Internal access to 901 gearbox
 

1969 5 speed 901. Is it possible to inspect the joint between the longitudinal shift rod and the inner shift rod with the engine/transmission in the car? The joint is apparently held together by a simple clevis pin. I want to inspect for wear/slop.

I have replaced all bushes, etc. in the external gear linkage and have now fitted a Rennshifter but I still have a lot of trouble selecting first (at rest). If I adjust to try to make this easier then I snick reverse when changing 1st to 2nd.

When in 1st, even with the Rennshifter, the gear lever has a lot of play left to right. This may be normal but I would like to inspect the joint between the two rods.

I don't fully understand your reference to a clevis pin. Did you remove the cover plate at the rear of the center tunnel (under carpet below and just forward of the rear seats) and inspect the shift coupler and its bushings? The cover has four screws, remove them and lift the cover to gain access.

The joint I am referring to is within the gearbox. I have replaced all of the bushes in the linkages outside of the box, including the ones in the shift coupler.

I have never seen the inside of a 901 but, from the parts manual, it appears that the longitudinal shift rod - the one that has the shift coupler you mention on its external, forward end - joins inside the box to a short inner rod that runs cross the box at 90 degrees. It is this inner rod that engages the shift forks. The connection between the two rods appears to be via a simple fork and flat setup, held together by a clevis pin and split pin.

Richard,

The pin you describe is accessible (sorta) if you remove the shift pivot on the lower side of the transmission (two M8 nuts). You will want a new paper gasket. Be sure to loosen the oil fill plug first and have new transmission oil available.

I have never seen that joint ever show any looseness or sign of wear. That is not to say some PO didn’t screw something up.

While subjective, visual inspection of the contact places on the pivot and the ‘finger’ may give you an indication of shift linkage wear. You can see (poorly) the contact places of the ‘finger ball end’ to the shift rails.

In general, 901 internal shift linkage parts are VERY long lived. You are correct in investigating the external linkage first.

Lets look at what you have inspected/replaced.

Have you replaced the two bushings at the shift coupler?
Have you replaced the plastic ‘ring bushing’ around the main shift rod in the tunnel?
Have you replaced the ‘ball cup’ at the end of the shifter?
Have you dissembled the shifter and replaced the 1-R lock-out plate?
Have you inspected the main shifter housing when disassembled?
Is the shift handle still in one piece?

There is probably more.

Some years ago I posted some good exploded diagrams of all this.

Best,
Grady

Richard, years ago I bought a short shift upgrade, installed it and made the car much easier to drive/shift and more fun to drive. Steve

Thanks Grady and Steve. Grady - I have replaced all of the parts that you mention other than the lock out plate. It seemed OK other than a small indentation on the metal edge where the shift lever contacts it. I used a peen hammer to bring that edge back to original alignment. Sounds a bit brutal but it was a very small indent and the metal was still there - just pushed up a little. I replace the two springs while I was at it.

Steve - I have now purchased and installed a complete Rennshifter. Problem remains. If I adjust coupler to be able to get into the 1R plane fully when I move the lever to the left then, when box is in 1st, the springs move the lever to the right a sufficient distance that I completely miss the reverse lockout on shifting out of 1st and, rather than 2nd, it goes into reverse. If I adjust to avoid this then I struggle to get the lever far enough to the left to get into 1st. Reverse is never a problem.

Last night I changed to the manual reverse lockout in the Rennshifter. This allows more movement accross the gate to the left. I will road test this today. Fingers crossed.

Thanks again for the information. Changing from the automatic to the manual reverse lockout on the Rennshifter has been a definite help. With the manual lockout set-up the amount of movement available to the shift lever, left to right across the neutral position in the "gate", is increased. It can go further to the left.

This has helped as there is now a little more separation available between the 1R and 23 shift planes. I can still snick reverse on shifting back to 2nd if I am not careful - even with the lockout on - but I don't have to be quite so careful. I have also increased the spring pressure that must be overcome to get into the 1R plane This is simple to do with the Rennshifter.

Thanks again for the help. Unfortunately I have only just changed the oil in the transmission and so, taking the guide fork cover off the side of the box will have to wait till the next oil change, unless I get desparate.

Thought I would give an update on my gear selection problem. I had wondered if my box had wear at the pinned joint between the longitudinal shift rod and the internal shift lever. As suggested by Grady, I drained the oil and removed the guide fork cover. Could just examine the joint and it was tight.

Bit the bullet and dropped the engine/transmission. On dismantling the gearbox to the stage where I had everything out of the main housing I could see that the selector shaft control forks or actuating tabs were badly adjusted. Instead of the specified 2 to 3mm clearances, the forks on one shaft were about 5 to 6mm clear. This is why I was struggling to find an external adjustment that let me get both 1/R and 4/5. The line up across the three tabs was also not perfect.

I decided to dismantle the box completely as it has obviously not been well assembled at some time in the past. Very glad that I did. I found that the big retaining nut on the input shaft was loose and only held in place by the bent tab washer. Whether as a result, one of the cages on the double row ball bearing in the intermediate plate was cleanly broken into two pieces. More evidence of poor assembly.

In spite of this, the gears, etc. all looked very good. I have decided to replace all four bearings, four of the five synchros and the sliders for 1/R and 2/3. All parts were ex stock from Pelican and arrived in Australia today. Now for the rebuild!

Richard,

I hope you can contribute to this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/571557-1970-911-01-transmission-refurb-issues.html


Please share more of your experience.
It seems you and Mike are solving similar transmission issues.

Best,
Grady

Richard,

It will be interesting to see what you've got. The closer I looked the more problems I found. We're on the upswing though, hoping to reassemble most of the box this coming weekend.

Best,
Mike

Another update and a problem. On full disassembly and checking of my transmission (1969 901 5-speed), the only other problem I found was that the input shaft was on the limit on runout. I have decided to go back in with this amount of runout as I felt that I could not risk the shaft in having a shop attempt to straighten it.

The definite problem that I have hit is with my new double row ball bearing, the one located at the intermediate plate end of the input shaft. Inner race pressed onto input shaft OK. Outer race pressed into heated intermediate plate OK. However, when I placed the intermediate plate onto the two shafts and pressed on the other half of the inner race it almost locked up the bearing. Far too much preload.

I have tried assembling the bearing on the shaft with the intermediate plate not involved and same problem occurs.

Am I right in presuming that there is no adjustment possible with this double row ball bearing? It has to have been precision machined by the manufacturer to give the correct preload on assembly? Current plan is to source another bearing from a different supplier and try it. Expensive trial. Any suggestions very welcome.

Richard

Switched races?
 

Hi Richard,

The only thing that comes to mind is a possible switch of one of the input shaft and pinion shaft races. I know, we're too careful and perfect to make dumb mistakes like that. Hmm. No, one of my biggest disillusionments during this restoration was finding that in fact I'm NOT too careful and perfect to make dumb mistakes!

The input shaft bearing race has a shoulder, which should meet the shoulder on the other side, and the pinion shaft race does not. If you put the unshouldered race on the input shaft it would press against the ball bearings. Alternately the two cages in the input shaft bearing may not have themselves been fully seated or straight. They can pop out.

input
http://forums.pelicanparts.com/uploa...1291128651.jpg

pinion
http://forums.pelicanparts.com/uploa...1291128671.jpg

Good luck,
Mike

Another update. The good but bad news is that the second bearing (from a different supplier) assembled with no preload problem and so the first bearing was/is an expensive dud. I now have the box all back together. I hope to get the engine/transmission back into my car over the weekend and find out whether it has all been worthwhile (presuming that I got everything right, which is a big presumption).

Richard,

I have heard of but not seen that problem.
I think the issue may simply be an incorrectly made bearing (a BIG deal for this expensive bearing).
What are the bearing manufacturers?
Any other clues to origin?
We need to identify these bearings.


My take of what happens is:
The inside faces of the inner race must touch when the input shaft castle nut is torqued.
If there is still space between the two races then the nut torque will load (overload?) the bearing.
This causes the bearing to seize.

Does anyone have more information?

Best,
Grady

Another update and a thankyou.

I got my engine/transmission back in over the weekend. I also removed the Rennshifter that I had installed six months or so ago when trying to fix my gearshift problems. I prefer the light touch of the original Porsche system and I also wanted to run the best test possible of whether the rebuild had cured my problems.

Road test was yesterday and very pleased with the result. There is still a baulk at times in getting into 1st when stationary. Seems best to go into 2nd, then into 1st. However, when on the move, shifting is great. Can go up and down the box with ease, including back to 1st.

So thank you to all those who gave advice and comments. It was very helpful and motivational.

I am following up my problem with the original new main shaft double row ball bearing. The outer race is stamped as FAG Germany with a number. However, the two inner races (which gave the preload problem) have no markings. On my limited experience this seems unusual.