Breaking into the Differential to find the Magnets

[Andy911sc]

So, tomorrow I am going to disconnect the entire Cruise Control ECU and take the car for a quick spin. Can it be ran without the cruise control ECU, I suspect that it can. Since cashman had 4 beeps as I did, it has caused me to take a step back and recheck things.

[frankc]

Originally Posted by Andy911sc

Yeah I just looked and saw that. SC's are the M8 then. Thanks for the link for the VW source. I will have to definitely pick them up.

Thanks for posting the VW link as I need to order a dozen M8 moon plates. Can someone verify that the VW moon plates are M8 and not M10 (did VW ever even use M10?)?

[Andy911sc]

I am also checking grounds. My cigarette lighter shares the same ground with the speedo and I have noticed when I turn the car off and the phone is on charge the speedo needle will jump up to 15mph. As soon as the phone is unplugged it falls back to zero. I am going to clean up G2 connection and just separate the cigarette lighter onto it's own ground. I know from experience with a 2000 jeep laredo that sketchy grounds can cause some weird s4!t to happen.

[88911coupe]

Just wanted to add my 2cents without having read each post in detail. I can confirm that on my '88 there are FOUR magnets, equally spaced, not eight with every other one having fallen off. It appears there are somewhat rare instances of 4 magnet discs. This caused me a lot of confusion when trying to resolve my speedo issue. I also found out that the sensor (from out host) would only work when inserted part way into the hole on the differential. I found this out by accident..it was a frustrating and confusing process since the advice was not syncing up with what I was seeing.
HTH

[cashman]

Originally Posted by 88911coupe

Just wanted to add my 2cents without having read each post in detail. I can confirm that on my '88 there are FOUR magnets, equally spaced, not eight with every other one having fallen off. It appears there are somewhat rare instances of 4 magnet discs. This caused me a lot of confusion when trying to resolve my speedo issue. I also found out that the sensor (from out host) would only work when inserted part way into the hole on the differential. I found this out by accident..it was a frustrating and confusing process since the advice was not syncing up with what I was seeing.
HTH

Yeah, I finally feel validated . I think there are only 3 people on this forum with the 4 magnet set up. (88911coupe, cashman, Andy911sc). I too was pulling my hair out when trying to resolve my issues. All the post I found referenced 8. Thanks for the confirmation.

[Andy911sc]

Thanks everyone for your input. I am glad I posted this and read more last night before just jumping into it. I would have been really frustrated finding out that no magnets fell out.

Tonight, my goal is to sort out a possible electrical gremlin. I have found that these components all share the same ground point and my speedo was reading normal before I tried using the cruise control that very first time.

[Andy911sc]

Originally Posted by cashman

Yeah, I finally feel validated . I think there are only 3 people on this forum with the 4 magnet set up. (88911coupe, cashman, Andy911sc). I too was pulling my hair out when trying to resolve my issues. All the post I found referenced 8. Thanks for the confirmation.

I wonder why only 4 magnets? I was feeling frustrated also because everything was saying 8 magnets. I was at my dads shop when I was testing it. I had him even come out and take a look. We both agreed that the odds of every other magnet falling out were super rare. He then proceeded to tell me to go buy a lottery ticket. I will let you know what I find out tonight.

[88911coupe]

I should probably go into some more detail on my comment about fitting the sending unit since that may be of some help to anyone reading this. I kept thinking my sensor was bad since if I inserted it I could not trigger continuity on my tester. Purely by accident I got a "beep" when I accidentally rotated the dif and noticed that the sender was only inserted about halfway into the hole in the side of the tranny. I got on the phone with someone at Pelican who did a great deal of checking and determined there weren't "versions" of the sender. I just fabbed up a solution by adding some heater tubing on the end of the sender to keep in seated about halfway into the hole. Works perfectly but I have NO IDEA why it only works when inserted halfway. That whole episode was really frustrating since I assumed my speedo was busted...turns out the wire to/from the sender had flexed enough to break but the outer cover was still in good shape. What a PITA it was to mail that whole issue down.

[Andy911sc]

I get continuity beeps with my sender. Plus my sender is different than yours due to me having an 82

[Craig_D]

Originally Posted by Andy911sc

Here is the picture from my test:

Hmmmm reminds me of something....

[Andy911sc]

Craig, that just made my day.

[Craig_D]

Originally Posted by Andy911sc

Craig, that just made my day.

hahahahahaha

[KTL]

Originally Posted by frankc

Thanks for posting the VW link as I need to order a dozen M8 moon plates. Can someone verify that the VW moon plates are M8 and not M10 (did VW ever even use M10?)?

Frank,

I have bought those exact moon plates from a VW supplier. Not sure if the one I posted is the exact place where I bought them, but i'm certain the VW part is indeed M8 size.

Andy,

I have my diff removed from my transmission, sitting on my workbench in the garage. I can take a picture of it to show you the speedo ring if you're not convinced you need to pop open the main case side cover. Mine is from a '79 with an '84 trans (with a Guard GT limited slip and '79 drive flanges- yah, a real Frankenschtein tranny) but the speedo ring is the same part from '74 thru '86. Part number is 915.318.045.03. Sounds strange that the ring is effective back to '74 but that's because it was also used in the Sportomatic trans before the 915 mechanical speedo was eliminated in '77 if I recall the year correctly?

Also note that if you do have a LSD, the magnets on the speedo ring can indeed pick up a bunch of metal debris. The friction discs are ferrous material, as well as other pieces in the trans of course, and those speedo magnets will grab & hold onto those fine pieces really well, even though it spins at a high speed!

There is no problem running the car w/out the cruise control unit. Disconnect it/remove the control unit and everything will work fine.

[Andy911sc]

Kevin, yeah please take a picture for me.

I removed the cruise control and still reading 30 mph when I'm going 36-38 on the GPS. Looks like I will be cracking open the differential. I wish I had another Speedo to test out just to confirm.

[KTL]

Here you go

[Andy911sc]

Thanks Kevin and thanks to everyone helping me through this frustrating process.

[Andy911sc]

Pelican Parts - Product Information: 999-113-183-40-M30

Are these the seals for the axles that go to the half shafts into the differential.

[frankc]

Originally Posted by Andy911sc

Pelican Parts - Product Information: 999-113-183-40-M30

Are these the seals for the axles that go to the half shafts into the differential.

Yep, those are the same seals I used for my '77 915 (output flanges).

[frankc]

Originally Posted by KTL

I have bought those exact moon plates from a VW supplier. Not sure if the one I posted is the exact place where I bought them, but i'm certain the VW part is indeed M8 size.

Kevin,
Thanks for verifying, I'm placing the order tonight.

Originally Posted by KTL

915 mechanical speedo was eliminated in '77 if I recall the year correctly?

I believe '76 was the first year for electric speedo, although I've read that mechanical speedos were installed in some early '76 cars.

Originally Posted by KTL

Also note that if you do have a LSD, the magnets on the speedo ring can indeed pick up a bunch of metal debris.

I noticed that even on my non-LSD diff with 102K there was some of that gray sludge stuck to the magnets. I view the speedo ring as a bonus acting like an additional magnetic drain plug to retain those tiny bits of metal floating around, except its just a little more work to get at for cleaning .

[Andy911sc]

So I will be starting sometime tonight. Have to take care of a skunk problem first. Dog got sprayed this morning. Good thing I am a chemist and new what to throw together to in a pinch to tame down the smell on her face. Poor dog.

Anyways, I will be just going into the differential. I am not going to mess with the cv joints this time around to save some time and money at the moment. They are solid right now with no play.

I will just be sourcing the new axel seals, differential housing cover o-ring and new hardware for the half shaft to axel connection (moon plates, new schnorr washers and M8 allen cap bolts). Of course new tranny lube.