Engine/Transmission (1998.5 - 2002) "passing gear" ?

[Tractorat]

My truck has always done this, and I think it is probably behaving the way it was designed. And the power of the diesel has always made it a none issue.



But, I think Ive noticed that if I am in lockup (usually tow/haul mode), if I want to step on it (to pass someone or going up a steep hill pulling my trailer and it is starting to slow down) it doesn't want to downshift. One hill in particular, if there wasnt quite enough power to grunt it to the top ( and was slowing down), it came out of lock up quite violently. I was trying to give it more throttle expecting it to either downshift or just have more power. Now, when I go up that hill, if I think there isnt enough to get to the top, I manually downshift to 2nd.



So, my question is: Should the trans be able to downshift out of lockup automatically ? Or is not downshifting just a function of lockup ? As I say, 99% of the time there hasnt been a problem because the engine has enough power (in lockup) to handle the load fine.



(Hope I said that right)

 

[JR]

I have the homemade version of the tc lockup. Relay removed and jumper wire installed to give tc 12 volts and a wire run from pcm to toggle switch and out of the toggle switch to ground. If im in lockup no downshifting will take place, no matter what. If i let it go, i would eventually stall the truck out. The lowest i will allow the truck to drop in rpm is around 1300 and thats only if im empty and on flat ground. If i need to downshift i flip the toggle off and let the trans do its thing. Eventually id like to drop the pan and modify my valvebody so that i can lock 2nd up as well as 3rd and 4th. Hope this answers your question



Sorry tractorat i thought you were talking about downshifting with tc lock up switch but i just reread your post and i totally blew it! Well in normal operation if i start falling out of my sweet spot the trans will downshift on its own no delayed shifts and no hard shifts when it shifts. How many miles on your trans?

 

[Tractorat]

Sorry tractorat i thought you were talking about downshifting with tc lock up switch but i just reread your post and i totally blew it! Well in normal operation if i start falling out of my sweet spot the trans will downshift on its own no delayed shifts and no hard shifts when it shifts. How many miles on your trans?

About 94k. The trans seems solid except for that one issue. I think it may have always been like that since new. I just havent run into the situation enough to notice it before. Is there some kind of linkage adjustment that would affect that ?

Thanks

 

[cerberusiam]

In the case of being locked up in drive, yes there is an adjustment to accelerate downshifting. Tighten the TV cable so the more throttle you give it the higher the TV pressure is.

 

[Tractorat]

Thanks cerberusiam, Ill take a look at that.
Is that a specific tightness ? Or adjust to taste ?

 

[cerberusiam]

Adjust to taste because every truck reacts differently and every cable\bell crank\lever reacts differently. I normally start with about an 1/8 from fully tight at WOT and adjust slack to taste from there.

 

[Tractorat]

Thanks
TRat

 

[Road Dog]

In the hills I always shift manually. Lift off the throttle, downshift, and go. If you're kicking the throttle to downshift you're shifting under load. It might be ok for a car but with a truck and trailer you're putting the transmission between a rock and a hard place.

 

[Dieseldemon]

Also a throttle downshift will not allow convertor lockup and make the trans run hotter

 

[JMcCoy]

I have found that double tapping the O/D swithch will allow the transmission to unlock enough to get the rpms up for the pass without the hard down shift. Just a thought.