78 280z differential rebuild, need some help. - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 13 (permalink) Old 08-07-2019, 11:24 AM Thread Starter
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78 280z differential rebuild, need some help.

Hey gang, I’m new here and not to sure how this works but I need some advice. I took on a 1978 280z project car a couple months ago and after a lot of time and money finally have it running. Now I have what sounds like the pinion bearing going in my differential. First and second gear there is a clicking but at higher speed I don’t hear it. I was gonna drop the diff and rebuild it but I wanna do it all in one go because it’s my daily. I don’t know all the seals, bearings, etc; and was wondering what all I had to replace in it. If anyone could give me a list that would be super! any other advice would also be great 🙂
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post #2 of 13 (permalink) Old 08-07-2019, 11:46 AM
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I have rear ends forsale in detroit will ship.

BLACK GOLD MAN OF DETROIT 78 280Z 80ZX 10TH ANV 83 ZX 2+2 GL

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post #3 of 13 (permalink) Old 08-07-2019, 01:30 PM
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Buy a second differential, either swap it or have the spare rebuilt professionally (the setup charge will be what the shims cost from nissan alone!)

Pick your ratio now and get it. I'm partial to 3.7 and 3.9's for stock engines. 3.9 if you have an early 5 speed, 4.11 if you have a later ZX one... 3.7 is perfect for the four speed and was what the world got.

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post #4 of 13 (permalink) Old 08-07-2019, 02:35 PM
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Originally Posted by Tony D View Post
Buy a second differential, either swap it or have the spare rebuilt professionally (the setup charge will be what the shims cost from nissan alone!)

Pick your ratio now and get it. I'm partial to 3.7 and 3.9's for stock engines. 3.9 if you have an early 5 speed, 4.11 if you have a later ZX one... 3.7 is perfect for the four speed and was what the world got.
first check the u joints
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post #5 of 13 (permalink) Old 08-07-2019, 05:51 PM
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Originally Posted by Tony D View Post
Buy a second differential, either swap it or have the spare rebuilt professionally (the setup charge will be what the shims cost from nissan alone!)

Pick your ratio now and get it. I'm partial to 3.7 and 3.9's for stock engines. 3.9 if you have an early 5 speed, 4.11 if you have a later ZX one... 3.7 is perfect for the four speed and was what the world got.

He's right you know. I have an early 5 sp with a 3.9 and an extra 3.54 laying around.

1975 280Z F54/N47 MSA 6-1 Header 2.5 Exhaust
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post #6 of 13 (permalink) Old 08-07-2019, 06:47 PM
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Going to a 3.90 from the stock 3.54 with the early 5 speed will feel like you added 2 more cylinders.
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post #7 of 13 (permalink) Old 08-10-2019, 12:28 AM
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If I may follow the sidetrack another step, I would note that the business of diff ratios is pretty much a matter of personal taste.

For example, having long ago shed the Boy Racer syndrome (especially around city streets), I have come, with much experience, to appreciate the value of "legs" for open road work. In such cases, a tall diff has numerous advantages, especially with the native torque of a sweet straight six. Even the mountains of the West have failed to occasion a downshift at road speeds, and the paybacks of middle revs and good mileage while making time are their own reward (not to mention the enhancement of longer engine life).

So, it depends on what you like; tearing around stopsign to stoplite, or comfy cruising for hundreds of miles at a time.

$.02 from the peanut gallery.



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post #8 of 13 (permalink) Old 08-12-2019, 03:46 PM
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I don't know about boy racer syndrome but I can tell you the ONLY difference in ANY of the ratios in terms of "long legs"on the stock engine is ZERO! The 3.90 will get you to 125 faster than 3.36 and do it all day long same as the 3.36 with or without a five speed! Same for the 3.7...

And they all pull between 22-27 on the freeway with SU's, depending on the speed you will be going. You gotta work into triple digits to get less than 20mpg on the highway.

I've pulled 17,000 mile road trips in my 3.90 car, driving with two drivers 36 hours straight...
As well as 15,000 mile road trips in my 3.70 car, driving for entire tank fulls at top speed in the middle of the night...

These aren't small block Chevies, they don't need nor like to run at 2,000 at highway speeds. It's bad for their bearings, if nothing else!

These engines are designed to run at 3,000 to 4,000 all day long and love it. Not overheat (the 3.9 was running at close to 4,000 rpms towing a trailer up the Palm Springs Grade with three people in it and 110F and was nowhere near even getting warm much less overheating!)

Use the revs the engine has to give you. If you want to run at 2,000 and shift at 3,000, get yourself a diesel Jetta!

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post #9 of 13 (permalink) Old 08-13-2019, 02:51 AM
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Mr.D:

Google "boy racer syndrome"; you might find someone you know well...

That's certainly an interesting concept of gearing and mathematics you have there. Makes one wonder why manufacturers have bothered to offer a plethora of ratios between 2.xx and 4.xx over the last hundred years. You do understand that for a given rev, top speed goes down as diff ratios go up, right? And isn't the real issue in this scenario, torque and not horsepower? And isn't maximum torque most often developed in the low to middle rev range?

And that old canard about "it loves to rev", the battle cry of adolescent fantasies, deep pockets, and frequent rebuilds (see, "boy racer", above). True, some engines tolerate that kind of abuse better than others, but none "love" it. Have you never wondered why racing engines of various stripes see very frequent rebuilds? Those mechanics must not be as smart as you about such things, eh?

I especially liked the part about how low revs are bad for the bearings; a novel notion indeed. As is the comparison of V-8s (all possessed of second and third order harmonics issues) and straight sixes, which have the best first, second, and third order harmonics of any cylinder configuration (save V-12s, of course). This fact just might explain why the recent rebuild of my Z's 200k mi, low rev engine revealed a crank, rods, cam, and valves and guides that were all still within "Std." specs. and provided over 60lb. of oil pressure.

Mileage? There's that old math bugaboo again; the direct relationship between revs and mileage seems to be well understood by any expert one could name. Hint: the lower the revs per mile, the better the mileage. You can look it up.

I admit that you lost me with the anecdotes about long trips; are you saying that one can only do such things with numerically high diff ratios and screaming engines, or that you enjoy driving irresponsibly in adverse conditions? I wonder, over 15K mi., do you think flooring it to road speed saved you much time in the process, or did it just make you feel fast?

And the Jetta thing.... very witty, I'm sure. Actually, around town, my usual shift point is around 2.5k rpm; city streets are no place for grownups to play "racer".

So I hope you'll see why I might think you missed the point of this intellectual exercise. My point is that if one gets his jollys from zooming around city streets, scaring old ladies and endangering kids, I s'pose short diffs are just the thing (of course, "pointless" comes in to play here, as most any econobox or faketruck today will outrun most any 20 or 30 yr. old car). But if you like road trips and love your car, there is no substitute for "legs" on the open highway.

Again, its an issue of personal taste, but its been my experience that real Road Warriors love tall diffs, tall tires, and overdrives (Leycock de Normanville forever... those Brits are a clever lot).

Just another $.04 from the peanut gallery...



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post #10 of 13 (permalink) Old 08-13-2019, 04:20 PM
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I get low 20s with my 3.9 diff and he early 5sp. The OD 5th gear puts it close to the 3.54 rpms on the hwy.

1975 280Z F54/N47 MSA 6-1 Header 2.5 Exhaust
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