Help Identifying Differential

[Brubaker]

I pulled the differential cover. The case has been marked, probably by a junkyard, as a 280zx. I have a 77 280z 5 speed mfg date 7/77. I spun the large ring gear and it is stamped:

H37 10 DO(?) 9 3 6. It also has been written with a sharpie 7 0 6 t 8.

Can anyone help identify what this came out of?

Here are some pictures

Thanks.

[Zed Head]

There should be more numbers stamped on to the ring gear, I believe. Like 39/11 or 39/10. You could also count the teeth on the ring gear and the pinion gear and divide the big by the little to get the ratio.

The 77 should be a 3.54.

[Brubaker]

I am counting 37 teeth on the large ring gear and 10 on the pinion - 3.70. What year was this made for? I read on the Datsungarage site a 3.70 was a lsd starting in 1987 which would be a 300zx. The stamping on the ring gear H37 10, does this refer to the 3.7. The yellow paint on the case showing 280zx has me confused. It definitely is an R200.

[gira]

Brubaker,

You've probably determined it's a 3.7. That's actually the easiest one they make to divide out. That ratio came in the 79 280ZX and all the 300ZX's. Your picture shows non LSD.

Greg Ira

[Zed Head]

If it's the 1979 3.7 R200 it will bolt right in. If it's a 300ZX R200 it will have a different bolt pattern on the pinion flange. But, apparently, you can easily (with a big wrench or an impact wrench) swap the pinion flanges between R200s.

Many of the 300ZXs came with open 3.7 gears. My understanding is that the LSDs were 3.54. Sounds like gira can tell from the pictures that it's open. I'm not that familiar with the insides to know.

[Brubaker]

I am guessing 79 280zx as it had the 280zx written on the case. Also if it is not lsd that would also indicate the 79. I was just wondering as the write up in the datsun garage listing all of the differentials did not indicate the 3.70 was available prior to the 300zx.

Thanks for the help.

[LeonV]

If it's the 1979 3.7 R200 it will bolt right in. If it's a 300ZX R200 it will have a different bolt pattern on the pinion flange. But, apparently, you can easily (with a big wrench or an impact wrench) swap the pinion flanges between R200s.

Many of the 300ZXs came with open 3.7 gears. My understanding is that the LSDs were 3.54. Sounds like gira can tell from the pictures that it's open. I'm not that familiar with the insides to know.

The 300ZX LSD was a 3.7, however, Greg correctly states that the differential in question is in fact open (not LSD).

I am guessing 79 280zx as it had the 280zx written on the case. Also if it is not lsd that would also indicate the 79. I was just wondering as the write up in the datsun garage listing all of the differentials did not indicate the 3.70 was available prior to the 300zx.

Thanks for the help.

Yes, it is from a '79 ZX. It came in the 5-speed coupe and 2+2. Look for a more detailed list on differential ratios at zhome.com; atlanticz.ca may have it as well.

[Brubaker]

Is there that much of an advantage in swapping to a 3.70 from a 79 280ZX over the stock 3.54 it came with? I am assuming the 7/77 build date came with a stock 5 speed and 3.54 rear. Is this not right?

Thanks Leon, ZH and Greg. I'll look at the sites mentioned.

[LeonV]

It's not going to make a huge difference, but it'll feel a bit more torquey especially off the line. If I were you, I wouldn't go through the effort unless the current diff is on its way out. A 3.9 or higher and/or an LSD will be more "bang for the buck".