915 Shift fork alignment

[UTKarmann_Ghia]

Spent some "quality" time with my tranny this weekend I was able to tear it down, all except for the 41mm bolt on the 3-4 shaft. Replaced the dog teeth on first and second along with their syncro rings and brake bands. I'll take the 3-4 shaft to the Porsche shop tomorrow and have them take off the nut so I can get to third and forth gears.

Everything went very smoothly, but I made a silly mistake and loosened the pinch forks and now I'm going to have to realign them. The Bently doesnt go into aligning those forks so I was wondering if anybody else had the pleasure, lemme know, thanks!

[Jim Sims]

Perhaps John Walker knows a short cut but I think you now need the P360a template:

Adjusting the 1st/2nd and 3rd/4th selector forks/shift guides.

We found the section of the factory shop manual covering this operation incomplete and with inconsistent nomenclature; we had to refer to our disassembly notes, the Haynes and Bentley manuals and the exploded diagrams elsewhere in the factory manual to make sense of the procedure. A plastic version of the P360a plate or template was installed on the shafts and selector fork rods. This template emulates the front wall of the gear housing for shift fork adjustment purposes, correctly positioning the shafts and the 1st/2nd and 3rd/4th selector fork rods. Then the thrust washer (item 31 per the main assembly exploded diagram), the 5th gear with its synchro hub assembly (includes needle cage and race), 5th and reverse speed sliding gear (5th/reverse operating sleeve) and guide sleeve (this is the equivalent of the spider) were installed on the pinion shaft followed by pinion shaft flange nut. The needle bearing and running surfaces (races) received a light coating of Swepco 201 oil. Then the castellated nut was put on the front end of the input shaft. Next the transmission shafts were locked against turning. This was done by engaging 5th gear (moving the 5th and reverse speed sliding gear over the synchro ring of the 5th gear)and by engaging 1st gear (at the same time) by sliding the 1st/2nd speed operating sleeve over the first gear synchro ring. This procedure means special tool P37a is not required; in fact the P37a tool wasn't required at anytime in our rebuild. Then the castellated input shaft nut was torqued to 94 ft-lbs (1-1/16" socket used) and the pinion shaft flange nut (36 mm socket) was torqued to 180 ft-lbs. 1st gear was then disengaged.

Next the 1st/2nd speed selector fork rod (this is the one with the integral shift guide) was turned all the way to the left (driving direction left) and then slightly back the other way so that the flat portion (in the middle of the shift guide section) is "almost vertical". We assumed this is to ensure there is some play to avoid the shift fork applying a constant radial load the operating sleeve. The 1st/2nd speed selector fork was then positioned to put the 1st/2nd speed operating sleeve exactly in the center of the 1st and 2nd gear synchro rings. We used a dial caliper to measure this positioning. Then the fork clamping bolt was tightened to 18 ft-lbs; note there is spring washer under the heads of these clamping bolts . This procedure was repeated for the 3rd/4th speed selector fork. Then the 3rd/4th speed shift guide was adjusted axially along the 3rd/4th speed selector fork rod so that it's vertical shift guide faces lined up with the vertical faces of the integral shift guide of the 1st/2nd speed selector fork rod. The 3rd/4th speed shift guide clamping bolt was then tightened to 18 ft-lbs. We ensured there is .080" to .120" (2 to 3 mm) gap in the vertical direction between the shift guides. We rechecked the "almost vertical" positioning of the flat portion of the 1st/2nd speed selector rod during this measurement; we measured about a .100" (2.5 mm gap). It is apparently important that this gap exist to avoid interference problems. Shifting was checked by moving both operating sleeves (1st/2nd and 3rd/4th) by hand to ensure the gears would engage. 1st gear was engaged again and the castellated input shaft nut and the pinion shaft flange nut were loosened and removed. 5th gear was disengaged, then the 5th reverse gear parts and the P360a plate removed.


Jim

[UTKarmann_Ghia]

Thanks Jim, doesnt sound too daunting. I cant believe I loosened those even though I must have read not to like 5 times The Bently does mention the part about the P360a tool but it's not clear on how to align the forks.

[wevoid]

Matt,

One fact I have never seen properly described is the rotation of the 1/2 shift rail.
The description above is good, except that the "almost vertical" is a difficult target to hit correctly.
I work with the transmissions vertical, you should stand it vertical, even if just for this part of the procedure.
Stand the main shift rod in the case, find a spacer about 13 or 14 mm long that can support the shift rod so that the dongle pivot bolt is the same height as the socket section of the 1/2 shift rail - when in neutral.
This way the dongle will be horizontal, and the radius the tip swings through, can be checked.
I set the rotation of the shift rail to a position where there is 1.5 to 2 mm gap between the tip of the dongle and the opposing face of the socket in the 1/2 shift rail. This position is locked by the shift fork in the 1/2 slider, so the number will vary +/- with that radial clearance.
With the 1/2 shift rail rotation and fork position set (relative to the drive teeth) the 3/4 rail, 3/4 flipper and fork can all be set with confidence using the information from Jim.
With the transmission vertical, gravity is not causing the shafts to hang and give false readings, plus on a bench top it's all at a comfortable height to look at and adjust.

Regards

Hayden