Tranny questions

[84XLT]

so i was driving my 84 big bronco the other day, and everything went fine. just a little trip to work, and then some errons around town. nothing too crazy and wild. the truck set for about 5 or 6 days, and when i went to drive it the next time, i had no third gear, and it will not shift automatically (C-6). now i have been around trannys and stuff all my life (dad had his own shop) but i have never had a tranny do this just from setting a few days. the bronco is not my daily driver, just a toy, and fun trip here and there. anyone got any ideas on where to start, and if i should rebuild, or replace.....

 

[miesk5]

yo!

Sounds weird to me too.

So, since it was ok before it sat there, let me guess @ simple checks first;

Check fluid level/condition

Check Vacuum @ vac. modulator; I think it needs @ least needs 18"; look for deteriorated hose, hose off mod, leaky mod, etc.

kickdown rod or cable is not binding.. doubtful

Clean governor

GL!

 

[Broncobill78]

so i was driving my 84 big bronco the other day, and everything went fine. just a little trip to work, and then some errons around town. nothing too crazy and wild. the truck set for about 5 or 6 days, and when i went to drive it the next time, i had no third gear, and it will not shift automatically (C-6). now i have been around trannys and stuff all my life (dad had his own shop) but i have never had a tranny do this just from setting a few days. the bronco is not my daily driver, just a toy, and fun trip here and there. anyone got any ideas on where to start, and if i should rebuild, or replace.....

C6 ? Try the modulator valve, especially if you notice any grey smoke in the exhaust (grey smoke is usually transmission fluid being sucked back by the vacuum line thru a blown diaphram in the modulator valve, white smoke is usually water vapor from a blown head gasket and black smoke is excess fuel or oil being burned.). You can also try shifting it manually and see what it does, often-times a bad modulator will show up like that by allowing you to shift there but only manually (but not always). If it's been just fine so far and all of a sudden 3rd is gone then put in a modulator valve. When you get the new one make sure the colored band near the vacuum port it is the same color as the one you remove (different valves for cars & trucks). The modulator valve is easy to find and replace, it's the round valve in the rear of the tranny (runs front to back, compared to the servo which is oriented sideways) near the tailshaft that has the vacuum line running to it. Pull the vacuum line off and unscrew the valve, simple as that. You could even give it a twist in the driveway to be sure it's not frozen, tighten it back up for the ride to NAPA and then change it in the parking lot. But like Miesk said, first make sure it isn't something simple like a old vacuum line that's cracked somewhere along the run, I'd replace the vacuum line first and see if you get 3rd back. If not then I'd swap the modulator valve next (I think they're about $15 bux but to be honest I probably haven't bought one for close to 20yrs) and if that doesn't get it then I'd look to the servo.

The intermediate servo might also be at fault and fortunately it's another one you can get at and clean. I scanned the relevant pages from the factory manual to show you where it as and how to disassemble & clean it. Sorry for the large file size but I'm not having much luck with the lower resolution scans showing the illustrations very well.