I have a 66 F100 and recently swapped in a 351W and FMX that were original to my 69 Mustang that now has a 460 w/C6. The FMX had been rebuilt with less than 10,000 miles on it when it and the engine were pulled out of the Mustang. However this was back in 1993 and the trans just sat for until I recently installed into the old truck. So I got the engine and trans installed and added fluid to the trans and it started working, initially not shifting on its own but it started working okay but a little erratic were it might not start shifting on its own until it was warmed up. The fluid level on the dipstick showed that it was way too full (checking it hot, idling in park after cycling it through all gears prior to checking) showing a couple of inches above the full mark. So today I drained off about two quarts and took it for a test drive where it clearly acted like it did not have enough fluid where it was acting like it was in neutral even when in gear and would kick into gear if a revved the engine a little and then would return back to acting like in neutral on and off when going around a curve or up a little incline etc. But when I check the fluid it still shows an inch above the full mark?? Has anyone experienced this and maybe something is stuck in the Trans that is preventing the dipstick to read accurately? It is the original dipstick and tube so I know that is not the problem. Any ideas? As is, I guess I am going to put two or so quarts back in and just drive with it like that, but I am perplexed on way the dipstick reading would not be accurate. Also I did also replace the vacuum modulator and it does not leak any fluid or show signs of foaming/aeration when it had two more quarts in it. Thanks in advance for any ideas about this.

 

Chances are you have the wrong dipstick.

Full running in Park level is close to the pan/case junction.
Run the stick down outside the tube and make a mark.

 

I can't imagine how the dipstick is wrong, but that sounds like a good idea to go ahead and check. I'll try it.

Thanks
NATE

 

One thing I neglected. Sitting that long mud wasps could have built a nest around the breather. If this is plugged you will get an erroneous reading.

 

Look on the dipstick for a stamped Ford ID number, post what it is.

 

Good idea. The dipstick is stamped with C90P-7A020-A3.

Thanks

 

C9OZ-7A020-A .. FMX Dipstick / Marked: C9OP-7A020-A3 / Obsolete

1969/72 Fairlane/Torino/Montego/Mustang/Cougar.

 

So it sounds like it is the right dipstick then. Maybe the breather hole got plugged at Stuart suggested and that is causing the faulty reading. If that is the case and run some wire down it to break up mud I would probably push the mud down into the Trans however which wouldn't be good. I guess I'll just add fluid back slowly until it starts working right and live with the inaccurate dipstick reading.

 

The breather tube exits to the rear of the transmission right side. Just in front of the cross member.

Just poke a small wire into it.

If push comes to shove remove the tube and give it a blow job.

 

Thanks Stuart, that sounds like a good idea. I know which tube it is, but does it/should it just pull out of the trans pretty easily? If I can remove it easily then I would feel much safer giving it a blow job and reaming... Ooh that does not sound good