Retarder Switch on LMTV1078 - 2000 Model

[hank0311]

I've been going through manuals on and off line and cannot for the life of me find anything regarding the Retarder switch on my truck. From a Google search I'm gathering that its a transmission "breaking" system for steep, slow, down hill decent. Am I correct in my recent findings? Also, is there any other use for it and what should I not use the Retarder for?

The other part of this question is regarding when the Retarder rocker switch is pushed to the 12 o'clock vs. 6 o'clock. On my gauge cluster a light comes on that says Exhaust Brake. But only shows on the cluster when the air brake is engaged. But when air brake is disengaged the light goes off? Can anyone explain whats going on here? To the best of my knowledge, my truck does NOT have an Exhaust brake. Any help on these matters is much appreciated.

Henry

 

[Ronmar]

I've been going through manuals on and off line and cannot for the life of me find anything regarding the Retarder switch on my truck. From a Google search I'm gathering that its a transmission "breaking" system for steep, slow, down hill decent. Am I correct in my recent findings? Also, is there any other use for it and what should I not use the Retarder for?

The other part of this question is regarding when the Retarder rocker switch is pushed to the 12 o'clock vs. 6 o'clock. On my gauge cluster a light comes on that says Exhaust Brake. But only shows on the cluster when the air brake is engaged. But when air brake is disengaged the light goes off? Can anyone explain whats going on here? To the best of my knowledge, my truck does NOT have an Exhaust brake. Any help on these matters is much appreciated.

Henry

What year and model truck are we talking about?

On the LMTV, Not retarder, exhaust brake... The retarder is a hydraulic brake system built into Allison 3000/4000 series transmissions as an option. The MD3070 AWD trans we use is incapable of it as the transfer case occupies the space on the end of the main trans housing where the retarder would go, and the retarder control circuitry(solenoid H) is actually used to lockup the center diff for 4WD operation on our trucks.

If your switch is labeled retarder, it is mis-labeled. the EX brake(4" butterfly valve after turbo) restricts exhaust flow out of the turbo and can serve double duty. Switched up, provides braking function. Switched down it provides backpressure load to help warmup the engine. requires park brake engaged and throttle at 0/idle for warmup. as ex brake, requires throttle at 0/idle and the trans will engage it when it is normally in lockup(3rd gear and above). It should also cause a gear pre-select command to 3rd gear to tell the trans to start downshifting in that direction as it is able, to increase effectiveness.

 

[Ronmar]

woops, missed the 1078 2000 model. cat 3126 should have an ex brake butterfly assembly connected to the turbocharger output...

 

[AKPacker]

It should be easy to spot if you have one, as Ronmar said it is a big butterfly valve assembly just downstream from the turbo. Up/12 o'clock on the retarder switch is for activating the exhaust brake when idling, it simulates putting a load on the engine to help it warm up faster. Down/6 o'clock on the retarder switch puts it in the driving mode where it activates the exhaust brake to help slow down when you let off of the go pedal.

They are awesome, I leave mine in the down/driving mode at all times and use the exhaust brake to handle the majority of my braking.

 

[GeneralDisorder]

Yep. Mine stays in the 6 position at all times unless I'm using warmup mode.

You DO have an exhaust brake - specifically a butterfly style PAC Brake. All 3126/C7 trucks have them unless it's been removed. Dramatically improves braking and brake lining lifespan. And if you didn't have one you wouldn't have the switch for it.

They do need to be used and occasionally lubricated. The butterfly style units have largely been superseded in the industry by the guillotine style as they are more reliable. The butterfly style tend to get seized up especially if they aren't regularly used.