G50 Speedometer Sensor Problem
 

My speedometer ('87) was dead below 30 mph and then would spring to life and work properly. The odometer has always worked right.

I found this and replaced the $70 sensor:

http://forums.pelicanparts.com/uploads15/G50impulse1248984991.jpg

I still had problems. The speedometer would come to life at lower speed, but then would operate erratically with no real relation to actual speed.

I figure the problem must be within the speedometer so I sent it off to North Hollywood Speedometer, along with $147.

I reinstalled it and now the needle bounces below 20 and registers erratically above that, generally settling around 40 mph regardless of speed.

What do I look at next? Dirty or missing magnets possibly? How many magnets do the G50's use? I know that earlier transmissions use eight. Any tricks to getting them clean without disassembly?


Thank you.

UPDATE:

I was going to try swapping back to the original sender and try it with the refurb'd speedo. I had originally swapped it from underneath with the car on ramps. This time, I put it on jack stands and removed the driver's side rear wheel. Much better. I was able to remove the sender through the wheel well. After removing the bolt, I pulled it out and tried cleaning the magnets (eight). I used a small piece of dowel and a rag. I poked the rag through the sender hole and turned the brake rotor by hand. I decided to pop that sender back in and test it out.

I was a little surprised and very happy to find that the speedometer now worked much better. It was a still few MPH off from the GPS, but I expected that and, overall, I'm satisfied.

Next time, I'll clean the magnets first and maybe I can save two hundred bucks.

thanks for this informative post, I wasn't aware of the magnets and their location, or their need for occasional cleaning.

I thought the magnets were on the inside of the tranny mounted to a spacer plate,..and the transducer was activated by the magnets ??? FM

I just got my Speedo back on the same car. The speed shown was slightly erratic and it wasn´t counting the miles. Its fine now but for what its worth my mechanic said the Tacho are like a good watch and the people who rejuvinate them need to know their stuff. Get down to Porsche and they should be able to pop a functioning replacement in quickly to see if it works. That way you can establish if the actual speedo is the problem or not. It only takes a second and should cost nothing. Mine had worn cogs that needed replacing.

When I got my car (also uses a g50) I was following a buddy
home. I kept wondering why in the hell he was in such a hurry
to get home. My speedo was reading 90mph, on a beer/food
break I asked what the deal was. He said he had his cruise
set at 75. At 70mph my car would be very near 90, my ony
guess was that it was for a different model and the gear was
incorrect for the G50?

I have the same problem--jumpy below ~30-40 mph and then solid as a rock above. My speedo's pretty accurate (within 5 mph) once it settles down. I bought the sensor last year but haven't yet installed it.

How difficult was it? It just bolts onto the outside of the transmission? If it penetrates the transmission case, any concerns about fluid leakage when replacing it?

Sorry for the dumb questions.

Thanks,
David
SmileWavy

David,

The only difficult part was snaking the wire up and over the transmission.

When I disconnected the old sensor behind the front seats, I tied a string to the end and pulled it up and over the transmission housing. Then I pulled the new sensor wire back over with the string. Just pull gently and help it along with your hands, as there are a lot of places where it can get snagged.

Use jack stands, not ramps, and remove the driver's side rear wheel (G50 cars). You'll be able to see where the sensor goes into the transmission from the side of the car.

Actually, I had a hard time pressing the rubber grommet back into the hole in the floor pan as well, but eventually it went in.

<a href="http://s175.photobucket.com/albums/w146/Woodyhfd/Porsche%20Harness/?action=view&current=PorscheHarness001.jpg" target="_blank"><img src="http://i175.photobucket.com/albums/w146/Woodyhfd/Porsche%20Harness/PorscheHarness001.jpg" border="0" alt="Photobucket"></a>

<a href="http://s175.photobucket.com/albums/w146/Woodyhfd/Porsche%20Harness/?action=view&current=PorscheHarness003.jpg" target="_blank"><img src="http://i175.photobucket.com/albums/w146/Woodyhfd/Porsche%20Harness/PorscheHarness003.jpg" border="0" alt="Photobucket"></a>

The second photo shows the hole with the sensor removed. The sensor wire DOES NOT go through the plastic clip as shown. I just put it through there to keep it out of the way when I cleaned the magnets.

When you install the new sensor, put a little oil on the o-ring, make sure the area around the hole is clean and make sure the sensor goes in straight. I used a new spring clip ($6) and I put some Loctite on the bolt. It's a small bolt so don't over tighten it. The the wire goes up and over the top of the transmission and back through the floor pan into the back seat area.

For what its worth when my Speedo went it was only a tooth on the Cog. They are actually soft and you could break them off with a finger nail. I still have the culprit part here.

[IMG][img=http://img522.imageshack.us/img522/1137/09102009169.th.jpg][/IMG]

When you cleaned the magnets what came off? Any ferrous metal?

It was just a greasy, dirty smear.

Worked great!
 

Thanks again for posting this information--I replaced my sensor today. Some other things to keep in mind: the speedometer sensor wire likely will be held down by ~3 clips if it hasn't been replaced (2 of these clips are on top of the transmission); you don't really need to use a string on the old sensor wire to pull the new one along; jack the rear up and put it on stands.

DavidSmileWavy

Thanks for the tip, I checked mine out w/ a DVM and got 5 sometimes 6 readings, cleaned the sensor and magnets with some cue=tips. Rechecked and I got 8 readings.
Thanks again for the post,

Do you have an open differential and have both rear wheels jacked up? Non-ferrous dirt on the magnets should not make any difference.

I was thinking, but don't know, the magnets on the ring gear should go around half as fast as the wheel if the other wheel is stationary.

Just the drivers side up, you can see the very top of the magnets as you turn the wheel... 8 per one full revolution. 189k on the clock so I'm sure the material was somewhat ferrous.

+2 on Jeff's post and procedure.

Based on Jeff's post above and followup emails, I followed what he did and it cured the problem. Like Jeff I cleaned the magnet area with a dowel rod wrapped in a paint thinner soaked Handy Wipe and the problem of an intermittent disappeared!

My symptoms seemed heat related. The speedometer operated normally for 10 to 15 minutes, then would start dropping to zero for 12 to 15 minutes, and then it would resume normal operation until stopped and cooled down. It repeated this cycle over the last 4 to 6 months with no exceptions!

I was surprised this cured the problem but it did and for now I'm a happy camper. If it occurs again I will replace the transmitter. Note: The transmitter on the 87 Carrera is on the drivers side, unlike earlier models. This change may occurred with the intro of the G-50 transmission.

THANKS JEFF!!!

Roger

I'm having a similar prob. Called a guy in Austin who really seems to know Porsche speedos and in my case I think I screwed up a diode (b31?) when I was taking the speedo in and out and accidentally may have gotten the wrongs wires to touch of the mess of speedo wires in the dash hole. More of an FYI to others to be very careful when pulling all those wires off. I'm going to send it off to be checked/fixed. I was never able to "test" my sensor (or it's dead) since I could not get any response doing the tests mentioned in another thread.. I'm pretty sure my sensor is okay since it seems unlikely that it would fail at the same moment I'm fiddling around with the wires behind the dash but the speedo guy says he'll test it first to see if it's working properly.

Can someone shed a little light on exactly what the magnets look like? I can rotate the wheel one revolution and only see what appear to be 4, not eight, dark spots? on the wheel like device just inside the sensor hole. Behind that when I spin the wheel are some large bolt heads or something. I tried to clean off the 4 things I could see, whatever they were, and got some dark gray dirt/grime off but this had no effect on the speedo. It was tested as fine by Overseas Speedo and I've put a new sensor from our host. The one thing that seems a bit odd is that the new sensor does not fit snugly in the hole, at first I thought it was missing the oring but it's on there...just not real tight. I tested the sensor with a VM and it seems to be working fine when I got a magnet near it.

Here's what the sensor ring looks like when it's installed on the differential

http://forums.pelicanparts.com/uploa...1302024400.jpg

Thanks! When I look inside the hole for the sensor I see what looks similar to the outer edge of what's in your pic but when I rotate the wheel I only see 4 little spots that look like those magnets. Are there different versions of the sensor wheel possibly? I cleaned what I could see and didn't see much change that I could tell, very frustrating!

There are two versions of the magnet carrier disc. One is for the G50.00, G50.01, G50.02 with open diff and the other version is for the same three plus the G50.50 ('89 930) with LSD. Regardless of type, the carrier disc is the same layout in terms of magnet count and location on the disc.

The one pictured is a LSD. I have seen a non-LSD carrier disc from my own '87 and my recollection from memory is they are nearly identical looking

88911coupe,

Check out this thread. I had a similar situation with the 4 magnets and undersized (loose fitting) sender cable. My comments start about halfway down the thread. I can't explain it but I have had no problems since I changed cables.

http://forums.pelicanparts.com/porsche-911-technical-forum/442139-speedometer-casis-cruise-problem.html

Cashman, thx this may be my solution. What was the part # from the dealer? I noticed the new one is slightly different than the old one and it does not fit snugly in the tranny hole.

#911-606-910-01 is the part number and it has been installed for 1 1/2 years and has worked ever since. I will be curious to know if it solves your problem as well. Like I said, I can't explain why the other (2) cables didn't work but this one did. Maybe third times a charm! Good luck.

OK...figurered it out with Cashman's most excellent help. If I put the "new" sensor in about halfway into the hole and rotate the wheel I get 4, yes 4 distinct beeps on the VM set to continuity...not eight. This might explain (I think) a couple of things.
1. This "version" sensor, as designed, does not work well with the 4 magnet wheel...it's too far away. Maybe version is wrong word...
4. Why I just get a weak (approx) 40 mph reading when I'm actually going 75-80.
The obvious question is how the heck do I get one that works with my wheel.
Thanks, at least I know what the problem is.
BTW, that's the part # I ordered from Pelican. I guess I'll try to exchange it.

Wrap up for the benefit of anyone else who may have to go through this complete PITA. After a lengthy talk with the parts guy at Autoscope here in Dallas we determined there is only one valid part # for this that is for the G50, however, I DO have a 4 magnet set up in my tranny, as did Cashman I think. I was told by one of the highly respected speedo guys (honestly trying to be helpful) that all are 8 magnets and if I am missing any magnets they fell off or something. In fact, there appear to be some with FOUR magnets. Note that this is not really an issue since my speedo is apparently set up to work with 4 magnets. The bigger problem others may run into is that the newer version of the sensor won't pick up the magnet "signal" UNLESS the sensor is only inserted about halfway into the tranny. Cashman returned one or two and maybe got lucky when he picked one up from a Porche dealer and, thankfully, his worked. I have no idea if it would only take me 2 or 3 tries to get one that worked so I fabricated a way to keep the sensor from inserting all the way into the hole with a piece of heater tube. Now it's registering the magnets fine but it's in now way a perfect solution...very kluge but I don't have any choice.
Just wanted to offer this suggestion in the event some other Pelican gets stuck in this situation. No way this should have dragged on for three weeks!

Thanks for the update. That gives me a little more confidence in my conclusion that I only had 4 magnets? For what it's worth the third cable I got from the dealer (with the same part) was definitely different from the previous (2). It was the same size diameter as the original (not smaller and loose fitting as we both indicated) and I believe the o-ring color matched the original (Green I think) where the previous replacement cables both were black. They may have had the same part number but they came from different factories/sources. Thanks again for the udate.

In my talks with the guy at autoscope he could not tell for sure if there was more than one manufacturer but I know there has to be. I just dont know a way to specify so I'll have to make due with my homemade solution

For future reference, if someone wanted to replace the speedo magnet ring? It's really not hard at all to remove the differential.

-Disconnect CV joints at transaxle drive flanges
-Remove drive flanges via center screw
-Remove transaxle side cover (takes a bit of fiddling to get the o-ring to release the cover from the final drive housing)
-Differential can now be lifted out of the housing.

Speedo ring is held on with just some simple spring clips. Swap in your new speedo ring and diff installation is the reverse of removal, as they say in the service manuals.

Help needed.
 

One morning, my speedo didn't register at all. After in town driving for 10-15 minutes I got out on the interstate doing 70-75 mph (used tach) for about 15 minutes and it suddenly popped up to the correct speed reading and worked fine: rock steady at all speeds even when I came to a stop. When I came out 2 hours later it still worked fine. :confused:
-I didn't drive it for a week and the same thing happened. Didn't work, highway, worked the rest of the day (even after stopping for a few hours).
-About 3 days later I cleaned the magnets and the sensor as suggested in another thread. After cleaning, I drove it and I had the same problem: pop up and work perfectly after 15 minutes on the interstate.
-Two days after that I got in it and it worked fine from the get-go.
-Two more days later: no reading. :mad: I drove it 35-55 MPH for 35 minutes. No joy. Parked it for 2 hours and then took it onto the interstate. 15 minutes later it pops up and works fine! I'm seeing a pattern so after getting it to work, I park it and immediately jack it up and put a meter on the wires in the tunnel. Continuity goes from 1 to almost 0 eight times per revolution. The sensor seems to be working fine.

What do I try next? I really don't want to buy a sensor if I don't need one (especially when some folks have had problems with the replacements and they had to buy 2-3 to get one to work).

Monday morning bump. Any ideas?

I think what was wrong with my original was that the sensor wire was broken somewhere and made sporadic connections.

"I'm seeing a pattern so after getting it to work, I park it and immediately jack it up and put a meter on the wires in the tunnel. Continuity goes from 1 to almost 0 eight times per revolution. The sensor seems to be working fine."


It should read accurately if you tested it while it was working as mentioned above. Try testing after it sat a day or two. My guess is you will receive no readings. That was my experience. Once the car warmed up a couple miles, it would work.
Mark

Cashman: I was planning to do that. Here's what I found:
After sitting 24 hours I tested it Monday afternoon. Readings were perfect.
Early Tuesday Morning: Continuity read a constant 0.05 without changing (the wheel was a little harder to turn but I guess that is just cold trans fluid).

Can it be anything other than a stuck sensor?

http://forums.pelicanparts.com/uploa...1318946320.jpg

http://forums.pelicanparts.com/uploa...1318946730.jpg

^ Another option for those who want to upgrade to modern times... a speedo that is hassle free with a lifetime warranty. As shown above installed on one of my Type 2's.

GPS speedo custom made to my specs by SpeedHut.

Takes less than 1 hour to install if that and is super light. It keeps your maximum speed, your real time direction (North, South, etc), your 0-60 mph time, your 1/4 mile time (exapmple; come to a complete stop, set the button to 1/4 mile, as soon as your car moves the timer starts....it gives you your time at the end of your run).

$315 shipped.

This speedo has NOTHING to do with the transmission. It's all done by SATELLITE.

You can choose from a variety of colors, sizes, number styles, kmh or mph, lighting ect. All info on their website.

GPS Speedometers Gauge, Revolution Gauges Series by SpeedHut

They have excellent customer service.

.

Thanks AA but I'm sticking with the stock look.

If it reads a constant number while turning the contact is either permanently opened or permanently closed. I believe that is your problem. Once warmed up it will operate correctly. Here is a picture of my sensor. I had to cut it open to see what I could figure out. The switch is within the glass bubble. I believe it is a mechanical connection. Once it is magnetized the switch closes and that is what provides the continuity. Off magnet, switch is open. The switch is so small I cannot see it actuate if this is in- deed how it works. Someone smarter than I am will have to elaborate if this is not how it works. Your symptoms are exactly as mine and I have not had a problem since I installed the new cable.



http://forums.pelicanparts.com/uploa...1318978359.jpg

I have exactly the same problem that Por_sha911 : not reading when cold and after 10/15 minutes driving, OK. When stopping 3/4 hours, not problem; when stopping a week, not reading.

So, is the solution to change the sensor?

Wanted to chime in here as well.. My car has this exact same problem. Let it sit for a day and neither the speedometer or odometer works but after 15-20 minutes of driving, it works flawlessly.

Subscribed.

I started this thread about two and a half years ago. The speedometer has worked flawlessly and the problem has never returned.