TobyZ28

Doing my homework on 3.73 gears for my A4, and notice a bit about 2 and 3 series carriers.. Can someone enlighten me on what Carriers are in some detail? Whats the differece between the 2 and 3 series?

I'm 90% sure i have 3 series in car now (3.23 stock rearend)...

Finally, what brand? This is for street use primarily but it will see the occasional track day (convertable too).

Motive sounds like the best bet from the posts, I've seen pple refer to it as Motive/GM. Are there "gm" 3.73 gears and motive gears? or does this mean the Motive gears ARE the GM OEM gears?

Injuneer

The "carrier" connects the two axles together, contains the differential (spider) gears allowing the left and right axles to turn at different speeds, and the limited slip (posi) device if so equipped. The ring gear bolts to the carrier. With ABS there is a reluctor ring bolted to the carrier. The carrier sits in bearings that are held in the differential case.

TobyZ28

Hence why its called a carrier.. awsome thanks injuneer! So what are some of the differences between the series 2 and 3 (and 1?) carriers that people refer to?

Injuneer

The main difference is the spacing of the surface the ring gear bolts to, relative to the pinion shaft. The geometry of the 3.08 and lower numerical rings gears (2-series carrier) has the ring gear mounting surface moved farther away from the centerline of the pinion. The 3.23 and higher numerical ring gears (3-series carrier) are spaced closer to the centerline of the pinion shaft.

So if you try and put a gear set made for a 3-series carrier in a 2-series carrier, its located too far from the pinion. It is possible to use a spacer between the carrier surface and the ring gear to fill the gap, or some manufacturers make a (for example) 3.73 gear that is thicker and can be put in a 2-series carrier.

Best thing to do is to use a 3-series carrier for gears numerically higher than 3.23:1. You get into the same issues with the much stronger 12-bolt rear axles, where you are dealing with 3-series (up to 3.73) and 4-series (above 3.73) carriers.

If your car has RPO code "GU5" on the build code tag, it left the factory with 3.23 gears and a 3-series carrier.

Motive apparently makes the gears for GM. I believe Superior gears are also made by the same company. Any of those will be a good choice. I've also had good luck with US Gear (also sold as US/Strange). Most of the complaints about noise seem to come from people who have Richmond gears, but I've never tried them, so that's just heresay.

TobyZ28

Perfect. I do have the GU5 Rpo code so I should be all set Its always hard to get objetive information online, but it sounds like Motives are a good route to go... Thanks for the info Injuneer... I feel a bit less stupid about carriers now