I Just Blew Another Tranny

[Jeff Higgins]

To be honest, it didn't actually "blow", but had I kept riding I bet it would have...

I just broke one of the dog teeth off of the countershaft third gear, and one of the gear teeth off of the mainshaft second in my old Ironhead Sportster. I'm pretty sure the dog tooth went first, then took out the gear tooth.

This thing has always been difficult to shift from second to third. It's the only shift that moves a gear on both the main and countershafts, so it has two chances at a "false neutral". If I am very deliberate, I never have a problem and it shifts like butter. If I get distracted, don't pay full attention and release the shifter too soon, it sometimes does not fully engage. I'll let the clutch out and find it's in that false neutral, but then it will bang, really hard, into gear. When I'm on the gas, with the clutch out. I'm sure that's what finally broke it.

So the tranny is out and with my buddy who does this kind of work. We're just going to replace all of the gear sets. The shift forks look brand new, as do the pawls and springs and other little parts. I'm going with Andrews gears across the board, stock ratios on first, second, and third but their "C" set for the clutch gear / countershaft gear. Stock is 27/17 for a 1.588 ratio, their "C" set is 26/18 for a 1.444 ratio. These trannies are notorious for their big gap from third to fourth gear, this "C" ratio set closes that gap a bit by raising the first three gear ratios (fourth is 1:1). I've heard good things about it.

Anyway, I think I dodged a bullet with this one. The broken teeth fell into the bottom of the tranny and didn't break anything else. Could have been a lot worse...

[flatbutt]

The best part of this is that it didn't lock up on you putting you into a nasty fishtail.

I had a similar false neutral on my R11S. I had to hold the shift lever until I felt the gear engage. IIRC it happened most often with 2nd and 3rd as well. Wierd.

[LWJ]

Yikes. A near miss. Love your Sporty! A classic.

[masraum]

Congrats on the save (not actually blowing it).

The good news is that it should shift good after this "rebuild" (I assume).

[asphaltgambler]

Jeff, I would look into a billet trap door to stiffen things up. I'm pretty sure they're still being made, makes a big difference in flexibility between shafts.

[Crowbob]

Eeeew.

[Jeff Higgins]

Originally Posted by asphaltgambler

Jeff, I would look into a billet trap door to stiffen things up. I'm pretty sure they're still being made, makes a big difference in flexibility between shafts.

Zipper's still makes them for Evos, but not Ironheads. Trock used to make a steel trapdoor, but they are as rare as hen's teeth. I heard Stociek (spelling?) made one, but they required a lot of work to make them fit. So, essentially, NLA for Ironheads.

I'm hoping going to Andrews gear sets, along with due care and attention in assembly, will be good enough. I did notice a small divot in one of the shifter cam plate slots, so I wonder if that was enough to momentarily hold up the movement of that fork. At any rate, we'll check everything. It may need offset forks or something, something to ensure full engagement on the dogs.

This is the third time already that this same gear has lost a dog tooth. Like I said, I think it's the nature of how it sometimes delays, then slams into gear with the clutch out and under throttle. We'll get to the bottom of it this time. These are ostensibly hell for stout transmissions, so to have broken the same part three times already in my brief span of only 45 years of ownership is concerning...

[KNS]

Whew,

Glad we weren't referencing some Lou Reed song...

[908/930]

I will say I was thinking something different when I read the title.

Jeff can you take a pic of the dog on the gear? I assume it is machined surface but is it a radius or sharp corner? What I have done in the past for my sailboat winch dogs (different but same problem) that were breaking is grind and polish a small radius in there, I have not had a failure after doing this. A small undercut radius is tougher than a sharp corner.

[Jeff Higgins]

I didn't take photos of my failed parts, but here is one of the Andrews countershaft third gear. Notice there are very slight radii at the bases of the dog teeth. The stock gears have absolutely sharp, zero radius corners in these areas. The only way to reduce stress in these areas would be to machine a very shall undercut radius as you describe. You can well imagine the difficulty in doing this just by looking at the photo.



The Andrews gears are of superior quality to the stock gears, and not just for this reason. Superior materials, heat treating, and held to tighter tolerances.

[masraum]

Originally Posted by Crowbob

Eeeew.

Not that there's anything wrong with that if it's your thing...

[908/930]

That is great that Andrews has a proper part available. A die grinder or Dremel with a 1/16 tool bit would be able to carve a small radius in there but purchasing a proper gear is the best way.

[unclebilly]

Does your wife know? I mean…

[spuggy]

Originally Posted by Jeff Higgins

So the tranny is out and with my buddy who does this kind of work. We're just going to replace all of the gear sets. The shift forks look brand new, as do the pawls and springs and other little parts. I'm going with Andrews gears across the board, stock ratios on first, second, and third but their "C" set for the clutch gear / countershaft gear. Stock is 27/17 for a 1.588 ratio, their "C" set is 26/18 for a 1.444 ratio. These trannies are notorious for their big gap from third to fourth gear, this "C" ratio set closes that gap a bit by raising the first three gear ratios (fourth is 1:1). I've heard good things about it.

Lot of long-time IH guys on XL forum rave about the Andrews C set. Almost as much as they react negatively to the factory 20 tooth 2nd gear...

[spuggy]

Originally Posted by Jeff Higgins

Zipper's still makes them for Evos, but not Ironheads. Trock used to make a steel trapdoor, but they are as rare as hen's teeth. I heard Stociek (spelling?) made one, but they required a lot of work to make them fit. So, essentially, NLA for Ironheads.

Factory trapdoors don't necessarily just interchange... Locating dowels were indexed to the shaft/bearing centers - but the bolts weren't and can apparently vary by "a lot". Like 1/4" or so.

[Jeff Higgins]

Good news today, I just picked up my rebuilt tranny. It wound up needing quite literally everything - all new gears, mainshaft, shift forks, shift plate, springs, etc. I went with all Andrews this time, including their "C" ratio gear set that raises 1st, 2nd, and 3rd gears so as to close the gap between 3rd and 4th.



Here is the carnage on the broken parts:



Ready for install:

[Scott Douglas]

Thanks for the pics!
This gear you showed earlier looks like it has a crack already.

Was it supposed to be a new gear?

[Jeff Higgins]

I just stole that pic from the Dennis Kirk site to show as a representative example. Probably just lighting, a piece of lint, or something.

[Jeff Higgins]

Woo hoo! Success! Que the Willie Nelson - "on the road again"...

I finished it up yesterday afternoon and took her around the neighborhood for a little test spin. All went well. So today, with a break in the weather, I took her out on about an 80 mile loop. It shifts wonderfully, no funny noises, and the new gear ratios work very, very well. This was through the Andrews "C" gear set mentioned above, which raises the ratios of first, second, and third while leaving fourth a straight 1:1. It really closes the gap between third and fourth, allowing me to cruise those 45 mph back roads in third without it revving high enough to get annoying, like it used to. All in all, very happy with the results. Except I did wind up riding the last 20 miles home in a pretty decent snowstorm...

[WPOZZZ]

So, it would have been better if you blew a seal.