Differential Advice, Please

[robox]

Car: 1971 240Z with an L28 engine and a "wide-ratio" 5-speed trans. Still got the original R180 diff with 3.36 gears.

I've read elsewhere on this forum that:

"The early five speed and 3.90 happens to perfectly match the power peak of an L28 curiously"

This suggests to me that it might be worthwhile trying to find a 3.9 diff to take full advantage of the L28 and the transmission, but as most of you probably already know, they are not so easy to find. Also, I can't wrap my head around why it would be good to go to the R200, due to extra weight and extra work. There's an eBay seller in Canada who has the R180 with 3.9 gears for about $560 shipped, which is quite high in my opinion.

I guess another option would be to try to find just the gears, and swap them into my diff, although those gears are probably just as hard to find as the diff itself.

I could go to 3.54 gears, but it's probably not worth the trouble.

Any advice is welcome...

Thanks!

Christian

[jmortensen]

If you did the 3.54, you would have stock 280Z gearing. Which sucks (IMO). If you did the 3.90 with the wide ratio, that would make 1st gear ridiculously low.

Best combo is a close ratio 80-83 280ZX trans with 3.90 or 4.11.

The R200 is a popular swap for those making more power. 3.90s were really hard to find in the R180s. I think that there are some Subarus that have that ratio now, so it's becoming easier to find. The 280ZX 5 speeds came with 3.90s, so if you wanted that ratio, the R200 swap was a very easy way to get it. In fact, the 280ZX drivetrain swap (engine/trans/diff) is a pretty easy way to liven up an earlier Z.

Really though, if this is a street car, it probably doesn't matter that much one way or the other. If you're racing or just nitpicky, the 2-3 gap in the wide ratio 280 5 speed is a problem.

[Travel'n Man]

I agree with the above statement - I have a 80-83 5 speed with a 720 pickup front diff (3.90). It is a great pair. One day I'll do the swap for a R200 but only when I have to.

[Travel'n Man]

This may help you with your search

Differential Ratios

[robox]

Thanks guys.

Mitchell I see that you have a 3.9 R180. You say you got that out of the front of a pickup? Cool.

There are 3.9 R180's on eBay that are coming out of Subarus.... they look similar to the Datsun variety except for the output flanges... there aren't any flanges! Could those be made to work?

The truth is that I have driven my 240 a grand total of about 3 or 4 miles since installing the 5-speed trans, so I am not sure how much the 3.36 gears are going to bother me. But what I don't want is to be out of the L28 powerband in 5th gear, needing to downshift to 4th to go faster or whenever I encounter a hill of any sort.

Starting to take the Canadian R180 3.9 option a little more seriously, as options for this diff seem slim....

[Zed Head]

Here's a link to the new seller of axles for the Subaru diff swap. Johnc, a forum member here, developed it over on hybridz.org and it's pretty popular. Tranny & Rear Diff Parts

For what it's worth, I noticed the difference between a 3.54 and a 3.9 in my 76 Z with a later ZX 5 speed (3.062 first gear ratio). It really depends on your driving style. If you're a clutch-slipper, you might not notice, but if you're a clutch-saver you probably will.

[Zedyone_kenobi]

Did you seriously not see my thread RIGHT below yours! HAHA

Yes a subaru diff will work, and flanges can be found to work.

[robox]

Hey Zedyone-

No.. actually I did not see your thread... HA HA! I guess that's because when I started my little thread I was just thinking along the lines of asking for advice about gearing options. The topic of swapping in a Subaru diff had not yet crossed my mind, so I wasn't looking for that kind of thing.

Anyway I just read your whole thread. Tons of great info in there!

I can only assume that people are willing to drop something like $1000 to do that swap because of the limited slip. I agree with one of the posters on there that $500 just for the output flanges is a tough pill to swallow. For me personally, limited slip is not worth that much $$. I basically just want a different gear ratio in the rear end, and a $600 R180 that will bolt up easily is more like what I am thinking.

At this point, though, I need to drive my car some more to see how much I really care. I am going to be more interested in freeway driving than burning rubber, so the 3.36 I've got now might be just the ticket. Or who knows, maybe the 3.54, which seems a bit easier to get one's hands on, might be a good solution for me, given my driving preferences.

Thanks again for that good thread. I gotta go back and re-read it to try to figure out what the "RT mount" is...

Cheers

[Zedyone_kenobi]

It just replaced the strap that goes over the diff with a solid piece of metal with a bushing on it. It should be technically stronger than the strap as you can wedge the diff against the OEM mount and the hard rubber bushing. Problem you will encounter is that you will will hear more gear whine with it, as solid connections transmit more noise to the cabin. Everything is a trade off man!

[tlorber]

That 3.36 with overdrive will probably let you cruise at 80 mph at 2300 rpm, but It will suck around town.

I put in an '82 tranny with 3.70 rear end from an 810 (early Maxima). It is a great combination.

[Walter Moore]

I have the 3.36 with a close ratio 5 speed out of an 83 S130. I also still have the original L24, which has less torque and develops it at a higher speed. First gear is too tall, and 5th is unusable below 60mph. But in between, it works fine. I just have to stay one gear lower than what everyone else tells me works on a given stretch of pavement.

[robox]

Thanks guys...

tlorber, I just saw an R180 with 3.70 gears from a Maxima on eBay. The driveshafts look different... well specifically the U-joints (or CV joints, not sure what the proper term would be) look different.

How much work was required to make that diff work in the Z? 3.70 seems like it would be a good ratio.

Thanks