I got a 1997 gmc jimmy 4wd my 4wd doesnt engage the front diff but it engages the ****** for low range ive checked my actuator pump and its moving but now i have a rattling noise in my front drivers side wheel and its my 4wd axle jumping around where it meets the wheel do i have a blown bearing or something up at my diff hope you can shed some light on this problem for me and if you have any ideas about why my 4wd isnt engaging that would also be helpful

check operation of vacuum diaphragm under battery that actuates 4WD cable

Could be the servo on the front diff not activating. Could be a power prob or failed unit.

on my 2001 jimmy i had the same problem i fixed by changing the actuator on the front diff very simple and inexpensive

It wont be the front differential they would of engaged but it doesnt engage the 4hi and 4lo 4x4 motor or the switch is bad

The 4x4 indicator light is turned on by the actuator at the front differential when it engages the ADD. This means the problem is not at the front differential. It may be an issue with the transfer case if it's the automatic electronic controlled transfer case.

Try listening to the transfer case try to engage.The vacuum actuater on the firewall above the distributor was not allowing vacuum to the front axle actator. You can put the truck on jackstands (all 4 wheels) and check to see if the front drive shaft engages. If so, then it's probably the vacuum actuator or the axle actuator.

I HAD A BLAZER WITH THE SAME SYMPTOMS REPLACED THE TRANSFER CASE MOTOR AND SOLVED PROBLEM. TRANSFER CASE MOTOR SHIFTS FROM HIGH TO LOW GEAR IN THE TRANSFER CASE AND TELLS THE FRONT ACTUATORS TO INGAGE FRONT HUBS . MOTOR WON'T MOVE TO 4 HIGH AND GRINDS WHEN TRYING TO MOVE TO 4 LOW, TRANSFER CASE MOTOR FAILING . CHECK VACUUM LINES AND ACTUATORS ON FRONT DIFF THEY FAIL, CAN CHANGE TO CABLE ENGAGEMENT INSTEAD OF FAILURE PRONE VACUUM ACTUATORS.

could be your front actuator or your actuator motor on the transfer case.

Rich. There is a vacumn engagement of the front differential. The switch is on the transfer case. There will be a vacumn motor(looks like a curise control unit if you're familiar with them) under the hood with a cable running to the front diff. Make sure it functions when you engage 4wd. Probably does. If not, make sure it is getting vacumn by removing the line. It should **** on your finger when covered. If this all works properly, you could have trouble in the front diff. Don't forget the simple stuff, like CV joints, axle nuts tight, etc. You're driving an 86 so I assume you have a little experience in maintaince. Good luck. TJ

Place vehicle in 4wd (high or low). This will hold the front drive shaft still for the rest of the test. Jack up the front end of the vehicle. Remove the actuator. Have a buddy spin the right front wheel while you use a long punch or screwdriver to try to manually engage the diff. The left front wheel should spin in the other direction if the diff is good. Also before you check the diff you need to grab the front driveshaft and make sure it is locked, If it spins freely when the truck is in park and in 4wd with the front end raised then problem is in transfer case. If you can't make the diff engage manually with punch then the problem is in the diff. If front diff engages manually then the problem is the actuator. Hope this helps..