Allison hard shift clunk

[Jimamatic]

I need some help to compare my truck with others.
When I first put my truck in drive, it goes into and sounds pretty smooth. But when I go to put it
in neutral or park after driving, it will shift
kind of hard and makes a big clunk. Seems a
little harsh. I have the 2001 2500 hd d/a cc 4x4
build date July. Is this normal or should I have it checked out.

[NFLDMAX]

Mine does it too. I remember from an earlier post that it is the parking "pawl" engaging and that it is normal.

[MudNurI]

ahhhh that's NOT normal....thats the NSBU heading south.

Ours started that about 6 weeks prior to losing the gear indicator- which was gone for 4 days before the truck basically wouldn't shift without sounding as if the transmission was throwing parts across the driveway....

Get the NSBU replaced, to be safe!
just make sure you get the NEW switch..TAN in color with a shield on it...NOT BLACK

Brandy

[Jimamatic]

Thanks for the replies. Please excuse my ignorance
but what is a NSBU, and what does it do? My truck
has always had a thunk coming out of drive but
has'nt thrown any parts across the driveway yet.
I don'nt think it is the parking pawl because it
will do it going from D to N. Then N to P is
smooth. It almost feels like the the converter
has a little to much grab in drive at idle. It is more pronounced when creeping up a hill and stopping, like my driveway. Thanks again.

Jim

[NFLDMAX]

After reading my post, that loud clunk only happens when I engage in park (which I believe is the parking pawl)...This does not happen in neutral.

Thank you for the correction MudNurI.

[MudNurI]

NSBU is the neutral Safety Back-Up Switch..I'm not sure what it's suppose to do, but since you have a '01 you have the old style. do a quick search on NSBU, and you'll find out how many of us with '01's have had this problem. mine didn't go out till bout 50K on the truck..but when it goes, it goes. Simple as that. Brother in laws 8.1/A went and all he had left was Reverse. Ours still had a few forward gears, if you could get it to engage. Just remember- when they replace it.... it should NOT be black...something about the black one gets moisture inside it and that's what causes it to fail.

I've heard the price range from $40-120 bucks depending on where it came from. Some guys on here have swapped out their own..it's on the driver's side of the transmission. I wiggled my way to get it covered under warranty..though it would have been a HECK of a lot easier to get do it myself.

One other thing- if you DO go to a dealer- REMIND them you have the ALLISON...there is a TSB out for the other transmissions- 460L (???) that requires replacing the IGNITION....yup, my wonderful dealer did that first...transmission/ignition. well, it rhymes!

good luck

Brandy

[DMAX-Hunter]

I have the same issue with clunking while shifting at stop between N & D, D & P, N & R, etc. I posed this question last week, but never got any replies. Perhaps I wasn't clear enough with my wording. Bottom line is, you are not the only one. I haven't bothered taking my in for this yet. I still have about 17K left on my warranty. If you do take it in, let me know what the end result was.....