Allison won't hold Park

[Cheavyduty]

I parked my truck on a modest incline this afternoon and was startled when it rolled back in park. Has anyone else had this occur?

[DmaxMaverick]

How far did it roll?
One foot? Two feet? Ten feet?
It is normal for the pawl to delay engagement due to the spacing. About 2 feet should be max. If it does not engage at all, it's broke.

[77TransAm]

Two feet is WAY more than too much. An inch or two should be plenty to hit the next tooth on the park pawl. The first thing to check is the shift cable - if it's broken it may have trouble pushing the shift lever far enough to engage park. If it's 4WD, the transfer case could also cause a neutral condition, even if the transmission output is locked by the park pawl. If it is neither of those, the park pawl mechanism in the trans has a problem.

[77TransAm]

Do you mean that it rolled back and then engaged park, or that you could not get park at all? The Allison has the largest park pawl made, so each gear tooth is quite large, but a couple of inches of rollback is plenty to hit the next tooth on the park pawl.
If you are just rolling back without getting park at all, he first thing to check is the shift cable - if it's broken it may have trouble pushing the shift lever far enough to engage park. If it's 4WD, the transfer case could also cause a neutral condition, even if the transmission output is locked by the park pawl. If it is neither of those, the park pawl mechanism in the trans has a problem.

[Gbenzx01]

Well Cheavyduty,

Did you ever find your truck?

Gben

[Cheavyduty]

It rolled back more than two feet. I first thought I was sliding on ice since it was iced over pretty good, but when I hit the brakes it stopped. I backed up a little then forward to see if it just did not "catch" but it did the same thing. I pulled into a level spot instead. I will have to get it checked out this week if I get some time. It shifts fine and all and nothing has happened to it that I feel could have broken anything but I guess I'll find out.

[Buckman]

Cheavyduty,
What is happening on your truck? Have you had the unit checked yet and if so, what did you find out. I would certainly have the linkage checked. Let us all know what happens. Best regards :confused: