i have an 02 f350 7.3l psd cc lariat short box with 117k mi and my buddy has an 02 f350 7.3l psd cc xlt long box with 184k mi on it both trucks with automatic trannys. now i was experimentin with my truck and when im going 40mph in Drive and when i drop it into second my rpms drop and its like its just coasting but when i go to accelerate i have to hit like 2700rpm just to start gainin speed. now on his truck he can do the same exact thing but when he downshifts from drive to second it automatically goes to 2700rpm doesnt want to coast. i guess if ur not understanding what im talkin bout its like when u pipe a v8 truck or car and when u want the pipes to wrap u just downshift and it will start to wrap. my buddies truck will do that, but mine acts like a clutch disengages or something. its really weird cuz my truck and his truck r the same year, tranny, motor, style, but i seroiusly dont know what the difference is. any information would be greatly appreciated.

 

It has to do with the programming. Our trucks are fly by wire, meaning everything is controled by the PCM. There are many, many different PCM programs that Ford used, even in the same year truck. What is happening is the torque converter is un-locking on your truck. When it unlocks, the engine goes to idle. It is normal for most PSD's to do this. If you want a cheap way to change how your truck shifts and pick up a little performance as a bonus, contact Jody at DPTuner.com and tell him what you want. You send him your PCM and he will reprogram it to do what ever you want and give you some more HP at the same time. Just make sure if you add more than a 40 HP tune, you install gages to watch your exhaust tempertures. I think the reburn is $75. You won't believe the difference. Of course you can go the full route as well with multiple tunes...just costs money.

 

Difference in torque converter lock up. His is staying locked your's is unlocking or not locked yet at 40 mph. There is a lot of variation in lock up strategy in these trucks depending on pcm programming and maybe other factors. Some unlock when the brake is pushed, some don't. They lockup at different speeds etc. all normal for that truck.

Edit: Westpsd beat me to it and explained in better detail.

 

so does it really matter if my torque converter is unlocked most of the time? or is it better to have it locked?

 

I believe that it is better to stay locked up. Anytime it is unlocked under acceleration, it is building heat. I had my shifts changed with my chip and it stays locked anytime I am over 30 MPH except in the tow modes. The tow modes raise shift points and converter lockup to help keep RPMs up for more power. Lots of folks on here have installed a TC lockup switch so they can manually control when it locks. Flip the switch and presto......converter locked. Do a search on TC lockup mod and you will get plenty of reading including exactly how to do it.

Jim

 

That's all wrong.

The engine WILL NOT go to idle if the torque converter unlocks. The torque converter will drive the engine.

What is wrong with YOUR truck is that your coast clutch has failed. It's way too common on these transmissions, usually it is the snap ring that retains the clutch has come out of it's groove. The trans needs to come out of the truck and be partially disassembeld to get to the coast clutch to repair it. Usually the drum needs to be replaced with one that has a deeper snap ring groove.

 

I stand corrected! Casey, is the coast clutch electric? Each of my tunes releases the clutch at a different MPH (different, but consistant). I wrongly assumed that it was just the converter unlocking. I wasn't aware of the coast clutch. How does it work? I love to learn new things!

 

All of the clutches in a 4R100 are controlled by the electronics. The clutches are all hydraulically applied, but the solenoids that turn them on and off are electronic.

The overdrive gearset is in the front part of the transmission. There is a one way clutch that only allows torque to pass when the engine is turning the trans, it overruns like the pedals on a 10 speed bicycle when the wheels are turning the engine in any gear below 4th. The coast clutch clamps the one way clutch in 1,2,and 3 to make engine braking in the lower gears. It is applied when the OD cancel is ON, and also when the shifter is in 1 or 2.

 

hmm... maybe I'm mistaken, broken, or just doing things a bit different.

I know (with my tunes from jody) that my converter is locked above 30 w/ od off. At 30 the rpms will drop to 1000 or so until I stop. Before jodys chip and when I had the tc lock wire cut for some mods, rpm would drop to 1k whenever I let off the gas.

I think where my misunderstanding comes in is because I never pulled it into 2nd, allthough I know in drive (3rd) I had no compression braking... does this mean that I also have a blown coast clutch? I know that now, with the TC under pcm control (unlocks @ 30mph w/ OD off) I can pull it into 2nd and still have some braking.

 

No, you probably do not.

In 1st and second the coast clutch is applied with the manual valve. In third gear it is applied with the coast clutch solenoid. If you have engine braking with the shifter in 1 or 2, but not in 3rd with the OD off, then it's the solenoid or the wiring to the solenoid.

 

So what would cause all 3 coast clutches to fail or not function at the same time? when mine stopped working ( it did work before) all three (1st, 2nd, 3rd) quit. i have no engine breaking unless im going fast enough in OD.... And it all happend at one time.

And i know thats not the t/c cause i have a switch that locks it, and i love it

 

casey-so is it my truck that the coast clutch has failed since my rpms drop or is it my buddies truck that the coast clutch has failed since his rpms stay up when we drop it into 2nd?

 

There are not three coast clutches, there is one coast clutch. It is used to provide engine braking in 1st, 2nd, and 3rd. It does not come on in OD, the OD clutch provides engine braking when it's on.

So you have one coast clutch and it isn't working.

 

It's yours. The coast clutch is there to keep the RPMS up in 1st, 2nd, and 3rd gears.