Tranny slip.?.?

F150 Man 4Eva · #1 Thu, February 11th, 2010, 05:36 PM

Well on my ride home from work today I decided to show OSS and TSS on my parameters. I was surprised to see how far off from eachother they were. But given, I know nothing about these values or what they stand for or what they mean...nothing. I am looking for some insight on how much slippage is normal. It seemed that at low cruising speed (30) in 3rd gear..they pretty much matched up. When accellerating...way off. While cruising at 60 or so they were like 600-700 off. Can anyone help me understand this?

***cleatus12r*** · #2 Thu, February 11th, 2010, 11:17 PM

Quote:

Originally Posted by F150 Man 4Eva

Well on my ride home from work today I decided to show OSS and TSS on my parameters. I was surprised to see how far off from eachother they were. But given, I know nothing about these values or what they stand for or what they mean...nothing. I am looking for some insight on how much slippage is normal. It seemed that at low cruising speed (30) in 3rd gear..they pretty much matched up. When accellerating...way off. While cruising at 60 or so they were like 600-700 off. Can anyone help me understand this?

Yep. It's easy.

In first gear the turbine shaft speed will be about 2.88 times the output shaft speed.

In second gear, the TSS will be about 1.55 times OSS.

In third gear, they will be the same.

In fourth, the TSS will be LESS than the OSS because of the .71:1 overdrive.

When the torque converter clutch is applied, the engine RPM should always just about match the TSS.

The sensor inputs to the PCM have to do with the gear ratios in the transmission and the computer's way of self-diagnosis to determine whether or not there is slippage and whether or not the commanded shift actually took place.

***Jackpine*** · #3 Fri, February 12th, 2010, 11:11 AM

I have a "hangup" with the description of this too, F150 Man 4Eva, so you're not alone.

What Cody was telling you is absolutely correct. The TSS will equal the OSS in 3rd gear only provided the TC is locked up. In any other configuration, they will always be different. I find the difference being labeled "slippage" as totally misleading - which can lead to unnecessary worry.

- Jack

***Power Hungry*** · #4 Fri, February 12th, 2010, 11:55 AM

For a visual person such as myself...

Engine --> [Converter] --> Input Shaft --> [Tranmission] --> Output Shaft

or more specifically...

Engine --> Input Shaft --> Output Shaft

Engine --> Input Shaft:

Same if Converter is locked
Different if Converter is unlocked (difference varies depending on load)

Input Shaft --> Output Shaft (Based on 4R75 Transmission)

1st gear - Input is 2.8387 x Output (2.8387:1)
2nd gear - Input is 1.5545 x Output (1.5545:1)
3rd gear - Input is the same as Output (1.0000:1)
4th gear - Input is 0.6984 x Output (0.9084:1)

Slip in the transmission can be easily calculated by finding the input:output ratio and see if it matches the current ratio for the selected gear. If it doesn't match, then slip is present.

Slip in the converter is only determined during lockup.

F150 Man 4Eva · #5 Sat, February 13th, 2010, 07:52 AM

Wow..ok, so it is more complicated than just looking and comparing the two numbers while driving down the road. I won't worry about it then. Tranny feels fine, its just when I read about the slippage and oss=tss...I was confused and wondering what was going on with my truck. Thanks for the explaination..I will remove those values from my parameters now and just not be concerned with it any more.