Taking Apart a 901 Gearbox -- How do I...?

[jluetjen]

...Get this pin out? There was a cotter pin that I've pulled out, but this pin doesn't seem to want to come out. I've tried tapping it out with a plastic headed mallet, and I've tried pressing it out with a screw clamp. Any ideas short of a BFH???

[BigD9146gt]

John, a big hammer and i use a socket on the other side to support it and allow the pin to fall into it. Now the fact that you have the intermediate plate in a knurled tooth vice makes me cringe.

[jpnovak]

check carefully. I see aluminum soft jaws protecting the Int. plate.

[jluetjen]

You're right Jamie. A couple of pieces of aluminum carefully shaped with the proverbial BFH!

I'm going to be swapping the intermediate plate with an aluminum version anyhow.

[BigD9146gt]

Aww now i see them. My bad. It was the knurling that caught my eye like a trackter beam.

On a second note, i would use a pin punch also to keep the pin from mushrooming.

[Grady Clay]

John,

I know I don’t need to remind you, but for Pelicans the ring & pinion needs to be reset when you replace the intermediate plate on a 901/911. This is particularly true with an aftermarket plate. You only find out there is a problem if/when the pinion is trashed. Not worth trusting to chance.

Best,
Grady

[jluetjen]

Good point Grady. I've already figured that I'll have to check/measure/adjust everything as I put it back together since there will be parts from 3 gear boxes plus the aftermarket plate in the final transmission.

[Grady Clay]

John,

You never miss a beat with CMA, hehehe.

Post the description of your upcoming 3-into-1 project.

Best,
Grady

[jluetjen]

It will just be a standard short ratio gearbox with a welded up diff. I've got a 914 box, a '71T 911/01 box and the aluminum 901/07 which is in my car right now -- plus a couple of gears that I've bought from people on this BBS.

I'm going to be building up the box using the 71T case and a mix of gears from the other boxes as well as the aluminum intermediate plate and an aluminum diff cover. In order to keep the aluminum box in the car for now it looks like I may need to pick up another M (22:29) gear or I may just start with an N gear (23:29) which will be one tooth away from my plan. Anyone want to swap an H (19:32) second gear (not the shaft mounted kind but the gear for use with a 904 mainshaft) for an M? If so send me a PM. Anyhow, the final set will be...

1st gear: A (11:34)
2nd gear: GA (18:32)
3rd gear: M (22:29)
4th gear: S (25:26)
5th gear: X (28:24)

The car will be a track only competition car with a 7500+/- RPM redline.

In the mean time I'm also collecting ideas on how to remove the shafts from the intermediate plate without the special tool shown in the shop manual. Any ideas?

I've also been thinking about a good way to store the extra gears an avoid my natural cluttered nature. The traditional method would be a box with each pair mounted on a peg. Alternatively I've been thinking about having the gears stored in a box on edge (with suitible padding) with each pair in a vertical slot. I figure a deep tool box with dividers would work if I removed the inner tray.

How are other people doing it?

[Clay Perrine]

This link will help you in the disassembly of your 901 trans. It has some details specific to the 914 side shifter version, but the disassembly of the gear stack will be the same.

914 Transmission disassembly article on 914Club.com

[jluetjen]

Thanks Clay for the link. I already have Redbeard's article as a secondary reference to the factory manual, now have a third source with some good pictures.

[Grady Clay]

John,

Cool project.

Does the 911/01 have the S/N and Type on the rib or rectangular boss? What S/N? While you have everything apart, it would be useful for everyone to post images of the differences between the 914 casting and the 911. Perhaps others can add images of a ’69 901 casting.

I assume you are changing to the ’71 case in order to use a pull-type 225 mm clutch and drop some weight.

Perhaps my memory fails me. Do I recall the intermediate plate is different thickness between the 901 aluminum and the magnesium 911?

For your use, having every gear ratio choice is very desirable. I carry all my gears in an aluminum water tight box. Each gear pair has its own small cardboard box. Each gear is in an individual plastic bag.
I leave the gear oil on the gears and consequently the boxes don’t last forever. I mark the boxes with the ratio, letter, gear position and S/N. The (914) gears that aren’t numbered, I electric etch my own numbers.

For a given transmission case, I swap back and forth between several R&P gears. You keep the pinion shims with the pinion shaft and the differential bearing shims with the ring gear. It spreads the wear and if I find a failure in the pinion, it is easy to replace in a hurry.

An unexpectedly desirable part is the 1st gear input shaft from a 4-speed. I grind the fixed teeth to press fit a 904 2nd gear and TIG weld the fixed gear in place. You can do the same with a 914 “F” or 911 “GA” 2nd gear input shaft and weld a 3rd gear on the shaft. Of course always used the “reinforced” input shafts.

The art is to use four gears around the track at racing speed. If necessary, I expend some clutch life if the start is too slow for the 2nd gear. Some use the very tall 1st but I’m not willing to stress that part at all.

With planning, practice, and preparation, you and one other can re-gear a 911 between practice sessions.

I have a modified jaw on a 6” vice. It has two pins that fit into the intermediate plate. The other side jaw has a brass plate. This lets you grab the plate very tightly and prevents any movement or damage to the surfaces.
After removing the 1-R gears, the detents, and the other shift rails &forks, I use a huge plastic face hammer (SnapOn S-305 that weighs almost 10#) to remove the shafts. One or two blows do it. I make sure I hit straight, holding my other hand under the gears to keep them straight and together. Don’t let the bearing inner races fall to concrete.
On reinstall, I heat the inner races slightly (250F) and they just slide in place.
I have done this on the same parts hundreds of times with no ill effects.

You can make an improved P-260 for adjusting the shift forks on the rails by cutting apart an old 914 transmission casting. Cut away everything not necessary and have easy access to the gears, forks, and pinch-bolts. You want to be able to fasten it to the intermediate plate with at least three studs and the two dowel pins. Make it where you don’t have to reposition the intermediate plate. You can get more consistent adjustment than with the Factory tool.

The P-256 input shaft holding tool can be made from a junk fixed 1st gear.

Some other tricks:
On the axle flange seals, in addition to sealing them in place, I add three little loops of safety wire to prevent the seal from coming out.
Inside the differential housing I made an aluminum piece that locates the input shaft and prevents damage to the input shaft seal. In the shop you should always install the seal after the input shaft is in place. At the track you just want to be able to plug the gears in and not have to deal with the seal.
I have two large Alnico magnets to collect any steel parts. If there is a failure, you don’t want hardened steel circulating through the transmission.
Carry the Helicoil and Timesert tools and inserts in case you pull a stud.

If you feel the need to use an electric pump and cooler, make sure the design and construction can’t cause or contribute to a failure. I have seen some come apart from poor design or construction.

I use a new input shaft roll pin and locking plate every time.

Develop a system. You should be able to lay out all the tools in advance. You should be able to get all the parts back in the right place. Lists, diagrams, and measured parts all help until you can do this in your sleep or the heat of racing.
A 901/911/914/904/906 transmission is exceedingly easy. There should never be an assembly mistake.

If (when) someone else has a transmission problem, jump in and help. It is best to learn from other’s mistakes.

Best,
Grady

PS: Basic 901 transmission 101 for Pelicans.

Porsche gears are a matched pair of gears with matching serial numbers (914 excepted).
First gear is specific to the first gear position and the fixed gear has the smallest spline.
For most production transmissions, 2nd gear fixed gear is cut on the input shaft. The gear-pair consists of both a free gear and the input shaft.
The 904 input shaft has a splined fixed 2nd gear and a free gear as production cars. The spline in intermediate in size between a fixed 1st gear and a fixed 3-4-5 gear. These are peculiar to the 904 input shaft.
Third gears are specific to that location as the gear is cut opposite to 4th and 5th gears. Some use them in the 4-5 position and vise versa but that adds (not subtracts) to the load on the pinion ball bearing – not desirable. It also reverses the ratio.
Fourth and 5th gears are directly interchangeable.
It is desirable to keep the needle bearings and inner races for the free gears with the gear if possible.

G.

[Racer Chris]

I am currently in the process of modifying a 914 mainshaft. I am installing an "I" third gear as second gear.
My machinist suggested cutting splines for the "I" gear to slide over, just like in the stock location. It seems to me that the gear still needs to be welded in place because there is no simple way to prevent it from moving against the bearing it is next to.
Questions I have are:
What is the best filler wire choice for the welding operation?
What direction does the fixed gear have to face? There is a narrow shoulder on one side. Do the gear ident markings face the same direction on both input and output gears?

Thanks,

[jluetjen]

Bump.

Anyone else ever try making their own 2nd/gear mainshaft assembly? Or would it just be easier to convert a 901/911 mainshaft/2nd gear assembly into a 904 style mainshaft by cutting off the gear and just cutting splines so that the stock gears slide on?

Grady; have ever run into this question before?

[Grady Clay]

Chris & John,

Sorry, I must have missed your post.
Too many doctor appointments.

Yes, I have done this many times. A 914 or 901 “F” second
gear/mainshaft will work well. If you are welding on a 3rd
gear, a “GA” mainshaft is a better choice as it gives more purchase.

Do not do any machining on the new fixed gear – just absolutely
clean in the splined bore. Have the mainshaft centerless
ground “D” using the ground surfaces of the input shaft ball
bearing and roller bearing. It is OK if some of the roots of the
old fixed gear still show. Have the diameter “B” where the new
fixed second gear is a press-fit. You should be able to heat the
gear to 250F and chill the shaft to 0F and have the gear slide in
place. It shouldn’t be able to move when the temperatures have
equalized.

I made a tool to locate the new gear axially. The tool locates on
the ground surface “C” and is held in place with the input shaft
nut (not shown.) The dimension “A” locates the new gear axially
while the temperatures equalize.

At this point I like to test assemble the gear clusters and
measure second gear backlash for every tooth. Once I’m
satisfied it is OK I disassemble and reinstall the locating tool.

I like to TIG weld only where the contact surfaces are and not try
and fill the gaps. This way if one weld develops a crack, the
crack won’t propagate. I weld one at a time and let the parts
equalize temperature. Once you have two welds on the engine
side you can remove the locating tool and alternately weld each
side, pausing to let cool. Sorry, I don’t remember what filler wire
I used but it was minimal.

Great care must be taken to prevent splatter from getting on the
splnes or other ground surfaces. Make some protection parts in
addition to anti-splatter cream. For the welding surfaces, as you
know, cleanliness is next to Godliness.

On final assembly, re-measure the backlash for every tooth.
Start with the same pair of teeth and compare to the
measurements prior to welding.




Sorry for the lame diagram but the last time I looked at one
of these was almost 20 years ago.

Since you are going to the effort, make several welded input shafts.
The H, I, J, K, and possibly L are most useful depending on the tracks you run.
For very short (tight) tracks and auto-X a welded E might be useful.

I am convinced that welded inputshafts are stronger than
splined gears on a 904 shaft.

Depending on engine size and power, an electric pump, screen
filter, cooler and spray tube might be worthwhile. Lots of oil flow
to the meshing side of the R&P is very worthwhile. I mount
several large Alnico magnets inside the transmission to capture
errant metal pieces. It is bad enough if something fails. It gets
worse in a hurry if the hardened steel parts circulate through the gears.

Best,
Grady

[Grady Clay]

Guys,

Some more thoughts on this:

Never, ever use the early 901 input shaft with the small (12 mm) threaded part next to 1st gear. It will fail. Always use the “reinforced” (14 mm) version.

On the new fixed gear to be welded on, note the slight chamfer on the edge of the internal splines. Grind a matching chamfer on the input shaft. This will facilitate good welding.

When test fitting the gear cluster, note the axial engagement of the second gear teeth as the free gear is at both extremes if it’s axial free-play. You want to insure maximum tooth engagement particularly in the “under load” direction. Prior to welding you can adjust the fixed gear axial position slightly.

When it got around to welding, I lament not having made better tube tools to protect the input shaft and gear teeth from the inevitable “pop” of an amateur welder.

I have seen this technique also used on a 915 where a fixed second gear was welded in place of a ground off first gear.

Best,
Grady

[randywebb]

Which trannies came stock with the “reinforced” (14 mm) input shaft?

[Grady Clay]

Randy,

‘68 had the reinforced input shaft for sure. ’66 didn’t. I think the change was during or at the end of the ’67 model year.

Of course Porsche introduced the “simplified” differential in ’68. It is a wonder that any ’68-’71 transmissions survived. The “fix” for the simplified differential came out in late ’71 as I recall. Do a search on my name and Simplified differential for all the particulars.

Best,
Grady