Speedometer

[Nick Triesch]

Hi. I just went for a summer ride in my 85 911 and noticed that the speedometer is not working at all. I had some recent work done on the car so maybe it came un connected somehow. It’s connected fine on the inside but can some of you tell me where it connects underneath the car. I just changed the oil but did not see anything hanging down. Thanks, Nick.

[nospiners]

Driver side of the transmission , there is a switch held on by a small bracket with a 10 mm screw.
If you follow that harness, it gets to the connection inside the tunnel cover ,

[Nick Triesch]

If it’s the speedometer cable, is that expensive to have changed ? I can no longer do it because I’m sick.

[Nick Triesch]

I can pay , just want a figure.

[gorskined]

a the 85 911 doesn't use a cable its electronic .

[E Sully]

This is where the pickup is mounted on the transmission, and the connectors on the right of the picture plug in to the wires to the speedometer wiring in the tunnel.
There are magnets in the transmission that send pulses to the speedometer to show speed.

[Nick Triesch]

Hi. I just had my speedometer rebuilt at Black Forest in San Diego. Cleaned and works great.

[Cmac95]

OP - is it just the speedometer? Or is the odometer also not working?

This is what happened to me. The speedometer and odometer both stopped working, though it would occasionally flicker to life. If this is the case, then as alluded to earlier, it's almost certainly the speedometer sensor wire pictured in the earlier post.

Replacing isn't particularly complicated (see attachment) but I would not call it easy simply because getting the bolt out that holds the sensor in is a tricky angle & the wire routing is a bit tricky to recreate. Lots of grunting and groaning to get the wire back up and over the transaxle. There is no good way as far as I could tell to get the wiring back into the wire clamp that sits at the top of the transmission. I think that is a job that can only be done with the transaxle out.

My trick was to tie the new sensor to the old sensor and use the old one to pull the new one up and over the transaxle. The old wire will be clipped into one of the wire holders at the top so once you get the wire over and installed, i simply cut the old dead wire in half (after tripple checking i was cutting the correct one!) to pull it through. It's not particularly hard to get the new wire seated in all the other wire holders.

As is typical, if I did it again, it would have taken me an 1 hour instead of 3

And I havent quite figured out an elegant way to seat the little rubber thingy that makes the seal btwn the inside and the outside of the car. Task for another day once I've refilled my reservoir of curse words.

Good luck!

[spuggy]

Originally Posted by Cmac95

The speedometer and odometer both stopped working
...
If this is the case, then as alluded to earlier, it's almost certainly the speedometer sensor wire pictured in the earlier post.

Another possibility to be aware of is that a voltage regulator going bad can stuff 18V through everything for a while until you notice.

The original capacitors in the tach and speedo were rated for 15V; electrolytics have a finite life span anyway. Originals are getting way up there in age now - a significant over-voltage doesn't help them last longer.

After my alternator was replaced (because the VR was boiling the battery), noticed that my speedometer behaved a little oddly for the next couple of years (would vibrate slightly around the constant speed reading, drop down a few MPH and then tick back up and resume).

Until one day it just no longer worked at all...

A lot of rebuilders will replace the caps with ones rated for a higher voltage as a matter of course.