LMTV braking question

[reelclassic]

I have an A1 LMTV with a 3126 Caterpillar. When I am slowing down and transmission downshifts. The closer I come to a stop the hard it jerks.
I think its an air brake that probably should only be on when pulling a trailer. Any ideas?

Thanks,

 

[NDT]

The air brake system has no idea if there is a trailer on or not, and is not modulated by anything other than your foot. If you are experiencing too early downshifts by the Allison, which result in jerks as the engine is spun up, I would start by seeing if your WTECII ECU is throwing any codes. As you know, both the engine and transmission are entirely fly by wire, so there is nothing mechanical to adjust.

 

[reelclassic]

Thanks for your response. I do have a retarder exhaust brake. It has a switch on dash for off/ warm up. Would this have anything to do with it?

 

[Suprman]

The 3rd to 2nd downshift can be hard or jerky on all of theses trucks. You should have a single digit wtec3 in a 3126 A1. It will display errors and parameters. The allison guide is available online. I would leave the exhaust brake off for normal driving. Are you in low or high idle? High idle would make it jerk more.

 

[tennmogger]

I have an A1 LMTV with a 3126 Caterpillar. When I am slowing down and transmission downshifts. The closer I come to a stop the hard it jerks.
I think its an air brake that probably should only be on when pulling a trailer. Any ideas?

Thanks,

This sounds like the very common hard downshifting due to too high engine idle speed. Many of us had to adjust (lower) idle set point on the linkage and also free up the linkage to the pedal so engine speed would drop. try lifting the accelerator pedal with a toe as you decelerate.

 

[Suprman]

3126 is electronic. There are 2 idle speeds low and high selectable but dash switch. I believe it always starts in low idle though.

 

[5tonmog]

Guarantee transmission is overfilled

 

[scottmandu]

The Allison transmission doesn't shift like a Cadillac. You know when gears change. M1084A1 does the same especially from 3-2 i did notice that with the retarder switch depressed it's much more pronounced.

 

[Floridianson]

Lots of people forget that hard shifting is what you want when you have heavy loads slow ground speeds and high rpm plus off road ruff running. You don't want slipping and as Scottmandu said it's not your slip and slide powerglide. As said above you might be able to tweek the trans and also if you are running MO then the only other thing is a 10 weight oil MO that it should have in it. Then if it was MO switching to ATV will help. Being up to full oil temps. helps sometimes too.

 

[tennmogger]

Guarantee transmission is overfilled

Why would you say that?

 

[5tonmog]

I am a old man and have several lmtv's. You stated when sewing down it is jerking. Do you mean like coming to a stop sign when it is downshifting it wants to throw you through the windshield if yes does it shift hard when accelerating. If yes check tranny fluid while hot look closely and make sure it is not over the full mark at all, if it is drain a quart. Tranny also likes a well charged battery.