Speedometer trouble

kevstens · 06-04-2011, 07:00 AM

I have replaced the speedo impulse sender on my 87 carrera 3 times and it still does not work. I've checked the wiring for continuity and had the speedo overhauled. I checked the wiring diagram in my Bentley manual and it is different than my car. Could someone please post a copy of the factory wiring diagram? Also the Bentley does not show what wire's go th what terminals on the back of the gauge. I am just verifying I've got every thing correct. My car is a 1987 carrera cab. Thanks, Kevin

j911brick · 06-04-2011, 08:37 AM

Are you actually getting an impulse from the impulse sender?

schumicat · 06-04-2011, 09:15 AM

are you sure the sender is facing the correct way? it should be installed so the waxy/resin side faces out, and the plastic side faces in.

kevstens · 06-04-2011, 09:57 AM

How do you check if you are getting a signal? The sender is installed with the flat face facing to the rear. Is that correct? Kevin

kevstens · 06-04-2011, 12:10 PM

bump

Larry_Ratcliff · 06-04-2011, 12:48 PM

My friend with an SC had a similar issue... it ended up being that the speedo itself needed a rebuild... good luck with your problem.

schumicat · 06-04-2011, 01:25 PM

the hard plastic side faces the transmission. the waxy/resin side faces away from it.

Quote:

Originally Posted by kevstens

How do you check if you are getting a signal? The sender is installed with the flat face facing to the rear. Is that correct? Kevin

j911brick · 06-04-2011, 03:42 PM

Quote:

Originally Posted by kevstens

How do you check if you are getting a signal? The sender is installed with the flat face facing to the rear. Is that correct? Kevin

You have to have a way of spinning the transmission so the sensor can read the magnets on the diff ring. The magnets have a history of falling out.

kevstens · 06-04-2011, 06:52 PM

Schumicat, The sensor's I have received from our host are all hard plastic on the end inserted into the trans. one side is flat and the other is rounded. I have the flat side facing rearward. Kevin

kevstens · 06-04-2011, 07:10 PM

When driving the car at about 60mph the speedo jumps to about 20mph at about 65mph the speedo goes between 20 and 50, at about 70 the speedo goes to 70. If I back off even a little bit the speedo drops back to between 50 and 20 swinging back and forth. Please help. Thanks, Kevin

mark4ton · 06-04-2011, 08:49 PM

i have the same problem on my 87. ive read and rothsport has told me, check the magnets (in the hole where the sensor goes) they might need a cleaning, if theyre all there... and when you install the new sensor, put a little something on the outside ring of it to prevent dirt from getting in there.

schumicat · 06-05-2011, 11:59 AM

sorry, I realize now your car has a G50 which apparently uses a totally different sender than the cars that use a 915 transmission.

Kidasters · Kidasters's Garage

Maybe this will help - just got my speedo back from Hartmut at the guys at NHS.

My car is an 84, but I think the speedos are wired the same.

the + should be the red wire with a black stripe
next terminal is blank
the "A" terminal is the white wire with a red stripe
the "31b" terminal is a brown wire with red stripe
the "-" terminal is bown/red and 2 solid browns.

Good luck.

Ken

kevstens · 06-05-2011, 02:46 PM

Well I took the side cover off the trans and cleaned the magnets (they were all there). I took the car out, same problem. I will wait for the third sensor to get here and put it in. Hopefully the third time is the charm. If any one else has any ideas I sure would appreciate them. Kevin

kevstens · 06-09-2011, 09:52 PM

I found that the new speedo transducers are different from the originals. The dimensions are slightly smaller and the magnetic pickup does not work. The new transducers have a black "o"ring, The originals have a green "o"ring. I have tried three of the new type and none work. I borrowed an original one from a friend of mine and it worked perfectly. I also noticed that the new ones have a smaller diameter where it goes into the trans.

ededoad@hotmail · 06-20-2011, 08:21 AM

I just recently had a simular problem and just unpluged the cruise control computer to fix it.

88911coupe · 10:24 AM

Had a very similar problem and found out there is more that one version of the little wheel with magnets. In my case there are FOUR, not eight, magnets. One of the well know speedo repair guys insisted I'd had some fall out. I checked again and I have 4 evenly spaced magnets. However, I could still not get the new sensor to trigger my continuity tester...untill, by ACCIDENT, I had the sensor only partially inserted into the hole and the wheel spun and VOILA...the scope beeped. OK...I'm onto something here. Turns out on my car (cars with FOUR magnets?) the the wheel with the 4 little magnets is set a little closer to the tranny hole and if I insert the sensor in about halfway it worked perfectly. The only problem is there was not an easy way to secure it...I finally made a "spacer" with some old heater hose so the sensor only goes in partway and it's still sealed up. Not very elegant but it works perfectly now. I will say that on the highway the new sensor would sort of work, I'd see anywhere from 30 - 40 mph. In talking to the Pelican parts rep there does not seem to be a dual part # so I was stuck with having to make the one I had work. Not sure if this is your situation but in my case it was a real head scratcher since the very knowledgeable speedo guys were sure they all have 8 magnets.
As a side note, you can test the sensor with a continuity tester and a plain magnet, you're just trying to see if the sensor works.

Canada Kev · 08-05-2011, 05:00 PM

Ok, I don't know if this is from the same issues above, but on occasion, my speedo just stops. It starts back up again after a couple miles, except last weekend where I drove about ten miles before it continued to work. And that was only after I parked at a restaurant and had dinner for a couple hours. When I drove away, all was good again.

I don't expect I'm missing any magnets as that would cause a problem ALL the time, no? Could the sender cause this intermittent problem? Everything works fine 95+ percent of the time. Just once in a while it dies for a few blocks...

88911coupe · 08-06-2011, 04:21 PM

Sounds like maybe the wire is somehow coming partially lose. I did notice wear on my old wire connection when I removed it which I thought may have been the problem. Have you checked the sender to make sure it's working even if you move it around?