94 tranny jumps out of first gear

These are new gears.

Those pics from Moto Bins look like square dogs and square windows. The pic below from Max BMW looks like curved dogs? This is a pic of 4th gear.



So is it allowed to mix dog and window shapes? I have seen it in a trannie I took apart but that doesn't mean it's allowed.

I couldn't find another pic of 1st gear. There was none on Max even tho they do sell it.

Are the new gear dogs and windows undercut to help them stay engaged ? How much ? How to measure ?

I have never heard of any undercutting. I have heard of recutting in rare occurrences by people that know more than the rest of us. I think somebody offers custom gear box blue printing that involves stuff like that.

Edit; Snowbum talks about undercut square dogs on 3rd, 4th and 5th gears. He does not go into much detail on this subject and does not state if it was all years of square dogs.

OK, I found it. Anton lists changes to the gear dogs on his tech pages; http://www.largiader.com/tech/airtrans/

The curved or round dogs are the earlier (I will later edit my ponderings so as to cut down on confusion) But there is still confusion because the dogs in the Max photo do look curved.

By undercutting I believe we're talking about a slight helix on the mating surfaces of the cogs and pockets - this is a tried and true industry standard on many automotive transmissions where the "suck together" forces that are developed under accel or decel are effective at reducing the tendency to jump out of gear.
I would utilize an indexing head (just gained one for a birthday gift) on the milling machine to grind the surfaces, not sure on angles but probably easily found on a web search.

So now I'm thinking Jeff that the gears I have are not suitable for your '94 transmission. But they may work. So not sure if that is a good idea or how long they could last.

Maybe you want to take some time to look for suitable gears. They could happen. I do keep an eye on Ebay for parts transmissions, something like that.

If you decide you want to try the gears I have they are still yours.

Could somebody explain why Max BMW's pic of a 4th gear looks like curved dogs?

no explanation here (and thanks for the stash tour disston) but I would like to offer-up a red herring that comes to mind:
back on Jan. 17th in the /2 yahoogroups a fellow named Rich offered an observation that the gear selector cams - the profile of the slots particularly - appeared sub-optimal, resulting in the selector fork not driving the driving dog to full engagement in one direction.

I found this interesting but can't offer first-hand experience.
Within that discussion there was some talk of similar issues with other makes, not Getrag.

I should add that earlier 4-speed transmissions require adjusting/confirming selector fork centering between gears and Rich noticed the issue after confirming that detail.
Might be worth looking at - could be Getrag had that all sorted out with the 5-speeds.

I think Charlie's gears are the same as the Motobins pics.
It appears the Motobins gears are not square cut from new. The Motobins pic is not very clear, but the light shows the ends of the teeth and the top of the pockets are slightly rounded.
Thinking about this some more (at 5 am here) tells me they are slightly rounded to prevent chipping of the edge when the gears engage.

The ends of the dog teeth and the ends of the pockets clearly have a radius. Just to be clear, I'm talking about the corners of the gears that make first contact when engaging.
Clear as mud.

It's called Keystoneing, and was a dodge back in the early days to stop a trans from jumping out of gear. It was so effective that manufacturers started doing it on new gearboxes. I had a Mitsubishi Triton gearbox apart a couple of weeks ago, and was showing the apprentices at work the keystoneing, something so common these days no one even looks.

I found and re-read a thread on Practical Machinist about different methods of undercutting gear dogs to keep from popping out of gear .
There was some consensus about how to go about it , mostly involving equipment that many here don't have , but a couple of posters had claimed success with careful use of a die grinder .

I copied and pasted this , written by mgunner770x on Jan 11 , 2013 :

I had a high-performance 250cc two-stroke engine (offroad hill climber) that was popping out of 2nd gear. Like CalG mentions above the rounding was very plain to see and I simply marked the dogs with a marker and under cut them (very minimally) with a small die grinder fitted with a flat grinding disc. I worked and fitted both pieces together by hand until I had good contact on all faces. I realize this is a very "crude" process and I think you're on the right path with your plans, but wanted to let you know that this worked out just fine for me. It completely eliminated the popping out of gear and I continued to run the bike very hard for another year without any issue. During a subsequent (and un-related) tear down I inspected the dog faces and it appeared that they had "worn-in" together nicely, meaning that any of the areas where my crude grinding didn't allow perfect contact seemed to have worn into both pieces uniformly without any evidence of undue wear. Just as FYI

This has been an exploration into a rather vague part of the Airhead 5 speed transmission. The Shadetree die grinder fix is my favorite.

I have a 1978 transmission taken apart waiting for a new rear cover. It has curved dogs.

Jeff, I think you will be able to figure out what to do once you get the new gears. I'm including the 2nd gear, which is also a curved window for the other side of the 4th gear. So maybe at least you have matching gears on the output shaft.



BTW, these are possibly the gears that came off the output shaft I sent you 2 years ago.

Now I see what you mean about the curved windows, Charlie. For all intents and purposes it's the same gear I'd say, without knowing the bore size etc. Looks like the later gear got some weight reduction!

Other than a brand new 1st gear and possibly 4th, I don't think I'll find s/hand gears that are in any better condition than what I took out?
Having said that, I've just had another look at the 1st gear that came out of my 81 tranny when I smoked the output shaft. It is in better condition than the 92? 1st gear pictured in the first post.
The depth of enagement of 4th gear into 1st gear is clearly deeper. I'd say the '92 1st gear has been running with much less engagement for a long time, going by the contact pattern. I think this is evidence of the effect of the output shaft moving rearward by 1.1mm
The shallower engagement has most likely led to an increased angled contact face on the 1st gear pockets, helping it to jump out of gear. Interestingly, the corresponding contact faces on the 4th gear dogs appear to be square, meaning it has suffered less.
While I'm at it, both ends of the dogs and pockets are subject to wear. From powering forward, and also from engine braking.
The end of the pocket with the most wear, is from powering forward.

Course, I could be full of shit.



Hmmm, these two 1st gears are telling me an interesting story.
Fwiw, the first gear from my 81 tranny never gave me any issues.

I'm all in favour of a combo clinic including both the cam plate slot travel study in Renner's post, and the dog grinding procedure mentioned in Uncle Pete's post, once you've chosen your poison (that is gears to reuse).
Although I'd be looking to set up a jig for a repeatable back cut form angle on all mating sides - the easy part would be initiating from the peak where there is going to be more or less a uniform starting point on each dog, and each slot from running contact and through random combinations of engagement. The square teeth obviously easier than the rounded profiles, but doable. The amount of material to remove is negligible and resulting significant "gear lock in" would more than offset potential strength reduction with an end to clashing about under high load states.
Jeff, you are no stranger to setting up jigs I believe.

Although I'm capable of Barbaric Mending Work, if I were to look at recutting gears, I'd just take them to work and hand them over to the guy with the cnc machine centre.
Perfectly indexed.
As you said Lorne, the pockets would be the more difficult operation.
I do feel confident that the parts I have are serviceable.

And all I can imagine myself doing is cutting gears with files and sandpaper. What's a CNC?

Computer Numeric Control.

Computer controlled machinery.

I was kidding.

But I would love to have had the opportunity to learn machining. I enrolled in a shop class in High School but the class was discontinued because the teacher got fired for alcoholism.