allison transmission question

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let it idle for a second in park

.gibson6string.. thinks John Prine is the dude.... =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D

allison transmission question Group: alt.autos.4x4.chevy-trucks Date: Wed, Jun 25, 2003, 7:53am From: snipped-for-privacy@webtv.net (JCORVETTE=A072&75) my 2500hd sits a lot because i drive the vette on the nice summer days, but when i do drive it when i start it and put it n gear it just sits and i guess the pressure is building up before it moves. should i let it idle in park first to build up fluid pressure. other than that i love my truck i actually got 14.5 miles to the gallon with the 502 engine cruise control on and a.c. going. i want to replace the air filter too. its about due. probably get a k-n filter this is my 3rd new chevy truck. the best one so far. first 2 were good trucks. thx for trans. info.

"your flag decal won't get you into heaven anymore, it's already crowded from your dirty little wars" J.Prine

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Yes, some Allisons have a "leak back" issue if the truck sits for 5 days or more. You are supposed to start the truck, let it idle for 30 seconds or so, turn it off, then re-start to purge air out of the system.

Here is a useful link:

Ray

That topic has been covered a lot on the dieselpage.com (as mentioned in another reply).

Basically there is clearance around some of the regulating valves in the pump/front support assembly that allows for extra cooler flow at idle. Unfortunately, if the tolerances are exactly right (or wrong, in your case), this clearance allows a slug of air to get sent through the system at startup. The pressure switches on the valve body then fail to close and the TCM thinks it has no pressure, so you won't attain range. If the loss of prime lasts long enough, the TCM will throw a code and you'll have to get it cleared - otherwise you just have to wait a few seconds before there is enough pressure to close the switches and allow the TCM to command a shift to range.

Last month a bulletin was released that allows dealers to install a new reg valve and spring combination that prevent the problem, so if it's enough of a hassle you might want to look into that. Have your dealer check bulletin #03-07-30-011.

Mike

JCORVETTE 72&75 wrote:

when i do drive it when i start it and put it in gear it just sits and i guess the pressure is building up before it moves.