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Author Topic: Second gear slip (I know, boring again but with a slight twist)  (Read 1026 times)

Offline HayaCol

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Second gear slip (I know, boring again but with a slight twist)
« on: December 31, 2020, 03:01:56 AM »
Hi everyone from cold UK. I am new to this forum and have a technical query that looks like its been talked about a good few times before and members seem to be tired of talking about it.
It’s a problem with second gear!!
Firstly, this is not my bike. A friend of mine mentioned a while back about this problem and I am trying to help him.
The problem….
Under hard acceleration, when the revs reach between 5 and 7 thou it seems like a loss of drive. It does not slip out of gear; it just seems like the clutch is slipping.
He’s had all kinds of test done on the electrical system and had the bike on a rolling road but no one had been able to diagnose the problem (all those wishing to rush in with the solution, please be patient!).
When he told me, we decided to look into the gearbox.
We took the engine out of the frame in a novel way, because I have no hoist or strong roof beam to throw a rope over, we put the bike on a paddock stand and removed the rear wheel then lowered the rear of the bike to the deck. We then loosened the engine and lifted the bike off the engine leaving it on the deck. Not done it that way before!!!
Before I started this, I had a good look on websites to give me clues to the problem and there were many. It looked like the problem would be that the 2nd and 6th driven gear dogs (not drive) were worn and either needed undercutting or replacing. Also, I may find that this had caused wear on the selector forks and possibly a bent selector fork shaft.
On inspection of the gear box, I found little wear to the driven gear shaft components. I did find wear to the drive gear dogs on both 3/4th and 6th. The selector fork shaft I am yet to remove but the drive gear selector fork looks like it has usual wear from a bike that has done 30k miles. The 2nd/6th driven gear selector fork has some excess wear and some jagged edges on it (but is not seem to be bent) so looks like it will need replacing.
I can replace all the parts that are worn but my question is would these parts (3/4th and 6th drive gear and 2nd gear driven selector fork) cause second gear to slip or am I missing something?
Happy new year to you all  :db:, and stay safe both on and off the bike!

Online Stainless1

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Re: Second gear slip (I know, boring again but with a slight twist)
« Reply #1 on: December 31, 2020, 10:38:09 PM »
Don't suppose anyone took a video of the bike before, during and after the issue occurred... like on the dyno or rolling road?  Any metal in the pan?  if you back it down is it still in gear or do you hear it fall back into gear?  You've looked at the shafts and gears, nothing is worn?
Have 2nd and the dog back cut to help keep it locked in gear.  If the fork looks worn, it is, just replace it.
Yes the 2nd gear fork being bent can cause the issue, not shifting completely in gear, and wearing the dog and gear dog faster.
I've had the "won't stay in second" problem before, back cut and a new fork fixed it so far... yes, we are hard on transmissions basically drag racing the engines in an 1800lb car for 5 miles WOT
Bonneville 200 MPH Club
245 MPH Turbo Busa Powered Lakester
208.959 MPH NA GSXR 1000