The fluid wore out even quicker if it got hot.

Once there is damage on the friction material in the converter clutch new fluid will not fix the damaged material.

That's not how it works. It has designed in slip. Sometimes it will lock 100%, but not very often in those early 4R70W transmissions. They would go to a designed 20-40 RPM constant slip. That's what wears the fluid out so quickly.

It uses PWM strategy to allow the continuous slip. That's the reason the PWM was developed.

No, the shudder is caused by the ATF wearing out. The continuous slip was murder on ATF.

 

Mark,

Do you know why they were programmed to slip like that? What was the perceived advantage? I'm getting the feeling that this may not have been engineering's desire.

Did they go to 100% lockup at some point, or is some amount of slip still desired for some reason?

I've noticed that the 6r80 lockup in my 2010 feels very reminiscent of the 4r70 in my 1995. Perhaps not the same from a design stand point, but the very long application times in function (~3 seconds until the rpms stop declining on lockup after a downshift).

I always thought that PWM was developed to have a more controlled lockup strategy. Never knew it was designed to purposely allow a continuous slip condition. I had heard that they always slipped some, but in though that was a byproduct of PWM, not the reason for it. Very interesting.

 

Awesome, thanks for clearing all this up!

 

Great info guys, i truly appreciate it. Cooler is on the list at some point, i want to make this thing a sleeper kind of. One thing for sure, getting a tuner for the trans. I will inspect the fluid more closely but it looked mint when i checked it when we bought it. Somewhat off topic, how tough are these before i should start throwing parts at it, not counting a good tune? Thinking i want to slap a procharger to this thing.

 

I guess I could say this if you don't have a truck:
Join a site called TCCOA.COM They are the authority on these powertrains, even mustangs and crown vic onwers refer to them. I don't know if all the old school guys are around, but you can ask questions there.

Just look around and search before you ask questions, they were around since 2000, and they specialize in the car. One upgrade you can make is a PI intake.

They discuss what can and can't be done, and it is good they get new members.

There is a document written by Jerry W (he is ford engineer), the JMOD, he explains precisely how to mod the 4R70W trans for very high performance or longevity. I think Ford incorporated some of the improvements into the later models. There is a link to a vid on YT where a guy performs it.

 

Thanks for the info, i know this is a truck forum, but the other car forums ive tried, most are garbage. Be nice to find a good car forum.

 

It was to make the car smoother. An open torque converter will eliminate any vibration, shudder, or miss from the engine. A locked torque converter transmits any vibration, shudder, or miss from the engine right to the passengers, but gets about 3-4 MPG better fuel economy. We learned that if the converter was allowed to slip about 20 RPM you got all the dampening of an open converter with about 99% of the fuel economy gain of a locked converter. Seems like a no brainer, right? The problem was discovered in development. They shuddered at higher mileage like you wouldn't believe.

I've seen shudder described as going over railroad tracks. I was working in the AXODE at the time, and we ran into the shudder first, as our program was a year ahead of the 4R70W. When it went into shudder the steering wheel moved up and down about 4-5 inches and the dash vibrated so hard I couldn't read the speedometer. It did the EVERY time it locked. In the AXODE we didn't take the continuous slip to production. 4R70W told us they knew how to make it work. No, they didn't.

I didn't work on that program, and I don't remember if they ever went to 100% lock.

I've never driven a 6R80.

He was a Ford engineer. I knew him fairly well. He knows more than almost anyone else about the 4R70W. I left Ford in 2007, he left a couple years before I did.