1st gen RX7 help needed

Hey,

I am interested in swapping out the welded diff in my race car with a stock clutch type LSD. (Hopefully reducing understeer on corner entry).

I have never set up a diff before, but here's what I'd like to do:

1. Leave the pinion shaft alone
2. Unbolt the ring gear/diff assembly from the carrier
3. Swap the LSD in place of the welded assembly
4. Re-install, adjust the tooth pattern and set the backlash

Will this work? Or do I need to set up the whole thing again?

Also, I've heard about shimming the LSD plates to tighten the unit up, anybody have info on what's required for this?

Thanks, Neil

If you can set the backlash and tooth pattern and all that should work just fine but I have only done this once. That was 7 years ago and a mechanic double checked my work.

On the plates, the rumor is that you can just ad extra plates to tighten it. I would search on www.rx7club.com there should be a write up there. The rear diff is one of the next things on my to do list. Let us know how it works out.

I've just been through 2 of mine. The following is assuming you are merely swapping the diff carrier, i.e. reusing the same ring and pinion and not removing the pinion gear and its associated bearings from the diff housing.

If the gearset is not noisy and you plan to reuse it, BEFORE you take it apart check the backlash and write that measurement down. The backlash should be .003-.007. Make sure you solidly clamp the pinion so it won't turn or you'll get a false reading. You'll need a dial indicator for this. You should use some 'red lead' or diff setup paint (yellow sticky stuff) to check the pattern before disassembly also. You might want to take a picture of the 'before' pattern, you'll need it later when you go back together with it. As I said earlier, if you are reusing the same R&P and the backlash measurement is the same after replacement of the carrier, it's very unlikely you'll have any tooth pattern problems.

The diff is easily removed from the housing, the ring gear unbolt easily and going back together isn't difficult but you will need a 7" to 8" micrometer. On the bearing caps you will see 4 machined nubs, with the diff in place and the bearings properly torqued this measurement should be 7.3020 +/- about .002 either way. If this measurement is correct and the backlash is at the same measurement that you recorded earlier, you are in good shape. Double check your pattern (if you recorded it during disassembly) reinstall it and take off. The nuts which keep the diff bearings in place should be removed/tightened with a pin wrench but if you use a BRASS DRIFT! NOT STEEL! you can tap them around with a hammer. A steel drift can damage the cast iron nuts. I made a tool out of 3/16" steel plate and a 15/16" hex nut so I can tighten mine with a wrench.

I don't have the specs on the diff plates handy, Mazdatrix has them on their Web site. In the vast majority of cases, the plates are OK but the thrust washers and Belleville washers (conical springs) are worn. http://mazdatrix.com/G8LSD.HTM Using a whole bunch of thick plates and thrust washers will give a very aggressive lockup. I've heard (and am going to find out first hand soon) that new cone washers and thicker thrust washers with a set of in spec stock plates are all that's needed for an autocross/road race type of car.

You might also try this RX7Club. com link: www.rx7club.com/showthread.php?t=711712 You'll have to register if you aren't already a member.

There are two different hole patterns for the driveshaft for 1st gen RX-7 (non-GSL-SE). I don't know if it was a lsd/non-lsd difference or if it had to to with the year models ('82 diff swapped into '84) Swapping the flanges and retorquing the nut on the pinion worked well for 100k miles or so.

The pattern change came in the middle of the 83MY production.

The pattern change is not LSD or non LSD specific. I learnt something a few years back: all 1st and 2nd gen RX7 diffs have the same diameter 'pilot' which centers the rear driveshaft yoke on the pinion flange. So if you have a small bolt pattern driveshaft and a large pattern pinion flange, you can drill and tap the flange for the small pattern easily. That's how I did the diff in the Abomination; I used a small flange RX7 1st gen driveshaft and a 2nd gen pinion flange.

On Stinky (my much lamented '79 RX7) I had to swap the pinion flanges when doing a GSL diff swap. The seal protection 'flange' from the '79 was too small to fit over the diff housing and the same piece from the GSL axle was too big to fit the early flange. So I tapped it off of the early pinion flange, bolted it up and went on my merry way with no problems.

Thanks, for the replies.

Yeah, I've already run into the different flanges and big axle/small axle thing.

That's a good tip about drilling new holes in the larger flange.

My mode of operation to date has been to scrounge a used 4.88 gear or 5.12 off ebay or IT.com, run it til it explodes and repeat as necessary. Seems like each one I get needs a different axle housing or driveshaft or something.

Can anybody confirm that miata and 2nd gen non turbo LSD's will bolt into a large axle RX7 diff? Do the axle splines match up?

http://www.solomiata.com/Drivetrain.html