Breaking into the Differential to find the Magnets
 

Tonight I will be starting on project titled "Operation: Rescue Magnets." I will be draining the tranny, removing half shafts and cracking open the differential. Repair and back together.

Some while I am in there work:
Rebuild CV Joints
Inspect rear hubs (see if bearings need replaced)
Repair the mag ring so my speedometer read the correct speed.


Hopefully be done in 3 weeks for the Hershey Swap Meet.

And as always, pictures to follow the progress.

Question: Should I get all new allen bolts for the CV joints or reuse what I take out if they are in good shape?

up to you, there just bolts, how many you mangle is up to you! get new lock washers if you must but there made for reuse. You sure the magnet ring is the problem?

Yeah, when I had the multimeter set up for continuity beeps, it only made 4 instead of the 8. I had the speed sending unit disconnected and straight to the multimeter, so no interference from anything else. I would like to think it's something else, but when you only get 4 and everyone says 8, it kind of narrows things down. I was informed that I could have some corroded or gummed up magnets hindering the signal. My P-mechanic did tell me that he has seen this happen before. Either way, It isn't worth playing a guessing game about with the risk of a loose magnet getting caught in my differential gears.

yep, ok it is a PITA just to change that, just making sure. so WYIT, put in a posi unit!!

If I had the funding for a LSD, I would. Still recovering from last years medical bills. Right now, I am trying to keep it cheap with cv joint rebuild kits and possibility of new rear hub bearings (depending condition).

A box of 25 M8 x 50 socket head screws from McMaster Carr is like $8. Cheap insurance against stripping out a bolt head and having to fiddle with a pair of vise-grips to get it out.

For my racecar I chose to get 55mm screws, use the serrated lock washers (also get at McMaster) and also some moon plates from a VW performance shop. Had to get the plates from a VW shop because it appears the Porsche 901.332.191.00 plate (this is the part number that superseded 113.501.329) is no longer available

Vintage VW Parts | New last 6 months | torque spacer cv bolt to joint | 113501329

The plates are a bit of overkill but they do help spread the load of the bolt and give the serrated lock washer something hard to bite into. This bite is especially important when you consider some CV joint boot flanges are soft stamped metal.

I was considering moon plates. I thought our host had them. Also the washer, is that the schnorr washer? Highly considering new bolts anyway that weren't preloaded yet with the stress from the cv joints.

I would replace any allen bolts which show any damage from removal. peps boys has the correct bolts in stock (at least the one by me did) if you just need 1-2. it is really easy to get the diff out and back in. use a new o ring for the diff cover.

Yep that Schnorr type is a belleville spring-type that is serrated on both sides so it bites good.

The only moon plates Pelican has are the M10 size that I can find.

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.

I was looking for an o-ring for the cover but didn't have any luck. Would you know where I can source one?

I thought I remember seeing guys that used safety wire and wired two heads together along with moon plates and schnorr washers. Is there a kit for that, or did they just drill a small hole through the heads for the wire diameter?

I was considering doing this to mine. What you'd do is drill two holes on opposing sides of the allen bolt, then run safety wire through the hole, and rap it around the torquing side of the bolt (to the clockwise direction), then run the loop to the left side neighboring allen bolt.

You may only get 4 hits. Check out my posts here starting on post#13. Speedometer has been working ever since. I am convinced I only ever received 4 hits per rotation.
http://forums.pelicanparts.com/porsche-911-technical-forum/442139-speedometer-casis-cruise-problem.html?highlight=speedometer

FWIW I also posted a picture of the sending unit here on post #37
http://forums.pelicanparts.com/porsche-911-technical-forum/503635-g50-speedometer-sensor-problem.html?highlight=speedometer

The safety wire routine is nice if you can find the bolts pre-drilled. To drill your own you need to jig them in a holder to help you drill straight.

There's a picture in this thread that shows how they're typically done

http://forums.pelicanparts.com/porsche-911-technical-forum/739695-cv-torx-bolt-sources.html

The o-ring is not listed in Pelican's catalog. But any time you want, you can enter the Porsche part number and Pelican can get it for you. The diff cover o-ring is 999-701-392-40

+1 I have looked, can't find them.

Pretty sure the direction you are giving is the best route to go re: moon plates/schnoor.

Hi.

Diff cover O-ring is 3,5 x 202 mm

I think you can find it in a shop near you or on internet.

Daugaard

Cashman, I have an 82sc so my speed sending unit is different from your. I have the 915 transmission. I am not sure if I have an after market LSD installed. I noticed someone asked in your thread if an LSD would mean that the plate would only half rotate with a full revolution of one wheel. I am curious though, because my last speed sending unit read the same place this one is. I have just replaced with a new one.

Here is the picture from my test:
http://i1180.photobucket.com/albums/...ps1fd0fc04.jpg

That's pretty much the same pattern I have. I'm not a statistician but I found it very inconceivable that every other magnet happened to fall out. What are the odds of that?

Once I got the OEM replacement cable I have had no problems. 5000 miles and 6 DE'S Later.

I believe the test to check for LSD is to jack the rear, go in neutral, rotate one tire, observe the other tire, if it rotates the same direction you have LSD. Opposite direction you do not. I do not on mine. Do a search and double check me on that.

Being a chemist and knowing statistics the chances that I have every other missing, I would have better luck winning the lottery. I am reading slow on my speedometer though. Example (my gps which is very accurate would read 45mph and my speedo would only read 35 mph.) I just had my speedo out for repairs, but it was acting exactly like this before repairs (repairs where for the odometer gear). So, I replaced the speed sending unit and same result. My P-mechanic is leaning towards gumbed up or missing magnets. This all started after I tried to use my cruise control. He feels that it is unrelated and just coincidence. He told me that if I cancel out the cruise via switch then symptoms should go away and they haven't.

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.

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?)?

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.

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.

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.

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.

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.

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

Hmmmm reminds me of something.... ;)


http://forums.pelicanparts.com/uploa...1363718732.jpg

Craig, that just made my day.

hahahahahaha http://forums.pelicanparts.com/support/smileys/wat3.gif

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.

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.

Here you go

http://forums.pelicanparts.com/uploa...1363739904.jpg
http://forums.pelicanparts.com/uploa...1363739923.jpg

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

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).

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

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

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 :).

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.