budbon

I am ready to purchase a compression brake and keep reading about a torque convertor lockup for my 05, 3500 W/auto trans.
Some questions, I know what the torque convertor is but:

What does it mean to lock up?
Why not lock up all of the time?
Is it necessary to lock up when using compression brake?

Any help in understanding will be greatly appreciated.

HOV

The TC acts as a clutch would in a manual vehicle - a coupling between the engine and transmission. Instead of using clutch plates however, the TC uses a fluid coupling. The engine drives a pump that circulates fluid in the TC, which in turn drives the plate attached to the transmission. This fluid coupling is why automatic transmissions are also called "slushboxes".

The fluid coupling works well in 1st gear, allowing the engine to turn a little higher RPMs, creating more torque in the fluid that creates what's called a torque multiplication effect. This effectively reduces the gearing in first gear, and it's why auto transmissions only have a 2.XX drive ratio in first gear, as compared to 3.XX or 4.XX for manual transmissions. This is good to get a load moving

In higher gears however, fluid coupling isn't very efficient. It makes the engine turn more RPMs without transferring that power to the transmission. It's analogous to driving with the clutch half engaged. TC lockup solves this by mechanically locking the TC so that it transfers power directly to the transmission.

Lockup isn't possible all the time for the same reason it's not possible to drive with the clutch engaged at all times. You'd never be able to come to a stop! And shifting gears would be EXTREMELY hard on the transmission.

TC lockup is needed for exhaust brakes because an exhaust brake works by shutting off the exhaust and fueling, essentially turning the engine into a big air compressor. The pistons have to work hard to compress the air in the cylinders, which in turn slows the crank, and via the transmission, the wheels. If the TC were not in lockup, this would never happen. The engine itself would slow down, but the braking force would never reach the transmission at all because all the braking power would be lost in the fluid coupling.

Hope this answers your questions

budbon

Wow! Great info. Thank you.

Guess I had better have this available if I install a compression brake.

grantx5

The 48re in the O5's will not take an exhaust brake although PacBrake seems to have a solution. Make sure what you are putting on will work without destroying your tranny.

This is the biggest drawback to owning an '05 auto.

TAS05CTD610

See I don't understand why it'll work on any truck but not the 05's with autos? I know my dad's if you let off the gas the thing unlocks (not just like that) but at least the 05's stay engagued untill you hit the breaks (mine does) I would think all they need to do is tie into the tranny so that it grounds out the number 7 pin to keep it locked, then unlock when you stop??

grantx5

I hear you. PacBrake claims they have the solution. The trouble is, will it void the warranty, will it destroy the tranny? I have not read from anyone who has made the mod to their '05 and posted their experience.

Maybe someone will chime in with how it works for them.

no_6_oh_no

Nah, not even close to being true. The 05 will work fine with an EB with either a BD, Pac, or ATS lockup controller.

What ti does to your warranty is another question.

grantx5

Correct, the TC must be changed out. That is a HUGE problem. Who wants to spend that kind of money on a $40K truck? Not me. DC really screwed up when they put the '05 tranny together.

no_6_oh_no

Hmmm, since there is little or no difference in the TC on the 06 and 07 models that must mean they are junk also and the EB doesn't work on them either. Might as well extend that to the late 03's and 04's also as they have the SAME converter.

The ONLY reason DC will not warranty an EB on the 05's is due to the lack of ECU programming to make absolutely sure the TV pressure is ramped high enough and kept high enough when the EB is engaged and the TC locked. Its not that it didn't work but rather that it didn't work the way the engineers felt to be the correct way every time under every circumstance using ONLY the ECU programming.

Lots of 05's autos running EB's with aftermarket controllers and no issues. Its not as seamless as the later trucks but far from being a total loss.

Raspy

The engine brake issues are not with the TC. It's just that the TC must remain locked while braking, a programming issue. I think the issue is the thrust bearing. When the engine is holding back it puts a larger load on the rear thrust bearing. This is a bronze washer in the earlier trannys and a roller bearing in the ones approved for the engine brake. That bearing has been discussed before and can be upgraded to earlier models. Before the engine brake, the helical gears did not put enough load on the washer to be as issue, but with the brake it is.

This, despite what some have said, does not prove this tranny is junk. I find it sad when someone is able to find a place for improvement and uses that issue as proof that the thing is junk. I'm personally very happy with my truck even though I can find places where it could be better.


John

grantx5

Man, you guys are brutal. Who said is was junk? What I said is that DC screwed up with the '05.

It would have been just as easy for them to make it completely ED compatible and allow for locking out OD.

Who was the idiot that decided locking out OD was not a good thing. The 48re hunts for gears like a couch potato with a remote. They just didn't think through it very well and could have done a much better job.

Harold-Pacbrake

You can put the exhaust brake on the 05 truck you HAVE to lock-up the T/C. Our new klts come with the controler to do this. As for warranty We are the only ones that cover progressive damage if the exhaust brake causes a factory part to fail.

Raspy

[QUOTE=no_6_oh_no;1593051]Hmmm, since there is little or no difference in the TC on the 06 and 07 models that must mean they are junk also and the EB doesn't work on them either. Might as well extend that to the late 03's and 04's also as they have the SAME converter.


grant,

I wasn't refering to your post, but to no_6's post. Sorry to be so "brutal".


John

Raspy

"hunts for gears like a couch potato with a remote" Great term!

John

grantx5

[QUOTE=Wetspirit;1593591]No harm done.