Forum

[dave p]

i little while back I asked for advice regarding my gearbox jumping out of first gear. I've finally got around to stripping the box and the only thing I can find is what appears to be excessive wear of the notches into which the detent plunger locates. This is the only component which requires engine removal to get it out.(Deep Joy!) However, the amount of end float on this component, about 3/16,"is such that the detent plunger can engage in the notches fully at one extreme of end float or only about half the width of the notches at the other extreme.Is this normal?

On other gearboxes I've worked on this would require shimming so that the two components lined up properly. Has anyone else seen this condition and would there be any negative results from shimming?

Thanks in anticipation, Dave.

[stinkwheel]

You ought to be able to remove everything from inside the gearbox with it in-situ. The selector segment included. I know because I have. On mine, it gave a whole new meaning to "rough and ready". I fettled the notches and the profile on the detent a bit to make it engage more positively. However my main problem was damage to the dogs on the gear clusters.



You can remove the gearbox without removing the rest of the engine too. CLutch will need to come off. You'd also need to make up/buy a couple of 3/8" cycle thread half nuts then you can lock them onto the four studs that hold the box onto the engine and wind them out (may also need to move the mudguard aside). Undo the two triangular frame brackets and it should lift out sideways. You shouldn't need to mind, but it might save your back.



This was the damage to my gear clusters.











I just remembered. The pivot pin for the gear selector is held in by a large slotted grub screw on the rear of the gearbox. Remove this and the pin should come out backwards allowing you to remove the selector. You can see it clearly on the following photo just below the top right stud hole.

[Mark M]

I have had to replace a pin that was very badly worn at one end allowing too much movement of the swinging fork (is that what it's called?) which completely bu**ered up gear selection on a Redditch box, so yes, I'd say it is almost certainly the problem, or part of it. You'll have to remove the pin to shim it anyway so just replace it?

REgards, Mark

[Norm]

As we drive on the left out here the frightening bit was always from taking off from the lights and turning left, lean over and it would drop out of first. Took me a while to work it out but it was caused by the drive side bearing being loose in the housing and moving sideways causing it to drop out of gear. Not an uncommon problem

[Norm]

Sorry goofed up it should be turning right

[scotty]

No need for half nuts gearbox can slide back to allow stud to be grasper with thin slipjoint pliers on the unthreaded bit, then double nut with the secureing nuts.remember the studs are different lengths 2 long 2 short.on the s/h bike we bought previous clown had put the heavy duty washers that go under the nuts between the box and the engine, prim chain slipper was backed right off chain was drum tight. When you can go on this site and parts book section shows where things go. Doh.

[Norm]

This is a dropping out of gear problem, not a selection problem. What happens when the drive side bearing comes loose in the housing the mainshaft sleve can move in and out about 10mm and this knocks it out of gear

[dave p]

Thank's for your replies chaps. I've had a go at it today with mixed results! The locking half nuts didn't work although it usually does in other applications. I decided to sacrifice the studs and undid three of them with a very good pair of grips.They came undone with a crack. The fourth one, lower offside, I couldn't get at. I'll try again tomorrow.I can't slide the box back because the top rear stud that passes through the triangular plates atop the box is sheared leaving the nut and a length of stud still in the hole in the casting and it cannot be withdrawn from the right-hand side. This must have been done at the factory because I've never laid a spanner on it from new.

The four main studs have heavy steel washers under the 3/8" nuts. Well, three of them had, the fourth had a red fibre washer! The large bolt beneath the gearbox with the nut removed cannot be withdrawn from the left-hand side because it has a flanged head which hits the frame when I try to remove it. Oh joy!!

I'll report back when I've applied the Dremel and a few curses.

[stinkwheel]

Yes, I had a dropping out of gear problem too. It's what happened when a badly made selector lead to improper changing and damage to the undercutting on the gear clusters (over the course of 30-40K miles). As a result, it would jump out of first. Something that got progressively worse until I had to ride off holding the lever up with my foot.

[dave p]

Yes, I've been holding the box in first with my boot until second can be used. I'm still interested in the enormous amount of end float on the gear selector thingy. This is the first m'cycle gearbox I've seen without either a cam plate or a selector drum.Is this amount of end float normal? Around 3/16"to 1/4".