Jackaroo Transmision

Used to have thesame problem with aussie four speed boxes when rebuilding them with non genuine selectors (after a few years gen. stock not tenable) Could be similar but maybe not.
The selectors were that poofteenth different and because of the way it translated to the movement of the selector fork it wouldn't quite push all the way home and under conditions it would pop. Soundsrough but we used to touch the selector slots up with a grinder and this would allow the fork to seat all the way.
If they are saying it is a similar problem (your not quite clear as to what they actually said) then any good bloke should be able to do the Mod.
Good luck hope you get it sorted but i would think that even a few hundred was a good investment to prevent a gearbox overhaul which will cost $1000 plus with labour these days depending where you go.

when isuzu did the ubs update in 98 they changed the manual gearbox and had heaps of trouble with gear whine and excessive clearances in the gear shafts, (Although i never saw any that jumped out of gear), holden have done an awful lot of gearbox rebuilds under warranty so it may be an avenue to go down. Having said that, you will have to smack your head against the wall at the dealers quite a bit and the standard of the work can leave a lot to be desired. If this place has a good reputation and say they can go the easy fix, then spend the cash and save the hassles with holden. Moo... everyone knows what a Jackaroo looks like :-)

Tim ... Don't even try the dealer, go directly to Holden's Customer Relations department and state your case to them.

If the vehicle has 150,000km on it they will need to approve it first anyway, before a dealer does anything under warranty.

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Holden Customer Assistance