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trouble shooting not working speedo or testing one

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ScottFromNH

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Hey Guys.

is there an easy way to test a speedometer? I have a 73 spitfire that since I bought it the speedometer wasnt working. It came with new cable and today I installed it but the speedometer still isnt working.

Any idea's on how to trouble shoot this or test if its the speedometer or the outlet on the tranny that it plugs into?
 
Just unscrew the cable from the back of the speedo head, pull it around so it sticks out under the dash, dive around the block, put your thumb on the end, see if it's turning. Easy.
 
well before I screwed it into the tranny it was by hand. since I put it in the tranny and in the speedometer I am not sure as I wasn't sure if running it not plugged into the speedometer would hurt anything?
 
I have a similar problem with my 75 TR6 - still not fully sorted, I shoudl add - now the speedo works intermittently...

To test the speedo itself, just unscrew the cable from the gearbox end, grip the inner cable with a drill and rotate anti-clockwise. Depending on the length of your arms, you may need an assitant to tell you if the gauge is reading or not. If this results in no movement at the gauge, try reattaching at the speedo end to get a bit more/less of the inner cable into the gauge. If it works, then your problem is at the gearbox end. This is a bit more exciting to test - I did it with the car on stands, but you could do it on a quiet road, I suppose. I unfastened the gauge end of the cable and ran the car in gear, so the back wheels turned merrily in the air (I had about 8 stands under the car at the time). if the cable can be seen to turn, then that shoudl be a good indicator. If both tests are positive (mine were), I think it is really a matter of the difference in length between the inner and outer cable, which isn't something you can easily fix, I am told.

If you want to try replacing the speedo drive bearing etc. at the gearbox let me know - I bought all the parts, tried them with no difference so replaced to originals. I now have a selection of lightly tested parts in their original BL boxes which I feel I cannot return (to TRF) because I used them.

Hope that makes sense and helps
Cheers
Alistair
 
Thanks for the advice guys I will try this in the morning to see what is going on.

I will post more tomorrow.

I have to say before I changed the old cable out my speedo would jump around when the car was just idling and when I changed the cable I found the inner cable was broken. The new cable seems to screw in much further then the old one into the tranny.

Bash, Was it hard to change the speedo drive bearing if that is the case? I hope its just a cable issue in to the tranny or into the speedo. I will also reset the cable into the speedo too make sure its in their correct. Its hard knowing if it is in all the way when you cant see up under the dash all the way.
 
Won't hurt the cable at all to run it without the speedo attached. That is definitely where I would start.

Something to watch for, though, is a speedo head that turns when cold but gets hot and binds. I've had that happen several times now, once it ruined the angle drive (several times), most recently it tore up the cable (on a TR without an angle drive).
 
TR3driver said:
Won't hurt the cable at all to run it without the speedo attached...
Click to expand...

Also, if you're wearing shorts while trying this be real sure you've got the end of that spinning cable under control. Yeow!
 
ScottFromNH said:
Bash, Was it hard to change the speedo drive bearing if that is the case?
Click to expand...

Not at all, actually. I imagined a serious problem, and put it off for a long time, but in the end it took all of 5 minutes to get it out and maybe 10 minutes to put it together again. I understand that sometimes things don't cooperate, though. As I recall, the bearing came out with two screwdrivers levering on opposite sides, and a firm push had the new one in place. As I mentioned, there realy wasn't a problem with my bearing or the drive gear. The gear has plastic teeth, and I figured that those teeth were likely to be shot, but I couldn't see (or measure, with my simple tools) any difference between the old one and the "fresh from the BL box" replacement. The real difficulty is getting the screw that holds the bearing in place back in, but with a bit of care lining things up before assembly I had no problem.

Cheers
Alistair
 
One problem I have seen is on cars or speedometers that sat for years,the grease inside can turn into a hard dry cement type substance. It can strip the gears if not cleaned and libricated before using again. If the speedo cable turns,the speedometer needs rebuilding or replacement. If you buy a used replacement,service it before using.
 
John_Malinick said:
One problem I have seen is on cars or speedometers that sat for years,the grease inside can turn into a hard dry cement type substance...
Click to expand...

That happenned to mine -- unfortunately I broke a second cable before I figured that out.

I used the guidance of this page to disassemble, clean & assemble the unit:

https://home.comcast.net/~rhodes/speedo.html

Fiddlely but not difficult. I my case it was the shaft of the odo gear, they have a depression that holds a dab of grease. As John noted, it had hardened and there was a bit of surface rust -- they move pretty slow so it doesn't take much to bind them up.
 
Ok update on the speedometer.

I unhooked the new cable from the tranny and hooked it to a drill and it seems to worked just fine. My drill got up to 70 mph, then the battery died.

I then hooked the cable back up to the tranny and unhooked it from the speedometer and had the car on stands and put it in to drive and nothing the cable didnt turn at all :frown: so I am thinking its the gear in the tranny.

So now I have to figure out how to change that. I see a bolt on top of the tranny housing right by where the speedometer gets screwed in and am thinking that holds that unit in?
 
another update.

I was thinking and tried something. I took the old piece of the speedo cable and plugged it back into the tranny and drove the car up the driveway (it is not ready for the road yet) and the old cable was spinning in my hand, not fast but was moving.

So I guess my question is could the cable not be long enough? Or could it be the end of the shaft on the tranny is messed up and not catching the cable? Or could it be the wrong cable but not sure as the length seems correct and the ends are the same.


very confused now
 
Any of the above. For example, the speedo cable on my Jag doesn't like the speedo head. I had to put a piece of shrink tubing on the end of the cable and it works now.
Could be a buggered up drive end on the trans, could be a mis-match of end and drive, could be too short (but you should be able to tell that by looking).
 
Thanks TOC, I am trying to figure out what one it is. I pulled the Speedo pinion and looked at the end it looked ok but seemed like the hole was bigger then the cable trying to go in to it. Also noticed that my tranny might not be a 73. My speedo pinion is held in with just a bolt plug stop at the top and from my repair book that is a 70 tranny?


ok this is a stupid question. If I have my drill plugged into the speedometer shouldn't the drill max out the speedo? I am trying to figure out if I have multiple issues I am dealing with and where do I start?
 
Whatever the ratios in the speedo head are for the given rear end and tyres, on US cars, 1,000RPM is 60MPH, so, if your drill motor is about 1,000RPM, maybe not pegged.
 
Usually for Triumphs through the early 70s, the speedo calibration is a bit higher than 1000 turns per mile. A quick Google turned up an old post by Andy Mace that said 1248 tpm, for a 4.11 rear axle.

Then as TOC said, it's a question of how fast your drill turns. ISTR top speed for my Ryobi 12v is only 1200 rpm in high range, so somewhere around 60 mph. But my corded Milwaukee only turns 800 rpm, so it would read closer to 45 mph.

There should be a 4 digit calibration number somewhere on the face of the speedo, without any letters before it or slashes after it. That number is the turns per mile, or how many rpm the cable should be turning for an indication of 60 mph.

Lots of things changed between 70 and 73, so mis-matched parts is a definite possibility. People also sometimes change just the inner cable, and IIRC the commonly sold 'universal' inner cable is slightly too small in diameter to fit a Triumph.
 
Thanks TR3Driver and TOC. Do you know where you can get an orginally speedometer cable if the universal inner cables are slightly too small? Or do you know of a trick I can use to make it fit better?
 
So, just to clarify, the new cable that came with the car is a "universal" cable? I could look, but I'd almost bet the Trumpet supply houses have the proper inner or assembly. If it was mine, and I wanted a baseline, I'd do the assembly (inner and outer, matched). Your outer housing is probably original, and almost 40 years old.
 
Hey TOC

That I am not 100% sure. I got the cable in a box of parts when I bought the car so I am not sure if its an OEM replacement or a uninversal their was no label on the cable.

The only thing I am not sure is the speedo pinion only bolts in with a retaining bolt and my repair manual says that its a 70 tranny. From reading the book it looks like the 73 should have a retaining clip bolt on if I am reading it correctly so I am not sure what cable should go with it? Or should I look at getting a new speedo pinion gear and also a new cable that matches that gear?
 
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