Transmission questions, Shifter fork tolerance Options

[Bartlett 914]

I am rebuilding my transmission. The only real problem is the first / reverse operating sleeve. I had one on the shelf and a new syncro ring. The transmission had a problem jumping out of first. While I was there, I made some measurements. The shifter forks fit in the operating sleeves in a groove. There are 2 measurements I made. One is the wear on the thickness of the fork and how much slop there is in the groove. I used feeler gages to measure this. The other wear in more of a diameter of the shifter fork. As it wears the diameteter gets larger and the fork can rock in the sleeve. Here is a picture how I measured this.



The side clearence: Would rock (diameter wear)
first / reverse .010" .028"

Second / Third .003" .060"

Fourth / Fifth .003" .060"

It appears to me that the First / Reverse is worn thin. I think it is in specs.

The other 2 seem to be worn in a diameter (fork would rock back and forth) maybe a bit too much. Can anyone tell me if these forks are O.K.?

[jimkelly]

I would suspect a bad 1st gear slider ( you refer to as operating sleeve - has worn teeth ) or bad dogteeth on first gear or likely both - are you saying all teeth in this area were ok ??

lets see some pics - not from top but from side of teeth - the fronts of the teeth on your 1st/reverse slider and your original 1st gear dogteeth.

i can not imagine that a fork could be so bad as to cause gears to pop out provided it stays in the slider groove. i mean - the fork only moves the slider forward or backwards - once gear's dogteeth is engaged into the slider's teeth, the fork is not doing anything but waiting for a command from the driver.

[Bartlett 914]

The slider was worn. I am pretty sure that was the main problem the transmission had. It is why I got the parts to make the repairs. They were damn expensive. I was just a little supprised that it was not worn more than it was.

The fork questions were more of a follow up in looking for other things the transmission may need. I want to fix everything now and not later. I am pretty sure the first / reverse operating sleeve is O.K.. Haynes gives me a wear limit of .0197" for the fit in the sleeve groove. I am within that range. The others are almost new specs. I do not see specs for the other condition I measured. My concern is the amount of rocking the fork has in the sleeves. The .028" for the first / reverse may be fine but .060 for the others I suspect is too much. This is what I am hoping to find out.

[John]

I think I understand what you are asking, but the shifter only acts upon the shift rods inside the transmission in a fore/aft manor. (This would go hand in hand with the thickness of the shift fork and the width of the groove in the slider)

The "rocking" that you describe is somewhat normal. If this gap was too tight, there would be rapid wear. I don't think that yours is worn beyond service.

If you are concerned, post a WTB ad in the classifieds. I'm sure there are some spare 1st/reverse shift forks someone would be willing to part with. I don't know if another used shift fork would have any better tolerances than yours, but it may be worth a shot.


good luck

just my $0.02

[Bartlett 914]

I think I understand what you are asking, but the shifter only acts upon the shift rods inside the transmission in a fore/aft manor. (This would go hand in hand with the thickness of the shift fork and the width of the groove in the slider)

The "rocking" that you describe is somewhat normal. If this gap was too tight, there would be rapid wear. I don't think that yours is worn beyond service.

If you are concerned, post a WTB ad in the classifieds. I'm sure there are some spare 1st/reverse shift forks someone would be willing to part with. I don't know if another used shift fork would have any better tolerances than yours, but it may be worth a shot.


good luck

just my $0.02

Thanks for the reply John. AA has them on their site (in stock? Who knows) for 135 each. I would still rather find out the tolerance rather then dropping some coin and replacing a good part.

[jimkelly]

how about free - jim

give me a measurement of the width of the groove oin your slider and the inner diameter width of your fork.

i can check my spares parts tuesday.

jim

[Bartlett 914]

how about free - jim

give me a measurement of the width of the groove oin your slider and the inner diameter width of your fork.

i can check my spares parts tuesday.

jim

Nice offer and I appreciate that. Problem is I have assembled the transmission. The measurements I took were just prior to putting the stack in the housing. I went ahead with assembly because I THINK it is O.K. It is not too late to replace it but too late for another inspection.

[jimkelly]

to replace - if you need to - at least you do not need ot take intermediate plate off trans - just remove tail cover to access 1st/reverse slider : )

jim

[Cap'n Krusty]

Sorry I'm late to this discussion. Been out having a life ........

In the over 35 years I've been doing Porsche trannies, I've never seen a worn shift fork related shifting problem other than with the steel forks in early 356s. Bent ones, maybe. You need the slop to keep the fork from exerting unwanted pressure on the slider when it's not being shifted. You really need to use a fixture to align the rails and forks, and the 4mm spacing tool that goes along with it. Centering the fork/slider combination between the gears is done by eye, as is the rotational position of the fork on the rail. EVERY case of popping out of gear I've seen (except for the ones caused by missing coupler bushings) has been caused by worn dog teeth. Look at the slider and the gear. If the teeth aren't sharp and well defined, they need to be replaced. You can usually compare them with 4th or 5th gear dog teeth and spot the bad ones. The Cap'n

[Bartlett 914]

Sorry I'm late to this discussion. Been out having a life ........

In the over 35 years I've been doing Porsche trannies, I've never seen a worn shift fork related shifting problem other than with the steel forks in early 356s. Bent ones, maybe. You need the slop to keep the fork from exerting unwanted pressure on the slider when it's not being shifted. You really need to use a fixture to align the rails and forks, and the 4mm spacing tool that goes along with it. Centering the fork/slider combination between the gears is done by eye, as is the rotational position of the fork on the rail. EVERY case of popping out of gear I've seen (except for the ones caused by missing coupler bushings) has been caused by worn dog teeth. Look at the slider and the gear. If the teeth aren't sharp and well defined, they need to be replaced. You can usually compare them with 4th or 5th gear dog teeth and spot the bad ones. The Cap'n

Thanks Capt'n

I guess I was worying about the fork more than necessary. I am probably in good shape. I will stick with the new First / reverse sleeve that I installed. You mentioned a 4 mm tool for the fork spacing. I have never seen it. Haynes haves you space the forks 2mm for one and 3mm apart for the other. Any chance you have a picture of this tool?

BTW this is a side shift transmission.