Allison and Park

whitesnake01 · September 15, 2005

Went to the car wash this morning with the DMAX truck. After coming out I put the truck in park as I was standing on a 15% sloped driveway out of yhe wash. Pressed the brake pedal. But the truck slid for a foot or two until the front tires crept into a small pothole..

On my Suburban (4L80E) the P position feels mechanical. That is, it locks and gets stuck when I park it. You can feel this when you try to move from P to D on a slope. Does the Allison have a mechanical lock at P or some friction lock that may make it slide?

N900WM · September 15, 2005

It's my understanding that the Allison has a posative lock that engages when put in park.

My turck makes noticable pop when placed in park or taken out of park if on an incline.

But I have noticed that if it's put in park before the truck sets back, the truck will slide on a small incline if it's wet or snowy. It's a heavy truck!

renolaw · September 21, 2005

once in a great while, when i put the alison into park, it will roll slightly fwd or backward (depending on the slope) about 6" and 'click' into park. un-nerving? u bet.

what to do?

when i daily lift the shift lever into 'park', there is this crack sound as the detent (or linkage) locks into place. worrisome for sure, but it's one driving MF!

mb

TieRod · September 24, 2005

Yes, Ally's have a mechanical parking paw. It is very large for are trucks and it will allow the truck to move a bit before it engages.

SS Crew · September 24, 2005

I've got at 2500 and have even noticed this condition with my truck. I think it's from the power brake boost coming off the power steering pump. It's probably from the fluid pressure dropping, therefore you would need more pressure on the brake pedal. I've noticed when I'm in park with my foot on the brake on a slight grade and turn off the engine, the truck rolls ahead a couple of inches - not much, but enough to be noticeable by feeling the truck stop abruptly when the prawl digs into the notch in the trans.

I might be blowing smoke out of my rear, but it seems to make sense. (At least to me).

whitesnake01 · October 2, 2005

I've got at 2500 and have even noticed this condition with my truck. I think it's from the power brake boost coming off the power steering pump. It's probably from the fluid pressure dropping, therefore you would need more pressure on the brake pedal. I've noticed when I'm in park with my foot on the brake on a slight grade and turn off the engine, the truck rolls ahead a couple of inches - not much, but enough to be noticeable by feeling the truck stop abruptly when the prawl digs into the notch in the trans.

I might be blowing smoke out of my rear, but it seems to make sense. (At least to me).

<{POST_SNAPBACK}>

That might be what happened to me. I'm not one of those diesel guys who like to leave theirs idle when they are outside. I tend to shut it down before I get out. I was about to get out to get the mirrors back in a usable position. This is why I stopped and put it into P. I might have shut the engine off real quick, too.