Suburban "Slams" out of 4 wheel drive

I have a 1997 Suburban K1500 that seems to be making a humming or whining sound only when it's in 4-wheel drive. Then, when I take it out of 4-wheel drive, it takes a while (up to 1/2 a mile) and finally "slams" out of 4-wheel drive.

Could this be a bad transfer case, a bad transfer case motor, or maybe low fluid level? (I am at work as I type this message, I can check the fluid level tonight.)

Any ideas?

-Behrens-

Check the fluid level for sure?
Is it the auto 4W or regular?
4W is not made to run on dry payment in 4W.

Will it shift out and in good when you are stopped or back up a little?
Are your tires matched up?
Can you hear the noise in 4W low to?

Does noise change with MPH or engine speed or does it in any gear?

MT-2500,

Thanks for the ideas on how to properly test this. The fluid was down about 1/2 a quart, but the slamming still occurs as the truck shifts out of 4HI or 4LO.

I have an electronic shift button for 2HI, 4HI, and 4LO. (That would be auto 4W?) The owner's manual says that I can shift in and out of 4HI an any speed. (4LO at 1-3 mph in neutral)

The four wheel drive disengages very loudly even at 20 mph. At 10-15 it's not as bad, but it still feels like I am hitting a curb.

The hum or whine that I described occurs in 4HI and 4LO, but I'm not sure that it's not just the way it's supposed to sound. It sounds like "gear whine". The pitch of the sound goes up as speed increases and then down as soon as I let off the gas.

If I switch from 4W to 2W while sitting still, it still slams out 100' or so down the road. It seemed to come out of 4W the best when I backed up a little, but I'm not sure.

Any ideas?

-Behrens-

MT-2500,

Thanks for the ideas on how to properly test this. The fluid was down about 1/2 a quart, but the slamming still occurs as the truck shifts out of 4HI or 4LO.

I have an electronic shift button for 2HI, 4HI, and 4LO. (That would be auto 4W?) The owner's manual says that I can shift in and out of 4HI an any speed. (4LO at 1-3 mph in neutral)

The four wheel drive disengages very loudly even at 20 mph. At 10-15 it's not as bad, but it still feels like I am hitting a curb.

The hum or whine that I described occurs in 4HI and 4LO, but I'm not sure that it's not just the way it's supposed to sound. It sounds like "gear whine". The pitch of the sound goes up as speed increases and then down as soon as I let off the gas.

If I switch from 4W to 2W while sitting still, it still slams out 100' or so down the road. It seemed to come out of 4W the best when I backed up a little, but I'm not sure.

Any ideas?

-Behrens-

transfercase. the fluids require replacement periodicly...this is determined by a slower engagement of the 4wd as well as color..the fluid should be blue ...If the color is black their is a good chance that the transfercase is damaged...

this is determined by a slower engagement of the 4wd as well as color..the fluid should be blue ...If the color is black their is a good chance that the transfercase is damaged...

Thanks. The 4WD engages fine, it's the disengage that is giving me trouble.
The fluid is not black, but do you think that it would help to change the fluid now?

-Behrens-

this is determined by a slower engagement of the 4wd as well as color..the fluid should be blue ...If the color is black their is a good chance that the transfercase is damaged...

Thanks. The 4WD engages fine, it's the disengage that is giving me trouble.
The fluid is not black, but do you think that it would help to change the fluid now?

-Behrens-

when you engage the 4wd does the lite flash twice.?
what is the color of transfercase fluid.. and when was this last serviced.?
if this has 50,000mi of use on the fluid it should be replaced...if the fluid used was dextron III it is most likey the transfercase is in need of replacement.

I have found that if this fluid is replaced often the transfercase shifts into and out of 4wd faster...also when stopped it should shift easy and fast...something is binding ....it could be worn out...

Thanks j cAT.

The light DOES flash twice when I switch to 4HI. What does that mean?

The manual calls for Dextron III, so that's what I put into it -- The Red Stuff. Does the Dextron cause more wear?

So much thanks to you again.

-Behrens-

From your 2nd post you do not have the Auto 4wd t-case.

As far as the flashing lites. All lights should flash twice when the key is turned to the run position and then the mode you have selected should stay lit. When you select another mode (push a button) that lite should blink a couple of times and then go steady indicating the mode selected was achieved.

My question is what does the 2wd lite do when you select it before it "slams" out of 4wd? If it continues to blink until it comes out of 4wd and then goes steady you probably have a t-case problem.

Also, as MT-2500 stated, tires could cause the t-case to bind up. Maybe the fronts are worn and the backs are new or??

The GM AutoTracll (blue fluid) is mostly designed for the Auto 4wd t-cases, but I don't think it would hurt to swap into yours.

I am no mechanic by any means but I can relate this short experience I had with transfer cases.

I bought a 1984 Chevy S-10 Blazer which I believe was a new model back then. When ever I shifted into 4high, the thing would "grind" a pound of gear. I was told by the dealer and GM regional manager that this was normal to make this awful noise when shifting notwithstanding GM's "shift on the fly" marketing. I fought with the dealer and GM for about a year before I took them to arbitration and was awarded a new transfer case.

Point being, the bad tc made a very audible "whirring" sound when engaged in 4 wheel drive. Once the new transfer case was installed, it shifted seamlessly into 4 wheel drive and with no "whirring" sound once in.

Good luck. I hope this is some help.

I did recently do a bunch of work on the steering (upper and lower ball joints, pitman are idler arm, etc.) I got an alignment last week too. Because of the bad pitman arm and ball joints, my tires are indeed in real bad shape. So, I may have my new tires tonight and I will test the shifting again and report back.

I also have a slightly smaller tire on the back which could also be affecting things too.

The transfer case may still need replacement, but I want to rule out my janky tires first.

Thanks for the ideas. I will report my findings.

-Behrens-

Question answered. Problem resolved.

Thanks everyone for your advice. I posted this question in the middle of worn out tires, replacement of pitman arm, idler arm, ball joints, getting an alignment and many other repairs.

After getting my new tires this weekend, the transfer case and differentials are working flawlessly. The 4WD drive system shifts into and out of the different modes without so much as a sound or vibration.

Since I want in the middle of buying the tires anyway, I count this as a no-cost repair.

Thanks again,
-Behrens-