Advice needed - installing an R200 diff in a 72 240

[DAT240]

I'm looking for some advice - I'm installing the front crossmember on the R200 diff and the mounting holes do not line up nicely - the hole centres are about 3/8" out.
I've done the research, there's a hint in one post about "the bolt hole locations just didn't quite line up without the need for serious modifications" but nothing more. Rather than explain I took some photos (aren't lasers amazing?):

3 22 front diff mount 1.jpg
The moustache bar is installed like this:

3 22 front diff mount 2.jpg
And here are the 2 crossmembers that I have - the rusty 240 on the left, the 280 on the right - bolt locations on the crossmembers and the mounts appear to be interchangeable.

3 22 front diff mount 3.jpg

I researched diff mounts to find out if there are different bolt locations - discovered that any diff mounts are very scarce if not unobtainable.
I am considering elongating the holes in the diff mount to suit. I don't think that it would cause structural issues. I may have to deal with a driveshaft length problem later but that is an easy fix.

Has anyone encountered this problem before - and solved it?

Thanks!

(I really don't know the provenance of the diff - bought it many years ago, it has been languishing at the back of my garage until I recently refreshed it - I think that it's out of a 280)

[Noll]

I have a vague recollection of reading that the mustache bar needs to be flipped 180deg or otherwise modified.

Post #6 in this thread seems to confirm that (with pics). A later comment mentions that they swapped a R-200 specific mustache bar in after, so that's probably what you'll want to find from a 280 (or 280zx if the mounts are the same?):

https://www.classiczcars.com/forums/topic/60521-still-cant-figure-if-i-have-a-r180-or-r200-differential-on-my-72-240z/?tab=comments#comment-554725

Alternatively, as long as the bar fits when flipped 180deg, I see no reason you couldn't use longer studs and some washers to space it out to the correct location as needed.

[DAT240]

Noll - You are correct - the moustache bar was flipped to fit the bigger diff. But I still have the clearance issue. I've been scratching my head all day - hoping for a simple fix. All blogs that I've seen say that the crossmembers 240 / 280 are interchangeable, but the 280 is stronger. I think they are correct on both counts. The half shaft geometry looks good where the diff is now. Maybe elongating the holes in the mount is the answer?

[Noll]

Noll - You are correct - the moustache bar was flipped to fit the bigger diff. But I still have the clearance issue. I've been scratching my head all day - hoping for a simple fix. All blogs that I've seen say that the crossmembers 240 / 280 are interchangeable, but the 280 is stronger. I think they are correct on both counts. The half shaft geometry looks good where the diff is now. Maybe elongating the holes in the mount is the answer?

As long as the CV angles are good I don't see why not, the only other consideration would be making sure the driveshaft still fits given that the distance is shorter now (and that the diff/transmission angle is correct, but can't see why that would change). If so, seems simpler/cheaper than sourcing the R200-specific mustache bar, which I'd assume was bent to be that extra 3/8 farther back towards the spare tire well.

[DAT240]

I know that it is an R200 moustache (14 mm stud holes vs 12 mm for the R180, plus I compared directly with the original 240) and it's pointed in the right direction - that's what's perplexing. I turned my focus on the crossmember and mount, thinking that I had something backwards but to no avail. There was mention of long nosed diffs on the web but i couldn't find more info. It will be no big deal to slot the mounts unless someone else has solved this puzzle before. I'll deal with the driveshaft when I get there if its a problem. I've got a 5 spd close ratio at the back of the garage to fit in as well so i may have driveshaft issues anyway. This is gonna be fun!

[Noll]

I know that it is an R200 moustache (14 mm stud holes vs 12 mm for the R180, plus I compared directly with the original 240) and it's pointed in the right direction - that's what's perplexing. I turned my focus on the crossmember and mount, thinking that I had something backwards but to no avail. There was mention of long nosed diffs on the web but i couldn't find more info. It will be no big deal to slot the mounts unless someone else has solved this puzzle before. I'll deal with the driveshaft when I get there if its a problem. I've got a 5 spd close ratio at the back of the garage to fit in as well so i may have driveshaft issues anyway. This is gonna be fun!

Oh gotcha, I thought you had the r180 bar still. That is weird then, as you say though slotting the mount should be a-ok.

Nice! I have a 240sx 5spd that I'll swap into my Z at some point, but as I'm trying to just get it on the road and the bellhousing needs machine work to work with a L-series and that trans I'm going to be sticking in a ZX 5spd for now - should be a direct bolt in. If you also have the 240sx trans I've been told that an automatic 240z driveshaft is the perfect length (and indeed my transmission came with one when I bought it from another Z person), or of course a driveshaft shop can shorten a regular one.

[DAT240]

Before I start to modify the mount I did a bit of research - found this thread on classic Z cars - see "Namerow"'s epistle on front diff mounts - posted Aug 2017 - appears to be from Canada - one of us? Great info but doesn't actually solve my issue. Kudos to whoever Namerow is.

https://www.classiczcars.com/forums/topic/52894-differential-front-mount-insulator-for-a-1970-s1-240z-nla/

And then I went to my dog eared Black Dragon catalogue. I use it to compare parts from different models, very handy when you're bui a FrankenZ.
Here's the relevant page - shows that the "mount insulator assembly" is interchangeable for 240's 7/71 to 78 280's.


I could loosen the moustache bar, install the front mount, then tighten everything. That might work but I would be putting the rubber on one side of the mount in compression, the other in shear. I prefer to have everything fit nicely rather than going medieval. Especially on a part that is now made of unobtainium. So today I'm going to slot the holes in the mount and close this chapter, unless I get an urgent "don't do it" from the more sage members out there. I justify this by thinking that the mount is rubber and won't create enough force to make the mount shift - especially if I torque it down. This will solve the problem but not the mystery.

[Six_Shooter]

It's been a long time since I used the stock front diff mount in my car, but everything lined up fine when I did, no slotting, no forcing or pushing parts into place. My car is a '73, so this area of the chassis is the same AFAIK.

There must be something else off with the parts you have.

I'm thinking that front mount you have might not be quite right. I don't recall the bolt holes for the bolts that pass through the diff snout to be so far back on the mount.

You mentioned something about a long nose diff, that's what you have, all Z cars up to the end of the Z31 used long nose diffs.

[DAT240]

Thanks Six Shooter! I took your comment to heart, thinking that I MUST be doing something wrong. I went over everything, then recalled a post somewhere about the Z suspension that said "do yourself a favour, don't torque anything until you have the complete suspension assembly in place". So I loosened the moustache bar, which allowed it to be pushed back when I installed the from diff mount - voila it fits! In truth it should fit together regardless, but this is a 50 year old car that I'm hanging orphan parts on to, so I can't quibble. Problem solved - thanks for your opinion. Much appreciated. On to the next challenge!