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Discussion Starter · #1 ·
I've been out of the game for many years, but faced with a C6 problem, I return to what is hopefully still one of the best resources of Ford knowledge!

This one doesn't involve the Falcon which still rests under its shroud waiting patiently.

My nephew has a '79 Ford Bronco. Has a 460 swapped in in front of (I assume the original) C6.

We are having an issue of not shifting when hot.

Drove about 4 miles to the parts store without any issues. In drive down the highway. Drove home. Turned right around and headed up the highway again. About 2 miles out - so about ten miles of driving - the C6 doesn't want to shift into 3rd.

Decided to turn around and baby it home. After our next stop it didn't want to leave first gear unless we manually shifted to L, then to 2. Manually shifting into D did not get us into third.

We got home and let the truck cool overnight. Tried again with the same result. Good shifting through three gears when cold and losing shifting in D as it warms.

I have NOT looked at ANYTHING yet, but he is fretting about needing a new tranny. I can't see the clutches being worn if it shifts good cold. I don't THINK ATF thins much as it warms.

I'm leaning towards this sounding like a vacuum modulator issue.

Any advice at all would be much appreciated.

(Didn't see a C6 section, so posting in general)
 

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Discussion Starter · #3 ·
Reverse when hot... uh... hmm....

OH! yeah, we had to back up to do a 3-point u-turn. Reverse worked just fine.

Doesn't seem to slip at ALL in reverse nor in 1st. Just doesn't feel like it wants to shift into 2 or 3 automatically. Almost like a sticky valve in the vb, but works fine when cold.

I'm not afraid to drop the VB and clean thoroughly. I've been into my C4 so many times, I'm sure the C6 ain't much different.


Now, my ONE concern is that this particular C6 is under some stress. Full size bronco, 460 engine. 3.55 gears and 35" tires. Has a good cooler on it though. I may recommend a trans temp gauge - even temporary - in order to troubleshoot.
 

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Discussion Starter · #4 ·
There WAS transmssion fluid in the vacuum line attched to the vacuum modulator. Replaced vacuum modulator. Have not tested yet.
 
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