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MG TD TF 1500 - Swinging Speedo

I am suffering the swinging speedo problem. If I am going 50 mph the speedo swings between 45 and 55 about twice a second. Seems to be a fairly common problem with a number of suggestions in the archives I have followed to no avail.

1. check condition of retaining clips at both end
2. check the routing to make sure there are no tight bends
3. lube the cable
4. cable ready to fail

The instrument was rebuilt about 10 years ago and did sit for about 3 years with no use.

I did notice that the attachment at the transmission side had a small bend in the shaft which I tried to straighten but felt I was likely to break it rather than bend it. Not sure how that got there and if it did not happen recently, its been that way for decades when the speedo did not have this issue. That might be the problem but I wanted to be sure there was not something else to look at before I attacked that.

Perhaps it will just work itself out. Maybe the instrument needs some serious exercise.
Christopher Couper

When my TD was wrecked, the dash ended up under water. I dismantled the instruments and cleaned them during the restoration. The spedo has swong violently since the restoration was completed. When I go 50, the needle swings between 35 and 70. I had hoped this would improve, but it is clearly not going to, as it has not improved at all. I have the later dished chronographic spedo. I too would like to know how to fix this.
All the other instruments work fine, though the temp. reads high.
David
D. Sander

Find the source of the problem - is it the cable or the actual speedo? Take the speedo out and drive it with a drill running in reverse. Does the needle bounce around? If yes then the speedo is the culprit if not then it is most likely the cable.
If the speedo is the problem then it is most probably that there is some small irregular contact between the spinning magnet and the aluminum disc. Possibly carefully cleaning the disc will solve the problem. The bearings supporting the disc may be worn and allowing the disc to move slightly along its axis and contacting the spinning magnet now and then.

David, I was not aware that the later dished instruments had a chronometric movement. I'm pretty sure they were all magnetic.
Cheers, Hugh
H.D. Pite

I had an issue with mine from my '53 TD similar to yours. Turned out that when the trip odometer registered another tenth, the needle would go nuts because there was tension built up in the cable due to tight mileage dials/wheels. I found this out after hooking up a cut off cable stub and running it in a drill like Hugh has said. Took the unit apart, cleaned and lubed everything and it has worked well since. Apparently the wheels were sticky and caused the needle to jump a lot. This was sort of a desperation measure after replacing the cable and changing the routing many times. Mark
Mark Strang

You guys have given me a few more items to look at. Thanks.
Christopher Couper

Hugh, you are right, It is magnetic. Long day...
D. Sander

Chris there is a great article on this problem in the The Sacred Octagon June 1979 issue which I've copied & posted below. It seems a simple fix.

THE SPEED0 NEEDLE WHIPLASH SYNDROME

Prior to the introduction of the Y-Type Saloons almost all M.G.s used chronometric speedometers and tachometers, so-called because the internal mechanism of this type is quite similar to the inner workings of a clock. On these instruments the needle moves up and down the scale in a series of short jerks, much like the movement of the second hand of a watch. It's supposed to move like that, so don't try to "fix" it.
The late TD, TF and all Y Saloons use magnetic instruments, as do most modern cars. These are not necessarily any more accurate than the chronometric units, but under normal conditions they do provide a very smooth needle movement which seems to be more reassuring to most American motorists. Unfortunately, there comes a time in the life of most magnetic instruments when the old chronometric jerk begins to look pretty good. The syndrome is characterized by a wild whipping back and forth of the needle, even though road speed and engine speed are actually steady. The worst example I have ever seen was, unfortunately, on the way home from the Natter & Noggin this February. According to the speedometer in Len Renkenberger's Mercedes I was going 60 mph, but the speedo needle in my YA was whipping back and forth between 50 and 751 Three hundred miles of watching a speedo needle with St. Vitus's dance was made all the more annoying by the fact that it was my own fault. Barring a breakdown in the instrument itself, this condition is usually brought about by lack of lubricant in the drive cable. There's a lot of space between the inner cable and its housing, and when the lubricant dries up the inner cable is able to whip around quite a bit inside the housing. Although the rotational speed at the driven end of the cable is uniform, all that whipping around causes the instrument end of the cable to go through rapid cycles of acceleration and deceleration. The needle tries to follow the antics of the cable, so it whips back and forth. This problem also exists with the older chronometric instruments, but it isn't so noticeable at the needle because the chronometric mechanism tends to average out readings which change very rapidly.

The cure is simply to lubricate the cable. The thin graphited fluid sold by most auto supply stores as speedometer cable lubricant is useless, as it doesn't fill the void between the inner cable and the casing. It does lubricate the cable, but it doesn't stop it from whipping around. What is needed is lots of nice, thick chassis grease. Disconnect the cable at one end and pull out the inner cable. On some cables the ends are prevented from sliding back into the casing by circlips. If you have this type, you will have to disconnect both ends, remove the circlip from one end, and withdraw the inner cable from the other end.
Soak the cable in solvent to remove any dirt and old grease which may be present. When the inner cable is clean and dry, coat the first three or four inches with a thick layer of grease and push it into the housing. Then coat the next few inches, push it in, then coat the next few inches, and so on until the inner cable is all back where it belongs. Tight spots can usually be gotten past by rotating the cable as you push it in. At the very last you will have to rotate the cable slightly to line up the squared end with the corresponding fitting in the gearbox or instrument, depending on which end you are working from. This will cure the needle's whiplash problems 99% of the time, and it should be done every five or six thousand miles. The grease helps to prevent the inner cable from whipping around, and also acts as a damper to smooth out the speed fluctuations at the instrument end of the cable.

If you are on the road and can't stop to lubricate the cable, a cure suggested by Len is effective as a temporary measure. Reach up under the facia and bend the cable casing into a "U" as close as possible to the instrument, and anchor it in that position. The resulting extra friction on the inner cable tends to dampen out some fluctuations in cable speed, so the needle won't whip back and forth quite so violently. This is pretty hard on the cable, though, so straighten it out and lubricate it as soon as you get home. If you bend the casing far enough to kink it or break it, then you will need a new cable, so be careful.

Cheers
Peter TD 5801
P Hehir

Peter: I greased it up but I admit I did not 'pack it in' as this article suggests. I think I will take out the speedo and try the drill test just to be sure.

If it does not bounce then I will try this technique.
Christopher Couper

I was hoping this wasn't an OT bathing suit issue.
JE Carroll

Peter, it would be nice to acknowledge Chip Old (F.E. Old
III)as the author. Bud
Bud Krueger

If I'd known that Bud I would have. All I had was the TSO as the source.
P Hehir

Peter's reference to the '79 TSO reminded me - at the last meeting of our club a mamber brought in a stack of TSOs from circa '79 through '85. I picked up four copies (Aug '79, Apr '81, Feb '83 and Apr '83). In the Apr '81 issue I spotted a short note bylined "Northwest M.G. 'T' Register, Liz Dubois #4246" The note was submitted by "Dave DuBois" of Bremerton, WA, and mentions the then recent volcanic ash. Is that you Dave? If so, would you like this copy of the TSO after I've finished reading it? If so, shoot me an email at jchapin3 at aol dot com with your mailing address.

Jud
'53 TD25009
J K Chapin

I too have fought a wildly swinging speedo needle- for 8 years . The faster I went the worse it got.Cleaned the cable -lubed the cable -nothing. Finally bought a new modern speedo cable this year- No change!!!
Grrr. So stripped cleaned and lubricated the number roller mechanism on the trip and odometers. It now runs completely steady.
Another minor yet satisfying triumph in the up keep of my wee car !
Cheers, Keith
K. McKenzie

Keith: Can you advise a neophyte on the easiest and less damaging way to get to the roller mechanisms?

My experience with the instruments is to send them back to the home country and mount them in the car. I tried to fix my clock once and lets say it still does not work and probably won't work now without the loving hands of an expert.

I have the dished speedo if it makes any difference.
Christopher Couper

Chris, you may know, but if not, do not use WD-40 to live your instruments. Use click oil available from various sources on the web. Regards, tom
tm peterson

Chris,

If you want your clock to work again. Try Hal Kramer he fixed mine and its working again after many years of only being right twice a day.

hkramer at nycap dot rr dot com

For the speedo you could get a clock oil kit for Amazon.
http://www.amazon.com/Creative-Clock-Oil-Kit/dp/B0089SKKY6
Around $9 plus shipping.
Rod

R. D. Jones

Might help to take a look at this

http://www.magnetic-speedometer-repair.com/

AJ
A R Jones

Thanks for sharing that AJ - very informative.
Rod
R. D. Jones

There might be two Problems:
1. If you lubricate the cable too much there will becom grease between the magnet and the Aluminium disc. Then the grease turns the alu-disc too fast.

2. The axle of the Alu disc (with hand of the Instrument) is pivoted in a smal bore in the magnet. If the grease in this little hole is too hard, the axle of the hand turns until the little reboundspring is turned hard. Than the hand goes back quickly.

Klaus

Klaus Harthof

Gents,
Here is one to put in the books. The PO had the experience of pulling the speedo cable through the scuttle and allowed it to touch the hot terminal of the starter contactor. Current flowed through the sheath to the speedo which had a bad ground to the frame. No damage to speedo. The current continued to the tach where there was a good ground (earth) where it melted the hair spring like it was a fuse.

I would like to attempt a repair as I was trained years ago to work on precision instruments. Do any of you have a dish faced, magnetic, speedo that is otherwise damaged or surplus to your needs. If so I will be pleased to pay a reasonable price plus shipping.

Thanks,

Jim Haskins
J. M. Haskins

This thread was discussed between 13/07/2014 and 18/07/2014

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