Chronometric Speedometer needle wiggle - Jaeger in MGTC

[timberstone]

Accurate Chronometric speedometer shows wiggle of the indicator needle at any speed over 40 MPH.
Any idea whether this is from faulty cable or from something inside the mechanism?
The chronometric speedometer workings have been "Rebuilt" recently by very reputable shop. Shop now no longer rebuilds Chronometric instruments
The cable was disassembled, inspected and oiled properly then reinstalled.
(Noted that there is advice to make sure the cable is firmly attached to the connection on the back of the speedometer.)

Thank you for any help

[Steve Simmons]

If by wiggle you mean it moves slightly once or twice per second, then that sounds like a problem with the cable. If it's wiggling rapidly then that would likely be a problem with the gauge itself.

[Rob Reilly]

Here's an old web page about them.
http://www.mg-tc.de/articles/JaegerChro ... ments.html

[Duncan M]

I would be very wary of any instrument shop. I would not trust a chronometric with anyone other than a clock or watchmaker, if you felt unable to service them yourself. Also, I would not describe the act of slapping a vinyl face on a 75 year old instrument to be anything but vandalism.

The needle wobble you describe sounds like what happens when the Chronometric clockwork needs cleaning/oiling, which is the only service they should ever require. As the clockwork mechanism slowly gets more and more worn, the need for frequency of oiling will increase.

[Steve Simmons]

West Valley Instruments has been rebuilding chronometric instruments for decades. And they do not use stickers!

[Duncan M]

Steve-
Good to hear west valley doe not use vinyl. What do they use? I guess I am lucky to have presentable original faces.
Having a hard time figuring out what is meant by "rebuild." Can you elaborate?

The article link Rob supplied shows best in pic 5 (lower plate) the little holes drilled in the bronze plate. Those are the "bearings" that could eventually wear, and where oiling is given. Normal service (cleaning and oiling) can be generally done with the clockwork not taken apart. Removed from bakelite housing, but not taken apart. It may be desirable to separate the plates for cleaning if the clock is deemed unusually dirty or something is stuck in its dirty bearing. Duplicating and replacing those plates would be the only "rebuild" I could imagine.

When I had the instruments out and apart I found a little sticker and a date scratched into the back of the bakelite, indicating the instruments were serviced when the car was barely 2 years old. In Oakland, CA.

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[Steve Simmons]

I don't know what a standard rebuild entails, but obviously a rebuild includes replacing any worn parts, calibrating it to whatever gearing you're using, chroming the trim ring, cleaning or restoring the face and number rollers, painting the needle, etc, etc. Same as rebuilding any other gauge, only more complicated a job and therefore more expensive. I believe the faces are done with a silk screen type process as original. They can be color matched to your existing gauges, etc or even customized for special use. The sky is the limit so long as money isn't limited either! Original gauges varied in shade from silver-green to light green so it's unusual to buy a gauge and have it exactly match what you already have. So it's a good idea to send both gauges to make sure they end up the same.

[Duncan M]

There is another good article on the Chronometric speedo and tach mechanism.

Here: http://www.hells-confetti.com/Technical ... erhaul.pdf

They suggest sewing machine oil. I suggest a non-synthetic clock oil, because sewing machine oil and synthetic clock oil are not likely to last very long in this application.

I last oiled the movements 7 years ago.

[frenchblatter]

The most common problem is a kink in the cable. Check the cable run from gearbox to speedo head and straighten any sharp bends. Most common place is the exit from the gearbox. I light smear of whit grease is all that should be put on inner cable. Over oiling will lead to excess oil in the heads (tacho and speedo) and they will cease to work.

If, like mine, your instruments were left in a damp garage for 48 years and had rust over the face how do you "repair" that without repro faces?

[Rob Reilly]

<If, like mine, your instruments were left in a damp garage for 48 years and had rust over the face how do you "repair" that without repro faces?>

Tell me about it. Unknown number of decades outside, near as I can guess 5 or 6.
It would appear this car died at 182 miles while going 95 miles per hour.

[Duncan M]

Looks like the TA needles were white, unless that is a "rebuilt" unit?

[Rob Reilly]

No, that's natural metal color, almost all the black paint has flaked off.
The tach fared a little better.

[frenchblatter]

I got mine from a chap in Kent who had laser cut repro faces for speedo and tacho. Did a rubbish job on the clocks though. I found a father and son outfit that specialised in chrono gauges for bikes but they did a good job on mine, still working 5 years later.

[Rob Reilly]

Well, I brought my Jaeger speedometer into the house to see about restoring it. Now I'm reading this article.
http://www.mg-tc.de/articles/JaegerChro ... ments.html
I found a loose 2BA cheese head screw inside with a wire soldered on to the head. I wonder what that's all about.
I also found two of the spring tabs that ride against the odometer and trip meter number spools are bent out, probably means somebody has been in here before.

[Rob Reilly]

Well, I've figured out what the loose wire on a screw was for. It had to do with the 30 mph warning light.
There is a contact that swings (red arrow) and a contact that is fixed (gray arrow).
If I flick the shaft, the swinging contact moves around against the fixed contact, then it pops off again and back to zero.
Looks like somebody disconnected it all, but left the screw with the wire inside.

Another weird thing I discovered. One of the two screws that hold the bar that clamps it to the instrument panel is 2BA thread, but the other screw measures .193" OD x 34 threads per inch on my thread gauge. I don't find that size in SAE thread tables.
I'll replace it with another 2BA but I am curious to know where that one came from.
M5.0 x .80 is not quite right. Is there a metric 4.9 mm x .75 threads per millimeter?

[Duncan M]

Might be a ground wire to complete the circuit for the thirty light. I think all TABC's have them, except for the EXU's.

[Ray White]

Might be a ground wire to complete the circuit for the thirty light. I think all TABC's have them, except for the EXU's.

Australian export models didn't have them either. I just have two map reading lights.

[timberstone]

Searching my brain for the reason why the Speedometer needle wiggles around and above 40 MPH, reading all these posts and also having read Carl Cederstrand's treatise about the Chronometric internals -- decided me to take another plunge at having the Speedometer "Rebuilt" (for the 4th time).
This time by a reputable shop -- to Morris Mintz.
Also requested that the Thirty Light be looked at so that the speed at which the light comes on is increased from 22 mph to closer to 30 MPH -- which may not be "original" but sounds more logical.
Word from West Valley Instruments is that their turn around time is about 2 months -- due to being swamped by overflow from the "other" instrument repair shop that quit these repairs.
Will find out and spread the word.
Octagonally yours,
BOXLEY (Robert and MGTC 0820)

[tone]

sort of still on topic but what is the best grease to use the speedo/rev counter cables please.
Mine wiggle a little bit but I was told its because of the type of mechanism used internally, but what would I know, way too complicated for me to attempt to dismantle!

[Rob Reilly]

There is a graphite lube product for speedometer cables, I think Autozone and Advance Auto Parts carry it.

I have discovered that my Jaeger tach has two screws with that same unknown thread, for attaching the mounting clamp.
It has the letters LUCE scratched on the back; I wonder what that could mean?

Morris Mintz is the owner of West Valley Instrument Specialists in California. Thanks for the tip, I thought I would to send him my speedo and tach faces to restore.