• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

79 B speedo malfunction

Share this page

B

BobS76

Senior Member
Offline
My speedo died. Found the drive shaft through the angle drive had sheared. Replaced the angle drive, cable, and gauge. The plastic drive gear inside the transmission (pinion gear?) appeared to be OK so I did not replaced it. On the test drive I noticed that the gauge needle would bounce above the actual speed, more so as the speed increased - at 40 to 60 MPH, maybe 5 to 10 MPH above actual speed. Any ideas?

Bob
 
Make sure that the mechanism in the speedo itself isn't binding. It should move without any noticeable drag or binding at all. Stick a small screwdriver into the back, where the cable fits, and turn it to see if there is any drag. Also make sure that the cable is well lubricated and there are no unnecessarily tight bends.

In my experience, sometimes they just do this, and it's nearly impossible to fix completely. It might be that a lot of the new cables are unnecessarily stiff or something like that. I had the problem in my Bugeye Sprite and I was able to ameliorate it but never fix it completely.
 
Cable "whip" is a usual cause, one thing to try is pull the cable from the sheath (at the speedo head end) and lube it as you feed it back in with a light coating of grease.
 
Thanks to both Sarastro and DrEntropy. Turns our the speedo binds up onec every 20 turns. Old speedo shows 20 teth on the odo drive gear. With the spring loading in the cable, the speedo takes a great leep forward every so often.

Bob
 
I had a similar problem with my 56 TR3 speedo, except both the trip meter and odometer were binding enough to wind up the cable.
Not sure if your 79 speedo would work the same, but on mine the shaft that runs through the dials has a brass washer between each pair of dials that turns with the shaft. The friction surface of the dials was actually rusty, which was causing a lot of extra friction. Cleaning and (lightly) oiling wasn't enough, I wound up polishing the surfaces by smearing them with toothpaste and running the shaft in a drill motor while holding the dials with my fingers. Put it all back together and now the needle just barely wavers, just 1 or 2 mph. I neglected to document the process well, but you can see the cruddy surfaces:
DSCF0016.jpg
 
Back
Top