General TR Speedometer Woes

[RJS]

OK, had my speedometer rebuilt 10 years and 8,000 miles ago. Just recently, it stopped working. I replaced the cable yesterday and no luck. So, this afternoon I pulled the gauge out of the dash to inspect further. The input drive for the speedometer has a light coating of black looking grease which I expect is rather thick. Here's what happens when I spin it with a screw driver in the back:

• Going CW it spins freely until about the 25th or 28th rotation and then I get some stiff rotations which I can gently turn past until it gets free again. Repeats every 25 to 28 rotations. Needle does not respond at all
• Going CCW it spins freely until about the 25th or 28th rotation and then it gets very stiff to the point I am afraid to try and push through it. Needle does respond as expected and I am 99% sure CCW is the correct direction of rotation.

Any ideas on what may be going on? Is it a mechanical failure which can only be repaired by opening it up? Is it gunked-up from oil traveling up the speedo cable? If so, will a drop of carb cleaner in the input drive loosen it or would that be a fatal mistake. Any other ideas?

If repair requires cracking the unit open, I will most likely send it off as I tend to be ham-fisted with delicate, sensitive components like this. Just hope they would charge me to clean it, not completely rebuild it.

Thanks

Bob

 

[Geo Hahn]

CCW (as viewed from behind) is correct -- though it takes a quick spin to get the needle to move.

The binding you describe sounds like it may be one of the odometer gears, those can bind up and they turn rather slowly when in use. This, however, would not in itself account for the needle not moving as you drove -- that is a different binding, possibly the drag cup.

You do not want to spray any solvent in there -- things inside are delicate and if corroded, dirty or greasy will need careful cleaning.

I have taken mine to bits and got it back together again -- I'm no watchmaker but it does take some care, organization and a basic understanding of the way it works -- based on your description of your concerns you might be better off farming it out.

 

[dklawson]

+1 for George's comments that the problem is likely to be the worm and pinion drive gears for the odometer. The needle not moving could still be associated with the pinion gears sticking. However, once the gauge is stuck "that bad" you may find the end of the cable (top or bottom) may be rounded off from spinning inside the square hole of the drive gear or speedometer.

You do have to open the case to access these. I know you don't want to do that but you could. Once the movement is out of the case, a few strategically placed (not sprayed) drops of WD-40 on the pinion gears and where their shafts pass through the metal frame would be all I would try. After the WD-40 has soaked in for a while, try the screwdriver test again, turning slowly CCW and looking for any damaged pinion teeth. If you don't find any damaged teeth, the oil and some gentle persuasion with the screwdriver should get the parts moving freely again. Once you find you get things moving, supplement the WD-40 with a single drop of 30W oil (red bottle 3-in-1 oil) to the pinion gear shafts. Then reassemble the gauge.

There was a very good thread running earlier this month on speedometer rebuilding (link below). The thread discusses complete rebuild and calibration so it is beyond what you are looking at but it is a very good reference should you decide to open the gauge yourself. Also google for the 27 page PDF by Anthony Rhodes about Repairing Jaeger & Smiths Speedometers.
https://www.britishcarforum.com/bcf/showthread.php?94885-Instrument-Faces

 

[TR3driver]

I'll third most of the above. Since the first level gear drive for the odometer and trip meter turns all the time, the intermittent drag makes me suspect that the problem is after the ratchet and pawl mechanism, perhaps with the dials themselves. In my case, the speedo was still working, but wavered by 20-30 mph making it more or less useless. Anyway, I doubt that a few drops of oil is enough to help. Time for another rebuild.

 

[RJS]

Wow, thanks for the link to CJD's instrument faces. CJD, really impressive. The level of detail, precision and patience makes me think of watch making!

At this point I am pretty certain I'll package my speedo up and send it off - I am not so much ham-fisted as I stated above but, really challenged on time and patience. Quick question, what is the chance I can open the speedo, clean, relube and reassemble all in one evening or two? Or, once I open it up and remove the needle and face am I committed to re-calibrating? I think it is the time and precision to re-calibrate that makes me most worrisome.

Cheers

Bob

 

[CJD]

Hey Bob,

Cleaning and reassembly can be done in a long eveining, so long as nothing is broken. The calibration should end up the same as it was before you took it apart. The needle will need to be marked in relation to the aluminum disc, so it can be put back on exactly where it came off. You only need to re-calibrate if it was off considerably before it stopped working.

The only thing that could trip you up is if one of the plastic odometer gears has stripped. You do not have to remove the needle and face to inspect these gears...but you will have to remove the front glass and lift the mechanism out of the case to look at it.

From the description...it sounds like the "1" mile digit wheel on either the trip or mileage odometer is sticking. The "1/10th" wheel makes one complete turn for the tenths, but then jams when it trys to turn the 1's. So possibly something in the reeds, or most likely just gummy grease.

 

[RJS]

John

Much appreciated your valued input. I was able to finally turn completely through going CCW. So, I am encouraged it is not a broken odometer gear - just gummed up.

If you don't mind my asking, I didn't quite understand your reference to "aluminum disk". Also, from your note, once I remove the bezel and glass, is it possible to remove the unit from the case, clean and replace the unit all without removing the needle and gauge face?

Cheers

Bob

 

[dklawson]

As John said, you won't have to pull the needle off the spindle unless you find the odometer has to be disassembled. If you just want to focus on freeing and lubing the odometer pinion gear assemblies, that can be done with most of the gauge intact but the movement removed from the case.

The comment above about the aluminum cup will make more sense once you take the movement out of the case and look at the pieces. The aluminum (drag) cup is on the same spindle the needle is on. I cannot speak for John but I typically turn the needle up by hand until it is pointing at 60 MPH, then use a Sharpie to make an alignment mark between the movement frame and the aluminum cup. Using the alignment mark you will be able to position the needle back in almost the same spot it was removed so the calibration will be largely unchanged if all you are doing is cleaning.

 

[TexasKnucklehead]

Also important to note is Johns write-up is for a TR3 meter. The TR4 is very close, but you find some differences if you take it completely apart. The two screws that hold the magnet into the base were rivets in my TR4 unit. That makes it more difficult to get new grease where it's probably needed most. A spray can of WD-40 can clean out lots of dried grease, but can also leave a mess to clean up -and you can not leave anything (not even puddles of WD40) between the disc (drag cup) and magnet or base. And you probably don't want dried WD40/Grease residue on the odometer numbers. You will need tweezers and very small screwdrivers to get it apart and back together, not to mention patience.

 

[TR3driver]

You will need tweezers and very small screwdrivers to get it apart and back together, not to mention patience.

Another tool that I find indispensable is small surgical forceps. They really tame those little springs that hold the pawl to the ratchet for the odometer and tripmeter.

Be warned though, that hairspring is delicate, and any damage to it will alter the calibration. My calibration was way off anyway (not sure why), so I wound up adjusting the magnet strength as well as the position of the needle on the shaft. Fun project, but not for everyone.

 

[Geo Hahn]

...Fun project, but not for everyone.

Good summation.

I did not see a link to the Rhodes site so here it is: https://home.comcast.net/~rhodes/PDF/speedo.pdf

The shaft of the odo gear has a cavity inside it to hole grease (well, at least I put grease in it) -- I mention it because that shaft had a touch of corrosion and bound up on mine. Yours isn't as bad as mine was as mine broke the cable (twice).

Do not use anything like a solvent (incl WD40) around the number wheels if they are the kind that have embossed painted numbers -- the paint used on those will wash out quite easily (though they can be repainted).

If you do have to remove the needle it usually comes off by a gentle twisting motion at the center while the drag cup is held immovable -- as noted, index someway where you can return the to original setting. Once the needle is off then just 2 tiny screws hold the face on. You'll need a jeweler's screwdriver for those (and the odo reset shaft).

 

[RJS]

Hey All,

Tonight after work I was able to remove the chrome bezel, remove the glass, remove the trip reset shaft, remove the two screws on the rear and pull the unit from the case. All good. I had good light, a magnifying glass and dental picks. I inspected the operation while I turned it. No problems observed other than the same binding. The binding occurred at the same point on the odo drive gears every time they turned through 360 degree. I cleaned the little bit of black gunk off the odo drive gears and inspected very close. Hard to tell 100% for sure but, I am quite certain they did not look damaged.

I studied the mechanism for more than an hour. But, at this point, I will be boxing and mailing it to one of the "known" gauge rebuilders. But, I do not feel defeated. At the very least, I took a stab at it and satisfied myself it wasn't something I could easily fix myself at no cost. Going further was beyond what I willing to do and probably ran the risk of me dong more harm than good. Time for the experts.


Thanks again for all your tips

Bob

 

[dklawson]

Understood Bob. As Randall said, gauge work can be fun but it is definitely not for everyone.

 

[Geo Hahn]

Yep - knowing when to stop is a skill too.

 

[CJD]

That's actually really great news! It sounds like you caught it before it damaged itself. They'll clean it up and calibrate it as good as new. There used to be 3 speedo repair shops here in Fort Worth. I know I'm getting old when they are all gone now. Everything has gone to Chinese electronic that you can't rebuild like our good old gages.

 

[DNK]

Yep - knowing when to stop is a skill too.

One that can't get beat into for some people.
ME

 

[Jesus]

Hello,


I am trying to remove the speedometer mechanism from the casing. I’ve done it several times with other units, and had always to force or bend the odometer reset shaft that protrudes from the casing, even when pushing it home.



Perhaps, it is easier to remove first the needle and the face, but then I would not be able to mark some reference for assembling later the needle in the same position.



Is it any trick to remove the mechanism and face?



Thanks.


Jesús

 

[RJS]

Not sure if models vary but, on mine the trip reset shaft has a tiny set screw which, once you remove it, allows the shaft to come off. Otherwise, I would never be able to remove the mechanism from the case. I had to use a micro screw driver to remove it. The threads on the set screw were so fine I could barely see them with the naked eye

Bob

 

[TR3driver]

I think they do vary, some of them seem to have a tiny cotter pin instead of the setscrew. Maybe the difference is when they went to the flexible shaft?

Anyway, once the extension is off, I use a small screwdriver to push the reset shaft into the case, letting the mechanism turn slightly so the shaft goes over the side of the hole instead of the front. Obviously, you have to have the mechanism loose from the case at that point. You also have to tilt the mechanism slightly forward, on the side away from the shaft/hole.

 

[Jesus]

Thanks for the comments.


The extension is of course removed, but the shaft sticks out of the hole by about ½ inch and I am not able to push it fully into the casing. The mechanism cannot be tilted, even after freeing the face (but leaving the needle in its place).

Jesús