Holden Jackaroo Gearbox & Transmission Problems

THERE really isn't a rule of thumb you can use to determine if it would be beneficial to fit an external oil cooler. It comes down to the weight of the trailer you're towing and the conditions in which you'll be towing it. If the trailer or caravan you're towing is close to the rated limit of the tow vehicle, and you're planning to tow it in hot or hilly conditions, then it would be wise to consider fitting a cooler. Carmakers won't tell you that. They won't admit their cooling is inadequate or borderline. Most carmakers develop their cooling systems to cover average use, and some will offer an uprated system for those wanting to use their vehicle in more arduous conditions.

I’d be taking the vehicle to a transmission specialist (as opposed to a general workshop). A good transmission expert will be able to tell you a lot about the condition of your gearbox by giving it a once over. That will include an examination of the level and condition of the fluid as well as an inspection of the contents of the transmission filter which can offer up an enormous amount of detail on what’s happening inside the gearbox.

When was the last time the transmission was serviced? The fluid in these units is a bit like the oil in your engine; left unchanged for too long, it will degrade and won’t be able to do its job which, in the case of an automatic transmission, includes both lubricating the unit as well as providing the actual driving force to turn your car’s wheels. If your problem was intermittent or was solved (even temporarily) by switching the engine off and back on again, then I’d be inclined to suspect an electronic or sensor problem. But since the problem only happens when the transmission gets hot, it does sound potentially mechanical in nature.

It could be a blown head gasket as your mechanic suggests, but he should be able to test it to determine if it is blown or not. You should also be able to see evidence in the form of a milky substance in the coolant if it is a blown head gasket.

I wouldn't reconnect it. If the aftermarket cooler is designed to operate as a stand-alone one, and it's doing the job, then I would leave well enough alone.

There are two possibilities here. Either the shifter mechanism has jammed or failed and will only allow you to select second or fourth or, the gearbox itself has failed internally, and the ensuing mechanical carnage has jammed it up. The wild-card is the clutch which could have failed. If that was the case, though, I’d imagine you wouldn’t be able to select any gears at all with the engine running.

The first step would be to check from underneath whether the gear linkages and selectors have somehow got tangled up in each other – it can happen – but if that’s not the case, then I’m afraid it’s probably a gearbox-out job. Make sure you fit a new clutch when it all goes back together.