Conquering My Transmission Woes!

Several weeks ago, I had my first major transmission failure. (I'm not counting knocking the shifter shaft loose almost 2 years ago.) While on my way to work, I accelerated from a traffic light. When I attempted to shift into 4th gear, I heard a noise that was much worse than the typical missed shift. I made another attempt and it was clear that I wasn't going to be able to get into 4th. The transmission was making bad noises in any gear, so I quickly pulled off onto the side of the road. I was pretty sure at least one gear must have broken.

I was feeling pretty good about my decision to get towing assistance through my AMA membership. I called the number, gave them my membership info, and they worked diligently to get me a tow. I was told it would be about an hour, but almost as soon as I got back from buying some Gatorade from a convenient store (it was HOT outside), the tow truck showed up. I asked what the tow would have cost me if I didn't have the towing assistance, and it was 3 times what my AMA membership cost me.

I ended up taking my wife's van to work, and as soon as I got home that evening, I pulled off the primary cover. Everything in the clutch assembly seemed to be good to go. No magnets had fallen from the inside of the clutch basket. No metal bits were on the bottom of the case. But when I rotated the input shaft, I could occasionally hear gear teeth bumping together like maybe a tooth was missing.


The next night I removed the gear set, and I found broken gear pieces in the bottom of the case. I slowly removed each part from the gear set, taking a photo with each step to use as a reference later to help know how to reassemble the gear set. I inspected each piece as I removed it, looking for not just broken teeth on gears, but also for wear on the forks, spacers, etc. The countershaft gear had a tooth missing, and the mainshaft gear for 2nd gear was missing a dog tooth.

I have a theory about what happened. The 2nd main shaft gear is splined onto the mainshaft, while the third mainshaft gear is unsplined and spins independently of the mainshaft. When shifting into third, the 2nd mainshaft gear slides right, and the dogs on the right side engage with the third gear causing the mainshaft to turn at the same speed as the 3rd mainshaft gear. When I shifted into third, I believe the dog tooth broke off and fell down to the bottom of the case, where the countershaft gear eventually made contact. There's not enough space between the bottom of the case and the countershaft gear for the broken piece to pass, and I think this is what caused a tooth to break off the countershaft gear. Perhaps one of the pieces of the broken gears got between the 2nd mainshaft gear and the clutch gear, preventing me from shifting into fourth.

So at this point I'm pretty happy about having a old Sportster. Granted, the gears in this Sportster didn't hold up, although Sportsters are known for having solid transmissions. I also have no idea how hard the previous owner was on this bike. Because it's an old Sportster, brand new gears are still being made for this bike. I might be wrong, but I don't think I could get brand new gears for a Japanese bike from the 80's. These new Sportster gears are made by Andrews, and are probably higher quality gears than what Harley produced.

There's also plenty of used gears available on Ebay. This gave me an interesting option to consider. The last of the Ironheads had essentially the same transmission as the 4 speed Evo Sportsters, but they had different gear ratios. If in addition to the 2nd mainshaft gear and countershaft gear I replaced the clutch gear using the older gear ratios for the clutch and countershaft gears, I'd have the same gear ratios as the later Ironheads and the '86 Evo Sportsters. The advantage to this is that I could then gear up the final drive with different sprockets while still having a respectfully low 1st gear. That way, I would have an engine speed of about 3400 RPM at 70 mph without having trouble taking off in 1st.

There was a forum post that discussed this option. I knew I'd have to get older gears or maybe newer non-Andrews gears. From what I hear, there are some quite respectable gears made in Taiwan. I went as far as discussing this with a seller who had the clutch gear I'd need. But then I ran across another post on the same forum that discussed how this option did not work out so well for one guy. You can read the discussion here: http://xlforum.net/vbportal/forums/archive/index.php/t-1539783.html

So I ended up buying two Andrews gears from JPCycles. It cost me about $140, which seems pretty fair. The 2nd mainshaft gear was shipped much more quickly. This makes sense, since that gear spec has been used since about 1957. No doubt quite a few of these were in stock. I had to wait a little bit for the countershaft gear, but considering these are for Sportsters from '87 through '90, it's quite understandable that these weren't immediately in stock.

Waiting on the gears to come in gave me plenty of time to clean the remnants of the old primary gasket from the primary cover and case. I got a shard of plastic with one straight edge, and ground it to an almost sharp edge for a scraper. I really didn't want to resort to using razor blades - no sense in cutting into the case. I soaked the gasket bits in some solvent - can't remember which - and diligently scraped away.

Putting everything back together went smoothly for the most part. I did notice some major wear on one of the forks that looked like it must have been from rubbing up against a piece of broken gear. I was initially horrified and disappointed that I didn't catch it before I ordered parts. But after cleaning it up with a file and seeing how it fit with the gear, I decided it was almost certainly not an issue. I had my photos to look at as well as the Harley repair manual. I had studied the transmission diagram quite a bit while waiting on the parts to come in.

Inserting the gear set into the case was fairly straight forward. I did have to try a bit to get it to slide all the way in, but it wasn't too big of a deal. Putting the primary, crankshaft sprocket, clutch assembly, etc. went smoothly. Nothing else worth mentioning happened for the rest of the assembly. After adding some Mobile 1 75w90, I took it for a spin. I didn't even need to tweak the clutch adjustment.

In addition to taking plenty of pics, there were other things I did to make things go smoothly. As I disassembled the bike, I put all the small pieces in zip lock bags. I had several of these bags with the parts and fasteners grouped in a fairly straight forward manner. I had no problems finding these parts when it was time to reassemble. I also did quite well without using special tools. When removing the gear set, I simply tapped the sprocket end of the mainshaft that sticks out the right side of the case with a nylon hammer. When I was putting the gears set back in, I used the same nylon hammer to tap it back close enough into place to use the trap door screws to finish the job. When it was time to tighten the nut on the crankshaft, I simply put a wedge-shaped piece of oak where the chain met the sprocket. When I tightened the sprocket nut, the teeth of the sprocket dug into the wood a bit and held it in place.

Using a wooden wedge to hold the crankshaft sprocket still

There are obvious things I probably should have done differently. I definitely should have ordered another shifter fork. They may be cheap enough where I might should have just replaced both. I should have ordered spacers, and I should have checked the clearances between the gears. I did manually turn the input shaft and shift from 1st to 4th and back to make sure nothing interfered, but checking proper spacing would have been better. For each gear I replace, I should have replaced the complementary gear, but with my tight budget, I don't feel too bad about that. I might should have replaced the bearings that are easy to replace. Without a shop press, I don't feel bad about not replacing the clutch gear, mainshaft, or countershaft bearings.

Since the repair, the bike shifts very smoothly, but it sometimes has trouble between 2nd and third gear. It never takes more than two attempts to get it into 3rd, though, and the trouble doesn't happen often. I wonder if that has anything to do with the fork shifter I should have replaced. Also, I can hear a noticeable clicking noise that reminds me of when you coast on a 10 speed bicycle. Could that be a bearing showing signs that it needs to be replaced?  I hope not. But if I have to pull the transmission out again any time soon, I'm confident I can fix whatever the problem is, so long as the parts do not cost too much.

Potting

As I mentioned in a previous post, I've replaced the voltage regulator (and by this, I mean the regulator/rectifier combo) on my Sportster. I would like to have simply tested each device within the regulator and replaced only the individual device (transistor, diode, etc.) rather than have to replace the entire regulator. What prevented me from doing that was the block of black epoxy the circuit was embedded in. This stuff is called potting, and it's commonly used in electronic circuits. On motorcycles, potted circuits can and often do include regulators, ignition systems, and engine control units. Understanding why potting is used and why potting can be a hindrance when doing repairs may help you decide whether to pot your own custom motorcycle circuits.

You might be wondering why circuits are potted to begin with. Perhaps manufacturers simply don't want you servicing your own circuits rather than buying parts from your local dealership. But there are actually good reasons to pot, especially for a circuit that is a part of a motorcycle. Motorcycles often vibrate a lot. And even with relatively smooth-running motorcycles, there's bumps and potholes on the road that can jar a circuit. Circuits have to deal with thermal stresses due to engine heat and weather. These mechanical and thermal stresses can damage solder joints, circuit board traces, component leads, and wiring. Surrounding a circuit in epoxy or other hard substance helps hold everything together.

That's not to say that manufacturers mind that potting gets in the way of customers doing their own circuit repair. And that's not just a matter of greed. Most people are not qualified to do their own circuit repair, and even those who know a bit about electronics can accidentally damage something. Suppose a customer has engine problems and they monkey around with an unpotted ECU damaging it in the process. They bring it in for repair and it's under warranty. How does the dealership know that the defective ECU was damaged by the customer. If the circuit is potted, it's not even a consideration.

So as someone who may want to do component level trouble shooting or repair of an ECU or regulator, this means doing so is going to be a huge pain in the ass. It's not impossible, though. You can do a google search to find several pages describing the removal process. This, of course, can cause further damage to the circuit.

As someone who may want to build your own regulator, ECU, or other circuit for your motorcycle, you need to consider whether the benefits of potting are worth the future hindrance to repair. While potting can get in the way of repair, it might mean that you don't have to repair as often if ever. Then again, being that you don't have the R&D resources of a large motorcycle manufacturer, it's likely you'll need to diagnose design flaws with your circuit. That's kinda hard to do with potting in the way. Perhaps potting might even be causing problems by trapping heat leading to overheating components in your circuit.

Perhaps you can simply pot with something that's not so easy to remove. Guitarists sometimes use beeswax to pot their guitar pickups. Parrafin wax might work quite well. Using silly putty might be worth a try. Granted silly putty isn't as rigid, but it may still provide as much mechanical support as you need.

So while potting might prevent you from repairing circuits from a manufacturer, it has a purpose and can still be useful for your own custom circuits. Choosing an easy to remove potting material can make repair easier. And if you choose not to pot, you might find that you simply didn't need it to begin with. In a worse case scenario, you might simply have to resolder a joint or repair a circuit board trace.