'99 Suburban not shifting into 4LO

[Big T]

Push button shifting. I can get into AWD, 4HI, but not 4LO. The light simply flashes for awhile on 4LO and then goes out. Does not matter whether in Park or Neutral and I'm doing this while not moving. Also tried after placing it in reverse, then neutral.

 

[THEFERMANATOR]

You need to be rolling about 2-5 MPH for it to shift into 4 low. The transfer case control module normally won't try and shift it unless there is some movement of the driveshaft. But encoder motor failures on them are not uncommon.

 

[Big T]

You need to be rolling about 2-5 MPH for it to shift into 4 low. The transfer case control module normally won't try and shift it unless there is some movement of the driveshaft. But encoder motor failures on them are not uncommon.

Thanks, I'll give it a try. What's the fix for an encoder motor failure?

Also, what type/brand lube do I use in the rear differential?

 

[THEFERMANATOR]

The encoder motors are sealed and crimped together, so they are basically unserviceable. Unfortunately they cost about $300 for a new one last one I replaced. As for rear diff lube, I run a 75W90 in them of any good quality brand(don't cheap out with the wally world stuff as it oxodizes easily and doesn't have alot of rust inhibitors in it).

 

[Big T]

The encoder motors are sealed and crimped together, so they are basically unserviceable. Unfortunately they cost about $300 for a new one last one I replaced. As for rear diff lube, I run a 75W90 in them of any good quality brand(don't cheap out with the wally world stuff as it oxodizes easily and doesn't have alot of rust inhibitors in it).

Is that synthetic 75w90? GL5?

 

[THEFERMANATOR]

Is that synthetic 75w90? GL5?

Either one will work. If you have older seals though, I would stick with a non synthetic oil as synthetics tend to slip past seals fairly easily.

 

[Big T]

Tried shifting into 4LO while rolling and no go. Light blinks for awhile and then it just stays in 2HI.

How do you drain the differential fluid? Do I have to remove the entire cover and replace a gasket? Does the 75w90 need an additive for the G80?

 

[THEFERMANATOR]

Tried shifting into 4LO while rolling and no go. Light blinks for awhile and then it just stays in 2HI.

How do you drain the differential fluid? Do I have to remove the entire cover and replace a gasket? Does the 75w90 need an additive for the G80?

No additves needed, and to drain it you remove teh cover and it comes out in rapid order.

 

[bison]

Tried shifting into 4LO while rolling and no go. Light blinks for awhile and then it just stays in 2HI.

How do you drain the differential fluid? Do I have to remove the entire cover and replace a gasket? Does the 75w90 need an additive for the G80?

My 98 don't shift in 4 low either. i never use it so it don't matter.
2 hi and 2 lo,..its enough for me.

 

[Big T]

My 98 don't shift in 4 low either. i never use it so it don't matter.
2 hi and 2 lo,..its enough for me.

I don't use it much, but when I do, I would like it to be available.

 

[Big T]

No additves needed, and to drain it you remove teh cover and it comes out in rapid order.

Is there a gasket I need for the differential cover?

 

[bison]

Black RTV works just fine.

 

[btfarm]

Black RTV works just fine.

Agreed :agreed:

 

[Big T]

I just filled the differential with Valvoline 75w90 full synthetic. I was only $2 more per quart than their regular dino oil. We'll see how it drives as I'm headed up to Big Bear Lake this afternoon.

 

[THEFERMANATOR]

I just filled the differential with Valvoline 75w90 full synthetic. I was only $2 more per quart than their regular dino oil. We'll see how it drives as I'm headed up to Big Bear Lake this afternoon.

That's what has been in both of mine for the last 35K miles of DURAMAX abuse.

 

[Big T]

So far on the test drives it's been very good. No jumpiness on slow sharp turns. Now I need to do the front differential.