Differential Question

[garretthes]

While driving the 79 I notice a fairly loud whine coming from the rear. I'm assuming it's the diff. I have an 83 Turbo parts car. Will the diff fit? Should I change the shafts as well?

[Zed Head]

It should be a direct swap, if both are R200s. You'll need to remove the stub shafts from the 79 diff and install them in the 83 diff, which should have CVs that are plugged directly in to the diff. The gear ratios will be different also, 3.54 for the 83 turbo diff and 3.7 for your 79, if they're both stock. So you'll need to swap the speedo gear in the transmission to get the speedometer to show the right numbers.

After all of the work, the odds are pretty good (bad?) that the 83 diff will whine also. They all seem to have some whine to them, I've even seen it noted in some old Car & Driver new car tests. You might have better luck trying to isolate the noise.

[garretthes]

Wow, it would be a lot of work. The 79 is pretty loud though. What about rubber? Should I try replacing the Diff Mount Insulators first?

Also, how do I tell which Diff I have?

[Zed Head]

The R180 is smaller and narrower and has a more square back cover, the R200 is more rounded and bigger. It's easy to tell if they're side by side, but difficult to describe. Compare the 83 to the 79 and it should be apparent, the 83 Turbo diff should definitely be an R200. There are pictures around the internet. Post a picture of yours and someone will be glad to identify it.

I realized also that your 79 could have 3.36 rear gears. Still not the 3.54s that the turbo diff would have.

If they are both R200, it's really not as complicated as it sounds. The stub axles and the CV shafts both use internal clips to hold them in, so they are designed to pop out with a dead blow hammer or a wedge against the housing. The speedo gear can be a little more difficult because you'll probably need to remove the roll pin to get the gear off. Still not a huge undertaking. Is the turbo an automatic? I'm not sure about the speedo gears from those, you might need to do some research on it, or find the right gear from a different manual trans car.

Worn mounts can allow more vibration to enter the cabin. I don't know a bunch about ZX diff mounts though, they are different form the 280Z mounts.

[garretthes]

The 83 has no tranny but it was an automatic. From what I have read the S130 manuals all had the R200 diff so it should be a direct swap.

[Zed Head]

The ZXes had both available. They're shown in the FSMs, Prop and Diff section, all the way up to 1983.

Anyway, I've been in the same boat with two 3.54 gear R200s. Swapped one for the other and they both sounded the same, even though one had fewer miles.

One trick people do is to run 85-140W gear oil in place of the 75-90W or 90W spec. Lowers the volume of the whine.

[jmortensen]

3.70 on a 79 280ZX? I thought that would have a 3.54, seeing as how it has the 280Z transmission. Maybe I'm wrong. A 2+2 would have the 3.36 (automatic only???)

The pinion flange on the turbo will be different, but that can be swapped pretty easily since there is no crush sleeve. Just red loctite the pinion nut and torque spec is something like 137 -210 ft lbs. The differential output stubs just pop out with a prybar, so you could use the old halfshafts if you wanted.

If you wanted the CV shafts you could swap out the companion flanges on the stub axles and the rest should bolt right up, unless Nissan did something really funky and put 27 spline stubs on the NA and 25 on the T. I know the turbo has 25 spline. Read up on cutting the peened part of the nut off before loosening.

If you think that diff is bad, swapping really shouldn't be that big a deal, much easier to get to all the bolts on the ZX than it is on a Z due to semi-trailing arm rear suspension.

[Zed Head]

I got the ratios from the FSMs. Of course, they could be wrong. I thought it was odd also, but it's in there. The 3.36 R200 is an oddball also.

I didn't realize that the turbo diffs had a different pinion flange. By similar reasoning as yours, why wouldn't they have the same pinion flange as the 280Z 3.54 long nose R200s? Seems odd. I tried to deduce pinion flange type by the pinion flange special tool described in the FSMs. The tool changed in 1984, and the turbo supplements I have don't show a different tool. Oh well, new knowledge.

A few loose ends to tie up for garretthes, but overall not a tough job. Except for the pinion nut. Do you have recommendations on how to hold the pinion flange while removing or tightening the nut, if you don't have the Nissan special tool?

[jmortensen]

If you have an impact you can hold the pinion flange with your hand. If not, you'd probably have to stand on the brakes or something.

[coop]

Here is how I hold the pinion flange while removing the nut. Cheap and easy! I found a length of channel iron around three feet long and drilled a couple of holes in one of the side flanges to match the drive shaft bolt holes in the pinion flange. Then I just bolt the channel iron to the pinion flange using the drive shaft bolts. The channel iron swings around and is secured against something like the car body or ground or work bench etc. Then I just torque the bolt. I also have drilled other holes into this tool and use it to secure the rear wheel lug bolts while I torque the nut on the rear wheel bearing. It also holds the fly wheel in place if necessary. I've even welded threaded nuts to it and used it as a puller. I use this tool all the time and even take it to the race track with me. Hope this helps.

Edited November 29, 2011 by coop
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[garretthes]

I have an impact wrench.

Drove the car again the other day and man is it loud. I would say it's more of a roar than a whine. Very annoying. I'm probably going to pull the Diff and half shafts off the parts car next week if the weather holds. The parts car is in the back yard and I really want to get rid of it.

On a side note, the speedometer was running very fast. For example when driving approx 70 it was reading over 90. Then it quit working altogether. I have read where this can happen if the cable is loose at the speedometer itself. Any ideas?

[jmortensen]

If it reads the wrong speed then it has the wrong speedometer gear in it. The cable can disconnect from the transmission end (done that one) so I guess it should be able to disconnect from the gauge end too. Getting the cable out of the back of the speedo is quite a PITA on a 240. Don't know about a ZX.

It's usually the front pinion ball bearing that goes out on the R200. Pretty good chance that this is the problem on yours. I think the bearing is NLA, so swapping diffs is the right thing to do.