47 replies to this topic

[Leonrjohnson]

On the gearbox end, see if you can remove the single bolt(7/16 socket  1/4 drive with universal joint and long extensions down the back of the engine.). Then with the cable still attached, try to wriggle the drive housing out of the gearbox. You should be able to do this without disconnecting the cable from the speedo. The drive gear hopefully will come out with the housing, otherwise retrieve it afterwards. For re-assembly, I would try fitting the gear into the housing, attach the cable and then lower into position and refit the 7/16 bolt. A bit of thick grease on the gear shaft may help to hold it in place during refitting. I had a gear that had come loose on its spindle, and caused the needle to flicker after a couple of miles. I replaced the gear using the above method. All good after that.

[Guess-Works.com]

Only go on journeys of 5 miles, then the problem goes away

 

PS... take the radiator out, and save time and your knuckles.

Edited by Guess-Works.com, 27 February 2015 - 10:48 AM.

[Steve220]

Guys,

I don't want to defer the topic too much, but since refitting my dash and subsequently the speed cable to the back of the clocks, I get a ticking from the speedo that links to the needle bouncing ever so slightly. Around 1-2mm max. Any ideas what this can be?

[Guess-Works.com]

Sounds like the speedo cable is not properly connected on the back.

[Steve220]

I'll give it a look

[Dan]

Remove the rad to get to the speedo drive. The offset instrument binnacle is removed by releasing the 4 nuts on the bulkhead in the engine bay that are arranged around the master cylinders.

[maieth]

That's why I love this forum.
Thanks for all this guys. Some excellent guides and tips that should make things a lot quicker and a bit more predictable hopefully. I'll get started in the morning.

Edited by maieth, 28 February 2015 - 12:13 AM.

[maieth]

Okay, investigations are done.

I checked up by the speedo first. Many thanks to Dan for this:

Remove the rad to get to the speedo drive. The offset instrument binnacle is removed by releasing the 4 nuts on the bulkhead in the engine bay that are arranged around the master cylinders.

 

It made the first bit of the job much easier.

 

Speedo drive- looked great.  Clean and square.

Cable - speedo end - this was slightly misformed, but it wouldn't slip. Still obviously square in profile.  the cable and drive connect very snugly this end and turn easily without any slipping.  I can turn the cable both ways freely, however, which suggests something's not right the other end.

 

So I started to get really dirty getting the speedo drive out the other end.  Again, all the advice on accessing and removing the speedo drive was a huge help.  It took a while, but I got everything out and sure enough...

 

Cable - gearbox end - looked like this:

 

 

 

A nice, almond-shaped oval.  Obviously there's a very good chance this would slip easily, so my first fix will be to replace the speedo cable with another new one.

 

I nearly stopped looking at this point, as I thought I'd found my diagnosis.  Thankfully, I have worked on this car before and watched enough episodes of House M.D, so I knew better than to assume the problem stopped there.  So I kept going and had a look at the speedo drive itself.

 

Speedo Drive - socket for the cable was a perfect square. However, the nylon gear does this:

 

 

The spindle and gear turn smoothly in their little housing, but holding onto the spindle, it is extremely easy to turn the nylon gear by hand.  This looks exactly like what others have described to me at the moment. Can anyone confirm if this is normal?  At the moment I'm assuming I will need to replace this as if it warms up even slightly in use (say after 4-5 miles of driving) it's just going to spin freely on the spindle.

On removing the gear, as shown in the video, the splines of the spindle seem clean and well formed, but the inner surface of the gear is completely smooth.  Not aware whether it is made that way or should have corresponding spline.

 

Let me know what you think folks.  Do I need to replace both, or just the cable?

Thanks again for the help so far.

 

 

 

[maieth]

Further question:

 

As a previous owner transplanted this car with an MG Metro engine (and, presumably, matching gearbox) the speedo (a 1248tpm 120mph Smiths) has never given the correct readings. We've figured out the correct speeds with a GPS speedo and have learned the readings to actually follow, but the ratio is clearly wrong. Assuming the FDR is the standard 3.44, would there be any way to get more accurate speedo readings with a different speedo drive?

 

The one I removed has 17 teeth and seems to be THIS one, listed on minispares.  That already seems odd, as minispares lists it as being for 10" wheels.  Our mini has 12's, and if my research is right, the MG Metro would have had 12.5's.

 

Any thoughts?  Guess-Works, you got any ideas on this?   I had a look on your website calculator, and using the information I know, got these results:

 

 

The readings for 3rd gear look like what we get as readings, but those readings are about the same across the gears as far as I'm aware. I don't remember them changing drastically on gear changes.

Edited by maieth, 28 February 2015 - 02:55 PM.

[Guess-Works.com]

If it also have a 5 tooth worm, then odds are it's the MG metro gearbox as all metro gearboxes ( apart from a few ) had 5/17 ratio worm drives, and would make the speed read woefully slow.

 

Once you have the correct information, wheel size, diff ratio, speedo tpm you can calculate the drives you need...

 

http://www.guess-wor.../Tech/ratio.htm

[maieth]

If it also have a 5 tooth worm, then odds are it's the MG metro gearbox as all metro gearboxes ( apart from a few ) had 5/17 ratio worm drives, and would make the speed read woefully slow.

 

Once you have the correct information, wheel size, diff ratio, speedo tpm you can calculate the drives you need...

 

http://www.guess-wor.../Tech/ratio.htm

 

Okay, I think I can wrap my head around that now.  Took a while to figure out the table. It's definitely the MG box and a 5 tooth worm drive then, those readings match up exactly to what we found.

 

So it's looking like I have three options:

- To get accurate readings, I can replace the speedo with a 1000tpm guage, which will give pretty much perfect readings up to 50mph, and then only drift 1-2mph out. This makes sense as it looks like the metro would have had a 1000tpm guage.

- or, I can replace the worm drive with a 6 tooth and keep the 1248tpm speedo with similar results.

- or I can leave well alone and put up with the speedo being out.

 

How hard is it to replace the worm drive folks? looks like the more available part (I cant find a single 1000tpm speedo to fit a 3-clock mini)

[Guess-Works.com]

You can replace the worm with the engine in, but you will need to remove the LHS engine mount and bracket, plus the adapter block from the side of the gearbox. You will then see the cover plate held in with two 1/4"unc screws. Remove that extract the 5 tooth and replaced with a 6 tooth...

and if you don't have one....

 

http://www.guess-wor...play.htm?id=325

[sledgehammer]

It's a pity they never put a calibration screw on the back of the speedo's

[Dan]

It's not that easy to calibrate a speedo, you have to make the magnets more or less powerful to adjust them rather than winding something mechanical.

[Guess-Works.com]

It's not the speedo which you are matching the drive too, but the odometer. This is deliberately difficult to change as it is the record of the cars mileage... The rest I think you can work out for yourself...

 

Which makes me think, when speedy cables recalibrate the speedo, do they actually re-calibrate just the speedo or the odometer as well ???