915 Rebuild/Refresh and SSI Questions

Inniswhe · 09-05-2010, 09:15 AM

I have my engine out and 915 separated. I pulled the engine ( first time) due to a clutch failure ( had a separate thread for this). It turns out to be the pressure plate. My engine has 131K miles and still seems solid. Down the road I plan to rebuild the engine to maybe a 3.4 and possibly twin plug etc. but I don't want to do it until the rebuild is needed.

Right now my plan is do a complete clutch replacement including a new flywheel. I also plan on cleaning up the engine , fixing some vacuum leaks I found, replacing engine tin ( pretty rusty) and doing any while you have the engine out preventative maintenance like the head temp. sensor.

I also plan on refreshing or rebuilding the 915 gearbox and possibly installing SSI heat exchangers

The tranny has what appears to be the typical 915 shifting issues from 1st to 2nd. It used to grind until I changed to swepco and readjusted the linkage. I was planning on sending it to Gary Fairbanks for overhaul ( and I still may do that ) but shipping will probably be a pain from PEI to Connecticut and back.

I like to perform my own maintenance/learn as much as possible and am considering doing the 915 overhaul myself but I wonder if it worthwhile or should I just send it out ?

Will I spend so much $ on tools that I might as well have send it out in the first place?

For those who have done it themselves how was the process , would you do it again ? Removing the engine/tranny was pretty straight forward ( but I haven't reinstalled it yet! )

Has anyone used the excellent Pete Zimmermann tutorial on the subject ? It appears to be the definitive document for us would be Do-it -yourselfers.

Also on the exhaust topic would it be foolish to install SSI h/x's on a 3.2 knowing that down the road I will probably be rebuilding to 3.4 and twinplugging. Are SSI's too small for a 3.4 twin plug engine ? Wayne's engine rebuild book seems to indicate this .

James Brown · James Brown's Garage

The tranny rebuild at home is doable. You can check this site for all the tools and parts necessary. That will give you a cost estimate. The tools are not that much but you will only need them once. Using several publications and articles will give you the best overview on how to do it. As far as what SSI's to get for a modified 3.2 Try the 3.2 ones first with the rebuilt transmission and you might just like what you have and "down the road" might be 10 years!!

Christien · Christien's Garage

Absolutely the tranny rebuild is DIY-able. Cost estimate is difficult, because you don't know what needs to be replaced until you get in there. Mine wasn't too bad, just replaced a few bits here and there, probably under $1000 including tools. The tools aren't overly expensive. Small torque wrench, circlip pliers and a couple specialty things, maybe $200-300. But if there are lots of worn parts, it could get to 1500 or 2000. From the symptoms you describe, it shouldn't be too bad.

When I bought my car in 2004, I didn't know what a carburetor was, or even what it looked like. I had to look up what the fan belt was. I bought it to learn, and learn I have. I rebuilt my 915 in the winter of 08, with just info I found here and various places online. Start a thread, post lots of pics, and you'll get lots of help. It was a great project, and only once or twice did I hit major snags (36mm nut - you'll know when you get there

). It was a really satisfying feeling to feel the car move as it should when I got everything back together.

Pay attention to the detents!

RoninLB · 09-05-2010, 08:07 PM

some things take an experienced eye to catch although a simple rebuild is worth the shot

revmax · 08:38 PM

Peter Zimmermann- the author of the book "The Used 911 Story" has a great WIKI Tutorial going on the 915 tranny rebuild off his RedLine Technik site. It's broken up into 9 parts. It's a great read on the 915 regarding the in's and out's. It really gives you a good insight if you decide to rebuild the box yourself.

Click the link below:

Porsche Wiki

----------------------
'76 911S

jimrs2000 · jimrs2000's Garage

I did mine after a first gear failure, replaced lots of new parts, came to $1500 and it wasnt difficult.

I used this thread:

Can't Shift Into First

Worked a treat, now I love the trans.

Most of the tools I had or I made using advice from this forum.

Inniswhe · 09-06-2010, 03:50 PM

I am still tring to decide but I am leaning towards doing it myself. It is really down to the time involved with a busy schedule .

I pressure washed the exterior today to get things ready for the disassembly

I am reading through Pete Zimmermanns tutorial . It is great but kind of assumes you know quite a bit going in and there are not alot of detailed pictures. Once I read the Bentley manual then Pete's work makes much more sense.

The only part I am concerned with is if I get into the pinion bearing play issue that Pete identifies as a weak point in the 915. My tranny has 132k miles so I am not sure if I can expect that issue to come up. If it does it requires outside machining etc. which I will probably have to ship the tranny out for anyway.

Does anyone have a cost estimate on the minimum special tools required to do the job? Replacement parts will be required no matter who does it so the cost of that part really doesn't matter to me.

Thanks

James Brown · James Brown's Garage

It's kind of like baking bread, you put all the ingredients in but don't know if it works till you bake it or, in this case, it's all together and in the car. If you have any second thoughts, then send it out for rebuild.

yelcab1 · 09-06-2010, 04:22 PM

Quote:

Originally Posted by Inniswhe

Does anyone have a cost estimate on the minimum special tools required to do the job? Replacement parts will be required no matter who does it so the cost of that part really doesn't matter to me.

Thanks

You need an old cluth plate. Someone has mine for free so that person should lend it to your for free.

You need 2 sychro tools (maybe at least 1/2 synchro tool)
You need a home made socket for the gear stack (I made mine, and sold it after)
Engine stand, and the proper engine yoke.

Other tools are just what good mechanics have.

Inniswhe · 09-06-2010, 06:09 PM

Yelcab1 ,

Thanks for the info . I have a couple question on the tools mentioned

Clutch Plate - I have the clutch plate that came out and will be replaced. Is this to lock the transmission ? I thought this could be done by placing transmission in two gears at once.

Sychro tools ($200 for both) - Can get these from our host

Home made socket for the gear stack - What is this? I will need to search this item out. Is there a link to provide more info on this item

Engine stand - no problem will need one eventually anyway

Proper engine yoke - do I need this for the transmission work or only engine work?

Peter Zimmermann · 12:24 PM

Quote:

Originally Posted by Inniswhe

I am still tring to decide but I am leaning towards doing it myself. It is really down to the time involved with a busy schedule .

I pressure washed the exterior today to get things ready for the disassembly

I am reading through Pete Zimmermanns tutorial . It is great but kind of assumes you know quite a bit going in and there are not alot of detailed pictures. Once I read the Bentley manual then Pete's work makes much more sense.

Are you sure that you're reading my Tutorial? I worked very hard at making sure that the repair procedure/steps were clear to even a casual mechanic/DIYer who had never done a trans. If you think that more pictures (I couldn't think of a single one that might aid the Tutorial) would help, please list what you would like included and I will consider a follow up chapter based on your input.

yelcab1 · 09-07-2010, 02:01 PM

Quote:

Originally Posted by Inniswhe

Yelcab1 ,

Home made socket for the gear stack - What is this? I will need to search this item out. Is there a link to provide more info on this item

Engine stand - no problem will need one eventually anyway

Proper engine yoke - do I need this for the transmission work or only engine work?

The input shaft comes out with all the gears as a unit. The gears are stacked on top of each other and held in place by a big nut. The used pressure plate is screwed to the garage wall, and is used to hold the input shaft stationary. The big homemade socket is used to remove the nut from the gear stack and to reinstall it to the right torque. I have a picture somewhere.

The engine yoke is to mount the transmission on the engine stand while you are working on it. It works for both engine and trasmission.

Christien · Christien's Garage

Custom socket? It's just a 36mm socket, to be used with the biggest effin' breaker bar you can find (torque spec is huge - 200 or something). At least that's what I used. Bought a 36mm 1/2" drive socket, stuck it on a 1/2" drive breaker bar, and attached something to that to increase the leverage. It took all 200 lbs of me (literally, hanging off it) and lots of heat/cooling, but eventually it gave.

Peter Zimmermann · 04:45 PM

Quote:

Originally Posted by Christien

Custom socket? It's just a 36mm socket, to be used with the biggest effin' breaker bar you can find (torque spec is huge - 200 or something). At least that's what I used. Bought a 36mm 1/2" drive socket, stuck it on a 1/2" drive breaker bar, and attached something to that to increase the leverage. It took all 200 lbs of me (literally, hanging off it) and lots of heat/cooling, but eventually it gave.

The "other" socket...from Part 6 of the Tutorial.

Torque specs in the Tutorial...

Inniswhe · 09-07-2010, 05:12 PM

Quote:

Originally Posted by Peter Zimmermann

Are you sure that you're reading my Tutorial? I worked very hard at making sure that the repair procedure/steps were clear to even a casual mechanic/DIYer who had never done a trans. If you think that more pictures (I couldn't think of a single one that might aid the Tutorial) would help, please list what you would like included and I will consider a follow up chapter based on your input.

Peter,

The more time I spend reading your tutorial the better grasp I am getting on it . I am not through it all yet. I went back to the Bentley to get a better picture on what the assembly looks like . The entire assembly drawings in the Bentley make it easier to understand your descriptions . Keep in mind that I have not opened the gearbox yet which probably makes the tutorial much easier to understand but since you asked -

I am not suggesting you dumb it down for first time transmission DIY guys like myself but I suspect most first time non-mechanics could be confused with simple steps and descriptions. For example on the first tutorial the following simple steps right off the start lack photos:

"Remove the reverse light switch (22mm box end wrench), the switch activating pin (needle nose pliers), the throttle linkage bell crank (cut and remove the cotter pin), and, if the transmission has one, the small, right-angle metal bracket held by a cover nut just above the throttle bell crank."

Now I know that if you can't figure what these items are you should not go into a 915 but photos of all of the steps described would help . The Bentley manual is similar in this regard where not each and every step is detailed so one gets pretty used to reviewing all resources before tackling the more technical parts of the 911.

Regarding photos like the one below the text :

"OK, the cover is off, and set aside. In front of you, in all its glory, is the reverse idler, on the pin with the o-ring at its end, the small reverse gear (not synchronized), and 5th gear."

Arrows to each of the parts described takes the guess work out of which gear is which when looking at. The following link uses this technique which I find helpful.

TrannyRebuild

The only other comment I would have is that the tutorial appears to rely heavily on specialized tools which I can understand but in reality most DIY mechanics will probably want to search out the homecooked tool substitutions to keep their costs manageable. In addition to the obvious benefit of learning the intricate details of their car's inner workings most DIY mechanics like to save a few $ in the process. From that point of view I thought the tutorial might be even better suited to a real commercial 915 repair shop who can justify the proper tools. I understand if you don't want to go there as the special tools are obviously the best for the job.

Now please don't take my comments the wrong way. They were only meant as constructive comments to help you understand some of your readers . I am a mech. engineer by day and sometimes have to write process descriptions/operating procedures for systems I've designed and I always find it helpful to have someone with no prior knowledge on the subject read my narratives to help identify areas which are difficult for the reader new to a system to understand.

I thank you greatly for your work on this subject along with your other work . I have a copy of your book which I used extensively when buying my 911 and still refer to. I can assure you I would not attempt this rebuild or refresh myself without your tutorial as I believe it is by far the most complete step by step description that I have found. I also understand that the more photos and adding graphics like arrows etc. takes more time and since this is not a book being published its probably pretty hard to justify any more time on the project.

I have a question for you if you don't mind. With a 84 tranny with 132K miles and only typical 1-2 gear synchromesh symptoms is it likely that the "weak" pinion head bearing race/case issue will need work for a proper life extension rebuild. I am not close to any Porsche experienced machinists so that work will be a pain to get done if needed.

Also is the 911 engine yoke required for the transmission or is it a nice to have part. Will the transmission be damaged using just a standard engine stand ( 4point) without the special 911 engine yoke for the tranny work ? I can start this weekend if I don't have to order that yoke which will take a couple weeks to get to PEI Canada.

Thanks

Ross Wheatley

Rot 911 · 09-07-2010, 05:36 PM

Why are you even rebuilding your tranny? You said it was now shifting ok between 1-2 shifts. All of them need a slight hesitation between 1-2. At 131K miles I think you have plenty of more miles you can put on that tranny before any rebuild. I am talking tens of thousands of miles.

Peter Zimmermann · 09-07-2010, 05:49 PM

Thank you for your post, Ross, including the kind words about my book.

Your transmission weighs about 120 pounds, so if you can find an ordinary stand that is constructed to handle that weight you will be fine without the heavy duty stand/yoke that you can see in my Tutorial.

Your '84 could go either way regarding the pinion shaft bearing. I've read that there is a cut-off build number for transmissions with the large OD M/S bearing (that will likely have the loose P/S bearing race issue) vs the small M/S bearing (that will likely NOT have the P/S bearing issue), but have found that information unreliable. I can only offer that the later your '84 is in the build process for your model year, the better chance that your trans has the small M/S bearing (I've seen this but have not done enough late '84 transmissions to definitively say that it will be one way or the other). You will just have to open yours up and see what you have.

Regarding tools, so much emphasis was put on tools in the Tutorial because of all the DIYer jobs that can be done on a Porsche 911, the 915 is all about tools. They will make or break the job, simple as that. Like you, my father was a mechanical engineer, and he taught me that there are jobs that can't be done with an adjustable wrench and a battered screwdriver. The investment required for proper tools is considerable, especially when you know that they will only be used once. I appreciate that, but I also appreciate how the luck factor must increase every time that a home-baked tool is used in order to successfully complete the repair of a properly functioning 915.

100,000 miles is my goal; if I do my part (I always try), and if the driver does his part, every 915 will last 100,000 miles+. Unfortunately, few do, and many never work as intended.

I will look forward to your next post.

yelcab1 · 09-07-2010, 05:54 PM

I'll come to Peter's defense.

Peter has been the most useful on this board when it comes to transmission. The other person is John Walker. His comments are always helpful and perfectly geared toware DIY. He hides nothing, and always is willing to share his secrets. So does John Walker.

On the yoke thing, you don't need it. It is much better to have it though, especially on the assembly.

johnsjmc · 06:15 PM

The $200 syncro tool. Is that to remove the syncro teeth from the gear? If so then I do it with a sharp wood chisel and several hits spaced around the gear. More like $10 than $200. I hold the shaft with a used clutch disc held in a bench vise. Use a new nut and do it back up tight.
Good snap ring pliers are nice but cheap one will work.
Usually the 1st gear downshift crunch needs 1st teeth,syncro ring and 1/2 slider. I would replace 1 and 2 syncros ,maybe 3rd and flip over the remaining one if on a tight budget. I doubt you will have a ring and pinion issue on a SC or Carrera with that street driven mileage.
Take plenty of pictures when dismantling and mark stuff . Box is really fairly easy. Pay attention to the placement of detents and the reverse light switch pin is offset not centered.

Rot 911 · 09-08-2010, 05:14 AM

Quote:

Originally Posted by Peter Zimmermann

if the driver does his part, every 915 will last 100,000 miles+. Unfortunately, few do, and many never work as intended.

Really? I don't think I know anyone with a 911 with fewer than 100K miles and none of them have a rebuilt transmission and most appear/sound to shift just fine.