258 replies to this topic

[alexk243]

My bike is jumping from 3rd down to 2nd under any sort of load, What specifically would cause that? I was assuming it would be a mangled gear... could those cogs being worn cause it to jump down like that?

[TYREDNGRUMPEE]

My bike is jumping from 3rd down to 2nd under any sort of load, What specifically would cause that? I was assuming it would be a mangled gear... could those cogs being worn cause it to jump down like that?

Worn "dogs".

Yes it doesn't take much.

Look at the protruding "dogs" that come out of the side of the relevant 3rd gear. Look at the corresponding location holes that these engage in when the gear is selected. These areas take all the drive force you apply from your throttle hand, to the crank, thru the gearbox whilst in 3rd and out to the rear wheel.

Bear in mind, 3rd is the gear where you grab most throttle, 3rd is the gear that you pootle thru town in. 3rd is the gear that you pass thru on the way up and the way down in traffic.

Understand 3rd gear takes a hammering. So it's not surprising that it whines frequently.

Look at the "dogs" on your 3rd gear. They're worn aren't they?

When the torque from the spinning crank is being transferred thru the box, the slightest wear on the "dogs" will cause the gearbox to jump out of gear and it will ALWAYS jump out of 3rd and down into 2nd.

Now you should look at the channel on the selector barrel for the corresponding selector fork and see if the jumping gear has caused wear in that area of the channel or on the guide of the fork. It will have BTW!

It doesn't look like much I know. Check the arrows on the photos that Studders provided. This is wear. I know. I've had to change 3 FZR boxes to date.
Guaranteed fooked. 100%.

Photos?

Edited by TYREDNGRUMPEE, 10 January 2013 - 08:52 pm.

[alexk243]

haha ok then. Ill take some close up shots and post them and see what you guys think about the wear. So looks like at a minimum I will have to repleace the gears and possible the selector forks/channel guide thing.

[TYREDNGRUMPEE]

1992 Yamaha TDM Engine Removal

Liking the time lapse

[alexk243]

I was wearing a camera on my head also for the entire time and I filmed the complete engine disassembly, just for reference. Figured it couldn't hurt. Time Lapse videos are fairly easy to make, but instructional videos are a bit harder.

[Studley Ramrod]

haha ok then. Ill take some close up shots and post them and see what you guys think about the wear. So looks like at a minimum I will have to repleace the gears and possible the selector forks/channel guide thing.

Any progress on pics and identifying the cause yet Alex ? Just that I'm thinking there's no point you buying this gearbox if yours is fine and it's the selector barrel or selector forks you'll need.

[alexk243]

Naw, Sorry, Been a busy few days with some snow storms coming in. Ill try and get out there today to take some pictures.

[alexk243]

Ok here is the photos I could get. Have not figured out how to get the part of the trans that is farther in there out yet, but I took pictures of what I could by rotating it.

Here is a link to the full album I took

I will post some of the pictures on here,but the full album will have more pictures.



















Best picture I could get of the selector barrel.



Overall View:



I really cant tell by looking at it... Not sure what is wrong or worn beyond specs. Let me know what you guys think.

[TYREDNGRUMPEE]

Good pictures. Need more.

It would help if you could re-assemble the output shaft and orientate it in such a way that its gear positions reflect those of the input shaft gears that are still in the crankcase.
Post a photo or two.

This is because the gear dogs that are jumping out under load can be found on your output shaft. (The one that's out of the crankcase) .
These will be where the dogs are engaged in third gear.
Why not refit it and go through the gears 1 thru 2 thru 3 thru 2 to understand what happens when the gearbox spits the gear out in third and back down to second.
This is where you should be looking.
Mark these areas up with a dab of something bright and post photos.
Mark up the areas where the selector forks sit in third/second too and post a photo of the selector barrel.

[Studley Ramrod]

Well done on getting this far Alex !

I'll post up some 'example' photos so you have an idea of where and what to photograph.

[alexk243]

Ok, Ill put it in, Shift through gears and use some red markers to mark where the contacts are and Ill post those pictures.

From what I saw though it does not look too worn... would you guys agree?

[Studley Ramrod]

Difficult to say for sure. There's definitely a fair bit worn off the leading edge on a couple of the cogs in the pics.

[TYREDNGRUMPEE]

Difficult to say for sure. There's definitely a fair bit worn off the leading edge on a couple of the cogs in the pics.

Lets agree to call them "dogs", so as to avoid confusion.
They are called that because that's what they are. Nothing to do with rhyming/rapping/getting down etc.
"Dogs" are the fingers that protrude from the side of the "Cogs".

As for wear....., it doesn't take much. So we are looking to identify the guilty "dogs" + corresponding "recesses" and any other areas in the system that may contribute to your symptoms. The problem is, that the problem exists and cannot be cured through denial.

The solution lies in whether a cure can be obtained by purchasing a part here and there or replacing the complete unit by breaking a knackered engine or purchasing a S/H unit. Yeah, I know.

Studders has replaced portions of a box 'afore, so he'll be able to point out what may have the greatest benefit.

Must still see photos tho'.

[TYREDNGRUMPEE]

This is not good



And this isn't either



I'm guessing that those three elements sit alongside each other on the output shaft.

[Studley Ramrod]

I identified the gearbox part I needed and was fortunate to find the same part was used in a TRX gearbox. That said, the problem I had was different to Alexs' which is why I'm not sure exactly how worn the 'dogs' would need to be to cause it to slip out of the cog.

Looking at the gearbox I have for alex, I'd say it's as worn as the dogs shown in his pics, so probably not gonna be suitable if this is the case.

[TYREDNGRUMPEE]

That said, the problem I had was different to Alexs' which is why I'm not sure exactly how worn the 'dogs' would need to be to cause it to slip out of the cog.

I don't know myself, but think it's a case of "depends".
Depends on the bike, the motor, lubrication, past history etc.

But if it is jumping out of gear, as it is in this case, then the gearbox is at fault and some jiggery pokery is definitely in order.

[Rallyist]

Also look at the relevant selector fork

[alexk243]

Ill try and get out into the cold garage today and get some better pictures. How would I tell if the selector forks are bad?

[TYREDNGRUMPEE]

Also look at the relevant selector fork

You should look at everything really, as wear and bad behaviour in one area often leads to wear in another.
Check selector barrel, the channels that guides the selector forks. The selector forks. etc.

Look at everything. Be hypercritical. Wobble things. Even the bearings at the ends of the shafts.

Edited by TYREDNGRUMPEE, 16 January 2013 - 07:18 pm.

[laughin in a windstorm]

when I've had bikes that jump out of gear under load (high mileage bikes) I give the engine a clean out with one of those engine flush fluids, then change the oil a couple of times with cheap oil and it cured the problem, then replace with good oil, not much good with an engine in bits though,
my thoughts are that although the edges look worn it doesn't just hold itself in place by the edges, perhaps it is not getting engaged fully, look at the parts that push the gears together as much as what lets it come out, right must go and put some butter on my cod liver oil capsule

Edited by laughin in a windstorm, 17 January 2013 - 05:30 am.