2004 48RE tow/haul switch function

[cerberusiam]

Yes it locks up with TH on, otherwise I'd be burning up the TC clutches on every trip in the mountains with my 15K# 5'er, eh?

No, you burn the clutches up when it does not lockup solidly, ie the pressures are too low to hold the power.



A lockup TC is just a cheap way to get around the expense of building a converter that will hold the power and provide adequate efficiency at road speed.



The gen1's with a non lockup TC towed trailers all over before a lockup TC was introduced for CAFE ratings. Its all in how the TC is built.

 

[Prairie Dog]

No, you burn the clutches up when it does not lockup solidly, ie the pressures are too low to hold the power.



A lockup TC is just a cheap way to get around the expense of building a converter that will hold the power and provide adequate efficiency at road speed.



The gen1's with a non lockup TC towed trailers all over before a lockup TC was introduced for CAFE ratings. Its all in how the TC is built.

I had one of those first gens, I could over heat the eng with the amount of heat the trans poured into the cooling system. No way I'd ever have a non-locking TC again!

 

[WalterJ]

Some additional notes on 2004. 5 48RE torque converter (TC) Lockup:

1-The 2004. 5 48RE is designed to lockup (LU) between 45-50 MPH, regardless of TH/OD status. This transmission Control Module (TCM) schedule is designed for gentle/normal acceleration. The lockup (LU) Solenoid typically then drops out below 45 MPH.

2-During more aggressive acceleration, another TCM schedule takes command, regardless of TH/OD status, RPM, or vehicle speed, and energizes the TC LU Solenoid which applies full oil pressure to the TC clutch pak to ensure positive lockup. If the throttle is 'relaxed' then prior to reaching 45-50 MPH, the TC LU solenoid will de-energize and relieve the LU oil pressure.

This summarizes answers I obtained from my trans rebuilder earlier today, as I questioned my various observations during this trip to FL with my 'new' hvy duty transmission. He also reminds me the 2004, 2004. 5, 2005 are designed & act differently, and should be considered individually re: performance characteristics, driveability, etc.

I fortunately have a Banks diesel tuner with a PDA, so I'm able to monitor my TCC% (TC LU Solenoid) signal 0% or 100%. Hope this helps someone, it sure helped me understand more of my machine.

If you're near Racine, WI & need some critical transmission advice, I have every confidence in Greg Clark (owner) of GT Transmissions, 262-619-3288.

 

[cerberusiam]

He also reminds me the 2004, 2004. 5, 2005 are designed & act differently, and should be considered individually re: performance characteristics, driveability, etc.

That pretty much summarizes it. They are all a little different and even different with flashes from what I have seen.