New owner here with an imported 1996 series 7 FD. Did the usual changing of fluids after getting her and when I removed the differential drain plug I got these chunks of teeth out with it. The car still drives and the differential makes no noticeable noise. I'm not sure if these chunks are from the ring and pinion or the differential itself as I haven't opened it up. I'm guessing I need to drop the unit out of the car to even inspect this.

Of course already way over budget fixing unforeseen issues on the car, I'm looking at the most economical way to tackle this. The car has a 4.30 rear end and searching around on the suggestion of others I've found the RX-8 diff swap is most likely. As I understand it I'll need to find one from a 2004-2008 automatic to match the 4.30 final drive. Also the unit will not simply bolt up, I'll need to swap out the internals. Please let me know if I'm missing anything obvious here.

 

Yep, those are gear teeth off the ring and pinion.

Short term, you are OK. Damage is done.

Long term I'd get an RX-8 diff. Go for the 4.44 rear end, it's not much difference than the 4.30 and it's easily available. You should be able to get an RX-8 diff for cheap on Ebay or a junkyard. Read up on what models had what diff so you can make sure you get the right one. I did a thread about it a while back.

I'd find a shop to do the swap. You may want to go ahead and tear down the RX-8 diff and get the R&P out of it, that will save on labor and it's not too bad to tear down, especially with an impact gun.

Print out a copy of the ring and pinion setup pages from the shop manual. Shops that do a lot of 4x4 truck stuff do R&P swaps ALL the time, that's a good resource. You want someone that knows how to set up a ring and pinion in their sleep. The RX-7 diff is no different than other diffs out there, it's all the same principle.

Also are you certain you have a 4.30 diff? That's an uncommon option.

Dale

 

Thank you! In the short term, is there any risk to driving it other than eventually more teeth could go and the car would of course be undriveable? I did some searching around in the archives and I found information from you and others. My plan is to get at least the ring and pinion from a 2004-2008 RX-8 Automatic.

I'm fairly certain that my Series 7 RX-7 came from the factory with the 4.30 diff from my research before buying. Going with this as a replacement seems to suit my intent for the car.

Can anyone confirm the RX-8 ring and pinion part number matches the JDM 4.30 RX-7? I suppose as long as it fits it doesn't really matter.

 

Try to get all the pieces out of there. I once had a 1960 Triumph TR3A that had some busted teeth in the transmission. It ran fine except for a clunk-clunk noise in 1st and reverse, until one very cold winter day when I started it up and put it in reverse to back out of the driveway. The stiff lube lifted the loose tooth off the bottom and jammed it into the works. Couldn't budge the car after that. Replaced the transmission with a full-syncro one from a junked TR4.

 

If your Series 7 is an RS or an RZ it'll have the 4.3:1 diff, otherwise it'll be a 4.1:1. Easiest way to tell if you're not sure is to look on the id sticker in the drivers side doorjam. If it's not there, or has been cleaned into oblivion, measure the thickness of your front brake rotors. RS and RZ models also got the larger brakes, so your front rotors will be ~32mm thick.

 

I would probably fish around in there with a magnet to see if there's any other bits of large metal to be on the safe side.

Again, damage is done and I think worst case will be it could be a bit noisy. Really hard to say how that happened, that's not a common thing to just happen.

The RX-8 R&P are bolt-ins for the FD. Again, read my thread on it, I can't remember if there are certain models that fit and certain ones that don't. I don't know if they would be the exact same part number but again they are the right ratio and bolt in so there ya go.

Dale

 

I found similar bits in my diff once a upon a time. Continued driving it for a few more years until I replaced it with a used diff.

 

Of course, Dale, you know this, but axle hop is a known cause of diff issues...

 

Thanks so much for the help. I did fish around in the bottom with a magnetic pickup tool when I drained the oil, I didn't find any other chunks, just some glittery bits in the oil. Went out for a drive yesterday and had no unusual noises. Since I'm a bit overbudget getting this thing on the road I may continue to drive for a while and hope for the best. Going to try to find the RX-8 ring and pinion and other parts needed for a rebuild and have a shop take care of it in a few months.

 

If it's not giving symptoms, then you could probably button it back up while you replenish your funding. I like the 4.10 for Cali highways. Everybody goes 80 anyways.