Overdrive Speedo Pinion Square Drive Problem.

[AlanG]

I'm in the process of fitting a TR6 J type gearbox to my 4A. The square hole in the pinion gear shaft of the speedo take off in the overdrive is undersize and will not accept the square drive end of the angle drive. There is nothing wrong with the angle drive, it fits the 4A gearbox speedo take off and the speedo inner cable itself will not fit into the pinion gear shaft. Also, pinion square drive and speedo cable inner both measure the same size. Only thing I can think is the pinion shaft has been bodged to fit smaller/damaged speedo cable but no obvious signs of this. Before I order a replacement pinion shaft has anyone any idea of what might be the problem?

Alan.

[RogerH]

Hi Alan,

I had problems on a 4A last year where a new angle drive wouldn't fit the pinion.

I took the angle drive and pinion to Moss and had a play on the counter.

Another angle drive fitted the pinion and the original drive fitted another new pinion.

I suspect it is just tolerances.

 

Roger

[Graham]

Hi Alan,

I had problems on a 4A last year where a new angle drive wouldn't fit the pinion.

I took the angle drive and pinion to Moss and had a play on the counter.

Another angle drive fitted the pinion and the original drive fitted another new pinion.

I suspect it is just tolerances.

 

Roger

' took the angle drive and pinion to Moss and had a play on the counter.'

 

Roger I thought you had promised to give up the pole dancing

 

ATB Graham

[RogerH]

...I also do Lap dancing ..... like they do in Lapland

 

Roger

[Lebro]

I think the later boxes may have slightly smaller "square holes" When I fitten a 1972 saloon gearbox with "A" type O/D to my car, the speedo cable would not go into the gearbox. I added some silver solder to the square end to make it solid, Then ground the square size down a little at a time till it fitted. Had to do the same at the speedo end, having fitted a 2.5PI speedo innards into my casing.

 

Bob.

[AlanT]

The wire-stubs on the angle drives measure 3mm.

 

A 3mm piece of key-steel is an almost perfect fit in an original A-type pinion.

 

You need just a little relief of the sharp corners of the key-steel because, of course, the square hole does not have perfectly sharp corners.

 

Can you get a 3mm drill in the pinion? I mean the blunt end of course.

[AlanG]

The wire-stubs on the angle drives measure 3mm.

 

A 3mm piece of key-steel is an almost perfect fit in an original A-type pinion.

 

You need just a little relief of the sharp corners of the key-steel because, of course, the square hole does not have perfectly sharp corners.

 

Can you get a 3mm drill in the pinion? I mean the blunt end of course.

 

Great thinking Alan. Just tried 3mm drill and it fits perfectly so will relieve the key steel tomorrow as you suggest. I'll report back.

Thanks for all the comments.

Alan.

[AlanT]

The wire-stubs are NOT hardened wire. They are actually quite soft. Will file away pretty quick

Only a few thou off should be needed do it. Help a lot if you have a mic.

 

If you have a needle file it will do no harm too check for burrs in the pinion.

 

The difference between jamming and rotating is surprisingly small.

[BlueTR3A-5EKT]

There was an angle drive fitted to other Triumph cars that had a smaller a/f sq drive than the one (120694) that fits the TR series. That angle drive pt no starter 14***** something. It was used on the Tri saloon models as far as I can recall. That maybe why they are creeping in to the TR series as the saloon o/d gear box is being now used in TR models.

 

There was also a speedo drive cable with an end that was double elipse shape, rather than square. That I think fitted auto gearboxes of the saloon models and even perhaps TR7 Auto.

 

Peter W

[AlanT]

I have a length of "speedo" cable that is 3mm in diameter. Lots of speedo wire is like this.

Obviously when the flats are ground on the end, you finish up with less than the 3mm required to fit an A-type O/D.

 

This is exactly why I started using solid key-steel to fix the angle-drives, rather than bits of speedo-cable.

You can file this down to fit if required without loosing much strength:

 

 

This is accurate to better than 1 thou. So I can make precision parts in a small batch that convert it to the bevel-gear.

 

Edited January 15, 2016 by AlanT

[AlanG]

Right, have relieved the drive corners and then some more. Nope. Have reduced the 3mm flats some .010". Nope. Nothing to lose now so have carefully and gradually filed the drive until almost round. Nope. Tried to see down the pinion bore to see what was going on but too small and dark. Lost the will to live so have ordered a new pinion. ( AlanT you have new PM ).

Alan.

[AlanT]

Here is a virtually unworn stub I just took out a Smiths drive from a well known overseas Forumite.

 

 

And here is why it was removed before getting much wear:

 

 

See that the boss made almost no impression on the wires when crimped on.

You can just see a slight impact on the tops of the wires.

 

About half of those I just fixed were like this.

 

The trouble is that these go intermittent rather than just failing.

The "thread" can screw in and hold on for a while.

 

For comparison here is one with 3mm key-steel, sorry I can't get any closer:

 

Edited January 15, 2016 by AlanT

[AlanT]

By the way if this is a saloon OD and you try to put a TR pinion in it WILL IT MATE?

[AlanG]

Sorted. The kind people at Overdrive Repair Services have supplied a correct 20 tooth pinion and advised that the problem pinion is from a Triumph saloon on which the square speedo drive is smaller. Also 17 tooth and shorter which it is. Why this was fitted I've no idea. The O/D is definitely TR6 with ID No. 25/115838 and 8 start speedo gear. Just need AlanT to replace the 3mm drive. (Alan you have PM).

Alan.

[Lebro]

Don't quite understand how you can replace a 17 tooth pinion with a 20 tooth one. Would you not also have to change the output shaft in the overdrive ?

 

Bob.

[AlanT]

If the diametral pitch is the same it will mate.

Less teeth, smaller dia, same tooth size, I expect.

 

Otherwise it will just jam of course.

 

Most useful topic this.

[AlanG]

All the J type pinions and gears can be mixed and matched. Overdrive Repair Services confirmed this.

Alan

[Lebro]

If the diametral pitch is the same it will mate.

Less teeth, smaller dia, same tooth size, I expect.

 

Otherwise it will just jam of course.

 

Most useful topic this.

Same tooth size, but smaller dia. How will that work if the centre of rotation of the pinion does not move closer to the shaft.

I must be missing something here

 

Bob. (Confused.com)

[AlanT]

Well you are not alone. You will see I posted the question "will it mate" above.

 

Lets' suppose this really is a TR OD and someone put a smaller dia saloon pinion in it.

Presumably what happened is that it just engaged on the tips of the teeth.

 

When a 20 tooth goes in it will have more engagement.

 

Lets suppose the diameter of the 20 tooth is 0.5 in then the diameter of the 17 tooth would be 85% of this or 0.425in

 

The DP would be about 80 thou. The depth of tooth would be about the same.

 

But when the mesh of the teeth is set up its the radius that's important. So most likely there is still 30-40 thou engagement with a 17 tooth pinion. Which would be enough, probably!

 

You probably can't get a TR pinion into a saloon.

 

One of the reasons I rebuilt my OD rather than using a repairer is that they dismantle them fix the bits and reassemble. BUT they don't keep all the bits from one unit together.

 

Doing this makes the task MUCH harder. Especially stuff like cleaning in a tank.

I know because when I do the angle-drives and the wiper-motors I DO keep all the bits from each unit together.

Edited January 18, 2016 by AlanT

[AlanG]

Found this. Does it help?

Alan.

 

[Lebro]

Yes. I agree all TR's had a reduction ratio of 2.5:1 so TR6 should be 8, & 20 teeth.

Would like to know what the "Triumph of design" actually was.

 

 

Thanks for posting

 

Bob.

[Mike Graham]

Interesting thread, which I just found trying to sort out why my angle drive would not fit my OD.

 

When I rebuilt my OD several years ago, I recall having issues with the angle drive fitting inside the pinion shaft. The angle drive recently failed, perhaps at least partly because I filed the "speedo" part so that it would fit inside the pinion shaft. Now it sort of makes sense because I believe the OD I have came out of a salon car. The pinion has 17 teeth (overall length 61 mm, or 2.4 inches), and my speedo has read low since installing the OD. Roughly reading 40 mph (65 km/hr) when doing 80 km/hr according to GPS. Just measured the angle drive and the cable parts measures 3 mm on both flat surfaces. Anyone know what the internal size of the salon pinion might be? Difficult to see in and I have no reliable way to measure. I tried a 1/8 drill bit shank (measures 3.15 mm) and that slips in, so there can't be much holding the angle drive out.

 

Read in another thread that you can switch to a pinion with a different number of teeth (but apparently there are also different overall lengths), but that seems odd to me how different numbers of teeth would mesh properly. Assuming I could do this, how many teeth would I need on pinion?

 

I'd be happy just to get the pieces I have back together. Any suggestions as how to mate the two pieces much appreciated. Don't want to wreck the spare angle drive I just bought.

Cheers, Mike

Edited October 22, 2017 by Mike Graham

[Lebro]

For a TR3 you don't need an angle drive at all !

My gearbox is also from a Triumph 2000.

Yes the speedo drive is a different ratio TR is 2.5:1 Saloon is 3.5:1

 

I fixed this by using the insides of a Triumph 2.5PI Mk2 speedo, & fitted inside my TR case.

The turns per mile was just right to correct the odometer & speed reading.

 

 

 

Bob.

Edited October 22, 2017 by Lebro

[Mike Graham]

Hi Bob. Thanks for the reply. Sorry my reply caused confusion as I was not clear what car I was talking about. The OD is in my TR6 not my TR3. Would be nice to not use AD, but too tight turn in TR6. When I get my A type back together plan to add to my TR3. Cheers, Mike

[Lebro]

Ah that makes sense. My comments re speedo drive ratios still stands though.

 

Bob.