I recently completed a GSL-SE rear axle swap on my 85 GS and I am getting some pretty bad clunking noises form the rear end. Noise occurs any time your shift isn't timed absolutely perfect or during the deceleration if the engine sputters a bit as it sometimes does between 2500 to idle. I afraid the backlash on the ring and pinion or spider gears may be way out of whack. I've included a video so you can get a better idea of what its like. Let me know what you guys think.

 

Nobody has any idea if this is normal?

 

First off, the amount of play you show in your 2nd video looks normal to me - that's actually the transmission allowing the driveshaft to move a bit, and my -SE has the same amount of play. I assume you know the -SE rear axle has an LSD installed, but the ring & pinion setup is just as important here.

If the U-joints on the driveshaft were going out, you'd get a constant hum in the driveline that would get worse as speed increases, to the point where it would turn to a heavy 'whacking' sound as the U-joints get battered. One way to check U-joints is to get under it and try to move the center spider in any/all directions. If you can visible move the spider within the shaft with any play, then the driveshaft needs to be replaced. I've replaced one on my -SE in 222k miles, and that was at about 120k or so. They don't last forever, and they're not replaceable. The good news is that Mazdatrix has a service that will rebuild yours (*or sell you a rebuilt one) which DOES use replaceable U-joints for a reasonable cost. That's if it's the driveshaft.

The only way the rear-end pinion & ring can be checked is by taking it to a competent driveline shop that does gear alignment. There are a series of shims and crush cylinders in there that set the pinion spacing. If you remove the driveshaft (mark the orientation by scribing a line across the D/S and 3rd member Input - and be sure to reinstall so the marks line up), then grab the input and see if you can pull it out toward the front. There should be almost no play on that shaft, front to back. You can expect some play when you rotate it, however - as when the driveshaft is turning it.

 

There is no play in any of the u-joints. I figure there is definitely something wrong within the diff as none of my other rx7s make such a loud sound when I rotate the driveshaft back and fourth.

 

If this is all a normal amount of movement then what else can be causing the horrible driveline backlash and knocking that I am experiencing?

 

Knocking which is speed-dependent is usually bad U-joints. Aside from that, if it's internal to the pumpkin, there isn't anything I can tell you from here. If you're convinced it's gear mesh, it's worth having someone look into the 3rd member and get it sorted out.

The driveline movement in your videos look normal to me, based on my SE.

 

The knocking only happens going on or off the throttle. The u joins are new and have no slop in them. The sound is a very loud metallic knocking between throttle on or throttle off. Also happens as revs drop below 2500 rpm as the engine begins to buck a little. It's very noticeable and very annoying. Clutch is brand new, tranny seems to be working fine, all bushings in the rear are good and new u joints. That seems to me to indicate an issue with the diff.

 

Two things to consider;

1) LSD Additive - the LSD on our -SE's needs a specific GM additive (sold by Mazdatrix and others) for the plates to get proper lubrication and not 'chatter' when cornering, but I don't think thats your true problem. If you haven't added the stuff, it's worth doing to see if the sound goes away, because if not...

2) Missing ring gear teeth - on light loads or coasting, a missing tooth on a ring gear won't be noticed as the pinion glides right over that missing tooth, however - when you accelerate hard or decelerate with the car in gear, that missing tooth will be a gap in the conversion of rotational energy from the pinion to the ring (accelerating) or the ring to the pinion (decelerating), and you might feel that as a knock. That knocking noise would get slower and slower as you approach a dead stop, or would increase in tempo as you're accelerating.

If that's the case - you'll need a new ring gear most likely. If the pace of the knocking is very fast, you may need a new pinion. Good luck, regardless,

 

Did you ever figure this out? I've had the same problem since I bought my car and have been ignoring for the past year. It's exactly what you've described