How NOT To Rebuild 915 Tranny - Day Unknown
 

Grunt, grunt...snort, snort...

Okay, I got the gears off the shafts (many thanks to Chris Bennet for lending me the giant special Porsche 41mm socket)...I did it using the brutal force method recommended by Herr Walker, i.e. slamming the gear shafts onto a piece of (now destroyed) aluminum until the gears slide off like a yummy Borg shish-ka-bob. And it worked like a dream. But man, this didn't feel like I was "going medieval" on my car...it felt downright PRIMEVAL. When I got the last gear off the last shaft I felt like raising the shaft in the air and roaring like an ape who had just discovered fire (sound of "2001 - A Space Odyssey" theme music). Fortunately (amazingly), the shafts appear to be unharmed. However, the input shaft ball bearing seems to have suffered some catastrophic damage as little ball bearings went zinging all over the basement floor (would this constitute a "safety hazard" - visions of Scooby Doo and Shaggy madly running in place). Not sure if I should try to "fix" this ball bearing thing or replace it. I have no tools for "repacking" bearings (whatever THAT means)...probably costs a zillion dollars to replace...

I also sprayed the 911 cat bolts with some super-duper penetrating oil called PB...then it rained...Oh great. So now I am not only guiltily harming the environment by disabling my catalytic converter, I also contaminated the lawn with super-duper penetrating oil...lovely...There goes my Greenpeace membership...I did an internet search on "gut catalytic" and it seems everyone just gets medieval on the cat with a pry bar to tear the innards out...I was rather hoping there might be a more civilized drill bit tool I could use...but if I need to use the pry bar, then so be it...

Anyway, the tranny parts are soaking in degreaser. Figure next I'll start re-assembling the input shaft.

Soooo...I've been told I need to somehow "remove" the speedo threads on the end of 7:31 pinion shaft before transplant into the later aluminum transmission. Since the shaft is hardened steel, this seems like a challenge. Will it involve a hack saw? Torch? Hammer? Trip to the machine shop?

Thanks,

disc cutter.

Ball bearing is history as is any precision rolling element bearing when it is dropped or parts of it drop to the floor. You'll need a new one. If the balls and cage came apart easily it was probably failing anyway. Good luck. Jim

"Ball bearing is history as is any precision rolling element bearing when it is dropped or parts of it drop to the floor."

Wow...troubling...where do I get a new one? Internet search of Pelican, Vertex, Performance, etc shows no such product. Should I replace ALL of the bearings and cages? Am I a bad person for slamming my gear shafts on the ground (or am I bad person for enjoying it)?

Thanks,

i have never done a 915 tranny but, bearings are bearings. 1) look up bearing number- it should be on the bearing race or in parts manual. 2) look in Yellow Pages under BEARINGS. 3) call them - they will cross reference the part number- it may not be a Porsche OEM part, but it will get you back in the game. they will have different grades from different manufacturers. see what they recommend. lots of shops buy from these suppliers instead of waiting 2-3 weeks from OEM.

Re: How NOT To Rebuild 915 Tranny - Day Unknown
 

Don't gut your cat, buy a bypass pipe. Using a gutted cat increases backpressure thereby reducing HP (been there, done that and the butt dyno said "bad move") ;)

No, you do not need to replace all the bearings, only dropped or otherwise damaged ones or those showing roughness or overheating (usually have discoloration) or pitting of races and balls or rollers. 915 bearings are probably not fast moving items to retail customers so the lack of catalog listings is understandable. Pelican can probably order them for you. I recall one of the paper catalog vendors showing exploded diagrams of 915 internals, it may have listed bearings as parts they sold. Good luck, Jim

"Don't gut your cat, buy a bypass pipe. Using a gutted cat increases backpressure thereby reducing HP (been there, done that and the butt dyno said "bad move")"

Really? I was planning to reduce the cat to an empty tube - as though it were one giant bypass pipe. Seemed easier (though less cool) than learning to weld.

NOTE To Law Enforcement Officials: My car is old enough in my state to be emissions exempt...

After scratching my head for a few minutes, I just figured out what the "butt dyno" is and laughed out loud...d'oh !! :D

Hey, serious question about this ring/pinion transplant - perhaps a bit involved:

I just came up from the basement after removing the ring gears and differentials from both the aluminum tranny and the magnesium tranny. And it appears that the differential in the aluminum tranny is considerably bigger and beefier than the older version. So I did some research and discovered that while many people like the 7:31 ring and pinion gears, they don't like the weakness of the earlier differential. So I looked up the parts on the Pelican parts diagrams and it *appears* that the ring gear can be removed from the differential. If this is true, is there any way I can transplant JUST the 31 tooth ring gear from the earlier tranny and attach it to my stock (1980SC) differential?

Thanks,

Ring gear and pinion shaft are matched and should be kept together. Jim

"Ring gear and pinion shaft are matched and should be kept together. "

My mistake. I should have explained I intend to keep the ring and pinion together...I was just wondering if I could remove the 31 tooth ring gear from the early differential and bolt it on to the later differential.

Thanks,