Continuing to pull apart the '71, which has been modified by POs.

Documentation obtained with the car indicated it had a 4.11 R180 differential installed. We replaced the U-Joints in the stock Half-Shafts, and pulled apart the differential today, only to find out it has 3.545 gearing. It also has a large "K" stamped on the top, which I understand is from the 84-88 200SX.

So, someone has replaced the stock R180 with a later replacement R180, geared identically. I understand there's some work involved to get this to bolt up with stock halfshafts, so someone spent some time here.

I guess I'll be looking for a 3.90 differential now, and will be doing the R200 swap. Not something I was looking forward to. You can't buy new replacement gears for these K-R180's, can you?

Frustrating. I wonder where that 4.11 ran off to along the line.

I'd probably go poor, but would ordering P/N 38100-U3400 from Nissan replace the gears inside my R180? It can't be this simple, but frankly I just don't know much about differentials to know why it wouldn't. I think I've read every diff thread today and its making my head spin.

Catalog: http://www.nissanusa.com/nismo-web/Nismo-Motorsports-Catalog-2012.pdf

A couple issues:

1. Unless you're a registered racer with Nissan you cannot order directly from Nissan Motorsports. You'll have to order the parts through a cooperative dealer.

2. New R180 ring and pinions have been NLA for at least 5 years. Maybe Nissan Motorsports has sourced a new stash of parts or is sourcing new from Hitachi/Subaru, but I doubt it.

3. You best source for a 3.90 R180 is from a 2004-2006 Subaru STi - plus you get a CLSD.

John - I recall something from years ago - wasn't the "K" casting used for R180's with 4 spyder gears? Or didn't the Nissan Comp. R180's come with 4 spyder gears. Or am I confusing that with something else.?

ksbeta - Swapping in a different Ring & Pinion, then setting the differental up correctly - takes some experience and can require additional shims that you may not have on hand. I'd check with a local differential speciality shop - to see how much they would charge for the job - or if they will even take an old Nissan differential in to begin with. Otherwise - like John suggests - just buy a good factory unit or used factory unit..

FWIW,

Carl B.

I've heard of 4 pinion/spider gear open differentials in the "K" R180s but I've never seen one. I assume it would have to be in a heavier duty non-sporting application then a S30 or the front of a 4x4 pickup (some Japanese market sedan?). The Nissan Comp diffs were all 4 pinion/spider. Nissan had an OEM CLSD that was installed in the R180 and R190 that had two pinion/spider gears. For the R190 it was referred to as a R192 and I've had two of those with a 3.90 gear. Parts for this unit are very hard to find.

Carl, John, Thank you. After my frustration wore off I realized I wasn't going to be buying gears from Nissan.

The car's drivetrain was purported to come from an S30 race car built in the '70s that was totaled. The transmission was an early roadster 5-speed / 240z conversion. That being said, I have good reason to believe the car was built in it's current configuration prior to the 200SX being produced, and having spoken with both PO's since the car was built, nobody ever swapped the differential. So where this particular 3.545 R180 came from is beyond me.

I apologize for the poor photos; they're all I have on my phone at the moment. More at home.

3:54 R180s were stock in an automatic 240Z. Maybe the PO converted an automatic car to a manual. Doesn't really matter. You have what you have and it will be far more important from a performance standpoint to install a LSD then to try and source a 4:11 ring and pinion.

Edited January 3, 201312 yr by John Coffey