Crunchy bits in my 915 Transmission

[Adrock]

I've spent the best part of my weekends for the last year, rebuilding my 83, 3.0 engine.
All that is remaining is for me to add the CIS and fan back onto the long block.

I bought the car as a project car and have never actually driven it. The gearbox changed into gears easily when I purchased the car - not running.

I thought it was a good time to drain the oil from the transmission before re-installing. Inevitably upon draining the oil, I found a couple of chunks of gear teeth and some fuzzy metal on the drain plug. Given the luck that I've had with the engine rebuild, I was bound to find some chunkiness when I drained the fluid.

I popped the end of the transmission off and found some more chunks sitting behind the lip of the gasket. I also ran a magnet through the main part of the tranmission and found another bunch of small teeth. Ugh.

I couldn't see anything obviously wrong when looking through the shift rod plate.

I assume that these are 'dog teeth' that have broken off? Somebody suggested that this can happen when the car is kept in gear in park and the car is hit by another car?
I have suspicions that this car was involved in a rear end accident at some point.

So, on top of an engine rebuild, it looks like I have a transmission rebuild ahead of me. Hopefully I can get away with it relatively cheaply - as I have spent all my money on the engine rebuild!

My main concern is the tools that I'll need to do this. I know that I can put it into two gears at the same time instead of using a holding tool. What other tools are 100% required to do this? I read that there's also a jig tool required?







This is a terrible photo because of the flash, but if you look at the gear on the right, you can see that there's a chunk of metal right there in the teeth. Surely this would have made a mess had I started it up!

['78 SC]

Originally Posted by Adrock

I assume that these are 'dog teeth' that have broken off? Somebody suggested that this can happen when the car is kept in gear in park and the car is hit by another car?
I have suspicions that this car was involved in a rear end accident at some point.

So, on top of an engine rebuild, it looks like I have a transmission rebuild ahead of me. Hopefully I can get away with it relatively cheaply - as I have spent all my money on the engine rebuild!

My main concern is the tools that I'll need to do this. I know that I can put it into two gears at the same time instead of using a holding tool. What other tools are 100% required to do this? I read that there's also a jig tool required?

This is a terrible photo because of the flash, but if you look at the gear on the right, you can see that there's a chunk of metal right there in the teeth. Surely this would have made a mess had I started it up!

[/IMG]

Condolences. I just finished rebuilding my 915 and can appreciate your situation (though I had some recovery time since the last engine rebuild).

Yep, broken synchro ring dog teeth. Good thing you didn't drive it.

Not cheap. I spent nearly $2000 on just parts:
new synchros 1-5
sliders 1-2 and 3-4
synchro rings 1-4
needle bearings 1-5
new pinion bearing
4 point bearing
Wevo one-piece retainer
gasket kit
I suspect you'll need similar, assuming there's no collateral damage from the loose teeth. If you're lucky, the pinion bearing race is tight and you won't need that machined and sleeved. My differential was ok, so I did not need any parts or tools for that. YMMV

Tools - I think I got by with the minimum.
extended socket to remove/torque main shaft nut
alignment plate to support main/pinion shafts when adjusting shift forks
something to hold main shaft when torqueing nut (I used and old 5th gear)
access to a shop press (I have the Harbor Freight 20T press)
I used homebrewed tools for synchro ring removal (see links below)

The best tools are Pete Zimmermann's priceless tutorial and Gordo's excellent rebuild. Here are some links I accumulated for 915 stuff:

Pete Zimmermann tutorial
Forum Categories - Porsche Wiki

Pelican thread on rebuild "Gordo's Rebuild" (long, detailed)
Gordo's 915 Transmission Rebuild

Flange removal
Transmission Seals?

Output shaft (flange) seal removal:
915 differential output seal

Seal installation
Replacing 915 output flange seals. Tool?

Seal installation details: depth
Also specifics of insertion tool
NOTE: measure depth of seal before removal
915 output shaft seal

More info on seal depth and tools
915 Differential Output Seal DEPTH?

Shifter shaft seal R&R
Shift Rod Seal R & R
See comment by Pete Zimmerman about seal removal and prep
Shift Shaft Seal in 915 Removal
Pelican tech article
http://www.pelicanparts.com/techarticles/mult_shifter_rod_seal/mult_shifter_rod_seal.htm

One-piece bearing retainer installation comments
915 Bearing plate Installation?

"Printing" differential pattern before disassembly
This is where printing it becomes essential, before and after. See how it runs now and make sure it runs the same after. If the pattern is terrible now, you can't use the current settings as your after goal because it has moved too much and needs to be reset.
From

Details of tool P259 for backlash measurement
915 – P259 tool measurement request… (With pics)

Steve Weiner VIDEO of 915 upgrades for track
https://www.youtube.com/watch?v=G8qsPFurN_Y

Good luck,
Steve

[yelcab1]

If you got by with $2,000 consider yourself lucky. Good luck. I would buy the syncro removal tools by the way.

[Matt Monson]

Make a really good inspection and see if that is old damage or new damage. If you have had no shifting issues and no event that you heard, this may be old schrapnel a previous owner failed to remove upon repair of the problem.

[gomezoneill]

If you're new at this I would recommend you have someone that knows what they're doing rebuild it for you. This is not a job for a amateur mechanic. Maybe go on the classifieds and look for a used box that's in good condition.

[Adrock]

Originally Posted by '78 SC

Condolences. I just finished rebuilding my 915 and can appreciate your situation (though I had some recovery time since the last engine rebuild).

Yep, broken synchro ring dog teeth. Good thing you didn't drive it.

Not cheap. I spent nearly $2000 on just parts:
new synchros 1-5
sliders 1-2 and 3-4
synchro rings 1-4
needle bearings 1-5
new pinion bearing
4 point bearing
Wevo one-piece retainer
gasket kit
I suspect you'll need similar, assuming there's no collateral damage from the loose teeth. If you're lucky, the pinion bearing race is tight and you won't need that machined and sleeved. My differential was ok, so I did not need any parts or tools for that. YMMV

Thanks everybody - this is all great info - especially Steve - that is a great summary of info and links that will be super helpful - thanks so much!

From what i've been looking at parts, $2000 seems super cheap for all of the parts you purchased. Did you get them all from Pelican?

I was actually thinking I was going to replace only parts that looked damaged or particularly worn. I'm not overly concerned about 'rebuilding', more so concerned about 'repairing'. As mentioned - I have spent more money than i wanted on the engine rebuild, so the discovery of the broken gears was a kick in the teeth (sorry!).

I'll open up the box and do some serious assessment of parts before I decide on what I will and wont replace. Upon first glance, everything in there looks ok... but I'm sure that will change once it's pulled further apart.

Make a really good inspection and see if that is old damage or new damage. If you have had no shifting issues and no event that you heard, this may be old schrapnel a previous owner failed to remove upon repair of the problem.

It shifted ok when parked, but I never drove it. Will be interesting to see what lies beneath!

If you're new at this I would recommend you have someone that knows what they're doing rebuild it for you. This is not a job for a amateur mechanic. Maybe go on the classifieds and look for a used box that's in good condition.

Thanks for the word of warning, but I like to do things myself and if I don't know, I'll learn. I have rebuilt 2 engines now in the last few years and I'm sure with all of the info available to me, I can repair a transmission. Plenty of times I've thrown money at professionals to do work for me, only to discover that 90% of the time, given the right tools - I could have done a better job myself and learned something along the way.

[yelcab1]

Originally Posted by Adrock

...Plenty of times I've thrown money at professionals to do work for me, only to discover that 90% of the time, given the right tools - I could have done a better job myself and learned something along the way.

that is 100% of the time for me.

[Adrock]

Originally Posted by yelcab1

that is 100% of the time for me.

Hehe. I would never bother to try and do a wheel alignment at home, when my alignment guy is a wheel whisperer. He's probably my 10%

Sent from my Pixel 2 using Tapatalk

[OsoMoore]

I did a rebuild of my 915 at home. I replaced the dog teeth on 1st gear, and some parts for 2nd as well. Total cost was ~1K. You can see my thread here: Can't Shift Into First
I have a set of tips/key points in the last few posts.

If you like, I can also post a big post-mortem I wrote up for a couple guys who asked.

This is scary, but not impossible to do yourself. Just take lots of notes and careful pictures, and keep stuff clean.

['78 SC]

Originally Posted by Adrock

From what i've been looking at parts, $2000 seems super cheap for all of the parts you purchased. Did you get them all from Pelican?

I was actually thinking I was going to replace only parts that looked damaged or particularly worn. I'm not overly concerned about 'rebuilding', more so concerned about 'repairing'. As mentioned - I have spent more money than i wanted on the engine rebuild, so the discovery of the broken gears was a kick in the teeth (sorry!).

I'll open up the box and do some serious assessment of parts before I decide on what I will and wont replace. Upon first glance, everything in there looks ok... but I'm sure that will change once it's pulled further apart.

I bought most of the parts from a firm in Sparks, NV that specializes in supplies for building engines. PM me if that is not clear. Some from Pelican. Wevo part from the manufacturer. If you're in a hurry, Pelican is probably the quickest source.

Like Matt Monson said, inspect carefully and decide what to replace. In fact, pay very close attention to anything Matt says re: transmissions.

While we're on the subject of expertise, let me make a full disclosure: I've built exactly one 915 transmission (but you knew that, right?). Take that to mean even a rank newbie can do it with some pro help. Also take anything I say with suitable quantities of salt.

Do you know the car's history? If this is an original 100k+ box, then expect a parts list like mine. Mine had been "rebuilt" (whatever that means), but tracked competitively since then. I disassembled it and took it to a friendly pro who inspected it and itemized the parts to replace. Maybe your transmission was fully rebuilt and the found teeth are old debris that worked their way to the drain (#dreaming?).

Bear in mind these parts interact, so the synchro teeth, synchros and slider for 1-2 or 3-4 wear against one another. Running a worn slider over a new synchro may not get you where you want to be. It all comes down to the condition of your parts.

Oh, I left out one tool - a micrometer (or a caliper) to check the synchro installed diameter. This alerted me to some synchro teeth (new parts!) that did not have the correct backcut. Something else Matt has commented on extensively.

[evan9eleven]

Here is my thread for what it’s worth. I went very nearly all-out, replacing almost every bearing, having the case machined for the Wevo insert, rebuilding the LSD, and doing an R&P setup. I also re-geared. See here: 915 rebuild and ITB/EFI project, here we go!

You can also see my homemade tools in the thread. Good luck!

['78 SC]

Originally Posted by evan9eleven

Here is my thread for what it’s worth. I went very nearly all-out, replacing almost every bearing, having the case machined for the Wevo insert, rebuilding the LSD, and doing an R&P setup. I also re-geared. See here: 915 rebuild and ITB/EFI project, here we go!

You can also see my homemade tools in the thread. Good luck!

Excellent resource, evan9eleven. Great info on "printing" the ring and pinion. I wish I had seen it before buttoning up my 915.

Thanks.

[Adrock]

You guys are the best!!! Thanks so much for all of this info.
When I didn't have the tools I needed yesterday to finish putting my engine together, I stopped to tinker with the transmission.

I had a heck of a time trying to remove the reverse idler at first, that was until I read Gordo's transmission rebuild, which explains that the box needs to be in 3rd gear to remove the 5th gear. This worked surprisingly well (so surprisingly that when it popped out, I nearly dropped it!).

Then I used a rattle gun to remove the 27mm and 36mm nuts. I had read that you can put it into 2 gears to hold everything still or even use a shop rag jammed between the gears to stop them from moving. With the rattle gun, none of this was necessary and the gun zipped them off with nothing but my gloved hand to hold the gears still. (careful you dont jam your fingers in between the gears in case they DO move!)

Anyway, from there, it was pretty easy to remove the rest of the gears and the top of the transmission to expose the fun stuff underneath.

Here's the joy that ensued:







Sorry, not the best photos, as it was dark and had to use a flash... but you get the idea. Quite a lot of missing or broken teeth there. I assume this is first gear?
I didn't really have enough time or light to do a proper inspection, but from what I could see - the main gears appeared to be in decent condition, I couldn't see any chunks or damage anywhere else. The other teeth that I could see on my quick inspection appeared to be in good condition too - but i'll have a look properly later in the week under better light. If all is well, I'm probably going just replace these broken teeth and the parts that interact with these parts - as suggested above.

Somebody suggested to me that this can happen if your car is left in gear and the car is hit by another car. Over the weekend I found previous evidence of the car being repaired in the rear (some spot welds in the engine bay). I'm wondering if it's the reason for this - rather than poor gear changes.

[yelcab1]

That does look like first gear dog teeth. I would suggest that you disassemble everything, clean up all the pieces before you inspect and judge their conditions.

You are here now....

[Gordo2]

Originally Posted by Adrock

You guys are the best!!! ... I had a heck of a time trying to remove the reverse idler at first, that was until I read Gordo's transmission rebuild...

Somebody suggested to me that this can happen if your car is left in gear and the car is hit by another car... I'm wondering if it's the reason for this - rather than poor gear changes.
[/IMG]

Good to see you are making headway and found my thread useful.

On the parked in gear & hit theory - I can't imagine how a few broken teeth would result. When in gear, the synch hub's teeth are fully meshed / engaged with the slider's teeth. As such, it would seem that a jarring impact would distribute the stresses across all the teeth evenly vice only breaking a few teeth.

Here's a more likely culprit from another Pelican member "Geary" (Guard Transmission founder - i.e. expert):

"In older 915 transmissions, the weak synchro band won't straighten a slightly ID-enlarged shift sleeve as it slides toward engagement. This slight cocking (and the fact that two or three teeth are first to see partial engagement) is why you'll usually see adjacent teeth missing, rather than random teeth."

In other words - the synchro's (bands and probably teeth) were worn causing poor shifting / grinding, and the prior owner continued to drive & shift until some of the teeth failed.

Good luck, Gordo

[Adrock]

Originally Posted by yelcab1

That does look like first gear dog teeth. I would suggest that you disassemble everything, clean up all the pieces before you inspect and judge their conditions.

You are here now....

hehe, my problem is that I'm really good at disassembling stuff - it's actually really fun!
It's the re-assembly part that I'm not so good at.

"In older 915 transmissions, the weak synchro band won't straighten a slightly ID-enlarged shift sleeve as it slides toward engagement. This slight cocking (and the fact that two or three teeth are first to see partial engagement) is why you'll usually see adjacent teeth missing, rather than random teeth."

In other words - the synchro's (bands and probably teeth) were worn causing poor shifting / grinding, and the prior owner continued to drive & shift until some of the teeth failed.

Now that you mention it - that does make perfect sense!

I will post more photos once I get deeper into it, later this week.

Thanks!

[Trackrash]

You are very lucky to find this problem now. Those missing teeth are a time bomb. After a few more break off BAM the synchro band flies off creating havoc.

Unfortunately you haven't driven the transmission, so you have no idea if there are any other issues like noisy gears.

You will have to be extra cautious in your inspection process to spot any wear that would cause a problem. AHIK.

good luck.

[Adrock]

Originally Posted by Trackrash

You are very lucky to find this problem now. Those missing teeth are a time bomb. After a few more break off BAM the synchro band flies off creating havoc.

Unfortunately you haven't driven the transmission, so you have no idea if there are any other issues like noisy gears.

You will have to be extra cautious in your inspection process to spot any wear that would cause a problem. AHIK.

good luck.

Thanks Gordon!
I'm glad that I decided to drain the oil transmission oil, before I connected it back up to the rebuilt engine and installed into the car, because that would have been a major pain!

Also, I'm kind of glad that I decided to rebuild the engine in the first place given that it only had one broken head stud. Some people suggested to just drive it and enjoy it until I was ready to rebuild. Had I done that - like you said - I might have had a lot more damage than what there is in there at the moment. At first glance, as it stands, everything looks pretty ok.

[OsoMoore]

I had a heck of a time trying to remove the reverse idler at first, that was until I read Gordo's transmission rebuild, which explains that the box needs to be in 3rd gear to remove the 5th gear. This worked surprisingly well (so surprisingly that when it popped out, I nearly dropped it!).

First time I took mine apart, I had the transmission on a table at waist height. I was yanking on the idler trying to get it off. Suddenly it came loose and flew up above my head. I made a split second decision not to look up for it, which was good as it fell directly on top of my skull.

It wasn't the first time my car made me bleed, and certainly wasn't the last.

[Walt Fricke]

Oso - I love it!

I had my engine on a roll around stand. I had neglected to put a big punch or other object through the holes in the stand and yoke which prevent the yoke from rotating, and was pulling the whole shebang across the garage floor by the engine cross bar mount. I had that Roadrunner moment when I was holding one end of the engine, and only air was holding the other. Holding up an engine by one end doesn't last long.

Happily, the yoke struck the long part of the T of the engine stand. Other than denting the stand a bit, the engine suffered no damage.

I now use a yoke holder bolted to a work bench, so this isn't apt to be repeated.

As to transmission repair, I found that having the factory manual, and the parts manual, were invaluable. Helped keep track of what went where on reassembly, and the manual helped with tricky stuff like which way a couple of washers have to face - stuff which isn't really intuitive. Of course, there are great resources here on Pelican.