The Stovebolt Site Forums The Shop Area General Truck Talk Speedometer? it's not the cable.

Well, imagine my surprise when I replaced the cable - all by myself, and the speedometer still screams when I get to 35 and the needle goes to bouncing all over. Takes a while after stopping to get it quieted down again. Sounds like I better get into the speedometer itself, huh. Haven't gotten that far in this old ride yet, but I'm not scared - just have to figure out how to get the bezel and gauge assembly out of the dash. Seems to be resisting removal. Just pull harder?? Any thoughts???? Yes - I will get some pictures up, and soon --- Dale

To get the gauge panel out: First disconnect the battery - the amp gauge has a 12 Volt power feed and could easily short out.
Disconnect the speedometer cable. Remove the 3 screws on the bezel. Disconnect the oil gauge line at the engine -it is easier to pull it out part way out with the panel and then disconnect it from the gauge. The panel will pull out several inches so you can disconnect the wires & oil gauge. Mark the wires as you disconnect them so they don't get mixed up. The panel will now be free to dissassemble on the bench.
Fred

It is a hard pull, Dale. You have to do some wiggling of it, cocking it this way and that. Once I had all of the connections/screws disconnected, it moved only about 3/8" in any direction as if it was jig-locked. I had to put a rag on the steering column and get a good grip on the lower edges. I've had it out probably about 3 times now, and it never gets easier- always a hard pull.

On a positive note, it is easier going in than out.

Bill

what I did to get it out (after disconnecting everything) is, I fold my hands around the dash panel, with my fingers on the back of the gauge cluster, and push it out with my fingers. quite easy. but I have big hands and strong fingers.
my other comment on this: I have never been able to fix my speedo (2 attempts). I have the same symptoms. so what to do when it does like that?

The spedo has small internal gears and some of them are plastic. They are usually gummed up with 40 year old grease or dry and stuck. I have had success taking the spedo apart and cleaning and lubing it. Be extra carefull taking the needle off. If you break the shaft it's over.
Fred

I'm at a disadvantage, just reading symptoms on a computer screen.

Try drill-turning the cable (connected to the speedo) from the transmission end of things. Next try drill-turning the speedo on the bench. This will isolate if the problem is in the cluster or the cable. If in the cluster, then the only thing I could recommend is clean & lube the workings. Maybe a speedo shop can work some magic. Aside from that, sounds like replacement time. New speedos go for $125. I got an old working odometer at a swap meet for $15.

Not much, but all I've got. Good luck!
Bill

Since you have replaced the speedometer cable, the speedometer head is the most likely suspect, with the noise and needle wobbling you describe. The head can be repaired by a speedometer shop. They should be able to keep the odometer reading you have.

Harvester

Thanks Fred, Bill, and everybody - I think I have the path now and your know how has really helped a lot. I'm not sure if I'll tackle rebuilding the speedo or replace, but now I can get into it and see what might work. I have located a few replacements, both reproduction and used originals so I know they are out there in case I screw it up. I'd like to keep the odometer if I can. I am really pleased with the response from all of you and have picked up 10 times more info this way than the books I've bought recently and my own experimenting. I'll get back if I have trouble with it -I'll get back either way -- thanks again guys Dale

Dale, You might try putting a little grease on the end of the cable that inserts into the speedo--mine jumped like crazy until I did that (along with greasing the entire lenght of the cable) -- after a couple of miles, it settled down and works fine--- worth a try before you spend any money--
Good luck,
Glenn

Call AutoInstruments, and have the speedo restored. He's a friend of mine, but I'd recommend him anyway, and here's why:
I was talking to him one day while driving my '62 Suburban, and the speedo was doing the EXACT same thing as yours was.
He told me to pull over right now, and unscrew the speedo cable, otherwise the guts inside the speedo head would explode, then they were unrepairable.
Well I thought "Yeah, right...it's not THAT big of a deal" and kept driving it.
Later that week, sure enough, it got real loud, the needle started going everywhere, and then there was one last noise, and the needle settled right on down. To zero.
So I had to find another one in the junk yard and send that to him.
The new speedo is restored, works like a champ, the number are new, the odometer is new, it's calibrated, and I'm very, very happy.

AutoInstruments: (276) 647-5550
-Brad

Good call Glenn! - I was just ready to throw in the towel and yank everything out when I read your grease trick. I used some vaseline instead of heavy grease and -- the speedometer started to settle right down. Still wobbles a little at the low end but steadies right out above 10 and makes zero noise. So far. I'll keep my fingers crossed - have only drove a few miles and I'm still smilin'. Got lots of advice on this thread if it goes haywire again so I'm set, but for now ----. Thanks, Dale

See: http://auto.howstuffworks.com/speedometer1.htm for a more in-depth explanation of how a typical eddy-current speedometer works. Basically they have a small cup that looks like a jar lid that the needle attaches to. That cup is spring-loaded so that it wants to return to the zero position. Inside of that cup is a magnet that attaches to the speedo cable.

As the magnet spins, eddy currents created by magnetism cause the cup to want to spin with the spring restraining it. The faster the magnet spins, the further the cup travels and the higher the needle registers against the number legend (speed) on the dial face.

What I've seen happen is that the parts within the speedometer either wear until clearances increace to the point that the cup "wobbles" and makes contact with the magnet, or contaminates (rust, grease, etc) get in there and allow the cup and magnet to touch.

The other common thing is for the spring to lose tension or break entirely. Either way, it causes the needle to fly around or act erratically.

Fortunately there are speedo shops around that can fix 'em. Unfortunately it's spendy. I need to get it done on my '37 as we speak ;'{

Dale, Glad to hear that it worked-- BTW, great looking truck! If you ever come toward Missoula, let me know.
Glenn

I've got a different problem with the speedo in my 61 Apache. The cable was unhooked when I got it. I hooked it up. The odometer worked but not the speedo. Today the speedo went up - to 70. I was doing about 45. It's still sitting at 70. Anyone got any ideas, other then sending it out to be rebuilt?

Tap the glass?? Do not laugh, I had to do it on the firetruck a few times...

My '54 3100 4 speed acted the same way. I replaced my broken cable with just a cable kit that I purchased at NAPA. It was wavy above 45 mph and soon broke. I ordered a whole new cable assembly from LMC or Classic Parts and the speedo acted the same way. Someone suggested putting some vasoline in the speedo and some on the end of the cable. I just put some vasoline on my finger and worked it into the speedo and used a tooth pick to push it in a little further. Also I put some on the end of the cable and reattached. It works like brand new. I can't believe it, something fixed without taking anything apart. The needle is as steady as can be.