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MG Midget and Sprite Technical - Speedometer drive

Well today the carbs are not overflowing so continuing the shake-down tests and fixes I jacked the car up, checked /cleaned and adjusted and re-bled the rear brakes. Drained the diff oil (the drain plug has been dripping so needed redoing) and refilled with fresh oil.

But the main purpose was to replace the speedometer cable as the speedo isn't working. Only I now find that the problem is the cable doesn't spin when the car is running in gear (back end jacked up) So there is something amiss with the drive in the tailshaft extension. I rebuilt this gearbox and am about 99% certain I remember fitting the drive gear onto the output shaft! But maybe the pinion isn't engaging. Is this something I am likely to be able to fix without removing the gearbox? I cannot remember what lies inside the nylon screw in boss that the cable attaches to, or even if oil will issue forth if I attempt to remove it.
GuyW

Guy,

I have had problems with the drive output shafts - the white plastic (nylon ?) gear wheel turning on the shaft.
Even had a new repro one (a few years ago when they were not the current silly money)turn - seems the ones I've had isues with were not bonded ? but pressed on ? - the shaft having been knurled.

You can remove it insitu with out taking out the box but its a bit tight, can't remember if its essential to drain the box if you jack it up ?
I'd just drain it anyway.

I think I've still got them - will look in the morning.

Worth checking the cable is free and not causing a build up of load on the shaft/gear take off etc.

R.


richard b

Its not the cable, its new, turns freely and has a good squared end. I couldnt find a clear diagram of the parts but the Moss site parts catalogue gives indicative parts. From that I surmise that the possible faults could be:

1. The socket end of the pinion has broken off or has rounded so it isn't engaging with the end of the cable.

2. The gear end of the pinion has stripped or isn't engaging with the worm gear on the output shaft

3. The worm gear is slipping on the shaft, or is damaged.

I think for 1 and 2 I could remove and repair or replace the pinion, but moss list it at £83 just for the pinion !! For 3 it is a gearbox out job.

In the meantime I just drive and do a bit of mental arithmetic off the rev counter as I go. Or use a sat speedometer App on my phone.😊
GuyW

From your list you can check No 1 by fitting the cable to the box (the cap is a long fine thread - it does seat but takes a lot of turns to get it fully home) and with the speedo end free, push the inner down and rotate by hand to ensure its gone down fully into square drive - it should locate and not be free to turn. You can then test it by running with wheels off the ground on stands etc.

I've only had one strip - on a 'B' when a gearbox company fitted the wrong colour combination of gears (they are different teeth counts for chrome and rubber bumpers.

R.
richard b

Richard, I did exactly that. Couldnt get the cable end to locate in anything - or at least if it did it's not such that I could feel with any resistance. And no, it didn't turn the inner cable when I ran it in first with the rear wheels jacked up.

That's why I listed those 3 possibilities, though I have thought of a 4th one. I wonder if I ever put a pinion gear in there!
GuyW

Guy,

Try disconnecting the cable from the box and pull a length of the inner cable out from the outer then try stuffing it into the drive pinion (could visually check it looks OK first !) and check for resistance.

It is possible to remove the drive pinion assembly with the box insitu - I did it a couple of times to sort my similar issue a few years ago.

R.
richard b

If it helps IIRC the spridget speedo cable has a 1/8" square section at the gearbox end, Ford Escort RWD 4 speed box 3mm square. I remember this as I had to adapt my speedo cable when I fitted the 4 speed Escort box into my Sprite and it required filing down to fit the Ford box. Might help determine what's going if you can find a suitable short section of 3mm or 1/8" square to poke into the gearbox speedo output and see what you can feel. Guy I have some 3mm keyway stock but don't where you are.
David Billington

My ribcase is in my loft. Would any pictures of the speedo with pinion removed be helpful Guy?

It's a long time since I had a rib case in mine(t9 now). But can't you see if the speedo pinion end is turning once you take the cable out?

Can't have stripped teeth between you building it and driving it for the first time.

I do vaguely remember having what might be the same trouble with my ribcase. Cable seemingly installed correctly, but actually not inserted into the square end of pinion.

anamnesis

The drive gear slipping on the mainshaft is not uncommon as it is not keyed to the mainshaft. Unless you omitted it (unlikely!!) or the main shaft nut (again unlikely!!!) usually the speedo registers something if rather erratically. Surely if you omitted the pinion then the oil would leak out? I would go for a replacement drive pinion. They in my experience rarely wear out and are quite common secondhand. I will have a rummage.
The other thought is that the square end of the pinion drive is blocked or damaged not allowing the new cable to locate.
Bob Beaumont

I didn't have the car high enough yesterday to get a view of the cable connection to the gearbox so was fitting it at arm stretch by feel. I thought from feel that the knurled connector was fully screwed in but maybe the inner had missed the hole. I'm not sure that when its in the car you can get a straight end-on view into the pinion but if not then a few close up mobile phone photos can get round that. Or I have a cheapy endoscope somewhere!
GuyW

Just wondering that if the square drive was worn so cable not engaging, how about winding some thin wire around the cable to get it to hold, at least temporarily to see if it rotates. Maybe a last resort as you don't want to damage anything but it does sound like wear/ slipping (assuming the square section is fully engaging).
Bill Bretherton

Its a new cable Bill. If the problem is wear it would have to be in the end of the nylon pinion drive.
GuyW

Guy,

Attached are pics of mine that failed - I assume it spun on the grooved shaft - it appears to be only an interference fit - not bonded.

I did consider adding some pin punch marks around the shaft to increase the interference to see if it would be OK as its still a tight fit. Don't know of any adhesives that would bond the nylon gear ?
Not sure if this is an original.

I did wonder if tightening the aluminium cable nut right down (as I assume its supposed to) removed any end float and it jamed in the casing ? - there does not seem to be anything that I've found in the manuals about it.
I did find that the aluminium cable nut was difficult to do up by hand as its thin and seems to drag on the nylon thread - so ISTR using water pump pliers !

If I replace one again I'm going to try checking for end float by turning and pulling it out a bit - should be able to see the angle on the square drive shaft and use it as a reference, albeit only a tad or two ! and turn the box over by hand to check alls well.

R.






richard b

Well its sorted. By poking a small flat bladed screwdriver into the squared end of the pinion I confirmed it rotated when it shouldnt and clearly wasnt making a proper connection inside. So, drain the oil and undo and remove the nylon bits. Sure enough, the little pinion gear was slipping round on its shaft. The shaft didn't even have serrations like Richards.
I have a spare gearbox (Smooth case, but those parts are identical) so I did a swap and reassembled everything. Still no working speedometer!

After some head scratching and undoing everything again to double check I finally checked the fit between my new cable and the pinion hole. It was very slack and just spun around. It did this on both the pinion shafts. Switching back to the old cable it fits securely at both ends and the speedometer now works.

So the new cable is definitely too skinny. I shall be sending it back! Quite a nuisance as I spent much of the afternoon disconnecting and reconnecting parts, double checking everything before I confirmed the real cause of the problem.

I must remember to refill the gearbox tomorrow!
GuyW

I can't think a brand new part would be faulty - you must have damaged it, but I bet you'll still expect a full refund. Tussss!

Hot drain of oil too I hope.










🤣

There are club t-shirts for this sort of thing, I would send you one but they're the wrong size, misshaped, split at seam and faded in the packaging, and they'd get lost in the post anyway. But you're not a full club member until you have wingnuts on the bellhousing.

(I think Les might qualify.)
Nigel Atkins

Bit premature for an oil change, Nigel. Its only done about 26 miles, though it looks pretty horrible. It's cloudy already, and sort of foamy. I was intending to re-use it for a couple of hundred miles, but I am not sure now.
GuyW

Guy,

Just curious, can you accurately measure the AF size of the square end of dodgy flexible drive and report back.
David Billington

David,

Thinking about refixing the gear - there is still quite a good interference fix to the gear wheel, so I thought I may drill through and either use a roll pin or make a taper pin - thoughts ?

R.
richard b

Richard,

Interesting you say there's still a good interference fit and yet it slips. I do wonder if these have failed due to the speedo drive cable becoming stiff due to lubrication running dry and then overcoming that interference and damaging the interface.

I personally would not use a roll pin or taper pin but rather make a soft metal insert with a straight knurl or serration and press that into the gear bore after having it opened out a bit, I'd keep the insert fairly thin so as to maintain as much strength in the plastic gear as possible. Initially it would likely need to be solid to do the knurl, a serration could be cut on the OD of a hollow part. Once in place the gear and insert could be bored/reamed/drilled to suit the shaft OD and pressed back into place.

Sounds like a 3D printed part might work, I've measured some of the parts I've made and the accuracy is quite impressive. The gear helix angle and pressure angle would need to be identified. I've only done stuff in PLA so far but have some ABS, both have good oil resistance. PET might be an even better option. Printing is fairly quick and sizes easily altered and if access to the underside of the car is good then IIRC the access to change the part is easy. It could always be tested out of the car with a gearbox on a bench as I've checked a few with a 1/2" drill running the input shaft.
David Billington

David, some measurements:
Across the flats of the new (not engaging) cable end : 2.74 to 2.77mm
Across flats of older cable (connects) : 3.07 to 3.10
Best internal measure of the drive spindle socket c. 3.45mm (caliper guage, not mic.)

Across diagonals of new cable c. 3.22, so not surprising it doesn't engage.

I suppose the socket end of the spindle would wear, but my 2 are much the same size.

Old spindle, that the gear was slipping on has no serrations as on Richard's and I don't think there are punch marks either, though it's corroded so it's hard to tell.
I am not repairing this one, but it would be easy enough to make a mini Woodruff key for it.



GuyW

As an aside; is it good practice to close down or leave open, a mic. between uses? Or doesn't it matter?
GuyW

Cranked open slightly I was told. I assume to stop expansion stressing it.

"Make sure that you store your micrometer in a ventilated place with low humidity, and ideally at room temperature.

Most micrometers come with a protective storage case to keep them safe when not in use.

When not using the micrometer, ensure that there is a gap between the measuring faces"

https://www.wonkeedonkeetools.co.uk/micrometers/how-do-you-look-after-a-micrometer#:~:text=Make%20sure%20that%20you%20store,gap%20between%20the%20measuring%20faces.
anamnesis

"I can't think a brand new part would be faulty"

I bet when you send it back, they say, "Well, no-one else has complained...about anything, ever"
Dave O'Neill 2

It actually came from what I believe is one of the Good Guys.
The whole inner cable is thinner so when the square bit is stamped on the end it is bound to be undersized.

Thanks Anam. There you go, the wonders of a Comprehensive education!
GuyW

Yes but who did he buy it from, a not-so-good-guys.

And there's you taking advantage of a good guys by returning an item you damaged, really, tussss.




The fresh oil you put in the gearbox last time has possibly lifted and suspended more residual crud and old oil that was left in the box from previous drainage and storage, refill with fresh new oil and you're at least diluting the old oil and crud.
Nigel Atkins

Nigel, by the morning the foamy look of the oil had disappeared, though it still looks cloudy, not like the clear honey that I put in it. On reflection, maybe I shouldn't have used honey?

The box and components were pretty well spotless when I rebuilt it. I don't think it's contamination in the oil, it's just fog.
GuyW

Guy,

Can you filter it to see if it leaves a residue or inspect it under magnification to check for particles.

When I drained one A series box in my car after something internal failed it looked like metallic paint with big flecks.
David Billington

David, I poured a bit onto a tissue and let it soak in overnight, and other than some colour staining there were no visible flecks left on it by the morning.
GuyW

Never in my wildest dreams did I think I'd be using my comprehensive education to google micrometers Guy. Lol.
anamnesis

Guy,
I was more joking really but didn't know the condition of the box, whether just s/h used, for some odd reason I didn't think of you having done work on the box (no idea why, I think my pea brain rolled out of it's slot).

As I remember your part of the world there can be an occasional moisture to the air any chance the box could have gained some in storage or before use. 26 miles of steady use might not have warmed the box enough to 'dry it out'.

Was the colour staining from anything you used on/in the box as fresh used oil wouldn't give much, other than what it picked up from the box.

Are you using engine oil, and using petrol with ethanol (that can cause carb leaking).
Nigel Atkins

Anam, yes you googled for it. That takes a deal of edjukation. But the first line of your message says you was told, so I assumed you listened, briefly, at school. I doubt you listened to anyone else since then. Too much of a free spirit for that.
GuyW

Yep I think I do remember being told about micrometers at school Guy. One of those brief moments when I listened, as you say. Ha ha. I've always been selectively attentive, aka bloody minded. 😁. But what I meant about google was I didn't imagine such a thing existing back then in my lifetime. Now though I won't be much suprised about what I see before I snuff it.
anamnesis

Anam: Encyclopedia Britannica.
Other brands were available.
GuyW

😁. Encyclopedia galactica soon. Lol
anamnesis

I have just emailed the supplying company with the measurements of the cable and drive pinion socket to see what they have to say about it.
Coincidence, perhaps, but the particular cable is no longer showing a price against it in their on line catalogue and the part number has chaged too, so perhaps thy have already found the issue and withrawn it.

Actually, the plot thickens as I now see that when I ordered the cable listed as YCS6035 it refered me to "Use alternative part no CS4056".
GuyW

Mentioning the part number YCS6035 is as good as naming the supplying company as it only came up with 3 hits on google and only one was to do with Healey parts.
David Billington

And wot's the problem with that?

ALL, and I mean ALL the suppliers generally know fairly quickly the quality of the parts they're selling. Just because they're some venerable name doesn't make them immune from the "that's all that's available, it's what's the others sell and all I can get". Whilst the purchasers' put up with this then it's all you can expect the sellers to sell to remain in business. Customers have demanded the race to the bottom of price and quality. A business can't supply to a market that sustainably doesn't exist.

Just be VERY grateful that it doesn't exit as much in things that are really important, in this country, as much, so far.
Nigel Atkins

I thought it might, David, though I wasn't aiming to "name and shame" until at the least I have their response and side of the story.

Their normally listed part is currently unavailable and their site helpfully forwards one to their recommended alternative part. Its certainly close; the same length and correct fittings at both ends. Listing it as a suitable alternative would be a very easy mistake to make. Whether it is supposed to be thinner for its main application or not I wouldn't know.
GuyW

Do you know the diameter of the good cable inner? I had a look the other day and found people selling spare inners for some US cars and it was said to be 0.130" diameter and came with an end a fitting tool, it was supposed to conform to SAE spec for speedo cables. I don't know if it would suit the spridgets cable.
David Billington

Its fitted now, David, but I could disconnect the top end easily enough to measure it tomorrow. It was noticeably fatter by feel than the supplied replacement. There's actually nothing wrong at all with the 'old' cable, but had assumed it was the cable at fault without checking it, when the speedometer didn't work.
GuyW

Dave, those dimensions:
The good cable is 3.7mm. This is the diameter of the cable away from the stamped ends. The other undersized one is 3.18mm

Ah, sorry I see you were quoting in imperial measure. - so that is 0.1345" and 0.125" respectively.
GuyW

They rang in response to my email. Apparently they had recently changed to a new supplier. He checked the new stock and agreed they were undersized. He went further and said some of them were badly stamped on the squared end sections which were distorted. He said they would take it up with their new supplier and in the meantime was sending me a replacement as they still had a few of the older stock ones. I hadn't actually asked for a replacement, simply saying I was reporting on the problem in case they wanted to check stock before supplying to anyone else.
GuyW

Guy,

That's a good result then, good customer service does still exist.
David Billington

This thread was discussed between 17/05/2021 and 21/05/2021

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.