MG T-ABC

The (presumed) original Jaeger speedometer in my TA has an unusual drive connection, at least I haven't seen it before.
There is a shaft 0.237" diameter, or probably 6 mm as I understand these Jaeger instruments are metric.
There is a through hole in it about 0.090" or about 2.3 mm diameter at about .300" or 7.5 mm from the end. Does anyone have a picture of the cable end that would fit this instrument?

If I spin the shaft, the needle jumps to 20 mph and sits there for awhile, then drops to zero.

My engine and gearbox are from an MGA, so the gearbox drive fitting is about .748" x 26 tpi or more probably 19 mm x 1.0 mm thread pitch with a square receptacle. I do not know the gear ratio, but I can probably find that from MGA web sites. I will probably have to get a cable specially made, unless there is something already existing.

Do you think this speedo will work with this gearbox?

Does anyone know what sort of drive connection the TA gearbox would have had?

Rob,
The gauge is chronometric as you probably know. A clockwork mechanism. The MGA has magnetic instruments with spinning discs. That said, I’m sure the instrument can be made to work. I’m not familiar with that shaft attachment. My TC has square receivers as most often seen. The ratios are a completely different animal. Once the ratios are established chances are either the gear in the trans or the instrument will need to be changed. If the ratios are known, the best bet may be a gear reduction box as supplied by Speedograph Richfield might be the ticket. They may also be familiar with the shaft attachment and could supply a box that attached to the speedo and have a square drive on the other. Maybe a call to Morris at West Valley Instruments. He’s very experienced with these chronometric instruments.
Cheers,
Rob Zucca
TC5464

Hi Rob,

this type of shaft is correct for a 1936 Jaeger Chronometric Speedo,
situable speedo cables for this type connection is available from spare parts dealer
cheers Carl

Thanks for the responses.
I found a couple of pictures on Doug's site.
The brass fitting is described as what the TA through TF gearboxes would have had. Does anyone know what thread that brass fitting has?
The shaft appears to have a slot in the end. Is that right?

I don't understand why there are no threads on the speedometer connection. How would the cable be attached there?

I'm not positive but I've seen connections like that on cars of the period that used a screw through the end fitting of the cable into the shaft. Or maybe the screw passed all the way through, can't remember. I seem to recall the outer housing slides over the fitting on the back of the speedometer and tightens down with a small clamp.

Steve is correct. My TC has a TA speedo fitted, so I’m familiar with this fitting the outer is just a tube that slides over the shank on the speedo and is held in place with a simple clamp. The inner is also a tube that slides over the drive spigot and held in place with a small screw that fits the hole in the spigot. It is known as a Jeager drive and Speedograph Richfield in the UK can supply, because they made a cable for me.

Here is a close up picture. The outer diameter is .431" I don't quite understand how you would tighten a screw on the inside cable if the outer sleeve is in the way.
I found the Speedograph website but they don't say anything about the TA.

Often you can pull the cable out just far enough since there's a bit of slack in it. If not, you can remove the clip from the other side and pull the housing away, assuming it has a clip. Then attach the cable, slide the housing back, and reinstall the clip.

Ok that makes sense. Sounds like a fun job connecting that cable under the dash.
Any idea of the length I should ask for? The fitting on the MGA trans is on the right and points at a forward angle of about 45 degrees and slightly downward.

Hi,
The speedo cable has on one end a little sleeve.
The sleeve is pushed over the shaft of the speedometer and secured with a small screw, there is a BA thread in the shaft from the speedometer.
The cover of the speedometer cable is slid over the stub of the speedometer housing and clamped with a clip these Boys can help you
https://www.speedograph-richfield.com/
hope that helps
Carl

I think cable length will be somewhat of a guess. If your tub is in place route a length of solid core wire and shape it with no sharp bends where you think it’s going to go. Then measure that. The stock speedo cable on a TC and assuming it’s the same on a TA is on the opposite side of the trans.