98 k3500 intermittent 4hi. 4lo is 100%

[blakes]

I have a 98 k3500 C&C 454/nv4500 with the manual shift tcase.

4lo works 100% of the time and the 4x4 light is on anytime the shifter is in 4lo

4hi is very intermittent. The light on the shifter comes and goes. It's almost like this thing has some sort of "auto 4x4" where it only engages the front axle when it detect slippage. This is an OBS truck. I think the 4hi light (and the front axle) should be engaged anytime the shifter is in 4hi.

What's going on?

 

[total newb]

Take the switch off the top of the case and push in the detent ball as you spray it with cleaner.

 

[Lowrollin70gmc]

Is it the BW4401 transfer case?

I have one in my project 53 (Nv4500/Bw4401) and I remember seeing a 4wd synchronizer thingamagig in wiring schematics.

That could be a rabbit trail to follow, it's a single wire on the tailshaft.

 

[total newb]

That should have the bw 4401 case, they have a mag ring in the back but people that used the case and not hooked it up say it works fine.

 

[BustedCrank]

Is it actually disengaging the front shaft, or it is just the light?

Have you checked the linkage, could just be out of adjustment to where you're not fully into 4 hi.

Could just be a pinched wire for the 4wd switch.

I like to start with the simple things.

Could be the actuator on the front axle, If I remember correctly, the light doesnt come on until that thing heats up and engages. Maybe it's going out, or the wiring to it is iffy. But would imagine it would be the same in low range as high, unless you're just not spending enough time in low range to notice it.

 

[BustedCrank]

That should have the bw 4401 case, they have a mag ring in the back but people that used the case and not hooked it up say it works fine.

Correct, mine isn't hooked up to anything, everything works.

 

[blakes]

Is it actually disengaging the front shaft, or it is just the light?

Have you checked the linkage, could just be out of adjustment to where you're not fully into 4 hi.

Could just be a pinched wire for the 4wd switch.

I like to start with the simple things.

Could be the actuator on the front axle, If I remember correctly, the light doesnt come on until that thing heats up and engages. Maybe it's going out, or the wiring to it is iffy. But would imagine it would be the same in low range as high, unless you're just not spending enough time in low range to notice it.

Remember, 4lo works 100%

I think this could be linkage out of adjustment like you said. When in 4HI, it's ALL the way back.

But the strange thing is the timing of when the light comes off and on while in 4HI. It definitely seems be related to some sort of traction control meaning that when you are driving along a flat icy road, the light is off. Then when I climb a hill and lose a bit of traction, the light comes on. The problem is that I'm usually carrying 6000lbs of water in the back and when it 'senses' that it needs to engage the front axle, the rear tires are already spinning causing a fairly violent front end engagement.

 

[BustedCrank]

AFAIK there is no such traction control like that on a 98 k3500.

I would be checking the linkage to start with.

 

[Fishnbeer]

I am thinking 2 possible failures. But check fluid level/condition on t case and front diff first.

The shift position sensor/switch on the t case is going out. It just threads into the case and it is a spring loaded ball detent, maybe just getting sticky/dirty/corroded/etc. This spring detent is what makes the 'notches' as you shift through ranges.

Or

The engagement motor on front diff is weak. The motor pulls/pushes on a locking ring that locks/unlocks the long shaft on front diff. It has to overcome driveline load/binding to move that ring. Maybe try this after shifting - drive slowly and turn wheel lock to lock a few times, then do same under slight accel, then same under decel (trying to release driveline binding).

Sometimes you get the binding out easier in 4lo. What if you shift to 4lo first to engage and then back to 4hi?