Rebuilding the original 100,000 mile Moss gearbox
Stop the gearbox jamming in first gear

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The cause of the first gear jamming in XK Moss gearboxes is the wearing, over time, of a rivet installed in the 2nd gear synchro sleeve to stop the first gear wheel/2nd gear operating sleeve over-travelling rearwards when first gear is selected. The rivet was installed from some stage in the XK120 production, and continued in the XK140 and XK150 models.

Being a rivet, and held in place by deformation of the rivet's shank, it is at best a soft steel, and prone to further deformation and/or wear over time. In my XK150, after 100,000 miles, the rivet was severely worn, and thus allowed the first gear wheel to over-travel.

The www.xklovers.org website contained details of the cause of the jamming, and the solution. In 1993-94, Rob Reilly first documented his experience with fixing the jamming first gear problem with his XK120 Moss gearbox.

worn-rivet


rivet old and new
The lower picture shows the rivets, old and new, at roughly equal scale.

 I consider myself fortunate that I was always able to work the jamming free without excessive force. But the problem had to be fixed.

Rob Reilly's document and extensive photos and drawings gave me the confidence to dismantle and rebuild my gearbox myself. I'd had previous experience with a Riley Pathfinder gearbox rebuild, and with rebuilding an Alfa Romeo Giulia gearbox that had not been assembled correctly and locked out fifth gear.

There is no point in me repeating Rob’s helpful words, but I will expand on two parts of his advice:

1. Details for preparing the first gear stop rivet, with dimensions etc.

2. A suggested way to deform the stop rivet shank after the rivet has been sized and then inserted in the second gear synchro sleeve.

First gear stop rivet

 

Deforming the new rivet