Popping our of third gear - Honda Motorcycles - FireBlades.org
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post #1 of 9 Old 01-13-2016, 10:21 PM Thread Starter
 
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Popping our of third gear

Picked up a '93 CBR900RR last night for a good price, because it's popping out of third gear. Seems to be a common problem. Reading some posts on this forum, it sounds like it's either worn shifter forks/drum, or worn dogs.

The symptoms are;
  1. It goes in to each gear quickly and smoothly
  2. It doesn't jump out of any other gear, just 3rd
  3. When in third, it will engage for a few seconds then either jump down in to second, or jump in to second briefly then back in to third

To me, this sounds like the forks/drum would be the most likely culprit, as the gear isn't being aligned and held in the right location. If the dogs were worn, it would be hard to get in to gear, correct?

Does this sound right?

Backdog's post looks pretty detailed to cover the replacement (https://www.fireblades.org/forums/how...placement.html)
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post #2 of 9 Old 01-14-2016, 1:51 AM
 
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Re: Popping our of third gear

its really hard to say whats the real problem until you get in there n look for damage. worn dogs can def make a gear slip out. if those mating surfaces which lay on one another at right angles are chewed up they usually do so in a kind of sloping angle so they cant hold and pop out. best advice i can give you is take it apart n look at all the components n buy the parts that look worn or damaged.

this isnt my pic but it gives you a good look at the dogs. you can see how they mesh together. when they get worn from mis shifting or general use/abuse they get chewed up towards the ends making more of a ramp than a deck so they just kinda push apart. it def could also be a fork or drum issue or likely a combination of the three. : )


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post #3 of 9 Old 01-14-2016, 1:57 AM
 
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Re: Popping our of third gear

btw welcome to the site!!! like i said man youll really just hafta dig in n see whats going on in there. transmission damage on the gears, dogs and forks is pretty easy to spot. if i took the time to pull it apart id replace anything that looked sketchy while i was there.

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post #4 of 9 Old 01-14-2016, 6:38 AM Thread Starter
 
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Re: Popping our of third gear

Thanks mate - I see what you mean about the dogs, now I know what I'm looking for when I pull it apart. I'll drop the sump first and have a look see. Cross fingers it's just the forks, save having to drop the motor! At almost 60k on the clock though, it's likely more in worn!
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post #5 of 9 Old 01-14-2016, 11:19 AM
 
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Re: Popping our of third gear

i should mention this pic is not from a 900 transmission. the mating surfaces of the dogs in this pic have been undercut. which is something you can do to a transmission to give better gear engagement. so your dogs wont have a surface that looks machined like in the pic, they would look more like the dog in the bottom right of the pic. when they are worn they kinda look like someone took a big hammer n beat the crap outta them.

do some google image searches with terms like "cbr 900 worn transmission dogs" and cbr 900 worn/bent shifter forks" "cbr 900 worn shifter drum." etc etc. the pics might be from a lot of different bikes but the more you look at them the better an idea youll get what kind of things your looking for once you get a look up in there.

ill say if its popping out of gear my money is on worn dogs unfortunately. bent or worn forks usually give it more trouble going into gear. drum issues are not out of the question but are less likely than the dogs. do those searches n youll see pics of damaged drums. the peaks get kind of rounded over in the slots typically. a bad drum can give poor engagement were it wont quite push the fork and in turn the gear over far enough to fully engage. if this is the case it could cause popping out issues but if its been like that long it will def cause heavy wear on the dogs. point being it could be a couple things in conjunction with one another that needs fixin.

get in n see what you can see. i should say too buddy im no transmission expert if you havent gathered that for yourself. : ) im sure there are guys on here with a lot more knowledge and a better way of trying to explain it than me.

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post #6 of 9 Old 01-14-2016, 2:10 PM
 
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Re: Popping our of third gear

My old 929rr used to go into 2nd then pop out for a split second and back in again, when ridden hard, a few unintentional wheelies and changes of pants were not fun lol
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post #7 of 9 Old 01-15-2016, 3:47 PM Thread Starter
 
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Re: Popping our of third gear

Thanks again mate, you've helped to clarify what I should be looking for a great deal. To be honest I've done a lot of mechanical work, but never anything on bike gearboxes, so this will be a good learning exercise. On the plus side, if the gears are the problem, they're available new - the drum and centre fork seem to have been discontinued, but all the gears and the outer forks are still available.

will keep you posted!
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post #8 of 9 Old 01-16-2016, 12:52 AM Thread Starter
 
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Re: Popping our of third gear

Got it apart today. Third fork is worn, and the third gear groove section is missing a fair sized chunk from the drum. The dogs in that gear have a slight wear - but only about 1/3 the size of he missing piece from the drum.

Will try replacing the forks and drum first (to save having to split the case) and see what sort of a difference that makes. In an ideal world I'd do the gear too, but there's about another full day required there to remove and reinstall the engine... Laziness wins.

Side note though, my clutch basket has wear marks on it, which I haven't seen in a bike before. Is this normal?
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post #9 of 9 Old 01-16-2016, 1:24 AM
 
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Re: Popping our of third gear

really thats about as bad a drum as ive ever seen. lol some wear on the dogs is normal but that drum is def toast. im not really sure about the basket. one of the 900 guys should be able to give you some insight on that.

"love is the feeling you get when you like something as much as your motorcycle."-Hunter S. Thompson
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