Breaking into the Differential to find the Magnets

[Andy911sc]

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.

[Andy911sc]

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

[James Brown]

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?

[Andy911sc]

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.

[James Brown]

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

[Andy911sc]

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).

[KTL]

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Had to get the plates from a VW shop because it appears the Porsche 901.332.191.00 plate (this is the part number that superseded 113.501.329) is no longer available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.

[Andy911sc]

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.

[schumicat]

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.

[KTL]

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.

[Andy911sc]

Originally Posted by KTL

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.

Originally Posted by schumicat

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.

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

[Andy911sc]

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?

[Craig_D]

Originally Posted by Andy911sc

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.

[cashman]

Originally Posted by Andy911sc

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.

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.
Speedometer, CASIS, Cruise Problem

FWIW I also posted a picture of the sending unit here on post #37
G50 Speedometer Sensor Problem

[KTL]

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

CV Torx Bolt sources?

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

[Bob Kontak]

Originally Posted by KTL

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.

+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.

[Daugaard]

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

[Andy911sc]

Originally Posted by cashman

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.
Speedometer, CASIS, Cruise Problem

FWIW I also posted a picture of the sending unit here on post #37
G50 Speedometer Sensor Problem

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:

[cashman]

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.

[Andy911sc]

Originally Posted by cashman

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.