Chevy and GMC Duramax Diesel Forum banner
  • Hey Everyone! Enter your ride HERE to be a part of this months Ride of the Month Challenge!
1 - 20 of 25 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter · #1 ·
So i went to put my truck in park today and it would only go into reverse. It then proceeded to only go in to neutral and drive gears....so its stuck in neutral and only the drive gears, wont do anything else. Also on the way back the trans started to get hotter than usual for no reason at all. Any ideas?

For some back ground, the truck has been having a problem every once in a while were it wont start in park...so i have to put it into neutral to start...also weird.

Any info at all would be more than benificial to me.


Joe
 

·
Premium Member
Joined
·
8,815 Posts
Sounds like either an out of adjustment NSBU (neutral safety back-up)switch or bad one. It is on the driver's side of the tranny. They should run about 65 or so at NAPA. What year truck?
 

·
Premium Member
Joined
·
17,806 Posts
X2 change the NSBU switch.
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #6 ·
ok i will replace the NSBU switch. How hard is it to Replace? Is it internal or external? Is it a plug and play kind of thing or is it more involved than that?

Thanks fellas
 

·
Premium Member
Joined
·
1,666 Posts
External switch, plug and play. May need to do a little adjusting to get the shifting just right, just pay attention when you take the old one off for the position it's in and replicate that w/ the new one!!!!!!! Easy fix, took care of my problems w/ the same symptoms!
 

·
Registered
Joined
·
328 Posts
What is a NSBU switch? - acronym for "Neutral Start Back Up". Sometimes also referred to as a PNP ("Park Neutral Position") switch.

Where is the NSBU switch located? - driver's side of the Allison transmission.

Why does the NSBU need to be replaced? - due to road salt/water/debris getting into the switch via the switch hub and contaminates and corrodes the internals. The crap gets kicked up onto the switch on all left hand turns which affects the operation of the transmission because transmission shifts and functions are controlled by this switch.

What are some of the symptoms that the NSBU switch is going bad?
- following DIC codes MAY suggest the NSBU as the culprit: P0700, P0708, P0847, P0872, P0875, P1711 and P1713.
- PRNDL display may not show up or only a partial display
- no engagement even though your shifter is in D or R (like you were in neutral)...this was my situation (and I received a SEL (service engine light) code P0700).
- you will only have forward motion in 3rd gear or reverse.
- SEL (service engine light) message that reads something like "shift range inhibited".

Is there more than one model of NSBU switch? There are 2 switches that I'm aware of.
- 2001-2004 Allison NSBU Switch (LB7). Part no. 29540479. Has 2 electrical connectors on the switch.
- 2004 - 2005 Allison NSBU Switch (LLY). Part no. 29541852. Has 1 electrical connection on the switch.

Why should I replace the switch as opposed to taking it to my dealership?
- because it's a "one beer" job that will take less than an hour.
- did I mention I purchased the NSBU switch at a local Allison dealership for $73.50 while the dealership quoted me $233.23? My dealership parts insider could only give me a reduced rate of $180.00. I believe Merchant Automotive sells the NSBU for $65. That's just the part...labor is EXTRA.

So what improvement is there with the new NSBU switch?
- as far as I can tell, the a white foam "rear shield" has been added to better seal the NSBU housing against the Allison transmission so water and crap does not get in to contaminate. Again, see the pics below for the white foam rear shield on the backside of the switch. The white rear splash shield and front black splash shield on the upgraded NSBU switch are designed to minimize infiltration.

What's the little connection on the new NSBU switch that looks like a vacuum hose connection between the wiring harness connections?
- one way valve to drain any water that may get into the switch.

How do I replace the NSBU switch? - instructions as follows...

1. My original switch is of the black variety. It does not have the white foam rear shield on the backside like the replacement NSBU switch (new one is tan in color).


The new switch also has a thin metal clip called a Neutral Assurance Bracket to ensure that the NSBU remains in the neutral position. DO NOT REMOVE UNTIL THE NEW SWITCH HAS BEEN INSTALLED.


2. Gather the following tools:

13mm deepwall 6 pt socket
15mm 6pt wrench (mine's the "gear wrench" variety)
6 inch extension
3/8" ratchet
small file


2. Put the transmission in neutral.

3. Disconnect NSBU wiring harness (2 in my case - I have a 2003 LB7...LLY only has 1 electrical connection).

This probably caused me the most grief as the top harness would not come out so I had to break off some NSBU switch plastic around the connection. Finally got it out and it looked like the ends were glued on...it has been suggested to take a hair dryer to warm up the connection to warm them up.


4. Disconnect the shift linkage/cable from the shift lever at the transmission. With a wrench keeping the shifter from rotating (out of neutral...you did put the transmission in neutral right?), remove the nut from the end of the selector shaft. Carefully remove the selector lever from the selector shaft.


5. Remove the 2 bolts that attach the NSBU switch (the front driveshaft will get in the way a bit but you should be able to access the bolt with the socket) and pull off the old NSBU switch. There'll be some resistance when you pull it off. I had quite a bit of crap behind the switch (small rocks, dirt, etc.)

6. If for some reason that the transmission is not in neutral, use a wrench on the selector shaft flats and rotate the shaft to its furthest clockwise position and then rotate counter-clockwise two detents.

7. Take a file and touch up the selector shaft at the end near the flats...there may be some burrs that could create some slop if the new NSBU switch is slid over the shaft without filing.

8. Slide the new NSBU switch over the selector shaft. The metal clip (neutral assurance bracket) on the switch helps to ensure the switch is properly aligned to the shaft. For the geeks out there, the bolts should be tightened to 18-21 lb ft. Now it's ok to remove the metal clip from the NSBU housing.

9. Slid the black splash shield onto the NSBU switch so that it fits securely against the switch. Do this BEFORE re-installing the shift lever.

10. Re-install the shift level. Again, I used an adjustable wrench on the shift lever while tightening the nut on the end of the selector shaft. Geek specs for the nut is 15-20 lb ft.

11. Connect the wiring harness(es) back onto the NSBU switch.

12. If you have any DIC codes as a result of a bad NSBU switch, you'll have to clear them.

12. Crack open a beer and tell yourself you just saved paying at least $300 to "the man".
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #15 ·
ok, went to napa yesterday and thought we had the right part...turns out they got it way wrong. So i give them the part number listed in the write up for the 2004.5-2005 lly....they say its a 174 dollar part...am i missing something? All evidence in this thread and in the writeup suggests that i should be able to aquire the part for 65 or so bucks.

Is there some place online that i can get it that cheap? Is the lb7 version cheaper or something? Would the 2 connector lb7 version work on my lly? I am guessing not...

thanks fellas
 

·
Premium Member
Joined
·
8,815 Posts
Umm maybe your napa store is raping you like the stealer would? The LB7 (in the write-up) one has 2 plugs according to that. Yours has one. Have you gotten the part number off of your NSBU switch? Have you tried gmpartsdirect.com? (about 100 from there) You dont have an allison dealer close?
 

·
Registered
Joined
·
328 Posts
To add just a little more, my truck is the LB7 so maybe there is a cost difference in between those two. I second the thought of calling an Allison dealer close to you, they are the mothership and know all! Last thing is that piece you said was $165... maybe that was one of the connectors, because I remember one connector costing that much.
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #18 ·
Well, i ordered the nsbu switch from gmpartsdirect.com for 119 shipped..not to bad i guess, just hope this fixes it. Thanks again for your help, its much appreciated.
 

·
Registered
Joined
·
328 Posts
Yes I am sure you will be able to get if fixed! Let us know if you need any other info and when you get it done tell us how it went.
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #20 ·
I tried looking up allison dealers to no avail. As long as the part number in the write up is right i thing i will be ok. If this does not fix it could it be an ignition switch issue? I think i had signs that something was going out when the truck wouldnt start in park, i would have to shift to neutral to start it. It didnt always do that just occasionally.
 
1 - 20 of 25 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top