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Mk3 Gearbox

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Mk3 Gearbox

Posted by mike_steer at June 14. 2017

Trying to put my Mk3 gearbox together.  I cannot fully engage 4th gear in that the camplate falls just short of the plunger, all other gears are fine  I have stripped it numerous times but can't see what the problem is, any ideas?

Re: Mk3 Gearbox

Posted by karl_nixon at June 14. 2017

Is the quadrant arm hitting the metal of the inner cover where it passes through the rectangular hole in it before the camplate rotates enough to let the plunger engage in its detent on the outer edge os camplate?

If so you have simply got the camplate an quadrant out of line by one tooth of their interlocking gears. This is a common occurrence that can happen to anyone and easy to fix by just reassembling them one tooth further around. Of course to move them you need to remove the selector forks and a few cogs.

Re: Mk3 Gearbox

Posted by Neil Wyatt at June 15. 2017

Engage 2nd gear before putting the outer cover on.

Re: Mk3 Gearbox

Posted by christopher_winsby at June 15. 2017

Try www.oldbritts.com  Technical Articles.

It has a step by step guild, plus useful mods.

Re: Mk3 Gearbox

Posted by richard_payne at June 15. 2017

The drawing in the official manual is a little ambiguous. Although it says to line the quadrant with the top stud, if you do it according to the drawing then it sits too high and as Karl says, you'll be contacting the opening in the inner cover.

It needs to be set in line with the lower edge of the stud.

Re: Mk3 Gearbox

Posted by mike_steer at June 15. 2017

Previously richard_payne wrote:

The drawing in the official manual is a little ambiguous. Although it says to line the quadrant with the top stud, if you do it according to the drawing then it sits too high and as Karl says, you'll be contacting the opening in the inner cover.

It needs to be set in line with the lower edge of the stud.

Many many thanks to all of you for the replies to my post. In essence the book is a little ambiguous for sure and needs clarifying, in a number of areas to help the rebuild process.  It has to be something simple such as the the quadrant needing shifting by a tooth or so.  I will have another go tomorrow evening with a fresh mind set now that I have had a break from it. One final question does it matter what gear the gearbox is rebuilt in.  For example to rebuild the same on the BSA Rocket 3 I have just finished it had to be in 2nd gear.

Re: Mk3 Gearbox

Posted by karl_nixon at June 15. 2017

I have not had any problems due to what gear the box was in. I have never even noticed so unless I have just been lucky in that respect I would say it does not matter as long as you assemble it with care an not just brut force (save that for LH nut that holds drive sprocket on sleeve gear Smile).

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