Transmission trouble: 2nd and 4th gear missing?

[daniel911T]

Got my 901 reassembled, tested the shifting before it was installed, and it was found to be satisfactory.

Installed in car, now I can't get into 2nd or 4th. All other gears engage correctly. 4th feels like it may be partially engaging, but I'm not sure.

I have not turned the input shaft at all, engine not running yet, but the pinion shaft has been moved. No change with pinion motion.

Transmission is not filled yet. I want to get this problem resolved before I go filling it with oil potentially have to disassemble and make a huge mess. There is some light assembly lubricant and action is smooth.

There has been one change in the shifting system that shouldn't matter... but maybe? I accidentally used the shift rod from my donor 902/1 box. The plug in the bottom of the transmission with the fulcrum for it is the one that came with the 901. Could this mismatch potentially cause a problem?

Any help is much appreciated!

-Dan

[jpnovak]

Did you adjust the shift coupler? Does it go into reverse?

It sounds like the coupler is not adjust and the forward motion of the shifter (R-2-4) plane is not engaging.

Disconnect the shift coupler from the shift rod and see if you can select all 6 gears.

[daniel911T]

Jamie,
I have tried the shifting both with and without the shift coupler. It worked before it was hooked up to the engine.

Now, I do have reverse (which I think is very strange) but 2 and 4 are inaccessable. I can clearly feel the shift rod going across all three shift forks in the transmission, and I can access all but 2 and 4, and all other gears are very smooth and kind of pop in. With 2 and 4 I can get the right shift fork, and I can move it forward, but it feels jammed going back.

Any ideas?

[jpnovak]

Put the transmission into what you think is the neutral plane. Pull the shift fork guide off the side of the transmission. Look inside. you should see the three recesses for the shift fork.shift rod sections. They should all be in alignment. Are they?

have you tried to rotate the transmission and see if it will engage? rotate the drive flanges a bit and retry the shifter. Sometimes the slider and dog teeth do not align and this prevents the gears from meshing.

[daniel911T]

I did try rotating the pinion shaft (by moving the axles) No change. I'll go take a look at the shift forks and see what I can see.

[daniel911T]

I just checked it out, all is in good order. Even better, I did install the 2/3 shift fork correctly! I was worried about that.

As I could get all these gears before the engine was connected, I think I'm going to try to connect and adjust the clutch to see if releasing the input shaft will allow 2 and 4 to engage.

Just to rule out one possible cause, I did go to the 902 shift fork guide. It was a different casting, but I think all the critical dimensions were the same.

[mcaterino]

Dan,

It seems like it must be something other than the transmission itself. It sounds like you've played with the coupler adequately to more or less rule that out. Any chance there's something in the tunnel blocking the actual shift lever's motion. Or something slightly loose that when pushing forward allows enough play that you lose your leverage?

Definitely a frustrating-sounding puzzle.

Mike

[Jon B]

Dan,

This is often the symptom of a bent selector shaft, a common occurrence, but you say it shifted well before attaching the engine. A bent shaft will bind when pushed into the transmission, in your case R/2/4 shifts.

Other possibilities- your shift rails weren't spaced properly, and are hitting each other when shifting... or best case scenario, your synchros are simply spun completely in one direction, and the servos are locking you out.

[daniel911T]

I was able to bump the starter for a revolution or two. Now 2/4 engage, although still without that satisfying "click" that all the other gears have.

I think it's probably time to just try it out. I have a bottle of cheap break in tranny oil anyway. only $11 down the drain if I have to drop it again.

Thanks for the help!

-Dan

[daniel911T]

So I threw it together and gave it a try.

No joy. First is very hard to engage, 2nd and 4th are totally inaccessible, reverse takes effort. *EDIT* 2nd and 4th will grind if I try to engage them. *EDIT*

I have tried shifting with the coupler attached and detached. Neither work.

I am fearful that I may have bent the shift selector rod during assembly. If this horrible fate has befallen me, how do I fix it?

Thanks!

-Dan

PS Car drives great except for the whole missing gears thing.

[jpnovak]

Are you sure the coupler is adjusted properly? This sounds like the symptoms of mal-adjustment.

Here is my method.

1. loosen pinch bolt on coupler.
2. shifter in vertical position (lower section)
3. put transmission on neutral plane.
4. turn coupler clockwise until it hits stop in neutral plane (toward DS looking at rear of car)
5. Push shifter all the way to the PS of car (4/5 shift plane).
6. Maintain locations of steps 3,4,and 5 while you tighten pinch bolt.

This should give you good fore/aft clearance for the R24 gears.

If the shift selector rod is bent the only option is to pull the gear stack and slide a new one in place. Only a partial diassembly is required but it all has to come out of the car. You do not have to separate the engine/transmission. Just pull the nose cone and then slide the gear stack out while still connected to the intermediate plate.

[daniel911T]

Jamie,
Thanks a lot for the advice. Sadly, the coupler and shifter are not the problem.

If I completely disconnect the shift linkage, such that the shifter is just flopping around, and grab the coupler to move the transmission: I can get the same, 135. Second and Fourth feel like they partially engage, but they never click in fully.

I think I have a shift selector rod problem. When I realized that I had accidentally mixed them up, I compared them, and selected the rod that was slightly longer. I figured it went with the Mg case because the intermediate plate was so much thicker. A long time after the reassembly, I tripped over the other shift rod, and noticed that it had the distinctive blue Swepco 201 on it. That means it came out of my original transmission.

Also, I am sure I worked all the gears on the bench during the shift rod clearance setting procedure. When I reassembled the gearbox, I checked to see that the rod moved, and that it was engaging the forks. I remember I got a lot of resistance, but I just figured the new synchros and dogs were just tight.

The feeling going back into R24 is like it's hitting a solid object. There is no increasing resistance or anything. In a case of bent rod, I would expect increasing effort as you approached the problem area. It is moving freely, then it just stops dead. It does not stick. I started doing some careful listening and noticed that every time I tried to get it into 2/4, the whole case makes a noise, like I'm beating on it with a hammer (lightly of course).

I need to take a careful look at my donor, but I have a feeling that the hole for the rod is not drilled all the way through, and that my slightly longer rod is bottoming out.

Bent, wrong part, or whatever, I can't see any way around dropping this transmission again. Ick.

-Dan

Another quickie question: When assembling the input shaft I set the nut on the 1st gear end to the specified torque. The shaft was completely bound up and unable to rotate. I reduced the torque until it could be turned and I inserted the roll pin. Is this OK?

[daniel911T]

Thanks to all for the help. Sadly, it did turn out to be a worst case scenario. The engine and transmission are disconnected from the car and sitting on the garage floor under the body, and I managed to pull out the whole gear stack, fix, and reassemble in situ.

There were two problems.

First problem, and most serious, the shifter selector rod was wrong.

Here's a little lesson learned: the aluminum 901 series gearboxes are drilled all the way through for the shifter selector rod. Straight through to the diff with no interruption. The Mag cases are partially drilled, so although the back of the hole is open, it's not drilled smoothly through. Mine has a step, and the 902 shift selector was bottoming out on that step. The 901 rod is about 6mm shorter, and it makes all the difference.


Second problem,

When setting shift rod alignment I was working in the neutral plane and concentrating on the spaces between the selector areas. I'm pretty sure all of the rods were rotated too far from where they should have been. Engaging 2nd and 4th was hard, but possible on the bench. Once the shift forks were reset with a strong preference to allowing the detents to find their "happy place" and merely ensuring they all cleared each other, rather than trying to set the 2-3mm spec, the stack easily found all 6 gears on the bench.

I just slapped the transmission together and am happy to report that I can still select all 6 gears.
Yay!

Now it's time to reassemble everything Gonna be a late night.

Thanks again for the help!

-Dan

[sballard]

I came upon this post while searching for a cause and solution to my current problem. My car (72 911T) has somehow acquired the identical problem. I dropped the engine (tranmission attached) several years ago and re-installed it with no issues. It was a breeze to adjust the coupler and the car shifted fine. A couple of years ago, I dropped the engine and transmission again to fix multiple engine oil leaks. I re-installed the engine and transmission, but I didn't drive the car for some time because I was doing body work restoration.

When I was finished with the body work, I found that I could not get the shifter properly adjusted. The symptoms were exactly what Dan describes - I cannot reliably engage 2nd, 3rd, and reverse gears. I have adjusted the coupler many times since and I can't get it right. In another post on this topic, it was recommended that I rebuild the shifter by replacing the bushings. This had no effect.

I am at a loss to figure this out. I have never been inside the transmission, so I doubt that the cause is what Dan found in his car. What in the world caused this and how can I fix it?

[daniel911T]

Originally Posted by sballard

I came upon this post while searching for a cause and solution to my current problem. My car (72 911T) has somehow acquired the identical problem. I dropped the engine (tranmission attached) several years ago and re-installed it with no issues. It was a breeze to adjust the coupler and the car shifted fine. A couple of years ago, I dropped the engine and transmission again to fix multiple engine oil leaks. I re-installed the engine and transmission, but I didn't drive the car for some time because I was doing body work restoration.

When I was finished with the body work, I found that I could not get the shifter properly adjusted. The symptoms were exactly what Dan describes - I cannot reliably engage 2nd, 3rd, and reverse gears. I have adjusted the coupler many times since and I can't get it right. In another post on this topic, it was recommended that I rebuild the shifter by replacing the bushings. This had no effect.

I am at a loss to figure this out. I have never been inside the transmission, so I doubt that the cause is what Dan found in his car. What in the world caused this and how can I fix it?

Hey Steve! Sadly, I don't think you'll find any help from my situation... My issue was due to mixing parts from two very similar, but different transmissions. The specific issue was the shift rod was different between the magnesium and aluminum case transmissions. When I accidentally put the shift rod from the aluminum case into the mag case, it wouldn't move far enough back to engage 2 and 4. My time consuming repair was to completely disassemble the transmission (for the 3rd time) and install the correct shift rod.

However, it may provide some insight for you! You should disconnect your shift coupler from the linkage and try shifting the transmission from the access hole behind the seats. That should isolate the issue to being either in your transmission (probably isn't) or somewhere in the shifting linkage. (much more likely.)

Good luck! Feel free to ask more questions!