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Speedometer wavers at high speed

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borjis

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On my 1971 MGB if I'm doing around 60mph the speedometer needle bounces back and forth at 5-10 mph increments.

less than 50mph and its nice and steady even at 10 mph.

I recently had the speedometer overhauled and tested as the odometer stopped working. The guys bench tested it right in front of me. It smoothly went from 0-80 mph with no bouncing around.

They said it was probably my speedo cable.
I don't think that it is because it did this on my first speedo cable, which I replaced with a brand new one from moss and it still does it.

could it be the drive from the transmission or angle drive out of the transmission causing this?

the angle drive on my speedometer is brand new.

while we're talking speedo's anyone know where to get that short cable for resetting the top odometer? Moss and VB don't appear to have them. Ebay has not turned up any either.

thanks!
 
It really could be the cable. I recently had to replace my speedo cable (I also got mine from Moss like you), and my speedo now bounces at all speeds below 50. One thing i haven't tried yet but am considering, is to remove the cable from the sleeve and apply some lithium grease to it. My particular bouncing speedo is in sync with a ticking sound coming from the 'service interval' counter mounted on my fire wall (i have a 1976).

It might be anything in the chain between the transmission and your speedo, but since you know the speedo is good that leaves from the connectors back.

As for the trip odometer reset cable, I would try Tony Barnhill ( link to his site is "The Autoist" banner ) on these forums. He is a good supplier of new and used parts. If it's not available new, he probably has it used.
 
Mine jumps as well and the cable actually jumps and thumps. It came from Moss and I am preaty sure it needs lubed.
 
According to MoMa (a gauge rebuilder) one culprit is that the speedo cables can be too long for the sleeve. I think that causes them to bind a bit. The cable end that fits into the speedo should only fit in about 1/4 inch.
 
hmmmmmm... food for thought that one...
 
Yes Rob what Shorn is saying can be a problem causing the speedo to jump around. My experience with this problem occurs at the other end where the cable connects to the angle drive. There should be a paper washer inside the female cap which acts as a seal as well as a distance piece keeping the cable end from bottoming in the angle drive socket. If that washer is not there you can fit a metal one. The center hole dimension is not critical, just so its clear of the cable . However, the OD of the washer should be close to the ID of the screw on cap so it does not foul the cable when installed. This effectively shortens the cable and may stop its binding.--Fwiw--Keoke
 
My '68 BGT has the same waving behavior. So how does one remove the cable for greasing? I disconnected it at the transmission and gently pulled on the core. It didn't come out, but I didn't pull hard because I didn't want to unwind it. Please don't say I have to disconnect at the speedo.
Thanks
 
yep you do mostly, chances that it would come otherwise are slim to none.
 
The most common cause is bad cable routing. Find an open road, large parking lot, or anywhere that is safe from other cars and distraction. (end disclaimer) While driving, reach under the dash and move the cable around. You may find a "sweet spot" where the gauge stabilizes. Once you find this spot, tie the cable solidly in place. It is also possible that the cable routing beyond the firewall may be the culprit. In this case you have to make adjustments, then drive and see the results.

Another cause is cable lubrication. Don't use oil because it may migrate into the gauge and cause the disc to slip. Try a graphite powder injected into the cable. If you must use oil, try first lubing from the bottom. If lubing from the topm let the oil drain down into the cable as much as you can before driving the car.

A third common cause is the gauge itself. If the disc becomes oily it will slip and grab, causing the needle bobbing you see. In this case, the gauge must be disassembled, cleaned and rebuilt. You can do it yourself, or pay a service to do it for you. Rebuilding usually costs around $100 and the gauge is returned to you in new condition.

Two rebuilders I recommend are Nissonger in New York and West Valley Auto Electrics in Reseda, CA.
 
Lubed my cable yesterday, solved problem. Came dry as a bone and I forget to check before instalation.
 
Jack,
So did you have to disconnect it at the speedo? I didn't look close, but it seems awfully tight in there. Did you hire some little pixie to reach up in there? Once unhooked, how did you snake the core out?

Sorry for all of the questions, I trying to get an idea if this is a 2 hour or 2 day job.
Thanks
 
On a Bugeye you can get to the back of the tac to remove the cable. Took a bit of time but was not a big problem at all.
 
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