Ring & pinion question

stick1975 · 07-13-2010, 05:21 PM

Bought a G28-10 5sp. awhile back, was just looking around on line and daydreaming about shifting gears. Think I bought an 85 non-LSD trans. Read about the Early 8 disk carrier upgrade. Would the G28-10 have the 2.20 final drive? If I install an earlier LSD carrier, could I change my final drive to, what I think would be the more desirable 2.72 gears?

Xlot · 07-13-2010, 05:45 PM

G28/10 is from an 85/86 Euro - according to the 928 Specialists website.

Its most likely 2.73 final drive ratio.

You can swap the diff to add an LSD, but you need to move the crown gear over from the open diff to the LSD, as the crown and pinion are a matched pair.

Not a tricky job - just have to work out the shims to set backlash correctly (measure the original open-diff backlash reading before disassembly, so you know how much wear there is beyond the spec etched on the side of the crown wheel, and aim for that as the "new" spec when shimming backlash with the LSD).

stick1975 · 07-13-2010, 06:08 PM

Thanks for the reply! Makes me feel much better about me buying it. Came from 928 WW.

stick1975 · 07-13-2010, 07:22 PM

If my G28-10 is the 2.73 final drive, as Xlot stated, then I will not be changing gears, just carriers. Want the LSD and the higher num. gears for better acceleration for the stop light grand prix one day. Good to know though. Thanks for the input.

Danglerb · 07-14-2010, 02:29 AM

The automatics have a pinon gear that comes off, but the 5 spds have a pinion that is part of the transmission internal shaft, so no swapping.

Unless you track it the LSD won't make much difference, thanks to the torque tube a 928 doesn't unload one rear wheel under acceleration, so decent surface and you get two blacks lines of burn out.

With a stock motor the 2.73 is nice, except on the highway, but once you do stuff to up the HP the tire spin gets a bit much and a 2.20 works better.

Xlot · 07-14-2010, 03:58 AM

Quote:

Originally Posted by Danglerb

The automatics have a pinon gear that comes off, but the 5 spds have a pinion that is part of the transmission internal shaft, so no swapping.

I think he means keeping the gears in the 5-speed case, and just adding an LSD.
You can swap just the diff carrier inside the casing of the manual - you simply remove the crown gear off the old dif and bolt it onto the new diff, then measure the required shims for 0.3mm bearing preload, and set the backlash.

Warning.. the 120ftlb crown ring bolts are mofos.. grind a 20mm socket down to remove the bevel, and get as much direct contact as possible with the bolt heads. you'll see what I mean when you remove the open diff and get ready to take the ring gear off.

Quote:

Originally Posted by Danglerb

Unless you track it the LSD won't make much difference, thanks to the torque tube a 928 doesn't unload one rear wheel under acceleration, so decent surface and you get two blacks lines of burn out.

On a decent surface yes.. but with one of each, I've found that no LSD makes for some major traction loss in the wet (steep wet intersections are just painful). Which is why I've just fitted an LSD to my '89

Quote:

Originally Posted by Danglerb

With a stock motor the 2.73 is nice, except on the highway, but once you do stuff to up the HP the tire spin gets a bit much and a 2.20 works better.

For a US 82 or 84, I doubt HP will be an issue

Fair point tho' - I've got the 2.64 rear end in all my 928's, and at highway speeds the rpm are a little too high for comfortable relaxing cruising.

Last things to add - get the 5-speed transaxle gasket set, and replace all the gaskets and o-rings (covers, input shaft, selector shaft, diff bearing seals etc.) before it goes in - its relatively cheap and much easier to do now. Also buy a new reverse-gear lockout spring (about $15 from memory) and do that just inside the top cover as its probably broken.

stick1975 · 07-14-2010, 06:32 PM

Again, thanks for all the info. Pinion gear must cut out of the main shaft some kind of way. Would explain why I couldn't find any after market gears in different ratios. My plain is to get all seals and gaskets, tear down just far enough for inspection purposes, install the pois, and seal it back up. Looks allot like the T-5 in the Camaros, Firebirds, and Mustangs, of the same era. At least from the outside, haven't torn my down, yet. Since my neck is problee redder than most, I plant on putting the 5sp in my 82 928 with either an iron headed LT-1 that I bought, or an LS 6.0 that I bought. Like I said, day dreaming. I have learned allot on this site. I thank all of you for help.