915 gearbox magnets

ajenks144 · 02-11-2021, 06:58 AM

Hello All,

First, I apologize if this topic has been covered, but I couldn't find it in search. I have a couple magnets missing from the magnetic plate inside my 915 gearbox. I am looking for replacement magnets that would work and I will JB weld them in place. I found a few posts about testing the speedometer, but not replacing the magnets. Can anyone point me in the right direction?

Thanks Everyone!

Andy

KTL · 02-11-2021, 07:26 AM

The thread linked below talked about the magnets pretty well. Start at post #46 where Jim discovers why his speedometer was reading poorly, on account of a magnet falling out of the tone ring on the differential

http://forums.pelicanparts.com/porsche-911-technical-forum/930053-part-dux-915-journey-2.html#post9298441

ajenks144 · 02-11-2021, 08:05 AM

Quote:

Originally Posted by KTL

The thread linked below talked about the magnets pretty well. Start at post #46 where Jim discovers why his speedometer was reading poorly, on account of a magnet falling out of the tone ring on the differential

http://forums.pelicanparts.com/porsche-911-technical-forum/930053-part-dux-915-journey-2.html#post9298441

Thanks Kevin for the quick reply. I saw that thread, which was helpful, but I am trying to find a source for replacement magnets. The aftermarket holders (with magnets) are very expensive. My carrier is fine, just need to find some magnets.

Thanks,

Andy

r lane · 02-11-2021, 08:49 AM

I just punched them out of a holder in a trans for a track car. I think I have all of them and you are welcome to them. Bob

ajenks144 · 02-11-2021, 08:56 AM

Quote:

Originally Posted by r lane

I just punched them out of a holder in a trans for a track car. I think I have all of them and you are welcome to them. Bob

Great. I just sent you a PM.

KTL · 02-11-2021, 02:04 PM

Sorry I overlooked the mention of needing a source for replacement magnets.

Just be sure to take note of the polarity when installing them.

kevingross · 02-11-2021, 06:39 PM

This is a frequent problem with 915s. I just finished a customer gearbox that came in for a Guard LSD. Unfortunately some of the magnets had come loose and done some damage. I reglue / reinforce with an epoxy.

My customer has his old disc, and would probably sell it to you for its magnets. Shoot me email if interested and I'll ask him. BTW, the disc is now available from Porsche Classic.

ajenks144 · 02-12-2021, 11:15 AM

Quote:

Originally Posted by kevingross

This is a frequent problem with 915s. I just finished a customer gearbox that came in for a Guard LSD. Unfortunately some of the magnets had come loose and done some damage. I reglue / reinforce with an epoxy.

My customer has his old disc, and would probably sell it to you for its magnets. Shoot me email if interested and I'll ask him. BTW, the disc is now available from Porsche Classic.

Thanks Kevin. Looks like I have some magnets coming my way. What did you use to glue them back in? I was thinking jB weld.

Andy

kevingross · 02-12-2021, 07:30 PM

Quote:

Originally Posted by ajenks144

Thanks Kevin. Looks like I have some magnets coming my way. What did you use to glue them back in? I was thinking jB weld.

Andy

Andy, I use the same stuff. Consider roughing up the existing epoxy surface to give the new glue something to bite.

toddetch · toddetch's Garage

Kevin - sending you a PM to see if the disc with the magnets is still available.

Rosco_NZ · Rosco_NZ's Garage

Posting here rather than starting a new thread .. Mag Case 915 with electronic speedo .. Mag pickup problem .. resto project so working through final snag list ..

Speedo totally dead ... Speedo has been tested and works fine in another car .. it also works fine in my car with a rigged up sender on a drill from the connector to the speedo. So looks like the magnets in the tone ring are missing ..?? There wasn't any junk / chewed up magnets in trans oil when I drained it a few years back. Maybe this trans doesn't have a tone ring at all .. could the diff from an earlier trans without the tone ring have been put into mine?? Looks like I'll have to take off the side cover .. 915 guru's please talk to me ..

dannobee · 09-21-2023, 06:05 PM

Pull the sensor out of the trans and look up there with a borescope camera and see if any magnets are missing. If they're there, suspect the sensor. If they're missing, or if you can't see the tone ring, you'll know the problem.

Rosco_NZ · Rosco_NZ's Garage

Good idea .. where’s best place to poke in the borescope ..?? No hole through sensor mount ..

dannobee · 09-21-2023, 11:27 PM

Take out the drain plug and snake it up there.

Rosco_NZ · Rosco_NZ's Garage

Gotcha .. thanks.

kevingross · 09-22-2023, 09:27 AM

I haven't looked at this thread in a couple years. The disc ("tone wheel") is available as a factory new part from the Porsche Classic program. Cheers,

Rosco_NZ · Rosco_NZ's Garage

Thanks for your response Kevin, that is really helpful information. I have a suspicion there is no tone wheel present. The diff could be from an earlier car which had a mechanical speedo. Will the tone wheel retrofit to an earlier diff without issues? Or are modifications required??

kevingross · 09-23-2023, 10:23 AM

Quote:

Originally Posted by Rosco_NZ

Thanks for your response Kevin, that is really helpful information. I have a suspicion there is no tone wheel present. The diff could be from an earlier car which had a mechanical speedo. Will the tone wheel retrofit to an earlier diff without issues? Or are modifications required??

Hi Rosco, y'know that is a very good question. I just shipped an 915/63 (late), so missed the chance to measure its diff. Have another late one in the queue, might be able to pop the diff out next week. Not sure I have an early diff on hand, may have one in storage, have to look when I am back in the shop next week.

I suspect the late differentials were machined (if not cast) a few mm. shorter on the non-ring gear side (S2) to allow for the tone wheel plus normal range of shims. If indeed that is the only difference, you might be able to use the earlier diff with 0.25 mm shims, one or more, if you get lucky. The late diff also has a 4 x 14 mm (IIRC) tension pin installed in a 4 mm bore to keep the tone wheel from spinning -- easy to retrofit and I suspect not really necessary.

Will dig when I am back in the shop Monday. Maybe others already have a better answer.

Rosco_NZ · Rosco_NZ's Garage

Kevin, really appreciate the knowledge sharing .. Sorting the Speedo look like the last issue to iron out which will stop me being able to register the car and get out in it! Looking forward to hearing back from you ..
Ross

Rosco_NZ · Rosco_NZ's Garage

Rounding out this thread .. the tone ring was not missing and all magnets were present. Contrary to info on another post, I now don’t believe the magnets need to alternate polarity… they drive a reed switch in the pickup open & closed. This should work regardless of magnet orientation. The problem ended up being the connection to the gauge .. the 2 wires from the sender connect to the lower 2 terminals on the gauge. Such a simple fix and so easy to get wrong!!