Transmission problem just went out

[OldGrump]

Hi Ya'll...I'm brand new to the forum and to working on my old truck
1978 K25 GMC Full time four wheel drive

I just bought the truck and drove it 70 miles home with no issues. I decided to test the four wheel lock in the back of the property and all work fine, pulled up to the house and tried to take it back out, which I've done several times and heard what soud like a chain slapping under the floor board and then nothing. I cannot go forward or reverse nor and it does not matter if I place the slector in 4H H 4L L

Thoughts?

Thanks all

OldGrump

 

[HotRodPC]

So it's obvously an NP203 Tcase since you mentnon 4L or L and said it's Full Time. It's in auto trans category, so must be a Th350 trans married to a NP203 Tcase.

So did you actually break the Chain in the Tcase, or did you break a U Joint? On the Full time Tcase, it works like a rear end differential, so if you lost your front driveline or drivetrain, including an axle the truck isn't going to move unless you are in 4L Loc or 4H Loc. So I'd put the Tcase in 4? Loc and see if the truck moves. If it does, then you have either a front or rear drivetrain issue. If not, then I'd next suspect the chain in the Tcase since you mentioned it sounded as if a chain was slapping.

 

[OldGrump]

Thanks for the quick reply. I started the truck up again and this time I could not place it into L or Low lock, so I noticed I was on a slight hill and little roll back in Neutral and tried L and it started working. I drove it back around to level ground and tried H and it started working and the metal slapping sound stopped. I must have had it out of balance or something...not really sure.

Again thank you for you help!

 

[HotRodPC]

I'm thinking you might have excessive slack or slop in your Tcase chain. I'd take it easy on the Tcase until I was prepared to find another Tcase or have that one worked on.

BTW, Weclome to GMSB OG.

 

[bucket]

I'd try lubing and adjusting the t-case shifter. Has somebody installed front locking hubs?

 

[OldGrump]

The truck/transfer case is bone stock.
I do plan on changing the oil in the case, as I do not have a maintenance history on the truck.

thanks.