Checking the mesh pattern of a 930 final, does that looks OK?

[kamaro]

I bought a used 930 transaxle and wanted to make sure I have a good mesh pattern of the final gears because someone swapped in an open diff instead of the LSD years ago, so I'm not sure if he did a good job of aligning it correctly. Here is a couple of pics of the drive and coast sides, do you think I'm good to go?

[ClickClickBoom]

Until Matt chimes in, try this:
http://departments.weber.edu/automotive/YouTube/Weber_Ring_Gear_Contact_Pattern_Interpretation.pdf

[Driven97]

I'm far from an expert, so YMMV. IIRC the coast side (concave) is the more important one to get right on used gears. You've got a big soft pattern which is nice, it looks a little high and a little towards the toe. The drive side looks centered vertically but again towards the toe. Looks like you might need to move the ring gear slightly away from the pinion. Fortunately you don't have to mess with pinion depth if that's all you are changing.

Did you do the official Porsche method for setting up R&P and are using the paint as a backup check?

[kevingross]

I've posted on this topic before. You cannot judge correctly for two reasons:

1. Your transmission is not under load. Under load, the teeth flex elastically (Young's modulus, etc.) and the pattern shifts.

2. With a required accuracy of +/- 0.03 mm, there's no way you can read that small a delta with marking compound.

The good news is that swapping in an open diff doesn't change the optimal pinion depth (shims under the bearing tensioning plate). So all you need to do is measure the ring-to-pinion backlash, get it in range. And get the differential carrier bearing preload correct. Both are controlled by the shims under the differential carrier bearings' inner races. You can home-brew a tool to simulate the tools used to measure this, pretty easy.

The remaining bad news is that getting the 90 mm inner race off the differential without a tool similar to the VAG1582 kit can be difficult. Just did a 930 four-speed, I have a tool, made by the German co. that makes the VAG1582 tools, that uses a collet mechanism to grab the bearing's rollers. Not at all cheap, but works great and is essential when working on LSDs. I'm not sure about 930.3x open diffs but looking at the WSM's pictures, it looks like may have room in the casting for a puller. Good luck!

Show and tell: the 90 mm bearing puller. Yes, it's pretty big. That's a 50 mm wrench used with a 41 mm socket / ratchet to operate it.

[Driven97]

I was able to pull my bearings off with creative use of a 2-jaw puller and some other stuff I had laying around the garage. Probably a good thing that photo died when Google Plus went away. Don't do like I do.

[kamaro]

It seems like it needs a lot of special tools and creativity, which I'm lacking both. I will go a head and install it the way it is and hope for the best.

[stownsen914]

Checking the backlash and preload is pretty easy, actually. It's worth checking them, and you don't need to remove shims just to check. And if the measurements are off, you can make a decision about whether it's worth fixing.

[Matt Monson]

Take all that paint off and look at the wear pattern. It’s used. You can see who it’s been wearing unless they put the open diff in right before they sold it to you.