate tabs breaking. I believe he said it made a funny/bad noise pulling out of somewhere and he drove it home and he swapped it out, and it was still full of oil so never investigated it seems. Pretty sure the oil it it was not LSD oil either (LSD oil is always blue in my limited experience and this was normal gear oil colour - probably figured it was a torsen and therefore normal oil is fine.)

Originally Posted by octanepwr :
" Is it normal for one wheel not to move when on stands in neutral and one wheel spun? "

Reply by dgeesaman :
" No. This would mean the Torsen components are blown and not engaging - ie. you have an open diff. "

Have to differ. With car on jacks and trans in neutral, spin one side, and the trans gears will spin in the neutral position. It takes more torque to overcome all the sliding metal to metal surfaces in the FD's Torsen, to spin the opposite wheel. Now put it in gear, locking the trans, and the opposite wheel will spin, but you will feel that extra torque to overcome the diff resistance.

Note: I just verified this since my car is on jacks right now.

The oem Torsen gets it LSD action from friction at all the rubbing surfaces for the outer gear pairs and the side gears, as a reaction to the forces on the gear ends and the OD of the outer pairs. I always changed the diff oil twice a year when I tracked the car regularly, with one change midseason, and one change at the end of the season. The oil was always black comming out from heat. At the annual trans oil change, it came out looking like I just put it in.