My MK3 jumps out of first gear...

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Jason

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May 14, 2010
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Hello all-
Returning member to the forum. Has been a while since my last post, so I had to re-up my info. As of late, my 75 MK3 will pop out of first gear when under hard acceleration. While taking it "easy" it seems to be fine. I restored the bike about 4 years ago and had the trans apart during that time. It needed nothing more than a clean and reassemble. Should I be looking for anything in particular when I take it apart again? Thanks in advance.
JD
 
DON'T TAKE IT APART!
Spring and detent on the bottom. Usually just the spring but for the price I replaced both.

This is the first place to check. You may find a reasonable replacement spring at the hardware store but the compression (critical) is not quite the same. May be good enough for testing and until the new stuff arrives.

I also purchased first gear on the layshaft to possibly replace, figuring that the fingers are slipping out. That part is on the shelf not needed.

If the detent spring is weakened by time just a little, first gear may not ingage completely nor hold under load.
See Captain' Norton's notes volume 2 28.5
Piece of cake!
04-0442 Spring, Detent Plunger
04-0034 Plunger, Shift Detent
 
I'd suspect the mentioned detent spring or lay shaft shift
if 1st jumps out under power, but if it jumps out on light loads
and easy let offs, suspect the thin 1st gear bush going away.

There is some danger to lose engine tire thrust when leaned
over 30' or so and going rather easy, bike can fall right over suddenly.

hobot
 
Ludwig's suggestion is the first thing that I'd check but on a Mk111, it's also worth backing off the neutral indicator switch. If screwed in too far, it has a more powerful detent effect than the plunger itself and will tend to pull the cam plate back towards the neutral detent. It should be set so that it only just switches.

That this effect has only just arisen may be due to small amounts of wear elsewhere. Cam plate bushes for instance.
 
pvisseriii said:
DON'T TAKE IT APART!
Spring and detent on the bottom. Usually just the spring but for the price I replaced both.

This is the first place to check. You may find a reasonable replacement spring at the hardware store but the compression (critical) is not quite the same. May be good enough for testing and until the new stuff arrives.

I also purchased first gear on the layshaft to possibly replace, figuring that the fingers are slipping out. That part is on the shelf not needed.

If the detent spring is weakened by time just a little, first gear may not ingage completely nor hold under load.
See Captain' Norton's notes volume 2 28.5
Piece of cake!
04-0442 Spring, Detent Plunger
04-0034 Plunger, Shift Detent
Click to expand...

This is intriguing but contrary to my understanding, that the detent plunger just provides a positive stop for the camplate during shifting, and that once a gear is engaged, it's the dogs that hold it in place?

I could well be wrong. It's been known to happen.... :oops:
 
I just reviewed John Hudson's remarks on AMC gear boxes and
he said the lay shaft bearing breaking up can cause jumps
out of gears and could lock up and very dangerous to try
to ride further once noticed, yikes.
Sure hope N cam indent don't matter much but glad to be alerted.

hobot
 
Are those remarks available online? I'd love to read 'em. Thanks. - BrianK
 
BrianK said:
This is intriguing but contrary to my understanding, that the detent plunger just provides a positive stop for the camplate during shifting, and that once a gear is engaged, it's the dogs that hold it in place?

I could well be wrong. It's been known to happen.... :oops:
Click to expand...

This gear box was disassemble and inspected. I can't help thinking that in many cases, the wear surface of the plunger and the compression and length of the detent spring is rarely checked. You mention that the detent plunger just provides a positive stop. This spring is required to be 1.5 inches and 21 ftlb of compression for a reason, to provide a positive stop.
As mention in the very first post, this gear box was disassemble and inspected. Again, for $2 to $3 and 5min of work, I suggest checking the spring. Just check the darn spring already.
Side note: Your gearbox lube will drain out.
 
Alright already!! I'll check the spring and detent! Thanks all for the suggestions--I hope it is not the worst case suggested, I don't want a locked up trans, especially if a buddy is riding my bike. My neutral indicator never worked, but I will check that as well. It is about time to service the fluid anyway. Much appreciated--I like this forum simply for the real people on it and the real feedback. I joined another forum for my bevel drive Ducati for a short while and quickly snuffed my membership. Bunch of whiney, pissy little girls debating the semantics to the point of insult. I can't believe the site admin allows that kind of behavior. Cheers.
Jason
 
Jason said:
Bunch of whiney, pissy little girls debating the semantics to the point of insult.
Click to expand...

I can't say we aren't free of that, but a majority of the time folks are more than helpful.
 
Pvisseriii, I didn't mean to suggest he shouldn't check the detent spring and plunger first - by all means, check the easy resolution first - I just meant it's probably not that (but will await the resolution of the checking with interest!)

If the box was redone already, I would sure hope any Portugese layshaft bearings were R&R'ed at that time, but who knows?

Anyway, best of luck to the OP, and do let us know what you find out.
 
swooshdave said:
Jason said:
Bunch of whiney, pissy little girls debating the semantics to the point of insult.
Click to expand...

I can't say we aren't free of that, but a majority of the time folks are more than helpful.
Click to expand...

Dave - who, us? :wink:
 
Briank,

John Hudson's and others remark were found in here, a boot leg
digital copy of NOC's Service Notes that apparently out of print now
so not cheating NOC but dispersing some very interesting history
of men and Norton Commandos. Definitely some gems on grear box
details to be aware of. I stumbled on this in this forum
this week catching up on what I've been missing out on.
Its got conflicting statements from the best in the business.

http://archives.jampot.dk/Book/Workshop ... _Notes.pdf

Hardest tranny task for me is indexing the quadrant
cam teeth, then tweaking the shift pawl spring arms.

hobot
 
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