Re: mystery switch and mystery noise

Posted by Peter Packard On 2011/12/19 15:36:38

G'day all, I would agree with Owen that Packard would have not intended for drivers to pull over to select from High to Low when in Direct Drive. I have driven Ultra and Twin-Ultra boxes since 1968 and have frequently towed car trailers etc up and down heavy grades. I have never had any dramas from going up or down in Direct Drive.
The Twin Ultra box does actually perform the shift from Low to High although this is without the Direct Drive clutch engaged.
Notwithstanding that there is a lock-up clutch in the converter of the Ultra, I would imagine that in a conventional Auto box that a shift from high to low would be stressful once the converter stall speed has been exceeded.
I would not hesitate to select Low range on a heavy, windy, downhill grade whilst in Direct Drive, especially with any single master cylinder drum brake system. i would also not hesitate to select Low range Direct Drive when going up a heavy, winding grade. The Direct Drive clutch application pressure needs engine revs to stay at max pressure so labouring an engine uphill is not going to do the box or the engine any good. Best regards Peter Toet