Speedometer, odometer issues

[clay1g]

The speedometer, odometer and trip meter have quit working in my '87 911. Does any one have an idea of what the cause is when all 3 go out?
Thanks.

[jimbauman]

One easy check is to pry the speedo out and make sure all the electrical wires are connected at the back.... they can wiggle their way loose.

JB

PS: Marietta eh? Go Oudin!!

[clay1g]

How exactly do I pry the speedometer out?

Yes, I'm rooting big time for Oudin!

[jimbauman]

It's just a press fit in the hole in the dash - held in place by a rubber gasket. Use your fingers to pry it out from the top and sides....

JB

[88911coupe]

My speedometer and odometer and trip all stopped. However I still have power to the lights for the gauge. I took it out to see if I could figure out why it suddenly jumped an additional 100k miles. I was able to put it back to 177k however after I got it all put back the odo and speedo both were not working. I've taken it out and fiddled around with it and everything looks fine. What can I check? Is there some way to check for power with a meter? There are 4 connections, 1 single red wire and then 3 double wire connections, all on spades. Can I test those somehow?
Thanks

[Mark Howard]

I had the exact problem a few years ago on my '88 911. I thought the speedo was bad so I sent it in to Pelican for a rebuild. Came back in beautiful condition, but still did not work! There is a much cheaper solution and had I done more diligence on this forum I probably could have saved myself $200.

Chances are, especially if it happened all at once and suddenly, that it is the Electronic Sending Unit on the transmission that is bad. The Unit sends an electric signal to your speedo to record speed, mileage, etc. Look under the electrical section in the gauges link for sending units. Find the Electronic Sending Unit for your year ($79 I think). Easy to replace.

I'm not an expert by any means, and did not stay at a Hoilday Inn Express last night, but this was my experience and resolution. Never had a problem again once i replaced the ESU.

[DRACO A5OG]

Gauge internal motor's Green Wire may be loose from/to the Control Panel.

1. Was the gauge ever cracked open to do some mods? If so, the green wires connected to the internal motor and control panel may have severed. These are very delicate wire solders. You will need to re-flow the solders to all loose wiring while you are in there.

A test, tap the back of the gauge and place back in the hole, I bet it will work temporarily, tapping on the glass will further separate the wire from the panel

Loose or Fouled Contacts at Terminal.

Clean and squeeze the contacts for a better continuity, Very rare these get that loose to fall off.

In Tunnel:

There is a connection in the tunnel next to the coupler, It has a see through housing you can see if the connection has slipped off or fouled. I used a small screw driver and pushed the connection together, yes one was loose from previous work down to trans. SPray some electrical cleaner in the housing for extra measure.

While you are in there, you can test the sensor at the tranny here. get a DVM and raise the rear end at the engine and in neutral spin the wheel while connected to the two wires, you should get a pulse, a test that the sensor is properly working.

At TRANNY aka ESU:

If above test fails you will need to replace the sensor at the tranny.

It may be possible the the wire was severed at the tranny connection, again very rare.

My 2 cents, and recent repair

Jim

P.S. if you crack open the speedo, make sure the needle is at the 1st tick mark or you will have the wrong speed calculation.

[88911coupe]

Mark and Jim, thanks very much for the help, I was wondering about that sending sensor on the tranny. I definitely have taken the thing apart a few times...maybe I broke a connection. I'll take a look.
Thanks again,

[DRACO A5OG]

Originally Posted by 88911coupe

Mark and Jim, thanks very much for the help, I was wondering about that sending sensor on the tranny. I definitely have taken the thing apart a few times...maybe I broke a connection. I'll take a look.
Thanks again,

Quite Welcome Brother,

I would still check at coupler to insure the ESU is the failing part, then the connections below before swap out.

[88911coupe]

OK...checking the see if I get a signal at the two wires in the tunnel but I don't seem to be getting anything but I may be doing it wrong. I hooked up a VM to the brown/ground wire and the power/green wire to the VM with the black lead hooked up to grnd and the red lead to the green wire. What setting should the vm be on? I put it on 12 and 4 then what I guess is the Ohm setting and when I kick/spin the wheel I'm not getting any signals. I turned the key to run position and same result....am I doing this right? I'm thinking the chance of the sensor going out at the same moment I'm fiddling around with the speedo seem really unlikely but I'd at least like to know I'm testing this thing correctly.
Thanks,

[DRACO A5OG]

Just to make sure, take a magnet across the DVM leads to insure it is operating properly. The response on the DVM will be similar to what you are looking for off of those to wires when wheel is turned.

I just forgot how I hooked it up to test it, it's been awhile.

Also reverse the connection just to make sure, I believe due to the fact our babies are "Negative Ground" system it may need to be in reverse order.

[88911coupe]

OK...I must be doing something wrong. I took a strong magnet and could not get the DVM to do anything on any setting...am I missing something?

[DRACO A5OG]

Try all settings on the DVM, you just need to get a pulse then test the wires to see if the ESU is transmitting a magnetic signal. ( I assume your DVM is working, correctly ?? )

Then check the connections at the ESU before you drop $$ into it.

[DRACO A5OG]

Just checked my DVM with a magnet, place on OHM's then hold the the leads about an inch apart with one hand then pass the magnet over the leads about 1/8" away, you should get a pulse in readings on voltage reading you will see it go from neg-0 up to .5 pulse readings.

[88911coupe]

Ok...my DVMs may not be sensitive enough or something...I can't get anything to happen. I'm going to focus on the internals since I'm pretty sure I probably jarred something loose when I took it out to work on the mileage. It seems more likely that that's what I messed up, as opposed to the sensor failing at the same time I'm removing the guage.
Thanks for the help!

[DRACO A5OG]

OH OK, check the green wires, if loose they need to be re-flowed. If you have a small holder to work on small gadgets like jewelry or device, it will help. I just asked my wife to help me, the extra pair of little hands really helped when I am holding the solder iron and solder. She also can not complain I am not paying attention to her ;-)

[kanadary]

i just had the same issue on the way home the other night. assuming the wiring is all tight and it does turn out to be the Electronic Sending Unit at the transmission, have any other than the one person i saw on another thread have any issues with the unit sold by our host? just wondering before i get one. thanks Ken.

[dshepp806]

no ohms setting...aren't you looking at "signal"? (i.e., "voltage)???????

[kanadary]

so the speedo suddenly started working for about 10 miles. then quit again. i think that should point to a wiring connection, what do you all think?

[brianlay]

It's most likely a bad connection, if it started working again after you were in there poking around.

You can test the sensor with an ohmmeter,or any sort of continuity tester.

You're actually checking to see that a magnetic reed switch closes when the magnets embedded in the differential gear pass by it. (some wiring diagrams mistakenly show this switch as a magnetic pickup, which it isn't)

The method I've used to test it is to attach an ohmmeter(the beep function is perfect for this) across the sensor leads (polarity doesn't matter), lift one rear wheel off the ground and rotate the wheel. You should get 8 closures per wheel revolution.