Glad to see the winter doesn't put the Cali-Kid into hibernation, git 'r done!

I found out that not all snub nose diffs are the same. The one I got out of a 240sx, has smaller componets that wont transfer over to the long nose. It's the 4.08. Also, no secret code....It would be 39 divided by the 10 gives you 3.9, and if dived by 11 gives you the 3.54. it's just Ring gear divided by Pinion gear.

Winter hibernation? Pshh. Winter is for building the car so you can go faster in the spring/summer! It gets dark too early though... really puts a damper on progress!

Paul, I know the ring gear + pinion from the r200 short nose don't work in the long nose r200's, but the center looks to be identical (even the side bearings look the same).

I do know that some of the 240sx that came with factory VLSD don't work. I think because of the spline count on the axles?

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Justin
1986 Z31 NA 2+0

Time to invest in a nifty flood light

Yea, I been through that with both on the bench seeing what I could conspire....nothing. I am happy having the 3.9 for now. If you have the cash you can by the ring and pinion from motorsports. About $1,600 bucks

Phew, $1600 is half of the car!

I think stepping up from a 3.7 to a 3.9 will be enough for me.

A question: The FSM states that the mating surface between the ring gear and the differential housing, as well as the bolts holding the ring gear in, should be assembled with threadlocker. It doesn't say which kind...

Do you think Loctite Blue (medium strength) will work fine?

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Justin
1986 Z31 NA 2+0

I think I know somebody who has a 3.54 NOS longnose ring & pinion set just sitting in its box. He would be willing to accept quite a bit less than $1600 for it too


Justin, I think blue loctite will be fine for this application. Considering the amount of bolts and their torque specs it should be more than adequate.

Hooray! Thanks!

I think I have heard of 4.xx sets that are very rare. I think they are out of a s12 / 200sx ?

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Justin
1986 Z31 NA 2+0

Bryan Little uses a 4.11 set in his 240Z; makes it take off like a rocket. He usually starts it in 2nd when he wants to play well with others.

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1970 240Z

Those gear sets are 3.154....4.875..and 5.143. Not your average find. Plus gear componets always cost alot. The 3.5 in most Z's are a dime a Dozen. The 3.9 is a little hard to find, but out there. Take it from me, that will be all you need. The 4.11 is real hard to find, and will not be good if you travel far to Z shows. I am already screamin down the Hi-way doing 60mph with the 3.9.

Agreed. I think I will be very happy with the 3.9!

More progress:



Some wire brushing, scrubbing, degreasing followed by rustoleum gloss black:

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Justin
1986 Z31 NA 2+0

I run 3.92s in my 240, but my 5th gear is overdrive, so I can run 65-70 all day long at easy engine speeds.

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1970 240Z

Frank, what is overdrive? I have heard of it a few times but honestly am not familiar with what it is/does.

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Justin
1986 Z31 NA 2+0

Overdrive is any gear combination which allows the driveshaft to spin at a greater speed than the crankshaft.

4th gear in most gearboxes is a 1:1 ratio (or 'direct drive"), meaning that if your engine is turning 2,000 rpm, so is your driveshaft.

With an overdrive gear (5th, in mine), a 2,000 rpm crankshaft speed can result in a 2,200 rpm driveshaft speed (for example).

There are several ways to effect overdrive, including a lower than 1:1 top gear ratio (mine), or a separate overdrive box added to the driveline after the gearbox, or even multi-speed differentials (hi-low range).

With manual gearboxes, OD (or O/D) must be selected manually by a lever, or electrically by flipping a switch. On automatic transmissions (like today's Ford Exploders) it's a standard feature which happens automatically unless the driver selects OUT of it.

Results in a big fuel savings, easier highway travel, lower engine speed (and wear) and sometimes greater speed. It's just a 'longer lever' for your engine to work thru.

If you had a 21-spd bicycle and put it into top gear, you'd be pumping your legs slowly, while the bike was flying down the road. That's O/D.

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1970 240Z

Ah very insightful, thanks. I had an ex with a ford focus and never understood what the overdrive button did on the A/T...

Also, on another note, I tracked down the correct speedometer pinion gear that plugs into the tranny. I'll grab a photo of it sometime.

Some useful info on that here:

http://z31.com/speedo.shtml

I am copy/pasting the info here because z31.com seems like it is dying and I don't want the info to get lost forever:

Speedometer calibration
How to correct your speedometer (and odometer) after changing your diff or tranny.

By WindigoZ 04/01/03
This writeup is meant to assist someone who is trying to correct their speedometer after changing their differential to a new final drive ratio, or after changing their transmission.Correcting your speedometer after putting different-sized tires on your car is beyond the scope of this writeup, and therefore will not be discussed except for this note: With a little math, it may be possible to use this writeup to get your speedometer a little closer, if not precise, depending on what tire size you've chosen.
How the speedometer works:
The speedometer (and odometer) are driven via a cable by a pinion gear in the rear of the transmission, right side. This gear meshes with the transmission's output shaft directly. The pinion gear can have anywhere from 16 to 23 teeth, depending on the differential you are using. All that is needed to make sure your speedometer is accurate, is to install a pinion gear that matches your differential (again, this is assuming you have the proper tire size). Pinion gears are also color-coded for easy identification.
Here is a listing of available pinion gears, their colors, the differentials that they are meant to be used with, and their nissan part number. Important note: If you use a pinion with 20 or more teeth you must replace the sleeve that holds the pinion gear. The sleeves for 20+ tooth pinions are offset to allow for the larger size of the pinions. Not using the proper sleeve will destroy the pinion gear and possibly the drive gear inside your transmission.

Examples:
You bought an aftermarket 4.11 differential cause you are shooting for 12's on stock fuel. You don't mind so much the high-revving all the time, but the fact that your speedometer is reading really high is starting to bother you, plus it's causing your odometer to tick off the miles too quickly. All you need to do is order the 20-tooth pinion gear, and install it into your transmission. Viola! your speedo is working properly again.
You recently installed a T5 tranny (84-86 Turbo) in your 86 NA car cause your NA tranny blew up. Since the 84-86 turbos came with a 3.54 differential, the pinion gear in your new tranny is the 17 tooth. Since your 86 NA differential is the 3.7, you need to put an 18-tooth pinion gear into your new tranny, which can be convieniently found already installed in your old tranny.
Caveats:
Some models may have the wrong diff for their model year, for example, it's been reported that early production date 87 turbos might still have the differential that came with the 84-86 turbos. To be sure of what differential your car came with originally, look at the model plate under the hood. (The ID plate is wrong for 88-89 models, see the differential page). If your car originally came with a 3.54 diff, it'll say RC35 somewhere, 3.7 diff will say RC37, and a 3.9 diff will say RC39
21, 22, and 23 tooth gears are nowhere to be found. They appear in the z31.com archives, but their part numbers are elusive. Perhaps they are used in big nissan trucks, but I sure can't find them.

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Justin
1986 Z31 NA 2+0