Popping out of 4H

[airheadpilot]

All,

I'm having a strange problem with the 4wd on my Burb. When I shift into 4H, it will stay at that setting as long as I'm coasting on the level or downhill. When I put any power behind it, like to go uphill, it pops out of 4H back into 2H. It's not a sudden or violent transition, it's as though the lockout tab isn't there and there's nothing to keep the lever in place. I have no similar problems with 4L - when I put it there it stays there. I'm looking under the plastic cover for the shifter in the cab and can't see any kind of retaining tab (or place for one that is missing), and the linkage to the transfer case is in good shape. Am I missing something fundamental, or is there a problem inside the transfer case? As far as I know, tranny and transfer case are original (tranny is a TH350; don't know what the TC is). Any suggestions?

Thanks!

Andrew in Belmont, CA
1987 GMC 2500 4x4 350 TBI, TH350, MM Premium hubs

 

[BowtieBlazer]

any haynes or chilton's manuals will walk you through the linkage adjustment (thats what it sounds like to me....) If that doesn't work it may be that the range selector fork is ground down which means time for a rebuild...

 

[stallion85]

Try disconnecting the linkage between the stick and transfer case. Then move the linkage on the transfer case till it clicks into 4 high, then put stick in 4 high and reconnect the linkage and make any adjustments between the two. I had the same problem and this solved it, if not it is probably your shift fork in the xfer case /forums/images/graemlins/thinking.gif