915 rebuild advice?

[fanaudical]

I disassembled the 915 transmission in my project car (I have no drive-time on the tranny to assess condition) to find lots of "distress":

- Badly pitted pinion gear, some pitting on ring gear (8:31)

- Very rounded dog teeth on the sliders, but the syncro hubs look good and pointy

- No unusual wear on the gear-set teeth and they look OK to me

- No visible issues with bearings

What do the 915 gurus recommend for "appropriate" repair while I have this apart? Replace just the seals, ring/pinion, and sliders? Or should I dig deeper?

Thanks for the help.

[SchnellSchweitz]

Must see pics to evaluate.

[Trackrash]

Pics are good.

There are a number of recent threads on 915s. Do a search; 915 and Peter Zimmermann.

[G450X]

I think you need some special tools when you get into a R&P swap - unless you plan on rebuilding quite a few 915's in the future, I'd say take it to an expert for a rebuild.

You saved a few hours labor on the removal, there are quite a few good shops in Portland or Seattle to take it to (Steve Weiner at Rennsport, or John Walker come to mind).

If you're on a budget, maybe a good used box is an option. I've seen good used boxes for as low as $800.00.....

[fanaudical]

Thanks for the replies. You're right - I should have included pictures. I will post some when I find the camera...

[revmax]

Pete Zimmermann has a GREAT 915 rebuild tutorial over at the RED LINE TECHNIK site. Pete is really switched on regarding the 915 gearbox. It's a great read, really informative, and it's a step by step rebuild from the master and the author of the book "The Used 911 Story" If your going to rebuild your gearbox it's a great example how. Good luck...

Porsche Wiki

[Marc Bixen]

Also some additional info. How many miles are on the box? What is the 915/? number? What year car?
Many times, especially high milage boxes require replacement of the input shaft and pinion shaft bearings. When inspecting these bearings it is most important to see if the outer bearing race is loose in the case. If so the case can be repaired on later aluminum housings, mag cases can't be repaired. This is done by a competent machine shop welding and re-machining the bores. I'd certainly replace 1st and 2nd dog teeth, brake bands, syncros and slider, check for chips on the slider hub and on early 915's you can update to the later, stronger slider hub.
Let's see some photos. Also don't forget to replace the locking nuts, ALWAYS.
As said before check out P. Zimmermann's tutorial on the Red Line Technik wiki site.
They're also great on parts prces on the web store.

[Marc Bixen]

If you need a referal for the case repair send me a PM

[fanaudical]

Thanks for the info and suggestions. I have read through Peter Zimmerman's wiki and am using that as my primary guide and reference for my rebuild.

This is a mag-case 5-speed in a 75 Targa (type 915/40 #7151839). Odometer reads just over 93k - I don't know if it's been rolled once (only 5 digits). I towed the car home on a flatbed because it wasn't drivable. Found broken clutch fork and many other issues on teardown, and am thinking that the previous owner(s) didn't treat this car well.

Found the camera. Broken 1-2 spider (broken end faced toward 1st):



Chewed-up pinion:



Pitted ring gear:



Funny-looking slider on 1-2 (pointy end was faced toward 1st):



Close up of 1st & 2nd syncros (have gloved hand on top to get the stupid camera to focus):





I do need to check the "tightness" of the input shaft bearing races again. I thought they were tight, but double-check is always good.

Opinions? I hate to get another used transmission only to find I need to go through the same kind of stuff. I'm thinking that I should rebuild this one if there are no case issues. (At least I know what I got at that point.)

[Jon B]

Originally Posted by G450X

I think you need some special tools when you get into a R&P swap - unless you plan on rebuilding quite a few 915's in the future, I'd say take it to an expert for a rebuild.

It would be nice to establish who actually has the tools necessary to set a 901, 915 or G50 ring & pinion. Not by loyal customers or hearsay, but by shop owners posting photos of the tools in their possession. Aside from Pete Zimmerman, I'm not aware of anyone else who's done this. It's not difficult to post a few snapshots on the forum. It would help to know who's equipped to do this properly, in any area of the country.

[Marc Bixen]

Fairly substantial pitting and wear. You may want to look for another box as this one will cost probably $4,000-$5,000 to repair "correctly". Even the $3,000-$4,000 range if you perform the majority of work yourself and have someone set up the R&P for you. I also notice the blue tint of Swepco gear oil. Switch over to Kendall NS-MP 80w-90, it will make a world of difference. If you check the many threads on Pelican and Rennlist about this you'll see the attributes.
Hell, after years and years of Pelicans moderators claiming "you don't need Kendall" " use our Mobil" or "Swepco's the best" they finally broke down, and virtually admitted we were right and started selling Kendall. I'll admit Swepco is an awesome product, but in a 901 or 915 you need Kendall NS-MP. Most people were buying it on line from Red Line Technik (then add the dot com), if they couldn't find it locally.

[Peter Zimmermann]

fan; those pictures only cause one response - OUCH! That is about as close to a throw-away as it gets. The amount of metal circulating in the oil has done harm to every bearing, and I'm sure a closer exam of the gear sets will reveal even more problems. I do not have acceptable used pieces in my inventory to repair your box for under $4K, and to use new pieces would not be cost effective.

Your odo might have gone over twice, but in reality the car probably has 193K miles + whatever was put on while the odo wasn't working. This can't be a 93K mile box. What are your plans for the car?

[Jon B]

Originally Posted by fanaudical

Chewed-up pinion:

The pinion in your photo was set too far from the ring axis, or you had a bearing/clamp issue. The path of contact runs off the nose of the pinion on drive; compare the area of contact to the photo below.

Find someone with all the specific 915 tools to set a replacement ring & pinion properly.

[Marc Bixen]

Bunin, you're awesome.
Regards,

[Peter Zimmermann]

Yep, I agree, Jon. I'll bet that P/S has been moving back and forth for a while...

[fanaudical]

"Ouch" was close to my assessment when I opened the case; I had some stronger language...

Thank you all for providing some great info and advice. Here's some additional comments to corroborate what you see:

- The PO had beat this car to death and really neglected it. I believe that it was driven until it could go no further. I have found the engine to be in similar shape; so far, the only major bits salvageable there are case (with some work), crank, and rods.

- Yes - Swepco (and lots of metal sludge) in the case when I opened it.

- I did see massive "pinion rock" when I first opened the inspection port on the bottom of the trans case and assumed bearing retainer failure.

Peter raises a great question - What are my current plans for the car?

When I got into this thing I thought I could get it running and assess "damage" at that point. I did get it running long enough to determine the engine was in no shape to be drivable, clutch was non-functional, and tranny a huge unknown.

(I bought a "cheap project" on purpose, knowing full well there are no cheap projects. I do enjoy the "challenge"...)

Now that transmission is no longer an "unknown".

I have been in "tear down" or a bit while I assess the full "potential" of the car. The body is in decent shape, I have the interior out for some refinishing, I need to rebuild the engine. It looks like the fastest path to "complete" may be to find a used transmission with some known history and then "rebuild" that.

Anybody have a gently used 915 that needs a home?

[JeremyD]

I do -

Want to wake up your SC or Carrera? 915 for sale