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Mk3 Gear Selector

Submitted by peter_merrick1 on Mon, 08/03/2021
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Commando

Hi 

Following a rebuild on the gearbox I couldn't select 3rd or 4th gear with the gearshift selector. I removed the outer cover and by leavering up the "Knuckle" I can get all 4 gears but noticed that the knuckle end of the quadrant was just touching the top of the inner cover "Window". I filed out the window and cleaned up the outer surface of the knuckle holder so as when 4th gear is engaged there is now clearance between the quadrant and inner casing.Trying to re assemble the selector mechanism I have failed to make the ratchet pawl engage with the ratchet plate whilst engaging the selector splines with the cross shaft! I have selected neutral for this procedure but it makes little difference what ever gear is selected. The ratchet spring is extremely close to the clutch lifting leaver, so I've ordered  new one, along with a new gear lever return spring, both via the club spares scheme, to see if this will assist the assembly.Whilst fitting the outer cover there is little room to see what's happening to the pawl if it should fall from its upright position!

I would be grateful if anyone could point me in the right direction for successful assembly as its the last stumbling block before the bike can be back on the road after 35 years.

Many thanks

Peter Merrick

Submitted by richard_payne on Mon, 08/03/2021

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You shouldn't need to enlarge the slot in the inner cover, but from memory the drawing in the workshop manual showing the quadrant level with the top stud is not accurate and it should be set lower.

I'm puzzled by the difficulty putting the outer cover on. The cross shaft can do its own thing. It only rotates in the primary case...if the gear change lever ends up at the wrong angle, simply move it round a spline or two...certainly don't worry about where it's hanging. The shaft splines can only engage correctly.

As long as you've got a finger round the back making sure the pin engages with the hole in the ball, all should be OK.

Submitted by dan_field on Tue, 09/03/2021

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Richard, if you watch Mick Hemings video he explains why you may need to file the window. I didn’t have to, but clearly the tolerances are such that it may be needed. 

Dan 

Submitted by richard_payne on Tue, 09/03/2021

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Dan, I have a feeling that In was rebuilding AMC boxes before I had a VCR to be honest...The video is not something that I have....and it's not a problem that I've come across.

 

Submitted by stan_thomas on Tue, 09/03/2021

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I seem to remember filing the top of the inner cover slot when fitting RH shift covers to an otherwise Mk3 box. Not much, just a matter of removing casting marks. Needed a touch get it to click in positively.

I find fitting the outer cover a shade more fiddley with the Mk3 spherical roller in the quadrant arm so I've always used the earlier cylindrical one. Wears better too. Although the Mk3 does save that Doh! moment when you realise you've put the inner cover on without the roller.

Submitted by peter_merrick1 on Wed, 17/03/2021

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Thanks to thoes who took time to respond to my predicament.

To let you know the outcome, the Quadrant was one tooth out when engaged with the gear on the back of the selector cam. 

You can loosen the cam pivoty bolt just enough to pull the cam forward and disengage with the quadrant, allowing the quadrant to be lowered.The clutch and main shaft remained undisturbed, but all the gears were removed for access. Even one tooth lower down the quadrant still looks level with the top stud in the gear box casing as per the manual, but what a palarver to access all the necessary nuts and bots with the gearbox in the bike. And being a Mk3 just makes it more inaccessible!

The moral of my plight is to ensure all gears are available via the gear selector lever BEFORE you put the gearbox in the bike!

Now, to sort out the rusty petrol tank, but thats another topic!

Cheers

Peter

Submitted by philip_ham on Mon, 24/02/2025

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I have found the same problem as Peter had when he started this topic.  After replacing the broken ratchet spring I'm having difficulty aligning the ratchet plate pin into the spherical roller.  I've tried following the instructions in the 1975 Mk3 workshop Manual, but to no avail.

Firstly, where does the O ring on ratchet spindle go?  Is it on the inside or outside of the ratchet plate?
Then with the ratchet plate assembly fitted into the outer cover how do you align the pin into the spherical roller, especially when you can't see it!  There doesn't seem to be any room to insert the right index finger to try and hold up the ratchet spring or hold the ratchet plate (as instructed in the Manual).

Whoever wrote the workshop manual could not have tried assembling one themselves.  Perhaps if this was done when the gearbox was built on a bench they wouldn't have to take into account that gravity making the slector pawl falling down!

Philip.

Submitted by stan_thomas on Mon, 24/02/2025

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If you mean #19 here:
https://andover-norton.co.uk/en/shop-drawing/128/gearbox-inner-cover
it shouldn't be there and is an error, possibly deliberate.

As you would when fitting a pre-Mk3 outer cover, you can use the shift lever to manipulate the ratchet plate while you engage the pin with the roller. Not easy on a Mk3 with the gearbox in the bike and an extra hand might be called for.
Alternatively, hook the ratchet plate pin with a coat hanger or screw driver.

Shine a light thru the outer cover inspection cover to help see what you're doing - again, an extra hand is useful.

 



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