Transmission Experts please! 901 vs. 911 question

[daniel911T]

Hey all,
My old 901 is toast, but I continue to drive on it lightly and carefully. The first, second, and third gear synchros are all grindy. Rebuilding her was a planned winter job, but the cost of new gears and synchros is honestly more than I can afford.

I have been very generously offered a solid 911 transmission. In the interests of out of control clutch costs, I would really like to keep the clutch actuation mechanism from the 901.

I am of the impression that the guts of the 901 and 911 are identical. Is this true? Could I put the 911 guts in the 901 case?

If not, is there a way to modify a 911 to accept the older style clutch?

Any other ideas regarding this are welcome. My goal is to get a solid tranny that will use my old school clutch, for minimum cash. This is just a weekend road driver. Sadly, she probably won't see any track time, just not that kind of car.

Thanks!

Dan

[Joe Bob]

A 901 is used in the 914. Check out "Dr. Evil" at 914world.com - A Porsche 914 Community / Forum / Club

He lives in Ohio and has access to a ton of parts, many that are interchangeable with your trans. He has a DIY rebuild video or can do the deed for you.

[Grady Clay]

Dan,

Yes, you can use the ‘guts’ of the type 911 in your 901.
There is a difference in the gear ratios (’69 type 901 = A-F-M-S-Z, ’70-’71 type 911 = A-GA-O-V-ZA).
You will also need to reset the three ring & pinion (R&P) settings.
This keeps your ‘number matching’ casting and the original 215 mm ‘push-type’ clutch.

I recommend this route, combining pieces so you retain your AFMSZ gearing (the ‘GA’ 2nd gear will feel ‘too long’).
You will probably still need to buy a few new pieces for syncros and engagement dogs/sliding sleeves.


Yes, you can easily modify the type 911 casting to accept the pivot for the earlier 215 mm ‘push-type' clutch.
This requires disassembly and (using a mill) drill and insert for the earlier pivot position.
The type 911 casting has the necessary boss for this conversion (your ’69 does not have a boss for the ‘other-way’ conversion).

The 914 casting will work (with some other mods) but is a different (lower?) quality magnesium casting compared to the type 911 (and 914-6).

EDIT
I recomend that you dissasemble and inspect the type 911 before you do anything to the 901.
Too often these suffer from old age and abuse (driven without the clutch completely releasing).
Carefully inspect and post images for our comment.

Best,
Grady

[Peter Zimmermann]

I think that lots more info is needed (mileage on your trans, repair history, etc.), but I have always deferred to dis-assembly and inspection of the existing trans before launching the project off a financial cliff with an unknown bottom. At the very least your trans should be taken apart to determine the condition of the ring & pinion before making any other plans.

[RWebb]

may be useful

There sure are a lot of parts in a 901 box - 914club.com

http://forums.pelicanparts.com/porsche-911-technical-forum/196697-taking-apart-901-gearbox-how-do-i.html


an old thread of mine re re-locating the ball pivot.
http://forums.pelicanparts.com/porsche-911-technical-forum/188355-moving-clutch-lever-pivot-ball.html



you can also buy a billet intermediate plate and do some other hot rodding on these things:

http://forums.pelicanparts.com/porsche-911-technical-forum/525976-901-gearbox-billet-intermediate-plate-suggestions.html#post5625358

Gear Threads:
http://www.early911sregistry.org/forums/showthread.php?38787

http://forums.pelicanparts.com/porsche-911-technical-forum/245339-how-identify-901-gearsets.html

http://forums.pelicanparts.com/porsche-911-technical-forum/258809-identifying-901-911-gears-versus-915-gears.html

http://www.typ901.org/showthread.php?t=896&highlight=gears


Rebuild Article on 901 Tranny is dead link now - may be somewhere else:
http://home.san.rr.com/pb914/

[Zeke]

If you get into the thing and determine exactly what you need and what will fly, you can use used parts for a lot of the repairs. The donor trans might sell for enough to fund what you need. Check the dog tooth rings for wear and good profile. The 901, 911 and 915 don't like bad dog rings. New, they can be over a hundred bucks, but they just have to be good, not great.

[TimT]

You can with a little bit of imagineering... use the 911 trans with a 901 push clutch

and vice versa...

The location of the fulcrum for the clutch fork is different between a 901 and a 911 trans..

The casting has the ghost of where the other location for the pivot is..

Bad pic of the bellhousing





As a footnote to how many 9XX things can be combined, I have a 914/6 with a 3.2L engine, and a pull type clutch with a Centerforce 915 pressure plate...

It can be done... just need to imagineer a bit

[daniel911T]

Originally Posted by Peter Zimmermann

I think that lots more info is needed (mileage on your trans, repair history, etc.), but I have always deferred to dis-assembly and inspection of the existing trans before launching the project off a financial cliff with an unknown bottom. At the very least your trans should be taken apart to determine the condition of the ring & pinion before making any other plans.

Pete,
Mileage is unknown, but I'm pretty sure it's never been opened. The body has about 80K, so I think the trans has something close to that. However, it's spent a lot of time sitting, or owned by people who didn't know or care about the car. Basically, it's had a short, in terms of mileage, hard life.

I'm quite confident that the R&P is especially soft. It groans under acceleration, and there is a very noticeable clunk when going from accel to decel. Cruising, it's kind of noisy, but otherwise ok.

The car had been driven for a very long time with completely worn out or missing shift bushings. There was over 1/2 inch of slop back and forth at the shift coupler when I rebuilt it. I'm pretty sure that contributed significantly to the death of the second gear synchro. Since it's had a new engine in it it's picked up some new tricks, like not going into first gear unless the car is moving, and grinding into all the "up" gears (R,2,4).

She's getting driven for the rest of the season, but she probably won't see 2K miles before rebuild. When it's time to get in there and diagnose, I'll be sure to post pictures.

The point of the 911 question was simply that a friend offered to sell me the matching tranny to my engine, both 1970 parts. I just really don't want to go to the newer, '70+, clutch style, partly because I don't want to modify the actuating mechanism, and mostly because parts for the later clutches are more than twice the cost. Besides, I have a freshly resurfaced flywheel, new clutch, pressure plate, and throwout bearing with less than a thousand miles on them. I want to stay with what I have.

The trusty 901 on my car is very tired. I'm trying to come up with a way to do a very expensive job for the minimum cost, and be able to have a stock tranny that doesn't grind any gears. This won't be a race prepped unit or anything like that, this car is pretty much limited to spirited street driving.

Thanks for your input!

-Dan

[daniel911T]

Originally Posted by Grady Clay

Dan,

Yes, you can use the ‘guts’ of the type 911 in your 901.
There is a difference in the gear ratios (’69 type 901 = A-F-M-S-Z, ’70-’71 type 911 = A-GA-O-V-ZA).
You will also need to reset the three ring & pinion (R&P) settings.
This keeps your ‘number matching’ casting and the original 215 mm ‘push-type’ clutch.

I recommend this route, combining pieces so you retain your AFMSZ gearing (the ‘GA’ 2nd gear will feel ‘too long’).
You will probably still need to buy a few new pieces for syncros and engagement dogs/sliding sleeves.


Yes, you can easily modify the type 911 casting to accept the pivot for the earlier 215 mm ‘push-type' clutch.
This requires disassembly and (using a mill) drill and insert for the earlier pivot position.
The type 911 casting has the necessary boss for this conversion (your ’69 does not have a boss for the ‘other-way’ conversion).

The 914 casting will work (with some other mods) but is a different (lower?) quality magnesium casting compared to the type 911 (and 914-6).

EDIT
I recomend that you dissasemble and inspect the type 911 before you do anything to the 901.
Too often these suffer from old age and abuse (driven without the clutch completely releasing).
Carefully inspect and post images for our comment.

Best,
Grady

Grady,
Thank you so much for the response! Typically, when a tranny wears out, are the gears themselves usually ok? I know all of the synchros and other bits associated with changing gears wear a lot, and that's going to be a major issue in this rebuild.

The interchangeability is great news! Now I'll have to talk price with the friend, shop around a bit, and see which way forward makes the most sense.

Thanks again Grady!

-Dan

[daniel911T]

While people are interested, I'll ask another tranny question:

When shifting, especially on 2-3, it feels very "notchy." It gives some resistance and kind of pops out of and into gear, not like synchro dead popping, like something just slightly misaligned but overcome by force (not much force). I know synchro dead popping because first gear does that to me sometimes.

Is it possible that I may have a problem with my shifter, shift coupling, or the mechanism in the transmission, that could be fixed by an adjustment?

Obviously the tranny has issues, but if a simple adjustment could make it's remaining life a bit better, then I'm all for it.

Thanks!
Dan

[Joe Bob]

If not during but NOW, it would be adviseable to replace all the bushings, coupler AND engine/trans mounts. Slop is what cause flex and bad/notchy shifting.

Put your hand on the shifter during accel and decel. Flex is evident from your worn parts.

[Grady Clay]

Dan,

I’m sure this is not what you want to hear but I would stop driving now.
All you will ‘gain’ with more driving is more damage.

Yes, the actual gear-pairs are typically less worn than the shifting parts.
Many (most?) times, the gears are reused with new shifting parts (engagement dogs) pressed on.
If there are hardened steel shards circulating from some broken part in the transmission, you risk damaging the gears.

Your description sounds like a possible intermediate plate bearing failure.
What shows up on the drain plug magnet?
Have you removed the shift pivot for inspection?

Depending on the cost of the type 911 transmission, I would buy and disassemble that one first.
That will tell you what you have for parts or if you need to look farther for a suitable ‘core’ – it may take several.
If you ‘buy right’ (and get good parts), selling the leftover parts will dramatically reduce your overall cost.

The two 4-point bearings in the intermediate plate is one of the ‘weak spots’ in the 901/911/914 (and 904, 906, etc.) transmissions.
While I used to routinely replace these (<$50/pair) every time a transmission was disassembled, they are now very expensive.
It will be your (difficult) decision to reuse an apparently ‘good’ used bearing.

Rebuilding a 901 (911, 914, 904, 906, etc.) is an easy DIY project.
The special ‘P-tools’ are easy to make from modified regular tools or parts or available from our host.
Only the set-up of the ring and pinion (R&P) requires unique tools and a high level of experience.
You can sub-contract this to one of the knowledgeable shops.

Parts cost is the issue.
Start yourself a parts list on the known new parts needed.
You will need a set of gaskets and seals.
You will need two CV joint gaskets and 8 M10 Schnorr washers.
Price bearings, sliding sleeves, syncros, engagement dogs, etc. – a bit of ‘shopping’ will help.
You may find another Pelican with a garage-full of transmission parts from a prior project.

I agree with Pete, don’t buy any new parts until you disassemble your 901 for inspection.
Buy core transmission(s) that you can resell without costing much.

Since the engine will sit unused for a bit, plan on draining the fuel and circulate preservative gas/oil through the fuel system.
Circulating fresh engine oil first never hurts. How about fresh brake fluid.
When the engine is out, add a bit of oil to the cylinders and turn the engine at least 720° (two turns).

Here is the ‘devil’: what ‘while you are there’ projects can you anticipate?

Best,
Grady

PS: Randy (Pelican RWebb),
You seem to have a good list of links. Are there more you can list?
I can think of http://forums.pelicanparts.com/porsche-911-technical-forum/571557-1970-911-01-transmission-refurb-issues.html
G.

[RWebb]

Grady, I think that's it on the 901/911 - will check and see.

[daniel911T]

Originally Posted by Joe Bob

If not during but NOW, it would be adviseable to replace all the bushings, coupler AND engine/trans mounts. Slop is what cause flex and bad/notchy shifting.

Put your hand on the shifter during accel and decel. Flex is evident from your worn parts.

Joe Bob,
Thanks a lot! I have some good news, all the bushings were just replaced, the coupler was rebuilt, and the engine mounts were replaced. The only thing that hasn't been dealt with is the transmission mounts.

I have a brand new set of mounts sitting around, and a 915 cross bar I'm planning on adapting. Purpose of the 915 bar is the intense desire to use standard motor mounts all around. It's also much cheaper than the Wevo solution.

With a hand on the shifter, what does the flex feel like?

Thanks!
-Dan

[Joe Bob]

Vibration and movement of the shift lever during accel and decel.

[daniel911T]

Randy,
Those links are priceless! Thanks a lot!

Time to get learning.

-Dan

[RWebb]

ok, post #5 now has all my saved links on the 901 & 911 boxes & gears

[mcaterino]

Grady Clay - helping people down the slippery slope since who knows when!

Dan, I was in a somewhat similar position not all that long ago. I can't add very expert advice on top of what you're getting already, but I think getting a spare box and tearing it down first is a great way to begin. It will get you tooled up, more or less, and let you get to know the assembly process before it really matters. I wish I had done that. It would have at least gone much faster, and given me a larger store of spare parts to swap in.

On your current box I would do a fluid change pronto if you plan to drive if much longer. The drain plug can give you good clues as to what's happening inside, and it can only be for the best to get some fresh fluid in there. I wouldn't take as hard a line on not driving it anymore. Certainly it's been driven in less than ideal condition for some time, and if damage could be done, much has been done.

On opening up my 911/01 transmission (previous condition unknown) I did find a whole slew of unpleasant surprises. Most of the synchros, most of the dog teeth, the pricey 1/R slider, one of the intermediate plate bearings (at least it was outright broken, and I didn't have to think about it too much), were all unuseable. On the plus side, I now have a practically new transmission. I love the way it shifts. I'm sure the vast majority of peoples' complaints about their old transmissions are due to them being in crappy shape. I wouldn't characterize the job as 'easy'. But it was doable for this novice, and pretty damn interesting to learn how it worked.

So I would start stocking up on spare parts (I have a few too - maybe a tranny/zenith parts swap is in our future!), change your fluid, and plan ahead for a big job.

Mike

[Grady Clay]

Originally Posted by mcaterino

Grady Clay - helping people down the slippery slope since who knows when!
Mike

Oh ... at least 50 years.

Best,
Grady

[daniel911T]

Originally Posted by mcaterino

So I would start stocking up on spare parts (I have a few too - maybe a tranny/zenith parts swap is in our future!), change your fluid, and plan ahead for a big job.

Mike

It's good to know that picking up the 911 tranny is probably a good idea. According to the owner, who also sold me my longblock, it was in perfect condition when removed. No grinding, no funny noises, no jumping out of first, no moaning R&P, basically just a straight stock tranny. I am certain there will be parts needed. I have a pretty big Zenith stash, trades are welcome! I also have a '70T longblock sitting around. The case and intermediate shaft are toast, but otherwise it looks very solid. If you need bits...

Originally Posted by mcaterino

change your fluid, and plan ahead for a big job.

This is also a good news story. It has about 2K on brand new Swepco 201. Sadly, it's started leaking, but it's just another another nail in the coffin. It's already known that she is going to need major surgery.

I had a kind of sick hope that with all new shift bushings, a new, properly adjusted clutch, and fresh fluid that it just might be ok. Nope.

I'll be learning a lot about transmissions in the next months. I've done just about every job on a car, but I've always had an irrational fear of transmissions. I've never actually taken one apart. I look forward to a new experience.


Grady,
I already have several "while I'm in there" plans:

-Heat exchangers need to be cleaned and finished in some way. I also need to cannibalize my old ones for good heater box bottoms. The new ones have perfect pipes, but rusted through heater boxes. Is this kind the kind of job a muffler shop would do?

-New gaskets for muffler and headers.

-Repack, reboot, and install clamps on my CV boots.

-Install new sound pad and repaint engine bay.

-Strip undercoat from torsion tube to the back of the car. Repaint. (it's already coming off in sheets.)

-Seriously considering doing trailing arm bushings, seeing as you need to remove the transmission to do the job anyway.

I just replaced everything in the entire clutch system, so I don't think I'll need to do much there. I just rebuilt the pedal cluster, so that's ok. There is probably some rehab to be done on the accelerator linkage, but I'll wait until the whole thing is out of the car to give it a good visual inspection.

The one thing that is for sure, is that this is going to be a MESSY job. Between gear lube dripping out of the tranny, dirty old CV grease, rust and giant dirty, dusty flakes of ancient undercoat, and digging into the depths of heat exchangers, this is going to be a filthy winter!

Thanks again for all the help!

-Dan