CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

03 gmc duramax with 350k (BBT) transmission fun

The lower steal pan is only sealed with rtv from the factory, there is no gasket. And you can remove it pretty easily. I remove the crossmember below it. Also some of the front bolts are tricky to get to, a swivel socket helps.
 
The lower steal pan is only sealed with rtv from the factory, there is no gasket. And you can remove it pretty easily. I remove the crossmember below it. Also some of the front bolts are tricky to get to, a swivel socket helps.
Cool, thanks. I'll give it a try, but probably wait until this summer.
 
I think I might be in for a new transmission after all. :( It's pretty much fine during normal driving, but while towing my RV trailer it pops codes pretty much every time it has to downshift going up a hill. That puts it into limp mode which means I have to pull over and clear the codes. The downshifts during those conditions are pretty harsh too.

Anybody have experience with the allison transmission? Am I looking at a rebuild, or something less drastic maybe?
 
Does your truck have the 5th gear lock out? It should be on the tow/haul switch...hold it in for a bit longer than just turning on the tow/haul.

My 02 and my kids 01 do not have it. 03 should.
 
Screenshot_20170413-070429.png
Those are my codes.

I do have the 5th gear lockout. Honestly, I forgot to ever try it.
 
Just looked up that code and the wording sounds familiar. It is possible that I've gotten that code. :(
Guess I'll have to keep an eye out for it.
Yes, when in 5th and it downshifts to 4th under hard throttle if the trans slips it'll kick this code. Once it does it'll do it easier and easier until 4th wont hold a shift.
 
Now the p0708, check the wiring harness on the trans under the truck. Does it have trans fluid in the plug? Does the shift indicator show what gear its in while it's acting up?
 
Yes, when in 5th and it downshifts to 4th under hard throttle if the trans slips it'll kick this code. Once it does it'll do it easier and easier until 4th wont hold a shift.
Yup, that sounds familiar too. crap.

Now the p0708, check the wiring harness on the trans under the truck. Does it have trans fluid in the plug? Does the shift indicator show what gear its in while it's acting up?
Now that you mention it, I did notice that occasionally the dash indicator doesn't show what gear it's in. Are you talking about the plug on the outside of the transmission?
 
Press and hold for 5 seconds on tow haul?
Yup. I put it into tow haul, but I never remember to lockout 5th gear when going up a steep hill. Hopefully by doing that I can maybe keep this transmission running a little longer. That is the only time I ever have issues.
 
Cool, never knew that. I'll have to use that next trip, but my trans does exactly what I want when I want. I often think the trans should downshift now, and before I'm done thinking its downshifted.
 
Yup, that sounds familiar too. crap.


Now that you mention it, I did notice that occasionally the dash indicator doesn't show what gear it's in. Are you talking about the plug on the outside of the transmission?
Yes. When it starts leaking trans fluid, it will short out the nsbu switch and cause some weird issues.
 
I'll look at it and see if it's wet at all. The leak was just from the pan, so I doubt it got up high enough but maybe.
 
It will actually leak through the plug. Unplug it and see if it is wet inside.
 
Top Bottom