Bouncing Speedometer Needle
06-09-2021, 06:18 PM
#1
Racer
Thread Starter
Bouncing Speedometer Needle
The needle on my ‘86 911 speedo suddenly stopped working. The needle just bounces around with every little bump. The odometer has not worked for a number of years. Is this a speedo issue or something else like a cable or sensor?
06-10-2021, 12:15 PM
#3
Rennlist Member
86 would have an electric speedo. could be a wiring issue, a sensor issue or a speedo issue. without more info to go on all I can suggest is start trouble shooting each item in the system.
06-10-2021, 01:07 PM
#4
Burning Brakes
If it's like my '85 (I think it is), there is a sensor on the transaxle that generates an impulse on each rotation.
https://www.germanautosupply.com/GEN...911-606-209-01
PN 911 606 209 01
The signal wires from that sensor run up through the shift linkage tunnel to the speedo itself. The signal is used by both the speedometer (to move the needle) and the odometer (to turn a motor to turn the gears [which eventually fail] to move the odo number dials).
But I'd guess if that impulse generator went dead, your speedo (and odo) would just stay fixed rather than bouncing.
I see you say your odometer has been stuck for years (I'll keep that one between you and me, BTW
), but if it had been operational, it could serve as a good clue here. If it was still working, that should confirm the impulse generator is good. The much more common failure is for the odometer gear to fail, resulting in a speedometer that works and an odometer that does not move. So you probably had that common odo gear failure before the speedo needle failure. Very easy DIY repair if you can take the speedo apart and put it back together.
In my experience with other cars, a bouncing speedo needle indicates a mechanical failure inside the speedo itself. I bet if you call up a speedo repair shop (is Palo Alto Speedometer still going after all these years?), they can make a 100% accurate guess within seconds of a clear explanation.
And you probably now have two failures in that speedo.
https://www.germanautosupply.com/GEN...911-606-209-01
PN 911 606 209 01
The signal wires from that sensor run up through the shift linkage tunnel to the speedo itself. The signal is used by both the speedometer (to move the needle) and the odometer (to turn a motor to turn the gears [which eventually fail] to move the odo number dials).
But I'd guess if that impulse generator went dead, your speedo (and odo) would just stay fixed rather than bouncing.
I see you say your odometer has been stuck for years (I'll keep that one between you and me, BTW
), but if it had been operational, it could serve as a good clue here. If it was still working, that should confirm the impulse generator is good. The much more common failure is for the odometer gear to fail, resulting in a speedometer that works and an odometer that does not move. So you probably had that common odo gear failure before the speedo needle failure. Very easy DIY repair if you can take the speedo apart and put it back together.In my experience with other cars, a bouncing speedo needle indicates a mechanical failure inside the speedo itself. I bet if you call up a speedo repair shop (is Palo Alto Speedometer still going after all these years?), they can make a 100% accurate guess within seconds of a clear explanation.
And you probably now have two failures in that speedo.
Last edited by oldskewel; 06-10-2021 at 01:19 PM.
06-11-2021, 09:57 AM
#5
Racer
Thread Starter
Thanks for the info. It is in a racecar and I don’t use the speedo, but the bouncing needle is annoying. I guess I could take a nice picture of it and tape it in place or just leave the black duct tape over it.