915 input shaft flange nut hex size

[Jim Sims]

My son and I are overhauling his 73's 915 transmission (installing new seals, synchro rings and whatever else is worn) over the holiday break. We're having a great time; have the transmission on an engine stand and are working in a heated garage. So far tools haven't been a problem: found a 36 mm GM spindle socket to get the forward flange nut off the pinion shaft and a 1-1/16" (substitution for 28 mm) socket to get the castellated nut off the input shaft. We're at the point where we have removed the gear housing from the transmission housing and are about to remove the input and pinion shafts after measuring the shift fork positions (although we have the shift fork template). Looking forward, I note from the Porsche shop manual that special Porsche tool P252a (a very deep socket) and Porsche tool P355a (a plate with an internal 6 flute spline) are required to get the input flange nut (PN 915.302.281.00, the one closest to the differential) off. This nut has a 30mm x 1.5 mm internal thread and my Machinery's Handbook indicates this size should be 46mm across the flats (hope! hope! as this is the engine cam shaft nut size and I have access to this tool). I plan to use the cam nut tool and hold the shaft using the clutch splines after making a holder using the internal splines salvaged from an old clutch disk. DOES ANYONE KNOW THE HEX SIZE FOR THIS NUT? If its not 46 mm I can ask my wife who is in Albuquerque today to pick up a metric socket of the correct size. Thanks, Jim

[ChrisBennet]

Hold on I'll go look at my P252a...(sounds of footsteps going to cellar)..it's 41mm.
Don't remove/loosen the shift forks on the shafts. You don't have to. I take a shop rag and tie it around all the gears and then wiggle all the gears and forks out of the case as a single unit.
If only some syncros are in need of replacement don't just replace the worn ones. The little experience I have suggests that the syncros and sliders should be changed together. I.e. if 2nd gear syncro needs replacing, replace 1st and 2nd gear syncros and the slider that they share.
Chris

[Jim Sims]

Thanks Chris! 41mm is an odd size but I'm not too surprised. 41mm equals 1.599" so maybe a 1-5/8 (1.625") socket will work. If it'll fit I'll bore out the drive square and weld on a 1/2 drive socket on the side. If not, I can get the nut off with a big open end wrench and then order a P252a and P355a with the synchros, seals, new nut, etc. Cheers, Jim

[Doug Zielke]

Originally posted by Jim Sims
My son and I are overhauling his 73's 915 transmission .... I can ask my wife who is in Albuquerque today to pick up a metric socket of the correct size....

Great family you have there, Jim!

[my72911t/rs]

My stepdad and I are planing the same deal. A great thing when we can get along and spend time together. Good luck in your quest...Matt

Just did the nut myself. Mounted the 41mm nut in the vise and removed the swedged portion. Then put the castle nut back on the other end (first gear), put a 27mm boxed end wrech on and inserted a 4mm drift punch to keep it from moving. Gave it a turn and it came right off.
Just a thought and probably luck on my part to get it off so easy.
Chris

[Jim Sims]

I plan to take off the 41 mm nut by putting the clutch spline in an old clutch disk mounted in my vise and using a big Stilson wrench on the nut. Work is stopped as my son is out on a date! Its getting the nut back on later and properly torqued that is the issue. I'll use the clutch disk splines again as the reaction point but I may make a substitute 252a socket by taking a 1-9/16" or 1-5/8" 3/4" drive socket and grinding open the 3/4 drive square so it'll pass the seal diameter (a little over .9" in diameter) of the input shaft. Then I'll weld a 1/2 drive socket to the side of the big socket. This'll cost about $20 for the sockets. Then with a little calculation to account for the offset I can use my 150 ft-lb torque wrench to properly seat the 41 mm flange nut. Jim

Well I was going to do it a bit different.
Wack the 3/4 drive portion off the socket and insert a piece of pipe and weld it back together.
Chris

[ChrisBennet]

Originally posted by Jim Sims
I plan to take off the 41 mm nut by putting the clutch spline in an old clutch disk mounted in my vise and using a big Stilson wrench on the nut. Work is stopped as my son is out on a date! Its getting the nut back on later and properly torqued that is the issue. I'll use the clutch disk splines again as the reaction point but I may make a substitute 252a socket by taking a 1-9/16" or 1-5/8" 3/4" drive socket and grinding open the 3/4 drive square so it'll pass the seal diameter (a little over .9" in diameter) of the input shaft. Then I'll weld a 1/2 drive socket to the side of the big socket. This'll cost about $20 for the sockets. Then with a little calculation to account for the offset I can use my 150 ft-lb torque wrench to properly seat the 41 mm flange nut. Jim

A friend of mine made his 252a something like that. I impact the nut off. If you don't destroy the nut flange you can reinstall it so the bent part of the flange is in the same place instead of torquing it. When bending the flange back into the detent in the shaft be sure to use something rounded. Something like a punch or a nail will tear the flange.
-Chris

[Jim Sims]

915 pinion shaft and input shaft assemblies taken apart; parts labeled, marked for orientation and bagged. I now know why people find a loose needle bearing on their drain plugs after a transmission overhaul- it is very easy to dislodge the needle that resides in needle cage seam or joint! Used an old clutch disk (splines were reaction feature) and Stilson wrench to remove input shaft flange nut. Bearings easily pushed off both shafts using a hydraulic shop press. Press platen plates used for input shaft reaction (against 3/4 operating sleeve or slider) and a piece of heavy wall plastic pipe (ABS sewer drain pipe) for pinion shaft reaction against rear ball bearing flange. Ordered a Snap-on 1-5/8" (Snap-on lists this for a 41 mm nut) flare nut crowsfoot to reinstall and torque input shaft flange nut. Synchros taken apart and given a quick preliminary inspection. 1st and 2nd likely need new synchro rings, brake bands and probably new synchro hubs and operating sleeve (slider). 3rd and 4th likely also need new synchro rings and operating sleeve. 5th probably only synchro rings. Noted all the thrust (4 or 5?) washers have a crack going all the way around the edge; looks like a lap or weld in the steel sheet the washers were stamped from; will likely replace these washers too. Need to now sort out the first gear synchro hub/operating sleeve asymmetrical/symmetrical part availability or upgrade issue. Having fun! Have a happy new year! We're now living in the future! Jim