I got a 5.4 Ford econoline 1998 edition.

I got me a odb2 code readin app with the bluetooth on it... and I also paid extra to unlock the premium Ford specific data... all kinds of stuff in there.

In the ford codes (or "pids") there is a parameter called "transmission slip ratio"

I don't know what that is intended to be a readin of exactly, but it sounds bad... cuz don't nobody wants there transmission "slippin."

So I been keepin a eye on this "transmission slip ratio."

Maybe if I describe what numbers it shows and when... somebody out there can tell what it is a readin of... and whether these readins are normal or not.

So here goes:

  1. If yer not movin, it will read zero in any gear.
  2. If yer goin above say 45mph, it will read "1.0" even if your applyin more gas (unless you ask for some much gas that it downshifts... then it'll start reading less than 1.0)
  3. If yer slowin down, it will read higher than 1.0... like 1.2-1.5
  4. If yer accelerating in any gear other than the very top gear ("overdrive"?), then it with read less than 1.0.... usually 0.8-0.5
  5. The more harder you are tryna make it go, the more different the number is from 1.0 (hey I made a rhyme!)
  6. The steeper the hill is that yer slowin down goin down, the more different the number is from 1.0 (that one wasn't as good)

Now if I'm to understand this right you got yer input shaft coming from the engine, then you got a torque converter (which is designed to "slip"), then you got whatever the heyl goes on inside the transmission... then you got the output shaft.

So I guess this must be reading the difference between somethin that spins someplace and comparin it to somethin else that spins in another place.

But why is it called "slip"? Slip is bad.

If it's just readin the difference between whats happenin before and after the torque converter then I guess those numbers make sense...

I know that it ain't a readin of gear ratio so don't nobody say it is cuz I'll come through the computer. The gear ratio shows up in a readin called "tranmission range." I figured that out myself and you can watch it change when you shift gears. I think... actually I cant remember now for sure or if it's just a reading of where the transmissin lever is set at.

Also please do not ask me if I am noticing other transmission "slip" symptoms because the question ain't asking if my transmission is slippin, it's asking what the "transmission slip ratio" is readin exactly.

Anyhow, appreciate ya... sorry if I got a little hot there.

  • 2
    All automatic transmissions slip. The torque converter slips until it is locked up. All of the clutches within the transmission slip as they are engaged. There is plenty to slip. Slipping too much is what's bad, and I believe this is what the pid is for, but I'm not sure. – Pᴀᴜʟsᴛᴇʀ2 Jul 1 '20 at 3:41
  • Found some info to support you Paul. "Notice that this screen capture (Fig. 9) is indicating that the converter clutch is fully applied (100%) and the TCC slip ratio is 1:1." >>>>>motor.com/magazine-summary/… – Moab Jul 1 '20 at 14:58
  • There are up to 8 slip values>>>>>>obdsoftware.net/software/fordenhancedparameters – Moab Jul 1 '20 at 15:00

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