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Discussion Starter #1
So I just got my early 99 F250, and while driving easy the transmission shifts nice and smooth...but when you get on it, it gets confused going into 3rd and OD and will go in and out harshly (sometimes), also my TCC is crazy...when you get on it some (about 3/4 throttle) it'll lock in, then when you ease off the throttle to cruising speed (maybe 1/4 throttle) it unlocks and won't lock back in until you are hammering on it again. Fluid looks and smells ok and it never slips...I know these trucks don't shift wonderfully, but I'm wondering if this is normal or if I have bigger problems...
 

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Former Ford Trans Engr.
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Are there any codes stored in the computer's memory?
 

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Discussion Starter #3
Not that I've seen. My buddy works at a Ford dealer and hooked it up on their computer and didn't see any. To give kind of an update on its operation...this should be more clear (I was tired when I posted that)

Normal operation (not a lot of throttle, no load):
Shifts normal and smooth as silk...but the TCC doesn't kick in under normal operation...you have to be at about 50% throttle to engage it...and it disengages at around 25% throttle...very frustrating.

Loaded operation (either towing or heavy throttle):
Shifts normal on the 1-2 shift, sometimes on the 2-3 shift...RARELY on the 3-4 shift. Normally slams into 4th. Again, TCC doesn't lock in until 50% throttle. Then unlocks when you go to cruising throttle. So, with a trailer, it's in/out/in/out/in/out...

No codes show...trans fluid looks and smells great. No slippage that I detected...I've been a mechanic 16 years but transmissions are NOT my specialty. Friend did a KOEO and a KOER test as well...with the Ford computer...
 

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Former Ford Trans Engr.
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My SWAG* is that you have a bad throttle position sensor.

*SWAG = Silly Wild A** Guess
 

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Discussion Starter #5
Lol I always say Scientific Wild Ass Guess! I put it on my scanner today, here are some things I noticed. It's shifting right when it's told. Doesn't appear to have excessive slip. Clutch coast solenoid never seems to engage. When floored, APP only registers 75%...I'll have to give the TPS a shot...transmission feels great, just feels like it's not getting the right inputs.
 

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Former Ford Trans Engr.
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The coast clutch solenoid should only engage when you turn off OD with the button on the end of the shift handle.
 

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Former Ford Trans Engr.
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3,103 Posts
I usually get parts from a parts store, a Ford dealer, and lately, Rock Auto.
 

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BigRed02
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542 Posts
Mark, would you recommend aftermarket valve bodies (or other parts/kits for that matter) for these transmissions?
Mine does fine, but at lower cruising speeds, it likes to lurch into 4th with the TC locked. There's a lot of hear say on what I "need".

Don't mean to hijack!
Thanks, Spencer
 

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Former Ford Trans Engr.
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If you put an aftermarket valve body on you will still have EXACTLY the same issue. Your problem is in the tuning in the computer, not in the valve body.
 

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BigRed02
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Ok, thanks for the advice. I'll look into tuners that would adjust it
 

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I had a similar problem and thought I had replaced about everything external.
after almost two years of research I finally found that the tachometer sender was defective. My truck does not have a tach but the engine still has a sender that tells the tranny how fast the engine is turning. It regulates the shifting of the tranny with the rpm's and vehicle speed. Hope this helps. I believe the sender was about $60 and you can test if it is working or not.
 
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