On the Crown wheel there should be a tooth count of both the crown wheel & the pinion gear. it should be right next to a little Nissan symbol, & be in the form of 39:10 . All Nissan diffs had this handy little feature & as the pair are a set, should be the final resort other than counting the teeth themselves.

If it's in the air you have to fix one axle and turn the other 2 turns counting the pinion shaft revolutions as you go.
At least that's what I do at the junkyard.

cant calculate in the air coz in a single spinner if only one wheel is being turned you would end up with 1.95:1 ratio(as spider gears double the speed from memory), unless you turn both wheels at once

thats why you wheel spin alot more with a locked diff and broken axle than you do with an open centre

Quote:You need to turn both axles exactly the same amount, which is why you push the car forward in a straight line while counting revolutions of the drive shaft.

Ensuring that both wheels, or brake drums turn exactly one revolution, or ten, or whatever, is extremely difficult when the rear end is in the air & we are discussing measurements as little as one tenth of a revolution here.

Looks like the book data & a little logic was right again.

Quote:

So did you take the time and calculate what centre you have yet? maybe it really is 3.9-1 maybe its just a rough guess.
I dont see any logic in asking how to do something and then just taking a rough guess.

If there is logic in just going off what a specs book tells, My 1200 just like 90% of the 1200's on this site, will have some strange looking A12 motors and various other parts. Specs books are very important, but so is a little common sense.

Maybe the wiki should be changed to ONLY show what specs are applicable to specific countries. God knows my Australian 1200 does not have anything only specific to Japan.

Thanks Burt. it was a good suggestion & helpful to read up on it.

I knew the cornering example of one wheel turns at a higher rate then the other but I didn't think it affected the axle rotation rate while not loaded (not sitting on ground) & not breaking free from the other axle, always good to learn something new.

If anyone care this was an interesting read on differentials:

http://www.houseofthud.com/differentials.htm#open%20diff

phunkdoktaspok wrote:
"So did you take the time and calculate what centre you have yet? maybe it really is 3.9-1 maybe its just a rough guess.
I dont see any logic in asking how to do something and then just taking a rough guess."

As I said "I pulled the diff" it's stamped right on it next to the little Nissan logo 39.10. Logic would dictate that's the correct ratio, seeing that it came out of a 1200 coupe whose spec book (factory manual) say it standard w/a 3.90 ratio. That seems pretty logical to me......but I could be wrong, I have been before.

In the end it was fairly obvious.
1. The car was a stocker & not a racer with Nismo parts.
2. It had an iron carrier H145 differential
3. Only two ratios were ever made for this diff, that being 3.9 & 4.11 to 1
4. Only one of these two ratios were ever used in new 1200's sold in the US.

As long as it was the original diff in the parts car, there was only one answer, ... there's no rocket science here, just logic & a manual.

The original question also asked should he keep the diff or throw it away. My advice would be to keep the centre, but pack it with grease or some other perservative, & stick it in a bag somewhere. The diff in your current car might last years, but it will wear out eventually, & will it be easy to find a good replacement, especially if its in a few years time. I always seem to through away something that would have come in handy almost immediately, i think it's called Sod's Law.

Ahh ok cool so its clearly stamped on it.
No logic was needed and definately no manual.
Just pure common sense to pull it and check it.

Any way Im off to get rego on my 1200, I will take the manual and specs and swear till im blue in the face that my engine can only be an A12.
Pure stupidity to think by that so called logic.

so Steve, (aka - phunkdoktaspok) let me ask you a question, what do you feel the point is of contributing to a thread if you have noting to add positively to it? you said nothing in any of your three posts in this thread that contributed in any way whatsoever, you reiterated something Burt said & then lectured on logic.

Burt pointed in a direction which was quite helpful & I appreciated it.

My take on forums like this is to share experience & knowledge which benefits everyone in a positive way regardless of their level of expertise. By telling people to "be logical" & "thinking a particular way is pure stupidity" doesn't seem to fit that bill.

There's an old saying which I'm sure you're aware of, I think it goes something like this " If you dont have anything decent to say then shut the f**k up!"