Automatic slipping? Or normal?

Okay so this is the first automatic transmission I've had since my 1st car .. a 1972 Ford Torino Wagon. What a beast!

Anyway today I was hauling about 400 pounds of brick home in the bed. Nothing major. I stopped at a place for about 15 minutes or so. Got back on the highway (heading up hill), and the tranny seemed to be shifting up then down then up for a few seconds like it was hunting. So I hit the gas, and it suddenly dropped into 1st or maybe 2nd (I was doing about 40), RPMs shot up to around 4000, and it had very little torque / acceleration. So I let off the gas, it dropped into a lower gear, and then from there home it was fine. I just had it into the dealer for an oil change, and they checked the fluid level. There are no visible leaks either.

So is it normal for an auto tranny to occasionally do this? Get lost in the gears so to speak, and shift wrong? No shudder, no vibrations, no codes thrown.

 

That happens when towing or hauling weight especially up hill. When it's doing that (hunting for a lower gear) shift it down a gear (into 4th) so your transmission doesn't overheat.

 

That effects RPM ?

 

I never noticed that before , I'm going to pay attention to the tach on my way home tonight

 

I hate homework .

And I didn't complain about hunting , I said IMO the truck hangs on to D for far too long into low revs and lugs

 

Also you can notice the stall in the torque converter in the 35mph range. You will know it in and around that mph when you ease into the gas and it feels like the RPM's have to catch up to the speed of the truck to accelerate and lock up the converter.

 

You can also test it by pressing on the brake while still accelerating, not enough to engage them, but that should tell the torque converter to unlock as well. Found this out not too long ago when I was trying to figure out what that little downshift was that wasnt 4th gear.

I noticed about a 200 rpm jump doing this

 

Interesting. I know not to drive in D when towing but didn't think that applied to hauling, especially if it's only 500 lbs or so.

 

It's because the auto has a fairly high final gear, along with TC lock it makes for efficient flat ground cruising. So it doesn't need to have a load of any sort; an uphill at certain speeds could do it. Anytime the transmission starts 'hunting', shift out of 'D' or change speed so the engine is in an optimum part of the torque curve for the gear it's in.

In addition to limiting overheating it saves tranny clutches. With a load, though, clutch wear is much worse and it becomes even more important to stop the hunting hence the well-known caution to downshift when towing.

 

Thanks for that. Good info.