915 Wear tolerance

GotaT · 05:33 PM

Hey guys my dad and I have been tearing apart my 915 box to install a New input shaft seal, which we have successfully done at this point. The job has been much Easier than anticipated. It appears that someone before me must have rebuilt this gearbox because of paper gaskets the way they were installed and such New gearbox oil when we drained it.
I am wondering about the amount of wear on the synchros hubs and rings as to what to look for .. inspection purposes. Whats acceptable and what isnt. I was planning on replacing the 1st and 2nd gear Synchros, hubs, and brake bands. Im realizing that I cannot pull the 1st and 2nd gears apart and back together becasue I just dont have a press or oven to heat the parts to get it back together. It seems the synchros are in acceptable shape, and everything seems clean, Thus, Im just not sure that tearing it apart is necessary at this point after my initial inspection. It seems the syncrhos are in acceptable shape. My concern I guess is the Hubs and Brake Bands. What are your thoughts?
Thanks
Attached is a photo of 1st and 2nd Gears/synchro/ring
3rd and 4th Gears/Synchro/ring

GotaT · 01-01-2007, 04:40 PM

Anyone know what the Wear Acceptability Is on these ???

boxermania · 01-01-2007, 08:25 PM

From the angle of the pic those synchros look in very good shape, there is no rounding of the end.....someone must have replaced them recently.

Why did you tear the tranny down? Do rmember that the Porsche transmissions are generally fairly sturdy, but they do not really like fasy shifting like a Muncie or a Ford top loader.

In answer to your question, I'm sure that you can find a pic of a worn synchro somewhere on this or the other Pelican threads, or in Wayne's 101 Projects book.

davidppp · 01-02-2007, 03:48 AM

Hello there.

The dogs look OK.

The synchro ring on lleft of shot is worn..but probably working?

I do not think the bands et are likely to be an issue.

there are several supercessions here, so my opionion may be suspect..!

Kind regards
David

GotaT · 01-02-2007, 05:07 AM

The tranny was working ok, sometimes tough to "slide"/push into second or first. (maybe cable slack... since the tranny has been out Ive replaced the cable also) ...
David, why would you think the bands would be in good shape after looking at the photo.. not that im complaining just for understanding.

the reason for tearing it down was bc of a Worn and leaking Input shaft seal. On this year 915 the only way to replace is from the inside.

tom.langborg · 01-02-2007, 08:02 AM

Here is some input from porsche workshop manual.

Walt Fricke · 01-02-2007, 12:09 PM

My 2 cents: just put it back together. It shifted acceptably before, so leave well enough alone. When it quits shifting well, pull it apart and get ready to spend real $.

I can't tell from the pictures how much wear there is on the dog teeth. The ones on the left look like perhaps they may have worn back some (the ends of some of the Vs look squared off). The ones on the right (different camera angle) look like their vertical up and down V tip may have worn so it is no longer a straight line. And you can't see the corresponding teeth on the slider. Usually if the replaceable dog teeth have worn, so have the slider teeth, since the two wear against each other when engaging a gear. So you tend to need to replace both at the same time.

If your synchro rings don't measure out, you might consider replacing them. These rings also hold things in gear - you can see in the diagram how the center of the splines in the slider/operating sleeve is recessed. The synchro rings click into this notch, holding the dog teeth into the slider teeth. But you haven't had a "popping out of gear" problem.

Even replacing some synchro rings calls for a lot more tearing down than what you have done so far (is this a '72 or '73 with the cast in TOB guide, which is why you pulled it so far apart for just the input shaft seal?).

I know - now that you are in there, why not - - - - -.

Walt Fricke

GotaT · 01-02-2007, 01:57 PM

Walt, I pulled it apart bc its a 72 which requires removal of all parts to replace the Input shaft seal.
Today I went to a local Tranny shop, ATC and had one of the guys there pull it apart and install the Hubs and Brake bands. He said the slider teeth and synchros were in good shape. I was excited to hear that the slider teeth were in good shape, I could see that the synchros were in good shape already. He put it all together for Only $35! Now its back to the bench to Assemble it all back together and put the Rebuilt Engine and Tranny back in the car!... A long Wait for this day...

Pics to come soon of the completed Engine .. on a new post.