Are these units reliable? Worth the effort? Issues to watch out for?
It seems like this would effectively make a 4-speed a 5-speed on demand.
Thanks!
Joe

 

I consider them worth the effort ~ If wired as Jaguar intends on 4th gear only, they effectively give you a 5 speed box when coupled to the correct diff ratio & about 12 miles per hour greater top speed. Better fuel consumption & a quieter ride at speed in general using lower revs. Few are going to travel flat out. They are pleasant to have at much lower speeds.

They are generally reliable.

The main issue to watch out for is that they are correctly wired to the gearbox cover inhibitor switches X 2 so that they cannot be engaged in reverse gear which would burst the one way sprag clutch & cause mayhem.

 

My father who raced, rallied and sprinted his Mk2 Jaguar in the 1960s disconnected the inhibitor switch so he could use the overdrive in all gears. This made changing from first to first O/D which was basically second gear much faster when accelerating. As Glyn said though not good if you engage it in reverse.
My MGB GT V8 had an overdrive and this had an inhibitor for reverse, first and second but you could use it in third and forth. Great for over taking.

 

Thanks!