4L80e 4x4 not locking up and 5 feet of snow!!!

[DieselDetroit]

Hello fellas,

I'd like to start by saying that I am happy to have found this forum. There is tons of great information and everyone has been super helpful.

I am hoping to get some help on a 4x4 issue I just started having. We have a huge amount of snow outside and it is dangerous to drive without it, so any help is much appreciated.

Vehicle
- 1995 K2500 4x4
- L56 396 cu in Detroit Diesel
- light body frame (14bolt sf rear, 6 bolt lugs, non-HD)
- silverado trim
- 4L80e with floor shift transfer case

Symptoms
- when I shift to 4H, light on floor does not engage and front wheels do not engage
- same symptom for 4L
- when I put the vehicle in 4L, I hear the transfer case engage and the gearing changes when moving
- when I put the vehicle in 4H, I hear the transfer case engaging
- in 2H, the front drive shaft moves freely
- in 4H, the front drive shaft does NOT move freely, it is locked to the transfer case

I don't know much about 4x4 and how it engages inside the front dif. My guess is whatever signal the t-case sends isn't being received in the front, or the system responsible for engaging it is broken

Please help! I really appreciate it. If more details are needed, please ask

Thank you


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[badazzbulldog]

actuator for front diff is not workinghttp://youtu.be/S55ZEQjmKnw

 

[DieselDetroit]

Is it a 2 pin 12v?

If I put my truck in 4H or 4L, and I am getting 12v to the connector, then it HAS to be a broken actuator correct?

Thanks

 

[Scrufdog]

do both sides of the front lock, or did you check only one side? Only one side means the actuator went out, very common on these trucks.

 

[badazzbulldog]

Is it a 2 pin 12v?

If I put my truck in 4H or 4L, and I am getting 12v to the connector, then it HAS to be a broken actuator correct?

Thanks

yes it is very common for them to go,take it out and put the truck in 4wd and plug it back in and see if it moves and holds in the out position

 

[SixSpeedSS]

FYI...The switch on the transfer case that turns on the front diff can fail as well. I had a 1990 4x4 that this switch failed. Obviously you want to look to see if the actuator is getting power. If it is, then I agree, you need the front axle actuator. If not, you could connect the two pins on the side of the transfer case and get it to engage. This switch is very easy to test - it should be open in 2wd and closed in 4wd.

IIRC when mine initially went, the part was backordered and it was middle of winter. I put a toggle switch up thru the boot in the floor to engage the front end. Drove it like that until I sold it to my father (and gave him the switch in a box). He left it like that for a year or so and then finally put the switch in. That was 10 years ago, so tough to remember the details.

My current truck has the f#$%ing electronic 4wd (1996) and it sucks as well. I would rather have the plain ole floor lever, but it is too much work to switch it over and not really worth the effort. I find my electronic setup switches over quicker if I put it in 4wd Low first, then switch to High range. If I put it in 4wd high, then it takes almost 30-40 seconds to engage (it is actually heating the fluid inside and it should be the same timeframe, but it really does seem quicker in 4wd low).

There have been 3 different designs on the front axle actuator for GMT400 trucks. Mine has the latest and still sucks. The cable setup is definitely the best setup.

 

[DieselDetroit]

Called the parts store, I'm looking between 110-130 depending on if I need a 2 pin or 5 pin.

Scrufdog - why would the actuator only engage one wheel if it is broken? That to me doesn't make much sense. Based on how it was driving, neither front wheel engaged.

SixSpeedSS - I will confirm this with a multimeter. I think I will start at the actuator and work backwards. The actuator should get 0 volts in 2wd and 12v in 4LO/HI correct? Can I do this with the vehicle off and the key turned to ONII and by putting the truck in 4HI? I'd like to avoid starting it while I'm underneath, this way I can play with the key and read voltages. How is the exercise different for a 5 pin?


I have a 6lug light-duty 3/4 ton with a 14 bolt SF rear, am I looking at a 2 pin or 5 pin actuator? I don't have the vehicle beside me and want to get the part ordered if needed.

Much appreciated fellas!

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[great white]

FYI...The switch on the transfer case that turns on the front diff can fail as well. I had a 1990 4x4 that this switch failed. Obviously you want to look to see if the actuator is getting power. If it is, then I agree, you need the front axle actuator. If not, you could connect the two pins on the side of the transfer case and get it to engage. This switch is very easy to test - it should be open in 2wd and closed in 4wd.

IIRC when mine initially went, the part was backordered and it was middle of winter. I put a toggle switch up thru the boot in the floor to engage the front end. Drove it like that until I sold it to my father (and gave him the switch in a box). He left it like that for a year or so and then finally put the switch in. That was 10 years ago, so tough to remember the details.

My current truck has the f#$%ing electronic 4wd (1996) and it sucks as well. I would rather have the plain ole floor lever, but it is too much work to switch it over and not really worth the effort. I find my electronic setup switches over quicker if I put it in 4wd Low first, then switch to High range. If I put it in 4wd high, then it takes almost 30-40 seconds to engage (it is actually heating the fluid inside and it should be the same timeframe, but it really does seem quicker in 4wd low).

There have been 3 different designs on the front axle actuator for GMT400 trucks. Mine has the latest and still sucks. The cable setup is definitely the best setup.

You need to switch to the servo actuator my friend.

My 98 is nearly instantaneous 4x4 when I hit the switch. It the OEM servo actuator from 1998 in there too.

I'm and old "lever guy", but for ice and snow covered street driving I'll take that pushbutton any day of the week.

1998 was the first year for the servo IIRC, but it is a retrofit right back to 88.

More info:

http://www.getdieselpower.com/cars/actuator_upgrade/GM_TRUCK_4X4_ACTUATOR_UPGRADE.html

 

[Scrufdog]

on these trucks one wheel is always engaged to the front drive shaft. The actuator locks to the wheels together.

 

[great white]

on these trucks one wheel is always engaged to the front drive shaft. The actuator locks to the wheels together.

True and yet not.

The drivers side CV shaft is splined into the differential side gear. This is always in contact with the spider gears. The drive shaft is in contact with the pinion gear, which is in contact with the ring gear. The side/spider/ring gear is all on/in the differential housing.

As long as the passenger side axle shaft is not engaged by the actuator, the drivers side just spins the side and spider gear inside the differential housing without turning the ring gear. Without turning the ring gear, the driveshaft does not turn with the drivers side wheel. So it's not really correct to say the driveshaft is "connected" to the wheel all the time, although it's not totally wrong to say it either.

It's more correct to say the drivers side wheel is always connected to the side gear, not the drive shaft.