Clutch parts for fitting a Triumph Overdrive gearbox onto a 1970 Triumph Herald 1200

[jagnut66]

Please bear with me, I haven't dealt with overdrive gearboxes before in terms of fitting them to a car that didn't originally have one, so some questions may seem 'obvious' to others but not to me.

13 hours ago, johny said:

Another thing Mike, did the gearbox come with an angle drive for the speedo cable?

There was no angle drive supplied with the gearbox, perhaps this was just as well, as a second hand one may be passed its best by now.

I didn't ask because I assumed the cable would screw straight onto the gearbox connection, from what has been said above I take it this is not the case and I will need to fit an 'Angle Drive'.

Does anyone recommend a particular Angle Drive, or shall I just go for one of these? https://www.ebay.co.uk/itm/392426804649?hash=item5b5e75d5a9:g:~hIAAOSwadNdfX1i

Looking at the images for the above, they appear to show the washer you mention, it appears to be used on the side that screws into the gearbox, is this correct?

11 hours ago, 68vitesse said:

If not mentioned the speedo gear might need changing to match your car.

I also see on Rimmer's site mention of a speedo drive pinion, is this what you think I may need to change?  https://rimmerbros.com/Item--i-506119

To confirm, the gearbox will be attached to my existing 1200 engine.

Thanks and best wishes,

Mike.

[Clive]

The quality of new angle drives is, or was, variable. New ones were failing very quickly. A good, original should last undefinately (or until the speedo cable or speedo seizes, which kills angle drives)

Hopefully somebody will have experience of a supplier. 

Canleys tend to be fussier than most about what they sell, as does Chris Witor (mainly big saloon stuff, but Chris does keep some stuff for the small chassis cars)

 

That speedo pinion looks to be from a D type OD. The type you need is

https://www.jamespaddock.co.uk/speedo-gear-j-type-overdrive-for-2500s-model-2

However, which version will be tricky to calculate. Your speedo has a TPN number (turns per mile) as speedos were matched to diffs. Later cars all had a TPN of 1000 and the drive gear swapped to match the diff. So a bit of head scratching required. 

If a suitable drive is not available you could get your speedo recalibrated. 

The following is my reasoning, but is likely incorrect!

your herald has a TPN of about 1250, 4.11 diff. 

SO what ratio diff would be needed with a 1000TPN speedo? An increase in ratio of 20%, making a 4.9 ratio diff. And I don't think there will be anything suitable? (this explains why several of my cars had speedos that under read by 20%)

[NonMember]

42 minutes ago, clive said:

The following is my reasoning, but is likely incorrect!

Surely it's incorrect as in "upside down".

46 minutes ago, clive said:

SO what ratio diff would be needed with a 1000TPN speedo?

The Herald speedo was originally a 1248TPM, a 1000TPM would be for a longer geared diff (fewer propshaft turns per wheel turn) so rather than 4.9 (which, incidentally, was the ratio of the 948 saloon diff) you want 3.3 - so a GT6 3.27 would be about right. Not that I recommend that as the approach. Not that I'm recommending that for a 1200 Herald - getting the right speedo and/or drive would be a much better approach.

[Clive]

50 minutes ago, NonMember said:

Surely it's incorrect as in "upside down".

The Herald speedo was originally a 1248TPM, a 1000TPM would be for a longer geared diff (fewer propshaft turns per wheel turn) so rather than 4.9 (which, incidentally, was the ratio of the 948 saloon diff) you want 3.3 - so a GT6 3.27 would be about right. Not that I recommend that as the approach. Not that I'm recommending that for a 1200 Herald - getting the right speedo and/or drive would be a much better approach.

Am I confusing myself? I was not suggesting a diff swap....

What I meant was what car would have the right speedo drive. The herald speedo is 25% more TPM than the usual J type 1000TPM.

So it needs the speedo drive to turn more, ie less teeth. So I think you are correct, and I was back to front?

A tr6 one may work or be very close? (3.45 diff and larger wheels) or 2500 saloon (3.45 and slightly bigger wheels)

Or have I got that back to front? 

[johny]

oh I think Clive has it right as a Spitfire 1500 would have a diff ratio of 3.63 so travelling a mile would give 1000 turns of the gearbox speedo output. This means with that set up his Herald speedo wouldnt read a mile travelled as it needs 1248 turns to do that so the propshaft needs to turn more times per mile and a diff ratio of 4.55 would be almost perfect...

However agree that a diff change is impractical and another drive gear would be much better! 

[NonMember]

Ah, but as I quoted, he asked what would be needed for a 1000TPM speedo, not what would be needed for a 1248TPM speedo to work with a gearbox set up for a 1000TPM speedo, which is the opposite question. And, as you point out, if it's a 1500 gearbox then it's set for a 1000TPM speedo BUT on a 3.63 diff, not a 4.11 - and perhaps what Clive meant to ask was, given that, what TPM speedo would you need - to which the answer is 1000*4.11/3.63 = 1130

Anyway, as you said, it's not too hard to swap the speedo drive pinion - quite a lot easier than the diff, and probably easier than the speedo!

[Clive]

6 minutes ago, NonMember said:

 

Anyway, as you said, it's not too hard to swap the speedo drive pinion - quite a lot easier than the diff, and probably easier than the speedo!

Yes, I was trying to work out what car would have a suitable speedo drive. As said, not diff change.

 

[johny]

Unfortunately dont think theres any Triumph (dont know about Marinas and Itals) that used a single rail box with a diff ratio lower than 3.63 so cant see there will be any speedo drive gear available that will give more TPM☹️

That leaves changing or recalibrating the speedo and maybe a Vitesse (3.89 diff ratio) unit would give a more accurate reading... 

[Clive]

16 minutes ago, johny said:

Unfortunately dont think theres any Triumph (dont know about Marinas and Itals) that used a single rail box with a diff ratio lower than 3.63

It just needs a J type OD, box is irrelevent here. Hence my suggestion of (late) TR6 or big saloon. 

[Colin Lindsay]

I dealt with these guys for the Herald, I needed a different speedo drive and they have a selection, as well as a lot of other good overdrive spares:

https://www.overdrive-repairs.co.uk/buy-spares.php?cat=J Type Spare Parts List

[johny]

Otherwise I see a Vitesse 2L Mk1 speedo is marked up 1152TPM which is pretty close...

[Clive]

Just now, johny said:

Otherwise I see a Vitesse 2L Mk1 speedo is marked up 1152TPM which is pretty close...

But the 1200 speedo is bigger than any of th eother cars, so not a swap.

[johny]

Course its a single centre unit is it? Well at least any calibration company has a range of components to choose from to get the right reading and I think thats probably the best way to go for Mike....

[Clive]

Yep, single dial.

Yes, recalibrate the speedo is easiest way forward, but if the right drive is available, it would be much cheaper. And should anything go wrong, easier to fix.

[Pete Lewis]

when its all together 

disconnect the cable at the speedo end so you can see it

mark 52.8 ft down the road 

fit a card needle to the end of the speedo cable 

position the car on the road mark and push it exactly 52.8 ft ans count the turns of the card needle 

Multiply the turns X100  and thats your TPM  

if its way out to the tpm on the dial you can now look for a different J type pinion tooth count 

if its a small linear error you can move the needle , but not a lot its the tension on the hair spring that 

can make it adjustable  ok  at 30 but less accurate at 70   

Pete

[Pete Lewis]

places like Speedy Cables or J D O can recal your existing to any known TPM 

[jagnut66]

11 hours ago, Pete Lewis said:

places like Speedy Cables or J D O can recal your existing to any known TPM 

I've used JDO a few times for recalibrating Morris speedos, notably when I fitted a 1275 MG Midget engine into a former two door Minor of mine.

Once it's all in place and working I'll take it for a spin and compare the speedo readings at 30, 50 and 70 to the app on my phone, which will tell me what I'm really doing......

Thanks for all your help and advice, so far, there will doubtless be more questions from me to come...... 😉

Best wishes,

Mike.

[jagnut66]

As a little update:

I tested the Overdrive solenoid and it clicked in and out a couple of times, it sounds quite healthy (touching wood at this point!), plus the gearbox now has a new inhibitor switch. Though the original cleaned up well and could be okay, what setting on a meter should I use to test the old switch and what reading should I expect to see if it's still healthy?

I have also renewed the little earth wire for the solenoid, as the sheathing was splitting badly, so badly that it snapped when I straightened it out. 

Whilst I was a it I made a threaded bar with my tap & die set to act as a pivot for the clutch release bearing's arm. The original wasn't with the gearbox, so I can only assume it was needed by another customer, prior to my purchasing the O/D box itself from him.

I am just awaiting the Angle Drive for the speedo cable to arrive, then I can think about getting on with this.

One question I do have though, relating to the power feed to the O/D solenoid, I want to fit an inline fuse when I wire this up, what rating of fuse would be suitable for this?

Thanks and best wishes,

Mike.

[NonMember]

9 hours ago, jagnut66 said:

what setting on a meter should I use to test the old switch and what reading should I expect to see if it's still healthy?

If it's off the car, set the meter to "ohms" at the lowest resistance range available. Across the switch should read infinite (probably a dash) until you press the plunger, when it should read close to zero (less than 1 ohm).

9 hours ago, jagnut66 said:

One question I do have though, relating to the power feed to the O/D solenoid, I want to fit an inline fuse when I wire this up, what rating of fuse would be suitable for this?

Which type of overdrive is it? I don't remember.

If a D-type, you need a 35A fuse minimum, with the hefty relay too. For a J-type (relay not needed) you only need a 10A fuse.

[Pete Lewis]

the early picture looks as a Jtype  solenoid on the left    Dtype has sol on the Right (viewed from drivers seat )

so no relay and light fuse as rob says    as current is much less than the D types 

Pete

[daverclasper]

I can't see this has been mentioned?. A washer is needed, I think, inside the angle drive ferrule at the O/D end. Pete can advise on this I think?, though not a special washer. Without it, wrecks the A/D, I understand

[jagnut66]

8 hours ago, Pete Lewis said:

solenoid on the left    Dtype has sol on the Right (viewed from drivers seat )

Yes Pete, on the left is correct.

 

1 hour ago, daverclasper said:

I can't see this has been mentioned?. A washer is needed, I think, inside the angle drive ferrule at the O/D end.

I believe it was mentioned but thanks for clarifying which side the washer goes, namely on the side that screws onto the gearbox / OD unit. From the picture, it appears the one I've bought off eBay comes with a washer suppled.

8 hours ago, Pete Lewis said:

so no relay

Less expense / time spent sourcing a suitable one, always a plus! 😃👍

 

11 hours ago, NonMember said:

For a J-type (relay not needed) you only need a 10A fuse.

As the consensus of opinion leans towards a J type identification, I will go with this.

Thanks and best wishes,

Mike.

[jagnut66]

The Angle Drive has just arrived, it screws onto the gearbox and the OD speedo cable cleanly, plus it comes with a copper washer for the gearbox side of things. So, good to go.

However, there is a slot screw on top (see picture below), which is loosely screwed in at present, is this for some sort of adjustment or should it just be screwed up tight?

Best wishes,

Mike.

[johny]

I think that screw is what holds the gears in mesh and it should be tight. However maybe it needs a washer so I would only do it up while turning the gears to check that the pressure it applies isnt excessive....

[Pete Lewis]

you will find if you remove the screw its just a short setcrew to blank off a means of greasing the drive 

it does nothing but bung a hole up 

Pete