915 Rebuild: Tool and parts question.

NY65912 · 04:31 AM

In preparation for my upcoming winter project, rebuilding my balky 1st-2nd 915 transmission I have a few questions.

I am going to pre fab the P 252a long socket, 41mm

For those of you who have fabbed their tools for the job. How long does the pipe have to be to clear the M/S.

I hope I don’t get flamed for this but, although I plan on purchasing the parts necessary from our host I noticed that on eBay the is a seller with synchros and dog teeth who is pretty well known, with the first name of Tom. His prices are quite a bit less, but I question the quality. Anyone have experience?

I am trying to keep the cost down but quality is the first priority but I do not want to pay dealer prices for original Porsche parts.

Thanks in advance,

yelcab1 · 08-31-2017, 08:42 AM

I fab a long socket but it is not long. I found a 3/4 inch socket that slides over the shaft to fit the nut. Then I welded a 1/2 inch extension to the side of the socket. It worked.

As for the synchro tools. Buy them, use them, and resell them. They are worth it. Don't try it without a tool.

OsoMoore · OsoMoore's Garage

When I did my rebuild, I bought the lower cost synchro rings from our host. They ended up being defective, and I had to return them and purchase the higher quality ones. It cost me a week of summer driving. I'd highly recommend you don't skimp on wear parts like that.

You can read about my rebuild at the link below. It was hard, but not too hard, and a lot of fun. I did it without P355A - I just locked two gears at once. Good luck, and don't hesitate to post here. We have experts who love to help others.

Can't Shift Into First

Matt Monson · 08-31-2017, 09:50 AM

Buy the Rauch and Spiegle teeth because they have the proper 9 degree backcut, but buy the German OEM synchros. Pelican stocks them both.

The SKF or FAG replacement bearings are high quality and you don't need to buy a bearing in a Genuine Porsche package.

Peter Zimmermann · 08-31-2017, 10:01 AM

Mike, the following LINK will take you to my Tutorial, which should be helpful.

http://r.search.yahoo.com/_ylt=A86.JyDUTahZEU0AKR0nnIlQ;_ylu=X3oDMTByb2lvbXV uBGNvbG8DZ3ExBHBvcwMxBHZ0aWQDBHNlYwNzcg--/RV=2/RE=1504230997/RO=10/RU=http%3a%2f%2fporsche.wikidot.com%2f/RK=1/RS=RLjouL5aXtBwd8MbcNytrW5jeQY-

Open the page, scroll down the left side until you see "915", click on that and you will be in a 9-part 915 "school!"

OsoMoore · OsoMoore's Garage

Quote:

Originally Posted by Peter Zimmermann

Mike, the following LINK will take you to my Tutorial, which should be helpful.

http://r.search.yahoo.com/_ylt=A86.JyDUTahZEU0AKR0nnIlQ;_ylu=X3oDMTByb2lvbXV uBGNvbG8DZ3ExBHBvcwMxBHZ0aWQDBHNlYwNzcg--/RV=2/RE=1504230997/RO=10/RU=http%3a%2f%2fporsche.wikidot.com%2f/RK=1/RS=RLjouL5aXtBwd8MbcNytrW5jeQY-

Open the page, scroll down the left side until you see "915", click on that and you will be in a 9-part 915 "school!"

It is very helpful - I actually printed the whole thing out and used it again later to help a friend do his rebuild.

NY65912 · 08-31-2017, 10:58 AM

Guys, thanks. I have about 50 threads bookmarked on the 915 rebuild and read them constantly. Heck, I would never have the pits to tear into it with out all of you!!

Pete, I have already printed out the entire wiki and have been studying for months.

Matt, thanks very much for the input. I was worried about the R&S dog teeth. I will abide.

For the first time I am looking forward to the winter, can't wait to get into the beast.

Gordo2 · Gordo2's Garage

Some info on the tools I made and used part way down this thread:

Gordo's 915 Transmission Rebuild

Gordo

Mahler9th · 08-31-2017, 06:34 PM

I have a bit of experience with 915 rebuilds, including one I just finished.

My application is racing.

I have a lot of friends and contacts in the biz, and I usually get parts at or near shop cost. I found Pelican Parts to have great prices so I bought most of what I needed from our host. I also bought some parts via ads here on PP from folks I trust, including some of the personal items sold by Mr. Monson.

And I also am a customer of Mr. Monson/Guard Transmission. I have a bunch of non-stock ratios in my 915s, and nearly all of these are GT gears. I have a bunch of lower-than-stock GT gears for sale in the classifieds.

I made my own tool for the main shaft nut for about $40-- $20 of that went to the welder... it took him about 10 minutes. In the end I did not use it--- instead I used a crow's foot sourced from Amazon.com for under $20. This worked just fine.

I did buy the 3/4 synchro hub tool which worked great. For future work, I probably will not buy the 1/2 tool, and instead borrow one from a friend or take the parts to one of several friendly shops in our area.

The wiki is an excellent resource, as are some of the great detailed threads.

I like the one piece bearing retainers-- the WEVO is what I have for each of my 915s, and WEVO has been an excellent provider of parts and advice. Top notch products and people (I have known them for about 20 year I reckon). Instead of using the the factory method to cinch the retainer down (nuts and split washers), I use metric jet nuts in one transmission, and bolts/safety wire in the other. I plan on converting the one with jet nuts to bolts this winter.

One thing I discovered last winter with my primary gearbox is that the studs for the cover can become brittle over time. As I inspected the tranny at season-end, I found a few loose nuts, and when I went to tighten them several studs just broke with very light force. PITA to deal with while the transmission is in the car. Again, my application is racing, so racing-type heat cycles may be to blame, at least in part.

I might just go ahead and replace all of these studs on a street car rebuild of a high mileage box.

I now use lock nuts on my cover plate.

NY65912 · 09-01-2017, 04:29 AM

Gordo, your thread is the insiration that got me going to rebuild my gearbox. I too found a 1st/reverse shift guide sleeve from a 901/914 transmission that I will fab into a P355a. I will be making the P252a tool as well. My shop does all kinds of welding fab so it's a no brainer to make these tools.

Mike, thanks for the advice. I will be purchasing a one piece bearing retainer for sure.

Cheers

KTL · 09-01-2017, 08:14 AM

Some things to look at closely when you get it apart:

>Check the studs on the shift fork guide (the "inspection cover" on the bottom of the trans) as these are notorious for coming loose or pulling out of the cover threads

>Check your bearing race fitment in the final drive/differential housing. You may find that lower one in the housing (pinion location) is loose. Best to have that machined for a steel sleeve to tightly accept the bearing race

>Check the studs for the bearing retainer(s). These can pull out of the case as well. Not extremely common but does happen.

>I would w/out question replace both ball bearings that fit into the retainer(s). These are notorious for loosening over time and that lets the shafts move axially, which apparently can drive the dog teeth off the gear.

>Check the fit of your splined 2nd gear on the input shaft. This location is notorious for loosening up both the gear and the shaft splines.

>Feel the inside of your "free" gears (those with dog teeth on them) to make sure there's no ridges in them from the pressure of the needle bearings. Especially 5th gear. These needles seem to get marginal lubrication and often times you'll find the gear oil is extra dark & extra stinky

>Since you're buying dog teeth and synchro bands anyway, consider doing the 930 conversion for gears 3 & 4. Not a big deal for a street car, but I figure since it's a better design of synchro band retention then why not. The 930 design uses an internal "star" plate and a wire ring to secure the band and its associated parts. Much better than the big flat annoying circlip of the 915 design. The brake bands are same part # for 915 and 930. So you need the 930 dog teeth, 930 synchro band, internal star lock plate, wire circlip and 930 stone and stop pieces.

NY65912 · 09-02-2017, 06:21 AM

Thanks Kevin,. The gearbox has 79k on it, all pretty mild miles on it so hopefully there's not that much Carnage. 1-2 is the problem, but I do intend to do all the synchros and dog teeth. I will start another thread on the actual rebuild and try to document the entire job. Cheers

Matt Monson · 09-02-2017, 07:13 AM

If you're doing teeth, make sure you're also doing sliders. My inclination is you will only need 1-2 teeth and slider. 3-4 are likely unhamnered in a box like that. Hopefully the 5/r slider isn't bad. That's the most pricey piece in the whole box.

NY65912 · 09-02-2017, 01:01 PM

Sliders for sure. I "hope" to do 1-2 but I am prepared to do 3-4 as well.

Cheers

Trackrash · Trackrash's Garage

That slider and dog teeth look OK to me.

Hard to tell from the picture about the synchro, but 5th is usually not much of a worry. Was it shifting in to 5th OK?

The actual 5th gear set is prone to wear. Was 5th quiet running? Any whine?

Trackrash · Trackrash's Garage

Hard to say why you are having that problem. Could be the shift fork came loose?

Try to engage fifth gear now, with out the shift fork installed. You should be able to push the slider over the dog teeth.

Why not move this conversation over to your other thread.

KTL · 09-06-2017, 01:49 PM

Yep hopefully not much carnage in a low mileage car like that. But you never know. My current '86 Carrera obtained from a RIP friend only has 77K on it. He repaired it with all new dog teeth 1st thru 5th, all new synchro parts around 15 years ago. Didn't do any bearings, didn't do any of the sliders. He just didn't know any better back then. Reason for the "rebuild" was 2nd gear was wasted from all the previous owner(s) speedy shift from 1st to 2nd at high rpms. 2nd gear crunched a lot. Too bad he didn't do the sliders and some bearings because parts were a steal of a deal back in 2002

Today it still shifts kinda crappy- 2nd is a roll of the dice for when it will go into gear smoothly on an upshift. Rather noisy in terms of clatter when idling in neutral with the clutch released. Under power from slow speeds there's a noticeable amount of "growling" from the trans. Almost as noisy as a G50!

So i'll open it up one of these winters and see what jumps out at me. Pretty sure it'll be a fresh start again with teeth, sliders, synchro friction bands and take a close look at the bearings. Also planning on adding a one piece bearing retainer because why not it's good insurance and a known shortcoming of the 915

Andy Somogyi · Andy Somogyi's Garage

Should you always replace the bearings and sliders?

I don’t have a lot of trans experience, only rebuilt an old Ford top loader a long time ago.

My 923 (912e trans, it’s a 915 with a 901 style input shaft) has 130K miles, and is crunchy going into 1st, and takes a lot of effort into 2nd. Other gears are fine.

I’m putting in new synchros and dog rings for all 5 gears, and ordered a new 1-2 slider, because I’m pretty sure the teeth are chipped. The other gears shift fine, I’m just replacing the synchos because I’m in there already.

But the 3-4 slider is expensive, and the 5 slider is ludicrously expensive.

Zimmermann recomeds new bearings, but I’m super nervous about pulling the races, so I’d prefer to leave the bearings alone (assuming they look OK)

tocobill · 03-27-2018, 07:31 PM

Synchros wear against the sliders. Usually replacing one and not replacing the other leads to poor synchronizing or expedited wear on other parts. The exception being the 5/R slider which is absolutely ridiculously expensive. I just did all new synchros, 1/2, and 3/4 sliders on my overhaul. 1 and 2nd rings were replaced as expected due to dull teeth. The 3-4 looked ok but were replaced with a better looking ring I was in there. All the bearings were replaced. Cheap money in the long run.

kevingross · 03-27-2018, 07:50 PM

Quote:

Originally Posted by Andy Somogyi

Should you always replace the bearings and sliders?

The sliders (shift sleeves) wear with the synchros. Meaning that if you replace a synchro, you should replace its shift sleeve. The dog rings also wear against the synchros and should be replaced if the synchro's installed diameter falls outside the factory spec, or there is wear / damage to the teeth.

As for the bearings, start by inspecting your current bearings' outer races' condition. If they show pitting of any significance or discoloration, replace. It can be a judgement call if the wear / pitting is slight, in which case you want to consider your interest in going back in there again in the (near?) future. Good luck!