Tranny Rebuild - Part #2

[red-beard]

Part 2, Rebuilding the gear stack



I hope you cleared a good work space cause this is going to be fun. Get yourself a 2 nice clean plastic boxes. Label them (If you’re into that) Pinion and Drive shaft. If you’re only replacing the 1st and 2nd gear synchros, you only need one box, and you don’t need to remove the shift fork from the pinion shaft

Remove the shift fork from the shorter shaft (drive shaft) and place in the drive shaft box. Don’t remove the shift rods from the intermediate plate. Do the same for the pinion shaft.

If all you want to do is fix 1st & 2nd gear, just remove the drive shaft by removing the large 30 mm bolt and pulling 1st gear off. Place all of the 1st gear stuff into the drive shaft box. You should be able to get down to the big washer, slightly angled washer. Put a label on this washer, as 1st gear.

Tap. And I mean TAP the drive shaft with a hammer. The fit of the bearing runner is very tight. You are not driving a nail! You are tapping. Tap tap tap. Tap tap tap. Once there is a little room, you could use a gear pulled, but lightly taping will work. Once the collar is off, put it in “the box”

Now, you have a couple of choices… The gear puller is the best solution. But all you need is another tool. I hear you cry. My gear puller also helps on pulling the CV joints apart, among other things. And it’s a cool looking tool. If ya got it, use it to remove 2nd gear which will pull the other collar and the other washer off. If you don’t have one, you can use the BRASS hammer to whack the gear stack down. It does work, just be gentle, but not too gentle. The brass hammer takes the abuse, the gears do not. Just turn the stack.

If you are repairing/inspecting 4th gear, do the same with the pinion shaft. You might want to do this anyway, since the pinion bearing is a weak point and ½ of them have been bad that I’ve seen. If the ball bearing fall out of the pinion bearing, you have a bad one. If the brass cage is shattered, you have a bad one!!!!!!!



Once 2nd gear is off, everything should be easy to access and should slide right off. Now is the time to look at the parts.

The gears themselves are always in mesh and spin on those needle bearing collars. So, they are NOT connected to the shaft, except when the slider engages them.

Take the slider, and place it over the synch band and press down. That is what happens when you engage a gear. The band compresses, and the slider slides over it and engages the dog teeth.

First lets look at the slider. It is a ring, with lots of little internal slots, in 3 groupings, and 3 large slots. The slider slides over the triangle member on these 3 large slots.

Now lets look at the slider itself. The small slots should have a point at each end (Except 1st gear which should have a point only on one side). Once the synchro band wears out, which is when you start to hear grinding, the slider is no longer engaging the synch band. It then engages the dog teeth at a different speed and uses the pounding of the dog teeth to get them to the same speed. Not good!

On my 2nd gear, At higher RPMs, I could get 2nd to synch. This is because the rapidly spinning shaft forces the synchband outward and allows it to engage the slider a bit, less or no grinding.

The slider can get some wear from the contact with the synch band, but the majority will come from moving contact with the dogteeth. 3 things happen.

#1. The Slider loses some (or all) of it’s pointiness
#2. The Dogteeth lose some (or all) of it’s pointiness
#3. As the slider wears, the metal is pushed back and mushrooms a little bit, making the slot uneven. This makes it hard to shift into a gear and may prevent the slider from fully engaging the dogteeth, allowing it to “pop” out of gear.

This is a slider with normal wear is could be put right back in (It’s a 4th/5th gear slider, but it is exactly the same as 2nd/3rd). I’d make sure the small slots are straight with a file. Also, use a brass brush and some solvent to remove any gunk in the slots.

The points will force the gear to rotate slightly as these points encounter the dog teeth points. Worn teeth require more force to get the slider into gear and may lead to the slider “popping” out of gear. 1st gear on my 914/6 comes to mind.

The little circumferencial scratches come from syncho contact and are normal.

If the points are a little blunted, OK. Clean up the ring as best you can. If the points are gone and flat. It’s done. Time for a new one. I am investigating the possibility of “repointing” the sliders; taking a blunted slider and grinding back on a point. Not sure of the success of this idea. Hmmm. I will report back on this.

The 1st gear slider is different from the other 2. 1st it has points only in one direction. 2nd, it has gear teeth (revers!) extending radially out from the edge, which makes it’s OD bigger. It costs about twice what a 2nd-3rd/4th-5th slider costs. This is the slider I am considering repointing. My concern is that after repointing, the engagement may be less and it may pop out of gear. If the dog teeth are good, you don’t need much of a point.

Remove the synch bands from the gear by removing the circlip with a pair of snap ring pliers.

Synch bands:

Take a look at these synch bands:



The bad one here is really bad. If you look at any synch band. The side towards the slider will wear more than the side towards the dog teeth. Porsche factory manual suggests that anytime you have one out, even if it is still good, turn it around so the better surface will towards the slider. And I thought this was just a mechanics trick. Nope. Porsche approved! Looking edge on, the side with more metal (thicker) is the “good” side, if you lost track.

If the bad side is so bad it will fit into the dog teeth loosely, it is absolutely done. Pay the $20 and get a new one. If it falls out, it’s too loose. It should compress slightly when going in.

Dog Teeth.

The dog teeth are press fit into the gear. The Porsche/VW removal tool is a 2 piece plate which locks onto the dog teeth. You then use either a press or a hammer to separate the dog teeth from the gear with the cylinder. (The tool pushes the gear). If you are replacing with new ones, it makes little difference how you pull the dog teeth off. If you are using a doner tranny, get this tool. It is cheaper than 1 set of dog teeth.



The “teeth” biting into the synchband here are the dog teeth. These are the part that engages the slider.

All Dog teeth are the same for all gears. All Synchro bands are the same for all gears. So, why do 1st gear dog teeth cost less in the catalog? The dog teeth come with brake bands, the little guys which sit under the circlip. 2nd-5th, need to be synchronized in both directions (Spinng the gear faster and spinning the gear slower – ie upshifting and down shifting). 1st gear only needs to be synchronized in one direction, down shifting. So only the down shift brake band is installed. The only time you would you would need to synch the other way would be if you were moving backwards and tried to synch 1st, which is a no-no. Don’t do it.



The Little bands between synchroband and the inside lip of the dogteeth, are the brake bands.




Part 2B – “Re-assemble the stack”.

Pinion shaft



Reassemble up to and including #6. 1-5 are on the other side of the intermediate plate and done afterwards.

Drive Shaft



Reassemble up to #11. 1-10 are on the other side of the intermediate plate and are done afterwards.

Slide both shafts into the intermediate plate and then assemble the rest onto each shaft. Don’t torque anything down yet. You may need to tap bearing collars back into place.

Using your fingers, snap the sliders for 2nd/3rd into 2nd and the 4th/5th into 4th. The gear shafts are locked together. Torque the castle nut on the pinion shaft. and put its retainer roll pin back in. Torque the main shaft bolt with the deep 30mm socket. Snap the sliders back to the central position. You may need a screwdriver to snap them off of new synchrobands.

Slide the shift forks back onto the shift rods for and put the nuts and washers on loosely. Slide the shiftfork alignment tool onto the gear stack. The shift rods can rotate slightly. Make sure that all three shift rod slots match up position wise.

Center each slider into the middle of between each gear set. Tighten the shiftfork nut. 1st gear, adjust the shift fork so the slider is just off of the synchband for 1st. Tighten it’s nut.

The gear stack is back together!

James