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MG MGB Technical - Speedometer question

My car is a 1973 MGB with the original speedometer. The speedometer has always worked fine. Today, I was driving up the expressway and suddenly I noticed it was not working. It WAS indicating my speed, but the mileage numbers were not moving. I checked the trip meter and reset it to see if maybe it was jammed, but it still would not work. I finally got frustrated and tapped on the front glass and the numbers jumped some but still not move. Then about five miles later they suddenly started moving, but jumpy when they clicked over. Are they suppose to move smoothly or do they sort of jump into place? Why would it stop working and then start again? Is it possible to take the speedometer apart and check it/clean it? Is it possible it is just dirty? Does it ever need to be greased or serviced?

Suggestions,

Thanks,

Robert
Robert Browning

Sounds to me like it's dirty and needs a service. Rebuilds cost around $100 USD or you can do it yourself it you're brave enough. There is a speedometer rebuild guide in PDF format out there if you decide to tackle it yourself.
Steve Simmons

Steve,

I have no problem in trying to do this myself.

Does anyone know a link or where I can find this PDF file?

Thanks,

Robert
Robert Browning

Robert -

I just emailed you the PDF file. It helped me clean mine last year.

Greg
Greg Smela

Robert, there's a little arm that moves in an eccentric motion, and turns a sawtoothed wheel that moves the numbers around. It's very common for old grease to hold this arm above the wheel to where it doesn't touch it.

I assume that file that Greg is sending you is Anthony Rhodes' work. Excellent description of how they work, and what you can do to fix them. If anyone else needs this file, it is at:

http://mywebpages.comcast.net/rhodes/speedo.html

Of course, with the tems the way they've been, you'd think that grease would be liquid, huh? - - Alec
Alec Darnall

Greg, Alex, Steve and all others,

Thank you very much. I will take my speedo apart and clean it and let everyone know the results.

As for Alex and your comment, I agree with you about the heat, as it seems the grease should be like water - the heat index here in Atlanta today was 105 F!!!

Thank you,

Cheers,

Robert
Robert Browning

I know what you mean - it hit 100 degrees (37.8 C.)here just outside of Memphis again today, and the humidity was pretty high. Makes working on the midget not too much fun.

Still, the Speedo is a great kitchen-counter type of job. Best of luck - - Alec
Alec Darnall

I'm in New Orleans this week. Lets just say it isn't a dry heat.
Steve Simmons

Steve,

Be sure you go down to Jackson Square have some beignets for all of us. (Cafe DuMonde)

Cheers,

Robert
Robert Browning

Robert,
mine did much the same. I took the case off and jiggled the number wheels a bit and it came good. A bit of dust or grit I guess. That was about 20 thousand miles ago now..
Peter

Hello,

This afternoon I took my speedometer apart and did a brief examination. Everything seemed to turn freely and smoothly and the unit was clean over all. There were some small pieces of grit, which I brushed out with an old tooth brush.

The only real problem I could identify was that the white plastic paw which pushes the drive gear, which in turn causes the numbers to turn, seem to be dirty and stuck.

Therefore, I took the retaining clip off and removed the paw and gear and found it to be very dry and the grease on it was old and gummy.

So I cleaned and regreased everything and now it seems to work much better. When I hooked the speedometer up to a drill, the numbers seem to click over smoothly.

Hopefully this was the problem and it was an easy fix. The hardest part was trying to work under the dash to get the speedo off!

However, I now wonder if the mileage on my car is correct as the speedo mileage indicator may have been malfunctioning for a long time and I have known it. The tenth mile number indicator now has two stop positions as it turns where in the recent past it had only had one position as it turned and the number just popped into position.

Hopefully it is fixed now. I will let everyone know. From my other thread you can see that I am having some "running problems", so until I get that fixed I cannot test the speedo.

Keep your fingers crossed and say a big prayer!!.

Thanks for everyone’s help.

Robert
Robert Browning

Hello,

I just wanted to follow up.

As I said before, I took the speedo apart and found the paw stuck and gummed up from old grease.

Well, I finally got my car back together today and drove it for the first time and the speedo works so much better. In the past the numbers clicked over in two stages - very roughly. Now they move almost smoothly through the transition from one number to the next, so apparently I found the problem and repaired it.

Now for the surprise. I am not sure why, but in the past the speedo needle use to sort of bounce - plus or minus about 3 mph. Above 60 mph it use to bounce really bad and you could only get a guess at how fast you were going. Now, for some reason, the needle is very still and steady at all speeds.

Why, well, I can only assume it is all connected together with the paw and just being dirty.

Anyway, just wanted to follow up and thank everyone for their help.

Cheers,

Robert
Robert Browning

Robert - glad it's back operating, and just wanted to thank you for the follow-up. So many people take whatever advice is offered, and never say if it fixed the problem, or not. Hope it lasts another 30 years!

Best regards - - Alec
Alec Darnall

the bouncing speedo can also be the speedo cable catching on the sheeth - it might be when you disconnected / reconnected it's moved the inner cable slightly.
Stefan Carlton 1

Robert - I'm going to have to tackle a speedo cleaning and I was wondering what solvent/cleaner you might have used, and what to lubricate with. Mine if from a car that hasn't been on the road for over 20 years. The trip odo won't reset, indicating that the grease has gone solid, and there are paint dust and chips all over from the cheap white paint that was used inside the case. I have the pdf file on cleaning and repairing but I don't remember anything about cleaning solutions. Thanks.

Paul Briggs
Paul Briggs

A bouncing needle can be caused by 2 problems - a cable which needs to be lubricated or the dampening fluid and/or magnet (depending on what type of mechanism the manufacturer used) is no longer any good.

Don't lubricate the last 6" of the cable as it may back up into the speedo.
Mike MaGee

Paul,

If you read the .pdf file on repairing the speedo, one of the main things it keeps emphasizing is grease or rather the wrong type and how to much will do far more damage then good. If grease gets on the magnetic wheel it will cause the speedo to not work at all.

For cleaning the parts after I took the unit apart, I used a solvent that I have used for years called, Bestine. Years ago a clock maker recommended it to me. It is a solvent cleaner, but mainly is used as rubber cement thinner. The nice thing about this stuff is that it cleans and will not any leave any residue. It is fantastic for the final clean up of anything you want to ever paint. It is available in a good Art Supply store or a craft store. If there is a Michaels Art Supply store in your area they sell Bestine.

As far as a grease to use, I am not sure what to recommend. I happen to have a small container of a special light weight grease made by Conoco, that was designed for small gears in small clocks and motors. The .pdf file says to just use a light weight grease. Maybe someone else can add to this thread and tell us what they have used.

The project was very easy. The hard part was getting up the nerve to take it apart in the first place.

Good luck.

Robert
Robert Browning

For any of you wondering like Robert if your mileage is accurate dont bother. It is more than likely that it isn't. They are so easy to reset that I reset them when I finish a car so I know how many miles are on my stuff. The only way I would trust mileage is if you had maintainance records from day 1.
R J Brown

Hello,
I have rebuilt my speedo but I think my magnet is not good enough to drive the drag cup. So the speed I read is about 25 miles/hour lower than the real speed of my car. Can I do something to improve this magnet? Is it possible to change it?
Thanks for any help

Philippe
Philippe

Robert - There is a Michael's about 25 minutes from here, so first chance I get I will look for Bestine. Thanks for the info. Now to find a light body grease to use.

Paul Briggs
Paul Briggs

The best grease is available from your local model shop, ask for a tube of grease suitable for model locomotives, it is a very lightweight, plastic compatible grease.

I have a tube of Labelle 106 PTFE grease, what your local shop has may be different.
The Wiz

Wiz,

Sounds like an excellent suggestion. It looks like two places to go tomorrow. Thanks.

Paul Briggs
Paul Briggs

Well, I finally got around to going to town and found both the Bestine and the Labelle 106 grease. Now I have to actually get started. Stand back, I'm going in! I'll report back on the results.

Paul Briggs
Paul Briggs

An interim progress report. Just for reference, the speedo (from 1969) appears to be a "late model" as far as the pdf instructions classifies them. The speedo is disassembled as far as I need to for cleaning. CAUTION! The recommended cleaner, Bestine, softens the number paint! I didn't cause too much damage but I will have to do some fine scraping and cleaning to repair the damage.

The original? grease is very stiff, so regreasing will be very necessary. I still haven't figured out why the trip odometer won't reset, but I just got it apart.
That's it for now.

Paul Briggs
Paul Briggs

This thread was discussed between 20/08/2005 and 08/09/2005

MG MGB Technical index

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