I have a 2002 2500 duramaxx alli tranny, i love this truck but have a couple issues......

1. the service 4 wheel drive light comes on occasionally, so quickly you could miss it, no codes...... 4 wheel drive works could this be the pump rub thing i have now heard quite a bit about? truck has 91,000 miles and I bought it with 84-85000 miles...... can someone post pics of where i should look and what i should check for with this rub thing?

2. sometimes and this again only happens occasionally, when you put it into gear (any gear) R or D you can hear and feel tranny shift out of gear and shifter light will blink, if you put it into park or neutral and try again it will stay in gear. one time it didn't and it went in for neutral safety switch (upgraded part) apparently this was a problem but it still does it, talked to dealer and they now say the connector to switch was bad too but now they won't warranty it....... I will have to fight about it i guess...... could there be any other reason for this as again there are no codes...........

thanks for any help, these new trucks are a puzzle to me. up until last september I drove a 74 blazer, that was a simple truck, but needed to haul hay and horses.......... :)

1. Pump rub, you will be able to see residual fluid on the underside of the truck. It will come from the backside of the transfer case. If the rear axle is wet rusty looking, you might have the problem. Best thing to do is get the fix from one of the supporting vendors on this site ie; Merchant Automotive or Kennedy Diesel, and just have it done at a local shop.

2. Sounds like your NSBU is going out but not all the way yet. This is a common failing item on the Allison an not very expensive from a Allison dealer. Dont buy it from the GM dealer as they will milk you for every penny. It is a pretty easy item to replace, just remember to put the truck in "N" and set the park brake when you do it. The new one has a clip holding the selector in place, once you slide it onto the shaft the clip will pop off and you bolt it onto place and enjoy your truck again.

Hope this helps,
Tony

FWIW I just bought a replacement NSBU for my LB7 for $62 + tax from te Allison dealer.

-Wardster

Nsbu?

Nsbu?

Allison Part #29540479

Nuetral Safety Back Up switch is what I think NSBU stands for. Someone correct me if I am wrong. This little part controls the trans electronically, even though it does have a shift cable!

Best description is found here:

http://www.merchant-automotive.com/allisonnsbuswitch2001-2004.aspx

thanks!

Might as well do the pump rub fix anyway.........

Thanks again! they replaced the neutral saftey switch but then said the connector could be bad, i told them to replace it and they said they couldnt be sure if that was it, now if its been an issue, why not just do it is what I say............
underneath has a little leak on the transfer case, can't tell where its coming from, gonna do that fix anyway..... better to be safe than sorry.......
Thanks for all your help!!!

Thanks again! they replaced the neutral saftey switch but then said the connector could be bad, i told them to replace it and they said they couldnt be sure if that was it, now if its been an issue, why not just do it is what I say............
underneath has a little leak on the transfer case, can't tell where its coming from, gonna do that fix anyway..... better to be safe than sorry.......
Thanks for all your help!!!

Just check out the oil level in the transfer case, if it's OK then I wouldn't worry about the pump rub leak unless it starts loosing oil from the t-case. Other issues have to be figured out as to what they are, the pump rub leak is just that, it will continure to work normally until it has enough damage to the internals to cause noise/shifting issues. If it still has a normal oil level then it's something else than the rub problem.

will do......... off subject anyone use the hypertech econo max module, with what results? , i have tried it in both a or b mode and it doesnt do anything for fuel mileage... although "A" seemed to have more power.. :):)

If you lose oil from the transfer case, you are already through the housing and need a new one to the tune of atleast $300! Get it done while its not leaking or cut through yet, trust me.

Just pile on the JB Weld if there is a hole, and save the 300 bucks on the case half.

Mine is still holding great, and all is well!

Instructions here
http://www.dieselplace.com/forum/showthread.php?t=140732