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MG Midget and Sprite Technical - Speedometer struggles

The speedometer on my 1971 midget isn't working, and I hope the problem might be the positioning of the inner cable.

Rebuilt the gearbox this past winter (with serious help from this BBS). Gearbox works, but the speedometer hasn't budged.

Pulled the speedometer end of the cable from the speedometer, drove in the driveway and the end is rotating. If I pull the inner cable out a bit, then it doesn't rotate. When I first removed the cable, very little of the square end was exposed, and I was hopeful that the cable end just wasn't out far enough to engage with the speedometer. Pulled it out a bit, reattached, but no go.

Yesterday I replaced the cable, just in case the issue was that the old cable was allowing too much play with the inner cable. Thinking maybe the inner cable was too far into the gearbox end, and a new cable would have the stops in place to prevent too much movement.

No go.

I'm posting this in part because I really struggle connecting the cable at the gearbox end. It's a challenge lining it up correctly and if some advice here could help me save that step, I'd much appreciate it.

My next step would be to pull the new cable off the speedometer and confirm the inner part is turning. What I haven't done is confirm that if I turn the cable from the gearbox end, the speedometer will work. If I do that and spin it by hand, should it be enough movement to make the speedometer needle move?

Hoping someone else has had this problem.

I don't think I did anything wrong reassembling the gearbox parts that turn the inner cable, but it's possible. I hope there's some trick to get the right amount of the square cable end exposed and engaged in the speedometer.

Thanks for any advice.

Mark 1275

Did it work OK before you rebuilt the gearbox?

You will need to spin the speedo reasonably fast to test it. If you still have the old cable, connect that to the speedo and use a variable speed cordless drill or similar to spin the gearbox end (inner bit of the cable, obviously).

AdrianR

Don’t forget to spin it anti-clockwise (CCW)
Dave O'Neill 2

This may be reaching a bit but is the cable housing seated properly at the gearbox end? If not, this in effect makes the housing longer which makes the cable shorter.
Martin

Great ideas!

The speedometer did work when it came off the road. I do have the old cable and will use it to verify the speedo isn't what's failed.

It's definitely possible I haven't tightened the cable housing all the way on the gearbox end. I made it as tight as I could by hand, but might need to use the pliers. If I do remove it, I'll mark the plastic part so I'll know when I'm at the full 3/8" depth of the housing.

Last night I put the car on jackstands and turned the wheels while in 4th gear, but the inner cable didn't move. Maybe I was doing something else wrong, but it might mean the cable seating is the issue with the new cable.

Thanks for the responses.
Mark 1275

Matt,

If the car was on stands with both rear wheels in the air, and you only turned one wheel, probably the drive shaft was not turning. Instead, the opposite wheel would just turn the opposite direction.

Charley
C R Huff

What Charlie says.

Also, you don't need to put the car in gear, as the speedo drive is coming off the gearbox output, so will be turning anyway. Putting it in gear would mean you would be turning the engine when rotating the wheels.
Dave O'Neill 2

I vaguely recall that when I put mine back together the gearbox end of the cable stuck out more than the speedo end, but it didn't seem that crucial.

I did have an MGB once where the square section on the gearbox end of the cable sheared off in the gearbox drive, but I guess you would have noticed if that was the problem.
AdrianR

Coffee break photo of speedo end.

Anyone know the overall drive ratio here? Turning the wheels by hand may take a lot of rotations to show anything on the cable?


AdrianR

Is it possible the gear is slipping on the shaft? IIRC you can take that out of the gearbox with it still in the car. For a laugh, look at the Moss Motors price, $259.99 for the little pinion on a shaft!
Stan Kowznofski

Adrian,
I think that the critical thing is how far the squared end of the inner cable protrudes at both the bottom AND the top. It is free to move within the outer cable. If it slips too far down then the upper end disengages, whilst conversely if it doesn't go far enough down then the bottom end doesn't engage. Some speedo cables come with a litle nylon disc on the upper end of the inner cable to stop it working its way too far down and losing contact with the speedo.

When fitting the gearbox end rotate the inner cable back and forth between your fingers (at the top end, before it is connected to the speedo!)as you tighten the fitting. As the square end slips into the end of the gear inside the box it will stop rotating freely so you know it has engaged properly. Finish tightening the outer but don't push the inner cable any further down as you do this. Check again that the cable won't turn.

Now thread the speedo cable into position and align it with the speedometer. It should just slip in and engage the top end as you do this and you should now be 'good to go'
GuyW

Stan,

Yes it can happen - I had it on a new gearwheel (when they were at a much more resonable price !) but still a repro. The shaft was only knurled - dont know if it was cast on or push fit.

Yes you can take the drive out with the box insitu - a bit tight but can be done.

R.
richard b

Thanks for the replies.

I won't have time in the garage until Friday, but I did try spinning the speedometer end with my fingers, and it turns freely. Sounds like I'm not engaged at the gearbox end.

First I'll verify the speedometer works using the cordless drill CCW. Then have a helper twirl the cable while I'm tightening from underneath. Hopefully we'll get the feeling it engages at the gearbox.

Is it normal to need pliers to tighten it up so the housing is seated?
Mark 1275

“Is it normal to need pliers to tighten it up so the housing is seated?”

You sometimes need pliers to undo it, but shouldn’t need them to tighten. The threads do tend to get a lot of dust and dirt in them, as they are usually oily. You also have to be careful not to cross the threads.
Dave O'Neill 2

Sorry Mark, and Adrian. I lost track of which of you was having the problem!
GuyW

Had a few minutes this evening, but it didn't go well.

First had a helper twirl the inner cable from the speedometer end, while I tightened the gearbox end. I was able to get several twists by hand, but couldn't make progress with the pliers. I have the feeling I'm now tightened up so the housing is seated, but she could still twirl the inner cable with little resistance. Not good.

Then installed the old cable on the speedometer, put it on the drill and the speedometer works just fine.

Put it all together, took the car off the jackstands, took a short ride in the driveway, and ... nothing.

Now I'm convinced something's not right in the gearbox. I remember there being a lot of parts to the speedometer fittings. Not sure if it makes sense to try to remove them now with the gearbox in place, or wait until the driving season's over and pull engine and gearbox again. Disappointing.

Fairly certain that I would have reassembled the parts just as they came out, so it should be put back together without any obvious errors. I was so encouraged when the cable end turned when disconnected from the speedometer and driven. The old cable is definitely broken in that the inner cable moves freely in and out, and the ferrule that's supposed to anchor it in place just falls out.

Possibility the part that turns the inner cable in the gearbox is just set back, or pushes back when the cable with the proper length square end is installed?

I'll re-run the experiment of disconnecting at the speedometer and seeing if the cable turns when driven, but I have the feeling I'll find it doesn't.

New cable came from VB rather than Moss. Anyone ever seen a difference between the two sources?

Really want this to work. Hope I'll know more this weekend. Thanks for the suggestions.
Mark 1275

Mark, in your first message you say that the end of the inner cable rotated when disconnected from the speedometer. So you know that the gearbox end does work. Or at least it did at that stage. You also say that when you pulled it the inner cable it stopped rotating. It seems to me that is your answer. The squared end of the inner cable needs to be inserted down into the matching squared hole in the end of the nylon drive gear in the gearbox.


If you rotate the inner cable slowly and gently with your fingers you should be able to feel when it aligns with the hole in the gear and then push it down to make that connection. Just not too far or there won't be enough length of cable to make the speedometer connection! Sometimes if the end of the cable is bent misaligned then it won't connect and just skims the end of the gear. If this happens you need to slacken the outer cable again and start afresh, connecting the inner one at the same time as gently tightening the outer. If this fails, it maybe that the hole in the gear has become damaged so that although the inner is engaged, it isn't tight enough and is just slipping round. If so it's either a new gear pinion or you may be able to get a more positive connection with some sort of packing, or JB Weld or similar.
GuyW

Thought I had it solved last night. Gave up on the new cable, just can't make it engage at the gearbox end, the speedometer end turns no matter what. Took the old cable, pushed it into the gearbox end until the speedometer end wouldn't turn, tried to maximize the exposed portion at the speedometer end, and reinstalled. It was night and I was just in the driveway, but I'm sure I saw the speedometer move. Thought I was all set, but this morning, no speedometer.

I'm thinking of taking the new cable, and cutting out about 1/2" or so of the outer sheath with a Dremel. Might try it tomorrow.
Mark 1275

This thread was discussed between 10/06/2018 and 16/06/2018

MG Midget and Sprite Technical index

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