Well, I took the main shaft apart almost fully today. 1978 Tranmission, apparently around 95k. Case was clean, and the selector forks seem to have beem removed before possibly? I can't tell. All the higher gears and sychros look very good, but there is very apparent rounding of the dog teeth on 1,2, and 3. The bands and blocks are not chewed up in anyway, so I may get away with the dog teeth either sharpened as Jean-Louie from Wisconsin did, or buy new ones (currently 200 a piece from 928intl), as well as new synchro mrings throughout.

A final issue that cropped up, and something that made me think someone was in here before, is that there is extreme chipping on every single reverse gear, as well as the lower reverse idler gear. They each seem to have been rounded off though? Possibly by machine or maybe just from more wear?

I have another early trans, so I may borrow that reverse set to make this unit whole again, as it will be also going in with new LSD plates

As I said, the higher gear dog teeth are basically still squared off like they are from the factory. The smoothing and rounding only starts at 3rd and gets worse to 1st.

I will take pics and post them when I clean up.

I am now interested to see how the 86+ tranmissions are so touted as much much better, with thier different synchro system. As has been mentioned, that could be mostly the switch in 87 to the single disk clutch.

 

Got the rest of the main shaft apart after letting it sit in the feezer over Christmas eve and this morning. Last gear, reverse gear, has a nut keeping it on, and that cam off very easily.

 

I guess everyone is busy with Christmas, but this is my time to spend fruitful time in the garage, so I take the opportunity.

The teeth that are chewed that I mentioned on the reverse gears ( input and lay - or what I will call the layshaft right now) - are actually also the same way on another early trans that I have in the garage.

I'm standing there wearing my new christmas underwear, staring at those teeth, and I remembered, or rather realized, that the reverse gear set does not include sychros. I mean I just finished taking apart the entire 78 trans last night, and so soon I forget!

So I assume the chewed and rounded teeth there are to smooth the chunky engagement of a reverse gear with no synchros.

Now, in this thread,here we have some people speaking to the strength differences between the early and late boxes as it pertains to strength.

How much bigger could the input shaft bearing get? The one on this 78 trans is just huge.

 

Here are some pics:

 

I think I am looking at the dog teeth for at least 1 and 2, if not 3 as well. I already have synchros for 1,2, and three.

I may just try and sharpen the teeth on the selector rings.

The actual stop blocks by the synchros look unworn.

 

8mm. IIRR difference is 92mm vs. 100mm in '78-86 vs. 87-95. If I would make stronger box first thing I would do is to install double row bearing. Single ball bearing allows too much play in input shaft which in turn allows pinion shafts front end to move.

 

However big they are, appears to be not big enough.

Anybody know of some better alternate sources for the input bearing?

 

Brendan, it will be interesting to see how this adventure plays out...

 

Brendan,

your several days ahead of me... just pulled the box yesterday, cleaned it and its on the bench now (balancing x-mas vaca and car work). Nice pics but those teeth don't look too bad to me... how bad was your shifting before? Any tips as I start the tear down?

 

Well, Those teeth are not BAD, but they are rounded, and each dog tooth unit is about 190 dollars or so. So I could do 2 or 3, but thats 600 dollars. Jeez. Never add up your hobby.

Anyway, tips.

Take off the R/P plate first. Then you can see the slector rods and where they will be pushed out. Its wierd but the manuals don't seem to mention that there are freeze-plug-like caps in the front of the trans that need to be removed before you can drive out the selector rods.

Each rod has two pins through the shifter forks. My pins were really hard to get out, and I had to use an amount of force that I was uncomfortable with. Bashing with the hammer onto those pins with the steel rod looked dangerous, and was for my hands.

With those rods out (I used the main selector rod from another parts trans to push these out), you can see that the lay shaft is going to have to be moved aside, just as the manuals say.

Um, to get the reverse shaft out you need to turn the input shaft cover at the back by the R/P - kind of like clock it for t he recess in the plate - which allows the reverse shaft to come out the back.

The manuals says something about non-threaded reverse shafts? Mine has no threads to pull it out like the manual says. I think later cars ARE threaded, so you will be able to easily use back-hammer to get it out. I had to push it out from the case area with a a long extension. Kind of messy, but it worked.

With that, you have to make sure the lay shaft gears (gears stay in, shaft comes out so they fall to the bottom) do not touch the main shat when you have finally gotten the HUGE Circlip out of the front and can see the meat of the main shaft. Does that make sense? The main shaft had 1-4 still on it when I removed it through the back. There is a circlip that is under the 5th gear set as I recall.

I actually had a hard time getting the bearing races off the shaft as I was disassembling it gear by gear. The races were always tight. So I froze it over christmas eve and into the day, and then just lightly heated the races and they slipped right off the (now) 30 degree main shaft.

I don't know if any of that helped, but it really starts to make sense when you are in there. Keep track of the synchro blocks.

 

Its goingt o sound weird, but the plan was to see how the trans worked with an S4 engine attached. Sounds like fun around town. No Place to go 180 around here anyway. I think it will wind out at like 160?

Yes, it is always interesting.

 

At least in '85+ boxes there is no need to remove those freeze plugs. All three selector shafts come out from rear with just pushing them through with bare hands from the top once small springs etc are removed from front end of casing.

On later boxes reverse gear shaft rear end has threads on small hole which allows mounting of a generic bolt into shaft. It will come out easily with bare hands once there is something to pull it from.

 

I removed the springs and pop-shafts from those bores, and tried sliding those selector shafts back just as you describe. I put on harder gloves so I could really push on them. But no luck. These needed to be hammered out. I think I will freeze them when I put them back in so there is no so much trauma.

 

Interesting. Do check if there is much wear on casing. Holes should be just even and straight through entire casing.

 

Getting Concerned. 928intl isn't open right now, but I had assumed I can get these Dog Teeth separately from the gear set ($$$). Sunset Porsche says no.

Pelican has them separately, at least they show they do, as does 928intl.