Differential oil

[tanny]

I am going to change the oil in my differential(previous owner put in a 510 rear end) so I checked for the filler hole and it is right up against a rear brace with about 1/2 inch of access(so there is no way to get wrench in there). Any suggestions on how to fill this thing other than removing the differential? I only stuck my head under there for a second, so maybe I missed something obvious. It is a 180.

[2ManyZs]

Hmm, if it is an R-180 it can't be from a 510 as the 510's came stock with the R-160. R-180's could be swapped into the 510's but it shouldn't make any differnce in how it fits in a Z since it probably came from a Z to begin with....

It is usually a bit of a PITA to fill a rear while in the car as it is hard to get the fill bottle up high enough and then you sometimes need a hose on the bottle to feed it into the diff.

Not sure what the problem is if you can't get the plug out at all as it should be accessible if it is an R-180.

[tanny]

Didn't realize 510's came with only 160 diffs. I had assumed it was a 180 because the former owner said no modifications were necessary when he installed it. So I asume the 160 diff can be installed into 240 with no mods then. If I could get at the fill plug to remove it, I could use a plastic tube as I used on filling the tranny, but there isn't any way to access that plug. If I have to remove the diff to fill it, I might just put the stock diff back in. At least he saved the old diff. Thanks. Victor.

[2ManyZs]

It is probably a 3.90 if it is an R-160 out of the 510, that was their stock ratio while the stock R-180 had a 3.36. Guess that would be the reason he changed it in the first place......They do bolt in easily into a Z, just not quite as strong as the R-180 would be.

In fact, I have one in the shop that was taken out of a 240....

[tanny]

Thanks for the info. I am undecided on which diff to use. Have not driven the car yet(have been rebuilding the engine and hydraulics because it sat for 20 years) so I have no idea how it will perform with the 3.9 diff. It has 3 webers and headers, but no cam that I know of. Has approx 1 inch front sway bar and 3/4 inch rear bar and has been lowered(don't know how much). I would doubt that the previous owner put in a different speedo gear, so will compare speed to another vehicle(so I can get estimate of speedometer error at different speeds. May try to get speedo gear if it's a problem) unless I put the stock diff back in.

[2ManyZs]

If it is in fact an R-160 with the 3.90 gear ratio, all you need to do is look in the tech articles here, I posted the correct speedo gears that apply to the different rear diff ratios. Match the color and teeth of the gear to the rear diff ratio and you are all set....

[tanny]

Looks like I would need the white speedo gear. Any suggestions on where to find these speedo gears other than rummaging through junk yards. There is unfortunately little(read none. A few 280s) in the way of junk 240s here in Durango. Nearest 240s are in Albuquerque or Denver. That was an easily understandable tech post on drive ratios. Thanks, Victor.

[2ManyZs]

Probably the best bet for finding the correct speedo gear would be from a Nissan dealer, Courtesy Nissan in Texas might be the best bet, but MSA might also have them. They are going to be kinda tough to find in a junkyard since so few came from the factory with the 3.90 rear. In fact, one of the only ones from the factory with a 3.90 here in the US was in the later ZX's.

You should find Courtesy's web-site in our web links here on the site.

[Royce]

Howdy,

Hmmm... drop the diff or take off the rear suspension cross memeber. Tuff call! I would be tempted to disconnect the rear suspension cross memeber before I would want to drop the diff. I would think then you would have full access to the fill/drain plugs on the back of the diff. However if you are going to swap diffs then that won't help!

Also, I always loosen the fill plug before the drain plug. That way if I am not able to get the drain plug out I can still lower the car and drive it until I beg/borrow or steal the correct tools!

Regarding the speedo gear, are you sure it was changed with the diff? Chances are it is probably the original one that came in whatever trans you have. Make sure you count the teeth on the old one before you go looking for a new one. Of course if the tire height has been changed, it takes a little more creativity to calculate which speedo gear to use to get the most accurate speedo.

HO HO HO!!!

[tanny]

Thanks to everyone for the info. I guess I am getting a little ahead of myself here since I still have to start up the engine for the first time. Just finished rebuilding and installing it, and am now replacing all clutch and brake masters and slaves, rebuilding calipers, and replacing pads and shoes, cleaning and testing the electric fuel pump, etc, etc. I really am just finding odds and ends to fix up so that I can put off turning the key and watching my rebuild melt or having to tune the 3 webers for the first time. I always worry that I forgot something during the rebuild that is going to surprise me when I fire it up. Get the jitters every time. Don't even know if the tranny and diff are functional, although the previous owners statements concerning the car have proven quite honest so far. The car hasn't been run since 1982.