Well here's a kick in the junk! The R200 3.70 LSD has a ring gear bolt that is M12 and the R200 3.90 ring gear is M10! 

Now I have to decide whether to machine the 3.90 ring gear to the new bolt size for the LSD or leave the 3.70 ring gear on and use the complete CLSD R200 as is. I will need to recondition the diff housing, of course. But man... all that work sourcing the 3.90 gear set and prepping the housing with powdercoat etc... to have to do it all over again!!! arrrgghhh.

But worth it I guess.

20 minutes ago, wheee! said:

leave the 3.70 ring gear on and use the complete CLSD R200 as is.

One other way to get screwed up, if you do the above, is to find that the 88 CLSD is actually a VLSD.  88 was an odd year and had both apparently.  I can't tell from your pictures what you have.  They use different axles.

I've heard about the bolt size problem.  If it was other way around you could use bushings.  In your case, you could use thread inserts.  It would be quite a test for them, but, in principle, they should work.  If you can hit the torque number, they should be fine.  Aesthetically displeasing of course.

 

It is definitely the CLSD and the 3.90 ring gear is smaller bolts. The problem here is, if I use the smaller bolt and try and centre it in the CLSD housing, there is a potential for movement and wallowing. If I re-drill the 3.90 ring gear, there is a potential for error and destroying a good ring gear. The other option is to sleeve the M12 opening in the CLSD and then use smaller bolts to attach the 3.90 ring gear. 
In the end, what am I really losing by going with the 3.70 rear end? A little bit of lower end pickup and gaining a better cruising gear in 5th....

Doesn't the gear center on the carrier?  "Hub centric", precisely machined.  The bolts just stop the gear from spinning, that's why people use bushings to sleeve the small bolts in the big holes.  Pretty common.  And it's the torque force of the bolts pressing the gear face to the carrier that stops the spinning, in principle, by friction or locking "asperities", so the bolts aren't really supposed to see anything but tensile force.  Some manufacturers actually use "thread" locker at the surfaces, between the gear and carrier, as a kind of glue.  Interesting problem.   Forces you to really think about how bolts and threads work, and the parts they're used on.

What transmission used would be the key for ratios, I think. 

You might check your clutch plates while it's apart.  I have a Ford LSD in my truck and they're known for wearing out the plates and going "open".

I have the 1978  5 Spd tranny. I agree that the 10 bolts holding the ring in place are more tensile than sheer strength, but I don't have any suitable bushing material at hand....

Edited August 9, 20186 yr by wheee!
corrected for year of tranny

http://zhome.com/ZCMnL/tech/240SX5spd/transmission.htm

3.321 1st...  And another project!  Whee.  

These are the comparisons for the 3.7 and the 3.9

Anyone care to post their thoughts on benefits or negatives of either ratio?

 

Edited August 9, 20186 yr by wheee!
corrected for proper year tranny

20 hours ago, Zed Head said:

http://zhome.com/ZCMnL/tech/240SX5spd/transmission.htm

3.321 1st...  And another project!  Whee.  

Mines an '78 (corrected from original post saying it was an 83)... I prefer the top end cruising over the tire squealing...

Edit: I just looked back at page one of the thread and realized I called the tranny a 78... even though I was sure it was an 83...! Is there an easy way to tell from the outside of the transmission?

Edited August 9, 20186 yr by wheee!
tranny correction

At least the cover is ready to powder coat...

... and here’s a pic of the CLSD. 

I recently removed a R200 with LSD and 3.70 gears and replaced with a R180 CLSD and 3.90 gears.
Substantial different feel from a stop and quickly revs in each gear.
It’s behind a close ratio 5 speed.
I do not put on many long runs on highway at speeds over 75. Very happy with it.


72 body and block, everything else 71, Tokico springs, Illumina, R180 CLSD, 83 close ratio, 3.90 gears, Ztherapy SUs, BRE 15X7 Libre wheels and BRE front spoiler.

28 minutes ago, 7tooZ said:

I recently removed a R200 with LSD and 3.70 gears and replaced with a R180 CLSD and 3.90 gears.
Substantial different feel from a stop and quickly revs in each gear.
It’s behind a close ratio 5 speed.
I do not put on many long runs on highway at speeds over 75. Very happy with it.


72 body and block, everything else 71, Tokico springs, Illumina, R180 CLSD, 83 close ratio, 3.90 gears, Ztherapy SUs, BRE 15X7 Libre wheels and BRE front spoiler.

Do you have a link to the calculator you used? The gear ratios in the first calc for the 3.90 are a little off for 3rd and 5th. Should be 1.308 and .745

1 hour ago, wheee! said:

Do you have a link to the calculator you used? The gear ratios in the first calc for the 3.90 are a little off for 3rd and 5th. Should be 1.308 and .745

http://www.apexgarage.com/tech/gear_ratios.shtml