GT6 What do I need for a speedometer fix?

[UmmYeahOk]

The speedometer cable spins. The Speedometer gauge turns. But these components only work manually. When driving, the area the cable screws onto does not spin at all. Is there something broken inside? Suggestions? Is this car (1967) supposed to have an angle drive? Would that work if the other square hole (in the pic) doesn’t spin?

 

[DavidApp]

I am not familiar with the GT6 but if you put a small screwdriver into the square hole shown in the photo and can turn the square it probable means the drive gear has stripped.
It looks like there is a bolt just above the opening that may be a retaining bolt. That would allow you to remove the drive. Check your parts book if you have one for details.

David

 

[Tr6easyrider]

Looks like your transmission mount is cracked!!!

 

[UmmYeahOk]

I am not familiar with the GT6 but if you put a small screwdriver into the square hole shown in the photo and can turn the square it probable means the drive gear has stripped.
It looks like there is a bolt just above the opening that may be a retaining bolt. That would allow you to remove the drive. Check your parts book if you have one for details.

David

Just checked. It spins perfectly easy with a screw driver. I see the bolt. I haven’t dismantled it yet, and don’t really have a parts book other than various websites that list parts for 70s spitfires. I am unsure what transmission this was used in, so I don’t know what parts cross over.

If it helps, the transmission number is KC 5302

Looks like your transmission mount is cracked!!!

No, that’s just the way it was casted. Though 10yo mount from Victoria British... ...with less than 200 miles on them, I should be thankful that they’re only now developing surface cracks

 

[CJD]

Yep, remove that bolt and the entire drive gear assembly will pull straight out of the tranny. It often gets stuck from the varnish build-up from old oil...but, bar that, it should come right out. Once out the gear is easy to replace.

 

[TR3driver]

Looks like the speedo gear is shared with Spit 1-3 and GT6 1-3. P/N 119100.

Bearing is 144621, apparently unique to GT6 1-3. However, it's available from TRF.

There is also a gear on the mainshaft, P/N 119131, which is shared with Spit 1-3 & GT6 1-3.

Canley Classics has an on-line copy of the factory parts catalogue https://www.canleyclassics.com/triumph-gt6-mki/ii-gearbox
and appears to have both gears in stock.

 

[dklawson]

It may be more complicated than the pinion drive gear.

It may be the worm gear on the tailshaft. I believe the worm gear our GT6 (also a '67) was plastic and had split. Therefore the worm gear did not spin and could not drive the pinion.

As suggested above, remove the retention bolt and pull the pinion gear from the back of the gearbox. Inspect both the pinion gear and the worm gear on the tailshaft.

 

[UmmYeahOk]

It may be more complicated than the pinion drive gear.

It may be the worm gear on the tailshaft. I believe the worm gear our GT6 (also a '67) was plastic and had split. Therefore the worm gear did not spin and could not drive the pinion.

As suggested above, remove the retention bolt and pull the pinion gear from the back of the gearbox. Inspect both the pinion gear and the worm gear on the tailshaft.

You win. At least the part about it being more complicated. So it’s not the pinion gear. How do I go about checking the worm gear? Would this require dropping the whole transmission, or do I simply need to disconnect the drive shaft, and have access from there?

Basicly, I’m trying to figure out if this requires way too much transmission work, and that it would be best to simply just wait for the need, and buy a GPS powered speedometer to get me through to the next decade or so.

 

[TR3driver]

There's a procedure in the workshop manual on how to remove the extension (and that gear) with the gearbox still in the car. Page 2-212

 

[CJD]

The steps to get to the worm would be:

Remove the drive shaft.
Undo the yoke bolt and pull the yoke off the rear of the tranny,
Undo the bolts holding the tail housing.
Pull the tail housing off the tranny.

At this point you will have access to the worm...but it may require a long puller to get it off. If it is plastic, you may be able to tap it off.

I've never seen a worm fail, but if they did, indeed, make the later worms plastic, then I guess that would be a weak link!

 

[CJD]

Randall beat me to it. I still don't think a lot of that is necessary, like draining the coolant or removing the exhaust??

 

[TR3driver]

I have no idea, that's just what it says. From the sound of it, I'm guessing you have to bring the gearbox high enough that it would strain the top coolant hoses if they were not removed. YMMV

 

[DavidApp]

Can you see in the hole the spedo drive came out of enough to see the worm gear? If you can you may be able to inspect it from there. With the transmission in neutral turn the drive shaft and see what the gear looks like. If it looks OK try to stop it turning with a screwdriver and gently turn the drive shaft. The worm may be lose on the shaft.

David

 

[Rhodyspit75]

I’ve been following your story for a while now. It sounds like you have enough problems right now. There are a lot of speedometer apps available for your phone. If this was my car I would want to start driving it and shake it out. List all the thing you are going to have to fix then start doing them one at a time.

 

[dklawson]

I agree with all the above. You should be able to access the tailshaft by following the procedures Randall and John posted but I don't think you will need to drain the cooling system. With the tranny supported and angled just slightly up at the rear you should be able to take the rear housing off the geabox to access the worm gear. If your worm gear has a metal hub, you will need a puller to remove it like John said.

You should be able to visually inspect the worm gear through the hole where the pinion gear was removed. Even if you cannot see it you should be able to reach in the hole with a probe or pick and find the teeth on the worm. You should NOT be able to spin the worm or slide it forward/aft on the tailshaft. If you can spin it easily there is a problem with the gear.

My Mini has a metric speedometer and while it is easy to multiply kilometers by 0.6 (round number) to get MPH, I tinkered with a few alternate speedometers. You can use a Sigma (brand) bicycle computer to have speedometer, odometer, and trip functions. However, the bike computers are battery powered and don't have a good solution for night illumination. It's not practical to push the "light" button so you can see the display for 15 seconds or so. Later I bought a portable, digital GPS speedo through eBay, $30 delivered. I believe the brand I bought was "LTC" or something similar. It is about the size of a pack of cigarettes but 1/2 the thickness. There is not a true odometer or trip function but if you just want speed, it's hard to beat. All you do is plug-and-go. However, you do sometimes have to wait about 3 minutes while satellites are acquired before the speedometer starts working.

 

[UmmYeahOk]

I’ve been following your story for a while now. It sounds like you have enough problems right now. There are a lot of speedometer apps available for your phone. If this was my car I would want to start driving it and shake it out. List all the thing you are going to have to fix then start doing them one at a time.

I agree with this, especially since we’re approaching inspection time in a month or two. The problem is, since my husband had to go and redo everything a professional has done, with the interior all tore up (transmission tunnel cover), I was hoping we could address this issue now, before I go and reassemble everything. We are fortunate enough to live in a low crime area, but that means that the cops target traffic violators the most. Out of all our cars, only one of them is from this century, and NONE of them have front license plates. So high targeted (old) cars driving around already in violation. Many of the roads are painfully 30mph, with the cops sitting off to the side just waiting, at the bottom of the hill of course, where you’d most likely speed due to gravity. I usually drive 5 over, but on these specific roads, 3 over with my foot hovering the brake. In the GT6, I couldn’t even go the posted. 3rd at 3,000 RPMs may be around that, but I expect them to pull me over, even if just to look at it. I have just been thankful that the two days I’ve ridden around there in it, there were no cops. Last day I drove our daily though, THREE!!!

 

[trrdster2000]

Be aware there were 2 different gears and the way they were installed. The early ones were pressed in place, the later ones had a "C" clip holding them in place with a small ball bearing acting like a shaft lock to keep it from spinning. If it has a clip and slop it's the later.
If you try and tap them off, a good chance to split the plastic. So a pipe clamp of so sort would be best in your situation between the seats.
You will have to look to see which one you have. Don't forget to order a new seal and gasket set. Have a good look at the shifter, it might need new bushings.
Wayne