Wow.

bummed-n-Md · November 22, 2002

I am very curious about something. when you engage 4x4H, does the 'truck' change the actions (shift points, TCC lock up, etc) on the Allison? ???

Let me explain.

Everynight as I drive home, I have this one stop sign I have to go though. It is at the base of a 1/4 to 1/2 mile long hill. As I go though the stop, I accelerate hard (foot to the floor) to 'blow out the carbon'. Last night was wet (rain), but the acceleration and shift points seem consistant with dry pavement runs.

Now the rub. Last night I had to pick my son up from football. I had another stop sign to cross (no hill this time). As I waited for my turn to go, I noticed the car in front slipped a little going across the intersection. As the road was busy with trancelike, homeward bound commuters, I didn't want to run the risk of the rear tires slipping as I start across, so I engaged 4x4H. A break in the on coming traffic presented itself so I slipped my foot off the brake and floored it to get across. I was pinned to the seat. This truck has NEVER accelerated that hard. I was very surprised to say the least. I'm serious, it felt like I dumped the clutch on a big-block muscle car with a manual tranny on dry payment. I half expected the back tires to breakloose and leave a patch of rubber with the accompanying 'chirps' (awh, the memories of a mis-spent? youth).

I have used 4x4H mode before but never had to accelerate hard in that mode. When the 4x4H is engaged, does the 'truck' modify the shift points, TCC lock-up, or the differential's 'slip'?

I'm not complaining mind, you, if this is 'normal' and an indication of what this 8.1 can do when everything is 'right', its good !!! I would just like to understand what happened. (I am going to try and duplicate it tonight on the way home) (there was too much fog to risk it this morning)

bummed (only about what GM considers normal oil use)

CMNTMXR81 · November 22, 2002

Nope.

It's simple physics. 4 wheels turning and grabbing will feel stronger than two that even on dry pavement may have a slight bit of wheelspin action going.

At the same time, you are being pulled by the front axle and pushed by the rear axle, therefore making it feel stronger.

BDBWTE · November 22, 2002

Nope.

It's simple physics. 4 wheels turning and grabbing will feel stronger than two that even on dry pavement may have a slight bit of wheelspin action going.

At the same time, you are being pulled by the front axle and pushed by the rear axle, therefore making it feel stronger.

front axle??

CMNTMXR81 · November 22, 2002

You know what I mean.

I'll rephrase it, front driveline.

bummed-n-Md · November 25, 2002

Thanks for the feed back.

It just seemed that the entire drive line had all of the 'slop' taken out when I was in 4x4, like when you 'tighen up the drive line' just before you dump the clutch in a race. In 2-wheel mode, it seems like that is done when you hit the accelerator (it does happen quick), but in 4x4, it feels like it is already done. I was wondering if transmission pressures or anything were mod'd. but if not, ok.

this is something I can definitely live with. :thumb:

Btw, I was able to 'repeat' the test on dry payment, and yes, it launches in 4x4. mode