Finally got my OBX differential a couple of days ago. It's been about a month and a half, thanks to the wonderful folks at UPS. What can brown do for you?? Answer: Lose my packages.
INSTALL: I took 36 pics and was thinking of doing a writeup, but a differential install is a differential install. They are pretty much all the same, so I'll just point out the relevant stuff.
First it was installed into an open differential. There was some question as to which type it would work for. It appears to be designed for the open. The shafts fit in where they should be, flush with the housing, and the depth appears correct also.
I installed the unit myself. I checked the backlash of both the oem unit and the OBX. The OEM @ 140K miles had backlash measurements of .0045, .0055, and .0070. The latter being slightly out of spec. It worked well.
I removed the bearings with a puller and reused them. I used the original ring gear as well. Everything lines up and is cake to install on the OBX. Ring gear applied with red loctite.
BACKLASH: This is important. I DO NOT recommend installing one of these without checking backlash. Some people do it with the s15 diffs, but that is an OEM Nissan part. I tried the OBX with stock shims and the result was ZERO backlash. Spec is .0039 to .0059. The gears interlocked completely with no play whatsoever. I had stock shims of roughly .083 and .103 inches. I thought of swapping sides of the shims, but they would have moved the diff housing the wrong way. I did not have a shim pack, so I cut my own shims. I don't recommend this, but it works. I cut a ~.063 shim from sheet and 6 .005 shims from aluminum cans. Hoffbauer lager, to be exact. I used these shims in combination to eventually get the backlash within spec. I took many measurements ranging from .0035 all the way up to .008. Again, that latter is slightly out of spec, but it is close enough for me, and pretty much the same as the OEM unit.
I checked the tooth pattern with prussian blue. It was pretty heel heavy, but I did not intend to adjust the pinion, so it will have to do. This cannot always be adjusted properly anyway, as it depends on the pinion bore to housing alignment.
I should also note regarding bearing preload: I did not have a spring gauge to test preload. The OBX with stock shims, fell into place pretty easily. It required more shims than stock to create some preload. I simply gauged the tension on the OEM diff and tried to duplicate it as nearly as possible. I ended up using all 6 pop can shims as well as the homemade sheet shim, plus the OEM .103 and spacer. I discarded the .083 from the non-toothed side of the diff. I probably ultimately added somewhere between .010 and .020 shims total.
OBX with bearings and ring gear:
Including removal and replacing the housing there are several hours of work involved to do the job right, depending of course on working conditions and tools. I did it over the course of a couple nights, off and on, while taking pics and making notes.
REVIEW:
This is a preliminary, first impression type of review. I'll update my impressions over the next couple of days and add any relevant information regarding its performance. And of course, if it breaks.
After the install I took it out for a 20 minute test drive. Normal driving operation is, well, normal. Everything looks good so far. So I took it onto a dirt road first. I stopped in a few different spots, leaving one tire on dry gravel/dirt and the other tire in the ice and hard packed snow. I gave it a little brake and a little gas and let the clutch out to spin the wheels in place. I did this for a couple of seconds at a time to verify that the wheel with the most traction was spinning. The results are as expected. Both tires spun, and the tire with the most traction (dirt) spun continuously. Note: This is hardly scientific, as the application of the brake gives torque to both wheels, really negating the effect that might be experienced without braking. But it does prove that the differential is functioning and transfering torque.
Here is a pic showing the marks left by the tires on dirt and snow:
Next I took it to a paved road and parked it once again, half on pavement, half off the road in a snow covered gravel field entrance. I repeated the same methods used on the dirt road and once again the tire on the pavement broke loose. I did this only briefly as my winter tires smoke like the dickens and they are almost new.
I also opened up the throttle a bit on snow covered gravel to compare its response with the open differential. Both wheels spin and the rear end steps out more dramatically and quickly than with the open diff (of course).
This is about the extent of the testing so far. I didn't want to flog the car so fresh off the swap, and I will post more when I do.
In summary. So far, so good. I will update as appropriate.
-Steve