4L30E Bang Shifting into 3rd

[iskiuskiweski]

Originally Posted by srpope80

Is your AC Fan blowing and turn lights working? I can't remember which one but one of those fuses controls the tranny shifting as well. I think it is the turn signals. I had a rear tailight wire get frayed and caused the fuse to blow and the tranny to shift like that; same symptoms.

Everything is fine now. I only had the problem when my vacuum leak got really really bad.

[trooperbc]

Originally Posted by jlpmba
1996 Honda Passport, 2WD, 4spd Auto.

Just had the trans rebuilt and noticed
that when when shifting into third the engine revs up and
"slams" into third. It also "slams", not as bad, back into first
when stopping.

Shifting from 1-2 is okay.

Transmission shop is giving me the run around. what do you
all think?

Originally Posted by iskiuskiweski

I recently had this same problem and I wanted to share what I found. I had known for a while that my intake manifold gaskets needed to be replaced but it got pretty bad the other day, I could hear it sucking air, and the idle was pretty rough. The vacuum leak was enough to cause the tranny shifting problems, I am guessing this tranny has some kind of modulator connected into the vacuum system. I replaced the gaskets and all is well again.

hey iskiuskiweski (that was fun to type),...thanks for the heads up with your experience of how fixing that major vacuum leak solved your harsh shifting problems...
i'm interested in figuring out why that worked. afaik, there is no vacuum connection that feeds to the 4L30E automatic transmission. it is controlled totally by the trans computer and the gear selector.

i'm thinking that one of the many inputs to the trans computer may be influenced enough by the vacuum leak to adversly affect the transmission shifting.

the inputs include:
rpms, vehicle speed, engine coolant temperature, ac info, throttle position sensor, kickdown switch, power/winter switches, mode switch, brake switch.

the trans computer is programmed to transmit specific commands for actions to the trans under a full array of different circumstances.

my guess is that the trans computer received conflicting data -- e.g. high rpms and low engine speed, and closed or closing throttle -- and thus sent conflicting info to the trans, which promptly took the conflicting actions, which results in the slamming shifts. (similar to the way when a bad gear mode switch sends incorrect gear position to the trans computer; the trans receives conflicting info from the gear selector and from the trans computer -- which can cause among other things very harsh up and downshifting.)

i think, iskiuskiweski, your feedback is very valuable, and the first i've heard of that connection. it should help many in the future.

i like trying to reconcile the symptoms and diagnosis's and actual results so that a future anomoly is easier to "see".
thanks again....

anybody have their own take on what's going on here with the IMG leak and the trans harsh shifting?
anybody else have this same problem/solution?

thanks

//bc

[davey_92_rodeo]

i had the same problem from 1st to 2nd. on mine it just meant that my tranny fluid because when my brother had the car before me, he lost the dipstick to the tranny so he never knew how much fluid he had-therefore, the transmission went out, he gave it to me, n i had to put in a new tranny in n ive got a dipstick in the new one n mines doing great