Getting Ready for 915 Rebuild - It's my turn.

[John D Brown]

Ok I need some of the experts advice - BTY this is a real good thread --- I have a 915 tranny that was jumping out of third gear - pulled tranny apart - syncro teeth worn - noticed that when I moved hub onto third gear it would jump back off, but when I moved it onto 4th gear it stayed. Is there something else besides the syncro that could be bad?

Thanks,
John

[arbita1]

Ok...mystery solved. Turns out I'm an idiot. Dentist's post above got me thinking, so I pulled out my caliper. Guess what the bearing race in my bellhousing is not 55mm...it's 62mm.

So I went back and looked at the new bearing. The bearing race is also 62mm.

The difference is, the new bearing race has a much thinner wall than the old one. So the roller bearing itself is larger to fit inside the larger inside diameter.

Ok...so I guess I'll have them pull out the old race and pop the new one in.

Sorry to screw everyone up.

Back to gears and stuff...

I want to reuse my 3rd/4th gear slider. It is in good condition. Can I reuse it?

[MBEngineering]

HI Matt
to get the pinion bearings off the shaft, you need a tube turning up like this P tool



the pinion roller bearing fits in the top and the rollers rest on the ledge in side,







with the tube on the end you can now press off the bearings and the gear stack in one go, the only thing with the Porsche tool I find is it is to short to fully press of the pinion bearings and I need to put a spacer tube under it.







regards mike

[coollx]

Matt asked

I want to reuse my 3rd/4th gear slider. It is in good condition. Can I reuse it?

I was told by JW and Peter Z that you should never use an old slider with new syncro rings so I bought a new slider. They said if you replace the syncro rings without replacing the slider, which is usually worn, you're likely to have shifting problems in those gears.

[MBEngineering]

HI coollx
correct, new parts, unless you turn the original bands, if you put aftermarket bands and slider in, do not mix and match from different places, get every thing from one place, as some times thay will not match and you get a tight change, or you will over hear.

regards mike

[arbita1]

Ok so new slider for 3rd/4th gear.

Now, I changed the 5th gear synchro. The slider for that is like $500. Do I really need to replace it?

Maybe I should put the old synchro back on?

[Peter Zimmermann]

Originally Posted by dentist90

I came across this same sort of confusion when I got a replacement final drive case for my '84 (remember I had that cracked web between the input and output bores). My damaged diff housing had the 60mm mainshaft (input)bore, but the replacement I got was a slightly newer model and came with the 55mm, so I found myself doing an unexpected bearing change as well. I wonder now if the 74E diff housing that my car had wasn't original? If it was, I guess my Carrera got the last of the old style housings. I noticed that the cutout for the flywheel sensors also looked different. The 74E case cutout looked machined, whereas the 74F case was obviously cast with the cutout.

There is certainly a fair amount of confusion with the bearings! I have an early '84 housing, and a mid-year '85 housing - both use the 55mm bearing. This thread confused me because I've never seen a 915/61 or 915/63 with anything other than the 62mm (actually 61.67mm) bearing. I've seen the sensor opening differences also, but never equated that with the size of the M/S bearing - I just wrote it off as a production change for efficiency.

[Peter Zimmermann]

Originally Posted by arbita1

Ok...mystery solved. Turns out I'm an idiot. Dentist's post above got me thinking, so I pulled out my caliper. Guess what the bearing race in my bellhousing is not 55mm...it's 62mm.

So I went back and looked at the new bearing. The bearing race is also 62mm.

The difference is, the new bearing race has a much thinner wall than the old one. So the roller bearing itself is larger to fit inside the larger inside diameter.

Ok...so I guess I'll have them pull out the old race and pop the new one in.

Sorry to screw everyone up.

Back to gears and stuff...

I want to reuse my 3rd/4th gear slider. It is in good condition. Can I reuse it?

So, to finish off the bearing issue - you will be able to use the 999 110 032 00?

Originally Posted by arbita1

Ok so new slider for 3rd/4th gear.

Good decision!

Now, I changed the 5th gear synchro. The slider for that is like $500. Do I really need to replace it?

Maybe I should put the old synchro back on?

What is the installed OD of the new synchro?

One step at a time...

[arbita1]

Yes. The 62mm is correct.

I'm at work trying to find a box to pack the bellhousing up in. Does anybody have the dimensions of the housing? I have a nice box here but I'm not sure if it's big enough.

[Peter Zimmermann]

Originally Posted by arbita1

Yes. The 62mm is correct.

I'm at work trying to find a box to pack the bellhousing up in. Does anybody have the dimensions of the housing? I have a nice box here but I'm not sure if it's big enough.

I think that you're going to need a box that measures about 14" x 15" x 17" or larger...

[arbita1]

I was just going through the parts on my mainshaft when I noticed these grooves at the 5th gear end.



Then I look at my 5th gear and there is a wear pattern on the face where reverse is next to it. Almost like they are moving seperately...which I find weird because they are supposed to be locked together.

So I put 5th gear on the end of the shaft and sure enough...it rocks back and forth in the grooves. What the hell was done to this transmission???

I'm guessing this means a new mainshaft and first gear. $$$$$

What now????

[sc_rufctr]

That's nowhere near as bad as the pinion shaft failing!
Believe me it could have been much worse.

I wouldn't even think about putting that back in your gearbox.

I'm guessing you could buy a second hand input shaft from a breaking yard. This should be a safe thing to do as the depth settings are not critical like the pinion shaft. As long as you got one that matched your gearbox you shouldn't have any issue. Peter Zimmerman or Porsche Monkey would know for sure.

Hope it works out OK....

Peter

[MBEngineering]

HI Matt
that is what happens when things are not torqued up correctly or NOT cleaned and assembled DRY, the gearbox parts need to be taken of the shafts "ALL OF THEM" including the bearings, washed, cleaned, dried, inspected and re-assembled DRY (as the workshop manual) not assembling dry is a lottery ticket waiting to happen and as the pinion depth and back lash is working in 0.05 of a MM if the parts are not assembled DRY, the oil between the parts assembled will add up to more, putting the setting out, as any oil between any of the surfaced will cause problems, so for those of you who pull the end of the gearbox and change 5Th gear with the AIR gun and put the S/H nut back to the locking position, it will later cause the box to fail.

As for your shaft, a later shaft would be good in the box, check hear for more info,

four speed 915 mainshaft same as 5 speed?

as the last post was ignored, I will try again , if no response I will take it, it is not needed and remove it and this one???

regards mike

[sc_rufctr]

Mike

I wouldn't take it personally about not getting a reply. The guy just found a pretty big problem with his gear box and he wasn't sure it could be fixed easily. I would guess he's a bit stressed at the moment.

Thanks for posting the pics of the P tool. Always good to see genuine P tools.

I think I can speak for most of the amateurs here. We really do appreciate the pros chiming in and helping us with our cars... And For Free! How good is that???

Peter

[arbita1]

Believe me I'm not ignoring ANY post on this thread. I need all the help I can get. I'm just busy at work and life and etc...so I may not get to respond to each post right away. But believe me I'm reading them closely.

Thanks for everyone's help so far.

Right now I'm a bit annoyed, since at this point I probably could have just rebuilt my transmission with less hassel. Instead I took a chance on an unknow core...and definitely lost. Lesson learned.

But I'm at the point of no return...so my options are (as far as I know)...

1. Replace it with a new (used) one.
2. Remove my transmission and swap it out (however, that kind of kills my hopes of selling my old transmission as a core).

Any other recommendations?

[Peter Zimmermann]

Originally Posted by arbita1

1. Replace it with a new (used) one.
2. Remove my transmission and swap it out (however, that kind of kills my hopes of selling my old transmission as a core).

Any other recommendations?

Matt: Mike's post is right on the money - clean & dry is the only way to be sure everything is tight (this is another reason to use a press to build the gear shafts, put the diff carrier bearings on, etc.), and all measurements made are correct.

Regarding your M/S, that wear is classic - was it you that discovered a loose castle nut during dis-assembly?

Regarding the trans on your bench. If you have established that all of the other components (gear sets, R&P, etc.) are good, then consider shopping for an 11:35 1st gear w/main shaft, and the reverse parts that you need. Don't forget to check the needle bearing surface on the mounting pin for the reverse idler - they fail also and I don't know how much a new pin is these days.

I've seen used main shaft/1st gear sets between $300-500, but haven't seen much used stuff for reverse. If you find a 1st gear have the seller understand that you reserve the right to return the part if you don't like it. A lot of gears have been lying around in barns (getting wet + light surface rust), and many now have unacceptable root wear, almost always on the smaller gear.

Be careful with used stuff, there's usually a reason why the parts aren't in a transmission somewhere. Call the guy that you bought the center housing from!

Sorry about the problem!

[arbita1]

Originally Posted by Peter Zimmermann

Regarding your M/S, that wear is classic - was it you that discovered a loose castle nut during dis-assembly?

Be careful with used stuff, there's usually a reason why the parts aren't in a transmission somewhere. Call the guy that you bought the center housing from!

Sorry about the problem!

Yes that was me. The only thing holding the nut on was the roll pin.

I think I have a line on a mainshaft and 1st gear from an SC out of a good gear box that someone has decided to part out instead of rebuild. I'm waiting on some pictures. I'm hoping this works out.

What a fiasco this has turned out to be.

[arbita1]

So fellow a Pelican came through and got me a good deal on a mainshaft and first gear from a SC 915 that was supposedly in good condition.

Here are some photos:





I think it looks good from these photos, but the seller is willing to refund my money if I'm not happy. I really hope this is the last bump in the road.

I can't fault the seller...he told me straight out that he had no history on this transmission, so I knew I was taking a chance. He had only driven it in 1st gear and didn't know anything else about it. If nothing else...I'm learning so much. (Trying to be positive.)

[Peter Zimmermann]

Can you post a better pic of the gear on the M/S? I don't want to worry you, but it looks like there is root wear on at least one tooth...

[arbita1]

You're killing me.