4 speed gearbox jumping out of gear.

[Dave Mann]

I've just been e mailed by a friend who I've not seen for a while, he's now got his Seven on the road and reports it jumps out of second and third under load. What is the collective thoughts on the cause(s) by our esteemed readers.

[Ruairidh Dunford]

The selector spring/s has/have most probably collapsed/broken. Quite common and best replaced on the bench.

Cheap to replace: https://www.theaustinsevenworkshop.com/p...nd-springs

[Dave Mann]

Thanks Ruairidh, I'd thought of the selector springs, but having Googled the problem I found a number of old threads which made me wonder if there was another cause. As it's coupled to a 4 speed engine & clutch assembly I agree it's best done on the bench.

[Ruairidh Dunford]

It could be any number of things Dave - that is the most common cause in my experience.

Until you get it on the bench and investigate you won't know for sure.

[Robert Leigh]

I agree with the bearded wizard; just one thing to check: if it can be held in gear on the lever easily he is certainly right; if it's trying to push itself out of gear all the time there may be something more serious.
Robert Leigh

[Parazine]

Sometimes the synchro teeth (the fine teeth) wear, especially if the box was used with gritty oil in the 1950's. This can, especially if the adjustment is a bit out, cause an end thrust, which will cause a jump out of gear. 

Also, excessive end float in the gears on the third motion shaft can cause problems; usually the bronze bush between the gears is worn in this case.

A clue to these more serious problems is gained by observing when the "jump out" occurs, if the lever "drops" out mildly when decelerating, blame the selector springs. If it "hurls" out under power, its usually end float or worn synchro teeth in my experience.