R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

[demo243]

Previous owner was an... interesting... fellow. He fetched quite a few parts from other junkyard datsuns... L18 (from a truck?), 280zx five speed, and now the rear diff... so bizarre. This car has been fun to work on (for many reasons!). Who knows what else I haven't found yet that's different.

Thats the beauty of these cars! They are kinda like legos, you can build em one way, tear em down and build em another. And its amazing how many parts are compatible off other/newer Datsuns and Nissans!

L18, 280zx 5-speed, even the diff swap are not uncommon swaps. These 510s took a back seat to the Z cars back then so alot of the mods seem to have been out of need, availability and cheapness...

[shaddai]

Thanks all... my son and I jacked one wheel off the ground and spun it six times - the driveshaft spun a bit more than 12 times - per his calculations this means it's a 4.11 ratio diff. This certainly explains a bunch of things!

Now... time for a 3.9 or something. 4.11 is too high for my tastes, I believe.

[datzenmike]

You won't have much trouble selling a 4.11

[shaddai]

You won't have much trouble selling a 4.11

Nice! That's probably the easiest thing, right? Find a new lower ratio diff and swap it in, then sell this one? Better than trying to regear?

[funwithmonkeys]

There should be lots of 3.9s around. Selling a 4.11 should be very easy as Mike said.

[Byron510]

An R180 with 3.9, 3.54 or 3.36 we available in the S30 and S130 chassis Z cars. The most common are the latter two in 1970 to 1975 250 & 260Z. The 280ZX automatic came with an R180 with 3.9 with the same half-shafts shown on your car (currently with 4.11’s and noted) the balance of the 260,280&280ZX modes had the larger R200 which is really overkill.
The last option for an R180 would be the Maxima of late 80’s and early 80’s vintage, but I am unsure of the exact specs for those models.
As noted, many have gone the other way with the gears. My modified car has run both 4.44 and 4.375 gears on 23” tall tires and the 200SX dogleg box, and it too is at the 4k RPM range on the highway around 75 mph. But for all the performance I gain with the shorter gears, I personally would not trade that off for the lower RPM. But that’s just because I love to drive mountain passes and twisty bits as much as possible.
If I were a long-distance boulevard cruiser, I’d have taller gears too. It’s really each to his own. But I do agree with what’s been said before, the L motor doesn’t mind revving.

Byron

[shaddai]

I could always try to find a 5 speed with a lower ratio than I currently have... it's making noise when in gear and probably needs a rebuild at the least...

Tach comes tomorrow, but I won't be able to install it for a while (this atmospheric river thing puts a little rain on my parade).

[datzenmike]

All 4 and 5 speeds have the same 4th gear. A wide ratio starts off at 3.592 while a close is 3.321 but they end up the same. Over drives can vary also. Most are in the 12 -18% but the '80-'83 280zx is the highest at almost 23% and 25.5%.

Wide ratio and 4.11 is what I have and there's no down side, I really like it. You said in first post you haven't driven it much. Well drive it and get to know and like it. No tach means you are relying on guess work for revs. Senses can be deceived. It seems revved up but probably not.

[James]

I echo Mikes comment - these cars are meant to be wound out a little more than what you are used to. The torque curve is higher than modern cars as well - so having the RPM down is going to put you driving a lot more below the torque curve. I would spend time driving it, and maybe you find that a wide ratio, will get you where you really want to be.