3.0 ltr Auto gear changing

[andywright]

my auto gearbox sometimes doesn't change to top at the normal 54mph when towing, if going up a steep hill for a few miles, you then have to increase speed to 61mph to get a change to top, the problem rectifies itself after a couple of miles of easy towing

[ffp42]

Auto box lock up point

Andy, I have done much 'searching' for the auto box lock up point whilst towing and have experienced the same situation you describe. The point at which the auto box locks up is not just speed dependent, it also takes into account the throttle position, i.e. power demand. If you are climbing a long hill the throttle is dominant over the road speed and thus will not lock the box until the demand drops, i.e. you reach level ground, or the speed rises considerably.
What I have found to work is to fool the system into thinking you have reached level ground by quickly easing off the throttle. Once the box locks up you can ease on the throttle again and continue to climb steadily. This knocks the revs back by about 2-300 rpm. If you use too much throttle the box unlocks again so it needs careful control.
I have also found that by gentle use of the throttle the box does not unlock at the same speed as lock up, it will run down to about 45 mph and can be brought back into the 50s without unlocking.

Colin

[surfin]

To lock or not to lock ...

Hi Guys ..
This is all very interesting.I took my 3 ltr.Surf towing to Spain for the winter last November and experienced exactly the same thing.Colin explains it very succintly.I have to say,that reading reports on this site,some vehicles never manage to achieve more than 45 mph "going up hills" - towing or not towing.This I cant understand.On most of the mountains I climbed - admittedly at 65-70-mph.at the start,I almost always managed to climb up to the top at an "exit" speed of between 58mph.and 62mph.Only rarely did I end up at 55mph.though never less than this,and believe me I climbed some big Sierras ! On the very steep ones I engaged the ECT,which I found helped me a great deal.This was moving a combined net load - car and caravan of around 1.25 tons.Maybe I have just got a good Surf ! I am relieved to have had this explanation since at the time I thought that there were some really odd things happening ! When the "new" speedo started registering 10mph.when I was,t moving - now that was worrying - Regards Surfin