Update: The diff is back together and sealed up! Just before wrapping it up I decided to check pinion depth and backlash again, as the shafts and have been in and out a couple times since I checked it before. Very favorable at +0.26mm in deviation, my factory spec is +0.27mm so I'm super happy with this. Backlash came in with readings between 0.15mm and 0.18mm against my factory spec of 0.16mm. So again, I'm pleased. Done with that. Finally! Anyone in doubt, setting up a diff is a long and tedious process. You've been warned.

Now on to checking shift fork alignment. When I pulled the gear stack on initial teardown, I took the whole works out together, shift forks, shafts and all. In other words the forks are still set as they were from the factory. The setting looks quite good.

Now comes the fun part. I have gone for shorter ratio 2nd, 3rd, and 4th gears. The fixed 3rd, part of a 1.550 pair, is about 8mm larger in diameter then the OEM fixed 3rd gear. And as a result, it doesn't clear the shift fork when 3rd is selected. There is clearance to get it in gear, but the gear can only rotate a few mm before it touches the fork. Whoops!

I'm not the first guy to install shorter gears, so hopefully someone can tell me what the fix is... help needed. SmileWavy

http://forums.pelicanparts.com/uploa...1519765895.jpg



Fixed 3rd doesn't clear the shift fork.
http://forums.pelicanparts.com/uploa...1519765895.jpg

3-4 slider in neutral:
http://forums.pelicanparts.com/uploa...1519765895.jpg

Congrats! I suspect that you have quite a lot of hours into the tool fab and R&P set up process. Good Winter project!

I used much more crude tools when I did my 968 box back in the day. In the end, after about 10 hours of adjusting and measuring, I decided to buy about 4 hours of shop time. That 968 box was mated to a 360+ bhp 951 racing engine.

I only have experience replacing one short gear with another. I have never adjusted my shift forks.

I suspect that you may have to adjust.

Incidentally, what ratios are you using 2-5? For what type of engine configuration?

I'm running a euro spec 3.0, but as you'll recall upgrading to the X-Faktory EFI/ITB kit. 1st and 5th are stock USA ratios for a 915/63 box. The new gears are a 2.056 2nd, 1.550 3rd and 1.174 4th.

It doesn't look like a simple adjustment is possible, I have massive interference with the fixed 3rd and the fork.

I am sorry, I meant what kind of bhp and torque... shapes of curves, et cetera.

Not sure what you mean by simple adjustment. 2.056 seems close to a ratio sold by GT. They apparently have a 17:35. The third and fourth you are using appear to be GT ratios, and the picture shows a GT gear. I am no expert, but I think all of these things must be able to work in a 915.

Are you absolutely certain your stacking orders are correct?

You get out the dremel, and not on the gear. :)

I figured that would be the answer! I just wasn't going to do any machining until I knew for sure that this is the normal course of action. I couldn't find any posts on the subject, so I'll report back here. Thanks! SmileWavy

A little work with the dremel and a file and I have clearance between the new 3rd gear and the shift fork. I made a little notch that allows about 1.5mm clearance to the gear face and 0.8mm clearance to the outer edge of the gear. All good.

I've also made some slight tweaks to the shift fork adjustment. In his tutorial, Peter says to shoot for 2mm-3mm in clearance between the black forks, at the extremes of the axial movement of the selector forks. I have just a hair under 2mm at one end and about 2.5mm at the other. If I install the shift dongle it clears the black forks nicely, with about 1mm of clearance between it and the forks. Hoping this is going to do the trick.

Only real concern I have: it is difficult to engage 2nd gear compared to the others. It seems that it takes more effort for the slider to compress the synchro on 2nd then the other gears. Should I be worried about this? I don't want to get the whole thing in the car and find out it is still difficult to engage 2nd.

Notch out of the 3-4 fork:
http://forums.pelicanparts.com/uploa...1520031720.JPG

2 - 2.5mm separation between the forks here. Was hoping for 2mm-3mm.
http://forums.pelicanparts.com/uploa...1520031823.JPG

Did you measure the installed diameter of the second gear synchro ring?

Yes, as I recall all the syncros were in spec (its been a while now.) The brake bands and blocks are reused, but the syncros, circlips, dogs and sliders are all new.

What is it that causes an installed synchro to be out of spec, by the way? They all went together nicely and without issues.

...

A few years ago I installed one of those dog teeth that did not have the 9 deg back cut.

Luckily I measured the synchro after I installed it and realized something was wrong. At that time no one was talking about dog teeth that did not have the back cut....

Difficulty Shifting Rebuilt Transmission
 

When I was bench testing and videoing my transmission I found that some gears shifted better than others, although all gears were rebuilt with new synchro components.

I don't think this is uncommon - the tolerances on the synchro components are incredibly tight and slight variances between components can make the difference (which seems crazy, considering they are wear items...).

Worse yet, sometimes I found that I couldn't get it to shift into some gears at all - which of course was quite concerning. For some reason second gear would seem to lock out sometimes.
I found that bench testing the trans (spinning the input / output shafts manually by hand while you try to shift gears) didn't really represent spinning the transmission at RPM's. The synchro locking mechanisms (anchor, energizer block and brake band) can get stuck in a locked position if there isn't sufficient centrifugal force, and counter force to unlock and re-center the energizer block.

Here's a short video I did trying to explain the synchro assembly if you haven't seen it:

<iframe width="854" height="480" src="https://www.youtube.com/embed/BbBxR8stYRE" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>


When I first installed my rebuilt trans, I ran it through the gears with engine running - without the axle shafts attached/installed (vehicle sitting in the garage). Initially some gears were very difficult, requiring considerable force. After I cycled the trans through the gears a few times (seemed like forever - my arm was tired from shifting...) - the shifting improved significantly, requiring an even amount of force to shift between the gears.

Great work - keep it up.

Gordo

I believe there are a couple other possibilities. One is wear to the dog ring teeth from the synchronizer, widening the inner diameter of the dog ring. The second is wear or damage to the synchronizer ring.

Hi, Kevin! I didn't mention those because Evan has replaced the dog rings and synchro rings with new parts. That said, you're absolutely correct; when those parts get some wear, shifting can get downright difficult. This is why I've always posted that synchro rings should never be flipped; the worn side will sit inside the dog tooth ring and the resulting measurement is usually well outside what's acceptable.

I remember, waaaaayyy back, early in my career, a new customer coming into my shop with a "I just had my trans 'rebuilt' but it shifts terrible" complaint. I drove the car (yes, it shifted so badly I almost had to use both hands to get it into an occasional gear), then looked over the other shop's invoice. Ah, ha! In order to save a few bucks, or out of simply not knowing, the other guys "flipped" the synchros.

I told my new customer that the trans might fix itself with time, but the life expectancy of the synchros would probably be drastically shortened because the sliders would be wearing away the synchro friction material at a high rate. He drove the car for a few weeks, and then sold it. Too bad, it was a pretty nice car.

Drum roll please... THE GEARBOX IS DONE! http://forums.pelicanparts.com/suppo...boldyellow.gif

First, thanks for all the input above. I think I was worrying for nothing. Of course we'll see when I get the box back in the car. As usual I followed Peter's tutorial to the letter for the last steps and buttoning things up. Curil T on all gaskets. A couple fine points:

Electrical tape on the splines before installing the main shaft seal. TIP: wrap from the inside outwards, makes it easy to unwrap afterwards when you can't get to all the tape.

http://forums.pelicanparts.com/uploa...1520187707.jpg


Valve cover crush washers... luckily I had an extra set, so all the nuts on gasketed case joints got these. Great tip Peter!

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Remember the yellow house paint I used to print my ring gear? I celebrated being done by painting the same nut the factory painted red. Kind of symbolic :)

http://forums.pelicanparts.com/uploa...1520188323.jpg



And here it is, looks like a gearbox again!

http://forums.pelicanparts.com/uploa...1520188404.jpg

Congrats on a daunting task well done!

Congratulations!

Yeehaw! Don't forget to add oil at install time!

Thanks guys!

Thanks for all your help Peter! I filled it with oil tonight while it is still on the stand (Kendall of course!) Easy to do now, and I got to check for leaks before putting it back in the car... cheers! :SmileWavy

EFI/ITB project starts here!
 

No sense in wasting any time, spring is coming and I have work to do! I got the engine stripped down to the long block, sent off all the tinware and fan for ceramic coating, and started getting the wiring in place. Earlier I pulled out all the unneeded CIS/OXS wiring before repainting the engine bay and changing out all the fuel lines. The goal is to have as clean an engine bay as possible. The Megasquirt is mounted, harness is run, and this weekend I'll do the majority of the EFI wiring. Yeehaw!

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