96 jimmyproblems

I actually have a couple of problems. The first is when I drive I can hear a thumping noise in the front end which turns into a vibration at a higher speed. The other problem is that when I put the Jimmy into fwd, the switch will not go into 4lo. It only goes into 4hi. The problem here is that it does not engage into fwd. You can hear the selenoid actuate but there is not power to the front. Also, when it is in this fwd, when turning left there is a lot of thumping coming from the front end. Can some one help out?

My 98 is doing the same thing - 4Hi engages, but stays in first gear. 4lo goes back to 2lo by default. I have P0740, and P0753 diagnostic codes. Check a post by 'skidude'; one 'reply' to his post has my solution, I hope...

Start with the basics. Check all vac hoses going from the transfer case switch to the main vac system and the actuator under the battery. Check the actuator under the battery tray for leaks or tears. If those are ok, change out your vac switch on the transfer case (15 bux). If that does not solve it, check your encoder motor.