[JrZook]

Hey all!

Just wondering if anyone knows the speedo drive ratio for NT and WT sierras ie how many turns of the tcase output to one turn of the speedo drive.

Dan

[want33s]

Why didn't you ask two days ago before I sold the speedo drive gear out of my spare case?

[JrZook]

want33s wrote:

Why didn't you ask two days ago before I sold the speedo drive gear out of my spare case?

Bugger! Next time tell me if you sell anything!!

Actually tooth count wont help me as its a worm and wheel drive setup. If you got a complete case laying around you reckon you could spin it over and find out the ratio for us?

Cheers
Dan

[want33s]

As near as I can work out it's somewhere between 2.75:1 and 3.00:1

[v.w.dave]

I have a bunch of cases apart in my shed. Tell me when you need to figure thiks out.

[JrZook]

want33s wrote:

As near as I can work out it's somewhere between 2.75:1 and 3.00:1

Thanks Jas

So u reckon roughly 3 turns of the tcase output to a turn of the speedo drive? What case was this WT or NT? Because im pretty sure they have different ratios due to the different diff ratio. Need to try and get a very accurate ratio as im specin' up an aftermarket speedo unit.
If you can try spinning the output more times to get the speedo drive to do a whole number of turns ie maybe 10 or 20.

Cheers Dan

[want33s]

JrZook wrote:

want33s wrote:

As near as I can work out it's somewhere between 2.75:1 and 3.00:1

Thanks Jas

So u reckon roughly 3 turns of the tcase output to a turn of the speedo drive? What case was this WT or NT? Because im pretty sure they have different ratios due to the different diff ratio. Need to try and get a very accurate ratio as im specin' up an aftermarket speedo unit.
If you can try spinning the output more times to get the speedo drive to do a whole number of turns ie maybe 10 or 20.

Cheers Dan

I'll see what I can do tomorrow. I looked at NT but I'm sure WT is same.. Speedo's are different not transfers.

[303zuke]

It's not a WT Vs NT issue for the tooth count, it's the 1.0lt ratio Vs the 1.3.

On transfer cases where the Hi ratio is 1.409 to 1 and Lo is 2.268 to 1 (All 1.3lt Leafies), the drive gear has 7 teeth and the driven has 20 (2.85:1).

On cases with Hi=1.580/ Lo=2.511 (1.0lt w/switch), the teeth are 4 and 12 (3:1).

All Suzuki cable driven speedos (LJ, Sierra, Carry Hatch, etc, etc) and in fact most Japanese cars are 637 revs per Km.

[want33s]

Cheers 303...
There you go Dan... I was nearly there when I said between 2.75:1 & 3.00:1

2.85:1 is your number.

[JrZook]

cheers guys!

Question still is if both nt and wt's run the same 2.85:1 speedo drive and 637rev/km speedos how do they correct the odometer and speed for the 3.9 and 3.7 diff ratios running the same size stock tires?

Another Q because my brain is sleepy:

If the speedo drive ratio is 2.85:1 and the diff ratio is WT 3.7:1 what wold be the effective speedo to axle ratio? Im thinking it would be 1.29:1? (3.7/2.85)

Dan

[303zuke]

Who says it's correct? Under ADR 18/03, a factory new vehicle can have a speedo that reads as much as 10% high, but must not read low (ie your speedo can show a speed of up to 110km/h when driving 100km/h, but never show less than 100km/h. likewise, odometer may show up to 1.1km per kilometer).

The NT Sierras (4.11 diffs in 1.0lt, 3.929 in 1.3) had FR78-15 tyres (or 6.00-16 bar treads on JA Spec!), and when the SJ50 widetrack (3.73 diff) was released they went to 205/70-15. The diff ratios were corrected to some extent by the different rolling circumference of the tyres

[31zook]

with 0.2 or a rotationaly difference, it would be within the 10%...

[JrZook]

Anyone confirm my final speedo drive to axle ratio of 1.29:1?

[303zuke]

JrZook wrote:

Anyone confirm my final speedo drive to axle ratio of 1.29:1?

If the output shaft of the T/case turns 20 times, the speedo cable turns 7 times.
If the output shaft of the T/case turns 20 times, the axle shafts turn 5.36 times.

7 divided by 5.36 gives 1.306:1