915 internal problem with rods/guides

[Roger 911]

I've posted some questions about this in the past, but I think this is probably a better description.

I have a '72 915. My problem seems to be quite unique, or at least I can't seem to find anyone else talking about it. The guide piece on the 3-4 shift rod (I'm not sure exactly what it's called, but it is the iron part bolted on next to the brass fork) rotates down so that the selector arm (with the ball end) gets caught on on it. When in nuetral, this prevents the shift selector rod (where the linkage connects to) from being able to rotate far enough to the drivers side so that the tab on this rod can engage the notch in the 5-R shift rod. In this state, I get 1 through 4 but no 5-R.

A little history. Back in Sept '06 the tranny got stuck in two gears while at Road America. A local Porsche wrench pulled the inspection cover and freed it up using a big screwdriver, and the rest of the weekend it was fine. This past May, I was back at Road America and I first experience the above problem, i.e., loss of 5-R. I pulled the tranny, discovered the problem, used a pry bar through the inspection hole to rotate the guide piece on the 3-4 rod back up, and the tranny worked fine...for a while. I was at Road America again in September and the problem reoccurred after a couple of sessions (maybe I should stick to short tracks where I don't need 5th!). The season was done so I just parked the car until after the holidays.

I got the tranny out and back on the engine stand last night (In the process I managed to snap the speedo drive off the front cover , so if you happen to have a front cover you'd like to sell me, let me know!) Sure enough, the exact same thing has occurred, the 3-4 guide has rotated creating about a 4-5mm gap btween it and the similar guide on the 1-2 rod. At this point, one should probably ask why does this happen? My theory is that it can be traced back to the Sept '06 "stuck in two gears" episode. This itself was possibly caused by a worn shift coupler (since replaced) and driver error (as hard as that is to admit). When the mechanic went in there with a screw driver to un jam it, he may have effectively loosened this guide on the 3-4 rod. Repeated hard use, with the ball end of the lever pressing back and forth on this guide, caused it to rotate slightly, just enough that the ball on the lever now catches on the base of the guide.

I realize now that simply pushing it back into alignment is not a permanent solution. To me, it would seem that I need to re-torque the bolt holding this guide on the 3-4 rod to prevent it from rotating. Since the bolt is on top, I have to pull the main case off to get at it.

1. Is there anyone out there who has experience anything like this before? If so, how did you resolve it?

2. Also, is there an "official spec" as to the gap/clearance between the two iron guides on the 1-2 and 3-4 shift rods? I know 4-5mm is too much, since the ball end won't pass through when in nuetral, but I don't know how close they should be?

I appreciate anything anyone can share with respect to this issue.

Thanks.
Roger

Note: I should probably mention that I had the tranny rebuilt in 2002 and it has only seen a few thousand miles since the rebuild. I must say, it looks pretty good inside from what I have seen. I'll know more once I pull the main case. It shifts great with no other issues than the above.

[Roger 911]

OK, just kidding. But seriously, I guess I got real a "stumper" here. Anyone???

[john walker's workshop]

iron guides? no comprende. you have the shift rods with brass forks clamped on them, then a separate iron piece below the 3/4 fork. is that what you mean? getting stuck in gear is generally caused by a previous "repair" when the detents are not in the proper position when the trans is assembled. there is also a slip on jig that holds the shafts and forks in the proper alignment so the shafts and forks can be adjusted. may not have been done right.

[Roger 911]

Yes, it is the piece that the ball end lever engages to slide the rod fore and aft. It is cast with a channel that lines up with the similar piece on the 1-2 rod when in neutral. It has rotated on the rod so that the ball end catches on it instead of passing through, when you want to engage 5-R.

Thanks.
Roger

[john walker's workshop]

you might want to buy the jig and do a decent adjustment of the forks.

[Roger 911]

Where can you buy the jig? Does our host sell it?

[Roger 911]

Yes they do sell it!

I don't have a factory shop manual. Are there any other sources for the fork adjustment procedure?

Thanks.

[john walker's workshop]

the shafts are turned lock to lock and then you split the difference. just an eyeball and feel thing. the forks and shift sleeves are centered between 1 and 2, and 3 and 4 gearsets, and the clamped on cast piece is positioned fairly close to the other shaft, like 3mm or so. be sure to stack the 5th gear bearing race, thrust washers and 5/rev hub on the pinion shaft and snug up the big nut before doing any adjustments. then there's the detents in the diff housing and intermediate housing to pay attention to on reassembly. these are NOT the two detents under the outer bolts on the side of the diff housing. the two detents under the bolts also need to be in place when you do the adjustments.

[Mahler9th]

I think you have already received some great advice. I am not sure which part you refer to-- it would be helpful if you post a picture or diagram. I have heard of some situations where some parts were bent, and not easy to detect... leading to some diagnostic challenges.

[Roger 911]

Yes, I certainly appreciate JW's advice. I'm ordering the jig right now. I will try to post some pics tonight. When you see it, it's pretty clear what is happening. As I said in the original post, everything else regarding the tranny's operation is fine, all gears engage easily and quietly.

Thanks.
Roger

[ChrisBennet]

You might want to stay away from Road America.
-Chris

[Roger 911]

Chris,

You may be right! I see you have an '89 944S2. Guess what? I totaled an '89 944S2 in '98. Where? Road America! Coming out of the carousel in the rain, whack into the wall.

There's no good excuse, It's just too awesome of a track to stay away.

Roger

[Roger 911]

I got a copy if a factory manual (from another kind Pelican) and it does indeed list the clearance between the two iron guides as 2-3mm. As I mentioned mine is 4-5mm. This should be pretty straight forward to fix.

[Roger 911]

OK, I pulled of the gear case cover and it was clear that the 3-4 brass fork had moved slightly on it's shaft (not perfectly centered between the two gears as well as the excessive gap between the slotted guides). I readjusted everything per the factory specs.

Question: Before I close this up, should I be using some type of Loctite on the bolts that clamp the brass forks to the shafts? The manual shows 16-18 lb/ft of torque but doesn't specify thread locker? There doesn't appear to be signs of any used previously.

[red-beard]

I never have used loctite and haven't had any backing off issues. I do like to use a finger painted (very very thin) layer of hylomar for sealing the tranny back up and holding the gasket/shims in place.

[tab tanner]

Curil T works very good as well to seal the gaskets and case, or use Hylomar

[red-beard]

Yep, any non-hardening gasket sealent.

[Roger 911]

Yes, there is definately a lot of discussion and suggestions on the forum regarding the gaskets and various sealants to use with them. Unfortunately, I can't seem to fing anything regarding thread locker on the shift fork bolts. I guess I'm inclined to agree with Red Beard and NOT use thread locker on these bolts.