Speedo Drive Pinon and Speedo drive gear questions used in J type over drive

[sujitroy]

I have two J type overdrives. One's from a Stag and the other from a Dolomite Sprint.

My plan is to rebuild one and put it in a Stag.

Both the Stag and Sprint use the same Speedo drive gear, NKC45, yet the Stag uses an 18 tooth speedo drive pinon, NKC50,
and the Sprint uses a 19 tooth speedo drive pinion.


Does the way the gears are cut make using different no. of teeth drive pinons possible on the same speedo drive gear?

I can not use the 19 tooth speedo drive pinon. It is 1/2" too short and the angle
drive thingy wire doesn't fit.


I always thought that gears had to match

Doing a search on the web, the Triumph 2000 series used the same speedo drive gear for some models, but used
2 different, no. of teeth drive pinions for different model years.

Sujit

--
Sujit Roy
Cupertino, California

https://triumphstagblog.wordpress.com/

[trunt]

Don't believe everything it says in the parts list! count the gears!

I'm pretty sure the gears can be mixed, never heard anyone say otherwise..

NKC45 is a 5 start drive gear, but check that its actually has that. There is a number stamped at the rear of the casting, it gives the number of starts, (thanks Gareth!) failing that look down the hole and count the number of times you see a coil "start" when rotating the output shaft 1 rotation.

The driven gear you select depends on the diff ratio and the speedo ratio, (and the wheel/tyre size) . Normally Diff should be 3.7 speedo should be 1000tpm (its printed at the bottom of the speedo face)

I would be interested to see exactly what you have in that Stag OD, as my math says otherwise!! By math It comes out at a 15 tooth gear assuming 185x14 tyres. I'm wondering if the 18 tooth was for the Triumph saloon that had an 850 tpm speedo..

Actually If you check your previous post, its all there.. check Neils post #4 and mine #5 it may help

https://socforum.com/forum/forum/sta...int-fit-a-stag

[trunt]

BTW 6 starts and 18 teeth will also work -- same ratio (3:1) as 5/15 that theory says is correct.

Terry

[Guest]

The Triumph 2000, Stag & Sprint type output drive gears are all similar and have no "dolly".
The gears used in Spitfire, Dolomite 1850 are different and somewhat longer and have a screw threaded "dolly" to which an angle drive attaches.
(I used this type of arrangement when I retro converted the Vitesse and GT6 to J type in the 1980s.
That was a quantum leap forward for those cars which used the very unreliable and too small D type.........

The Stag never had either the A type 28% unit (was 22%) NOR the J type 28% unit (was 25%).
This was a pity.

I recently became aware of a substantial difference in the speedos fitted on the Mk1 and Mk2 Stags.
The drive ratios for the speedo gears on the A type overdrive are totally different to those of the J type.
They varied mostly between the 4 and 5 start annulus worm gear, which can't be changed as it's cut into the A type annulus for good.

They appear to have got around this difficulty by using a different speedo for the later cars which should have J type OD with a different number of TPM (turns per mile).
I came across a Mk1 car in Germany where the gearbox had been retro fitted from A type to J type.
The speedo was clearly way out, so I'm looking forward to the day when I can take the back end off and correct it....

I have no idea yet what I will find inside, but I'm sure it's easy to correct 8-10% if you try hard enough!

[sujitroy]

Hello Terry , Just went back in the garage. and took some photos. From what I found from the web NKC45 for the Stag and Sprint. The speedo drive gear is six sided on the Sprints OD. The no. stamped on the back of the Sprints OD is, I'm assuming a 6 and not a 9. The stags OD has the same no. stamped on its end. The photo showing just the pinons show the differences between Stag, top, verses Sprint, bottom. The right angle drive shown won fit into the Sprints pinion. Notice the lengths are different too.


Sujit

[Guest]

I didn't realise this.
OK.
The speedo drive used in the STAG is the SAME type and generation as fitted to Dolomite 1850 (20 teeth-black), and the Spitfire Mk4 and 1500 models, green or brown...
(The brown 18 tooth pinion is the one used in USA cars).

This pinion is longer and uses a larger cable end, which is common to the angle drive, and also used on the TR6, as shown in those 2 photos.

The shorter pinion, (on the right) has a smaller cable end, and is used on the saloons and the sprint, because they have the bit that bolts onto the overdrive integrated into the end of the cable. They just bolt that direct to the little fork that holds it onto the overdrive.

All A type overdrives have basically the same sort of arrangement as the TR6, so the early cable for the Triumph 2000 etc will be different from the later ones, and use a angle drive , and the larger end!

I have no idea why they introduced this totally unneccessary complication into the speedo, and drive gears.
It makes no sense at all to me.

[trunt]

On the ODS site nkc45 is a 5 start, nkc46 is a 6 start, hence the confusion. I’m beginning to suspect that both were fitted at some time

Either way with a 1000 tpm Speedo you need the corresponding driven gear , 18 for a 6 start is perfect, Gareth seems to have hit the nail, you must need an 18 tooth “stag” type.

[sujitroy]

The no. NKC45 I got was from other forums. It is also listed at a NKC 45 on Rimmerbro.
As long as I use the 6 start gear with the 18 tooth pinon, "m good to go.

Thanks for every ones help.

Sujit

[Guest]

On the ODS site nkc45 is a 5 start, nkc46 is a 6 start, hence the confusion.

Either way with a 1000 tpm Speedo you need the corresponding driven gear , 18 for a 6 start is perfect,

Even worse things happened.
I really don't get this at all!

The STD speedo for the Spitfire 1500 is 1000TPM also, but uses 13" wheels instead of 14" as on the STAG.
The TR6 pi which has 15" wheels & 3.45:1 axle has an 8 start worm, but I don't remember the TPM figure!!!

I just looked at the one in front of me here, Non OD 3.7 axle USA LHD car and the mph speedo says 1120, and I think it's the same as GT6!

If you check the GT6 with 3.27:1 ratio axle it says 980....14% difference with the 3.89....
I get lost here...the difference between 3.27 and 3.89 is 19%!

For some incomprehensible reason the correct drive to use with that diff ratio (3.63:1- same as Marina 1800/TR4 speed/1850) is NOT 18 teeth it's 20 as per the Dolomite 1850.
They used the 18-6 tooth pinion on Spitfires ie 3:1 with the USA 3.89:1 axle, but the speedo TPM is also a different number.....
The original D type Overdrive speedo drive ratio is 3:1, which is of course why I copied it for the GT6 J type conversion.....

[sujitroy]

Sorry, you are way over my head now. But for people looking at this thread, here's a photo the overdrive cover showing the number stamped at the end. Look at the left top corner.
Regards, Sujit