1988 chevy k2500 no 4wd 4h only???

[k25001988]

here is the deal, bought this truck earlier this year from a good friend. tried 4wd in 4h and 4l at time of purchase and everything worked great. Been about 2 to 3 months and just tried to use 4h today to no avail, truck simply sits there and free revs, it will not engage tranny will not move truck like 4h gear is gone entirely. pushed the lever forward to 4l and 4wd works great, engages fine tranny moves truck and all is well in 4l and 2h. still no 4h though??? what the hell is the problem with this piece of junk? any help would be greatly appreciated, have checked linkage, its fine and can't find anything else wrong. Thank you in advance.

 

[Thunder]

There is an electrical actuater on the front axle that locks in the front wheels. When they go out the front end will not enguage. If you are in 4 hi and the front axle is not locked. All power flows to the front and you will not move. Locking in the x fer case in 4lo allows the xfer case to transfer power to the rear and your truck will move. Sometimes the actuator takes a few seconds to enguage. You have to put it in 4 hi and wait for it to light up the front end on the x fer case shifter thingy
If not
Replacing the front axle actuater should fix it. $60-80
It screws into the front axle and looks like this

 

[79k20350]

I used to have an 89 extended cab w/ 4 wheel drive, when he front axle is not locked you WILL move, you just only are in two wheel drive w/ the front driveshaft spinning. The thing that locks the front axle is called a Thermal Linear acuator. It uses heat and electricity to engage. On all ifs chevy the front axles are always spinning, the are just not engaging the ring and pinion, when you shift into 4 wheel drive that actuator moves a set of shift forks and engages the front axles to the carrier and puts the t-case into 4 wheel drive. being an 88 you have a 241 t-case. Im not sure of what specificly your problem is but it does not sound like the actuator. Hope this eliminates at least one potential problem for you.

 

[k25001988]

rear wheels won't move either?

this actuator you speak of will it also make the rear wheels not move too when i put the truck in drive while selector lever is in 4h position? this is the problem i am having is not only will 4h not engage but the truck wont even move period in 4h, however 4l everything works fine, doesn't make sense to me that the actuator would be the problem when 4l works and 4h truck wont even move period? thank you.

 

[Thunder]

I may be wrong about the actuator. But Last summer I was wood cutting with a buddy. His 90 K2500 was loaded and he blew his rear end. His truck would not move in 4 Hi. The rear drive line just spun even with the front enguaged. We had to lock it in 4 lo To get the front axle to work so we could get out of the hills
T cases act like open differentials in 4 HI. In 4 low they act like a locker and lock the front and rear drives. I an pretty sure he has a 241.
But
Also I just went out and checked. The 241 in my blazer will move the truck in 4 hi with the front unlocked.

Just wondering? Does the indicator that tell you if the front axle is locked in light up? If it does. The actuator is probabally not the problem

 

[k25001988]

the light will not light up

in 4h only in 4l