Oily speedometer

[AEX 31]

Dear All,

I've encountered a problem that I hope somebody on this forum might
have encountered or at least heard about.

After changing the gearbox in AEX 31 two years ago I find oil pushing up
through the speedometer cable, and subsequently filling the speedometer
with lovely gearbox lubricant! At First I preasumed that since the "new"
gearbox didn't have a breather, fitting one would solve or lessen the problem
but it didn't...

I've been thinking that something might be missing from the speedometer drive
in the gearbox. I've included an images hopping that somebody might be able
to tell me if there is a seal or gasket missing somewhere.

Very grateful for any help or learned opinions.

Kind regards Jonas

[Jam2]

I would not regard this as a learned reply,  but is it possible that the new gearbox has the speedo drive turning in the opposite direction, thus the scroll is pumping the oil up the cable rather than back into the box?

[AEX 31]

Thanks for your reply,

I have no idea if the speedometer drive could run in the wrong direction. Anybody out there that
know about that or have any other ideas?

Thanks Jonas

[B.P.Bird]

Jonas,
If the drive was rotating backwards then so would the speedo. needle. I do have a very dim memory that there could be an 'O' ring in the 'box drive housing somewhere ? However I'm not at all sure. Is the gearbox oil level correct, as I suppose overfilling would not help the situation ?
Barrie

[AEX 31]

Barrie,
That makes sense. Oil level is one of the things I have checked. Another experienced AC related friend mentioned that a very worn drive could maybe also be the cause of this.... also makes sense.

There is no O ring in the drive that I have got, so if anybody knows if there should be, please let
me know.

Thanks Barrie.

Jonas

[B.P.Bird]

Jonas,
Looking at your photograph again two things strike me:

1) Do you know if these parts were with AEX31 from new, or could there be a mismatch of parts so that the spiral oil channel is pumping oil up the cable instead of preventing it ? I have no idea if the Moss 'box was available with optional alternate rotation directions on the speedo. cable drive, but as the Moss 'box was fitted to such a wide variety of vehicles in period I suppose that it is quite possible.

2) If you look at the steel drive shaft in your photograph you will see a small circular groove which is positioned between the spiral groove bearing area and the driving gear area. I cannot see any purpose for this groove except, perhaps, to seat an 'O' ring.

I must say that to actually have oil filling the speedo. head it does rather point to some pumping or pressure effect. I take it that the speedo. head does actually record speed in the correct sense, in which case it is not reverse rotation. However maybe that spiral could be designed for another application with a reversed rotation.
Reminds me rather of that lovely Flanders and Swan song, 'Misalliance,'  about the doomed love between a 'Fragrant Honeysuckle' and a 'Bindweed' because one twined to the left and the other to the right.......

[AEX 31]

Barrie,

These parts wasn't with AEX 31 from new, this speedo drive came with a gearbox I got from Billy Bellinger some years ago. I guess it's from a two litre saloon and rebuilt by Billy with full synchro on all gears and a slightly different ratio on 2nd and 3rd gears.

I do have the original gearbox and the drive that was fitted originally but so far I haven't been able to get the drive off since it was fitted with loads of silicon by somebody, at some stage in its life.

So any comparison has so far been impossible. I guess that the problem lies in how the drive functions.

The Speedo did work fine until the oil made its way into that housing. In other words I never had these problems before I changed the gearbox...

If anybody out there has an original speedometer drive that is not fitted to their car I would indeed be interesting to compare if 1, they look the same and 2, if there is any O ring fitted.

I did listen to the Flanders and Swan song and though I have a bit of a problem seing the similarities with me speedometer problem it is indeed a lovely song.

Thank you.

Jonas

[B.P.Bird]

Jonas,
I am sure a bit of persistence will get the original speedo. drive out of the original gearbox. Silicone sealer does soften in petrol. If you can get it out you might find it spirals the opposite way to the one you are using from a 2 Litre saloon (hence my reference to 'Misalliance.') In fact I wonder if a 2 Litre saloon has a tacho. and speedo. which rotate in opposite directions ?
Barrie

[B.P.Bird]

Jonas,
Just been out to the workshop to get on with mounting the rear view mirror on AE 22, not the straightforward task one might imagine, when I was overcome with curiosity about your oily speedo. problem. So I pulled the speedo. drive from the original Moss 'box and here it is:



The brass outer bearing is a tight fit in its casing, but did tap out using an aluminium drift very carefully. There was no 'O' ring. This scroll is as fitted in Thames Ditton in 1954 so could be compared with the scroll in your photograph. What do you think ?
Barrie

[AEX 31]

Barrie,

Thank you so much for taking the time to pull out your speedometer drive and for supplying me and the community with an image.

It does look identical to the one I have fitted at the moment. I suspect that the problem with mine might very well be that the fit in between the brass housing and the steel axel isn't very tight. In actual fact I do know the axel came out very easily. I'll take it out and measure it soon. I suspect the tolerance in between the two parts shouldn't be more than 2 or 3 thou?

Barrie, with your experience do you think that this could be the problem?

Again thanks for taking the time and effort to help me solve this conundrum.

Jonas

[B.P.Bird]

Jonas,
The steel gear/scroll I took out has very little mileage and is without any detectable clearance in the brass housing. The brass housing does have spiral grooves on the bearing surface which will be designed to react with the scroll on the steel shaft. Interestingly the spiral pattern in the brass is a double spiral, one clockwise and one anticlockwise. It might be a complete red herring, but does imply that the brass housing would be compatible with both LH and RH scrolls.
However I would not suppose that a worn brass housing would start to pump oil up the speedo. cable. All things considered I am rather stumped. To move oil up the cable and into the speedo. head must require one of three things: A pressure at the lower end, a pumping action or a head of fluid.
We can discount the last as the 'box is well below the speedo. The pumping action could only come from the scroll which, of course, is designed to push oil back into the 'box not up the cable, but would work in the wrong sense if the rotation or the scroll were reversed. As we see from the photographs the scrolls are identical. So far as rotation is concerned you say that the speedo. needle rotates in the normal manner to indicate speed. This could only happen if the cable is rotating in the correct direction - if the cable was running 'backwards' then the speedo. needle would stay firmly pressed against the little stop, on the dial, near zero. Which being the case only leaves us with pressure and you have incorporated a breather which must vent any pressure: Unless, internally, not all parts of the gearbox are connected and you will see that the speedo. drive, on the Moss box, comes from a separate module bolted to the rear of the main case. As the mainshaft comes right through this housing it seems unlikely that it is not internally vented to the main case and therefore to your breather. In addition there would need to be lubrication within this housing which looks as though it carries the output bearing and oilseal, so again you would assume internal venting.
Are you absolutely sure that the speedometer needle is working in the correct sense when you drive '31 ? If it is reading zero when driving forward does it read a speed when proceeding in reverse ?

Barrie

[AEX 31]

Barrie,

Yes I am absolutely sure that the speedometer was working just fine until I fitted the "new" gearbox. It also took several miles, I would guess at least 50-60 miles before the oil made its way, in sufficient amounts to affect the magnetic discs in the speedometer.

I'm not sure if the time it took would indicate pressure or pumping beng the cause?

I am like you baffled about all of this. I'm still trying to get the old drive off. Maybe inspecting this will shed some new light on the mystery.

Jonas

[AEX 31]

Barrie,

I finally manage to get the old speedometer drive out of the old gearbox. I does look exactly like the other one I have. There is in big difference however, the holes in the steel drive shaft axel is filled up with silicon, please see the attached image, I assume there is a reason for this!

Any thoughts?

Jonas

[B.P.Bird]

Jonas,
Well as silicon sealer was not invented when the gearbox was designed it seems a safe assumption that it should not be there now. Of the three speedo. drives we have now photographed there is a common direction of the scroll and two of them are clear of silicon or any other gunge. This being the case the only variable which would affect a pumping, rather than an, as intended, 'sucking' action, would be  direction of rotation. Clutching at straws here, but please confirm that the speedo. needle, in AEX 31, does rotate clockwise as viewed by the driver. That is 0 mph at eight o'clock, 60 mph around twelve o'clock and 120 mph at four o'clock.
As the problem was not present when using the original gearbox there must be a difference between that and the substitute 'box. You say that synchromesh has been added to first gear in the replacement gearbox. Possibly this modification has blocked an internal vent so that the rear tailhousing assembly cannot release internal pressure except by way of the speedo. drive ?
Perhaps it would be wise to overhaul the original 'box in case you have to change back to it: Improvements to original factory specifications can often turn out to be anything but......
Barrie

[B.P.Bird]

Jonas,
I just had one last thought: That little speedo drive housing on the end of the tailshaft housing is bolted on and therefore must have a gasket in place. Supposing that Moss 'box gaskets are not readily available it seems likely that a gasket was tapped out and whilst doing this it would be quite easy to omit a breather vent hole which would then be blanked off upon assembly. One would suppose that a vent path would still exist via the tailshaft bearing unless the addition of a first gear synchro. block obstructed this. Entirely conjecture I fear, but it could be the kind of error chain that gives rise to unexpected results
Barrie