I recently obtained a nice 87 b2600 with an auto tranny. It runs ok but when you take off, the tranny does not seem to shift? it just runs like it is in 1st or 2nd gear. if you take it to about 25mph and then let off the throttle just a hair it will shift and be good to go, untill you stop? I replaced the vacuum modulator and it seemed to help a bit but still not right?? any ideas.

thanks

 

Mileage?
When was fluid last changed?
25 year old vehicle = new tranny.

 

mileage is 160k, fluid looks and smells good. It has a new head and new carb with in the last 6 months. This truck was owned by a grandmother and was taken care of. The part i dont understand is that it will shift, when you lift the gas pedal, it does not shift hard or anything. When i replaced the shift modulator on the tranny it seemed to help quite a bit.????

 

There may be a kickdown cable/rod going to the transmission from the carb, if that is bound up, unhooked or out of adjustment it will keep the transmission from shifting properly as well.

 

Tirol, would that be dif from the shifting modulator that i replaced? Thanks for the advise

 

Yes it is separate, the modulator uses vacuum to sense engine load, the kickdown rod/cable uses throttle position to sense driver input. It is also possible there is a vacuum leak somewhere that is making the modulator THINK that there is less manifold vacuum (therefor higher engine load) than there is.

 

ok sweet this is what i am thinking, i do not think the tranny is bad, because i can make it shift, I will go check this out. Thanks again!!!!!!!!!

 

Isn't that just for quick downshift when you step on it?
It's worth a try, but I am not totally convinced. The tranny should shift automatically without it.
You never know. It's worth a try!
Good Luck.

 

Sounds contradictory (new head). Grandmas don't know how often to change tranny fluid?
However, work on engine may have issues with linkage.

 

ok so i found the kick down switch, i backed it off and it seems to be doing 100% better, still not liking the shifting? its smooth just not at the right rpms. BUT way better than before. It seemed like the pedal was hitting the kickdown switch way to soon. Thanks for all the help guys!!!!!