Regular sounds 4lo & road testing 4WD, 2002 Tahoe

[Michael1972]

Hi tnere,

since I am new to the Tahoe I would like to get your feedback on a couple of things.
Just purchased a 2002 Tahoe LT 5.3, 4x4 with auto TC. About 120k miles, good condition, all fluids just serviced.

1- the auto TC on the 2002 Tahoe is basically a clutch pack driven 2 speed TC, without differential. Thus, in 4Hi it connects the front axle with the rear through the TC. In 4LO the TC engages 2:1 reduction gear, the rest is like 4HI.

2- The 4HI and 4LO shifts through the gears 1-3 plus OD. Some additional noise in 4LO due to the 2:1 reduction gears.

3- Are there any differential locks ( front, rear, front&rear) that are engaged in 4xx ? Any difference in 4HI or 4LO ?

Question 1- when I test drove the Tahoe, I enabled the 4LO -complete stop, auto in N. Indicator light went from blinking to solid in about 3 sec. Some very minor solenoid noise. Shifted to D, at about 6...8mph a single solid clunk-noise from the front was noticable- was driving a straight line on gravel surface-. The owner said this was normal. Correct? Or something fishy?

Question 2- how do I properly test the 4xx functionality?
I had in mind- on a mud or gravel road, engage 4Hi - 4LO and floor the accel...thus fromd and rear should be spinning, no strange aopperational sounds should be heard. All gears in 4HI-4LO should shift smooth, s slight understeer in tight turns-while on non solid ground is expected.
That about it?

Thanks,
Michael

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[PG01]

Solid clunk was tc going into 4lo, No reason to floor anything, Dont go over 10-15 mph in 4 low, turn wheel completely on a gravel or wet grassy area and make a few turns at low speed, it should jump but not be overly noisy jumpy. 4 hi is shift on the fly, do the same to check this.
I normally roll at less than 5mph and put trans in neutral and shift to 4lo ... not at a complete stop.

 

[Doubeleive]

^^^ what he said, you don't want to break it, it is for use exactly like it sounds 4lo-low speed, 4hi-up to normal speed
and yes the clunk is normal when it is engaging, you may also sometimes hear a similar lesser noise when putting it in gear (2wd) depending on the surface you parked on.

 

[Chubbs]

Ya you don't necessarily need to be in a low-traction situation to know if 4wd is operable. As you said, the under steer is unmistakeable. I wouldn't go around trying to break traction at-all-cost; you may be making a repair.

Your truck should have a factory locking differential in the rear axle. No need to test operation, just look for the manufacturing code 'g80' among those listed in the passenger glove box. It will be there ready to go when the situation calls for it.

The front diff is open, there is not even an aftermarket locking unit available for this model.

The electrical problems with this system is infamous. The encoder motor had to be replaced when i bought the truck and then I once had the system go completely offline when water intruded the main connector underneath. There are like 4 components that can fail, not including a poor ground-out condition.

Leaky axle seals behind the CV driveshafts is obvious. If you find this, be proactive about topping up the diff oil or you will fry the output bearings, even worse the diff itself. I cleaned-up some things before selling my vehicles so nobody is immune to it. GM p/t 4x4 is the poster child for leaky output seals, or so it's been said.

Finally, most techs & mechanics experienced with the 800 4x4 platform would advise you stay away from the 'AUTO4' mode. AND you will absolutely want to do an Internet search for "pump rub" and all of the info regarding that as it applies specifically to your transfer case and can most certainly affect you at any time. The PUMP-RUB and AUTO4 are the transfer case killers. you can either remove the transfer case, install a pump-rub solution kit & re-seal it, or frequently inspect the rear housing/tail shaft area for if & when it does break through and begins to leak and perform the repair then. But if you don't catch it in time, too much fluid leaks out & you have catastrophic failure. Just a big 1 that you should know of.

As it applies to most all vehicles, preventative maintenance keeps you on the road, neglect is the bane of all things mechanical. did you see the records & receipts for all of the fluid updates? Of course, I would still be checking the fill-level & color on every single system to verify. It's the least you can do, still doesn't cost anything. Good luck with your new purchase!

 

[Michael1972]

Thanks for the replies

One thing I do not understand is the proclaimed low speed on 4LO. The only difference between 4LO and 4HI is the 2:1 reduction gear, or are there additional ones, i.e. changed tranny shift algorithms?
Based on that I stay within certain rev-limits, it should be no different to drive thw Tahoe ałl day long between 30 and 40mph, that would equal 60-80mph in 4HI.
Is there a technical reason behind this?
I will be driving on steep rocky roads, using the 4LO extensively, downhill to use increased engine brake, uphill to pass hairneedle turns.
Question- The clunk comes from enganging the front axle? The front drive shaft engaging should be quite silent, since it is just the clutch pack in the TC, right? Therefore, is there a claw-lock type engagement.....I am still waiting for my shop manuals...and have not found a comprehensive explainattion on the net...

Regarding the fluid levels, thanks for the heads up. I am adament about keeping my things tuned properly, I will stay extra keen on those points. No, I did not see any receipt on fluid changes. I just have a written stytement in ths sales contract. The TC is leaky, curently the ouput seals are beeing replaced, among some other things.
Somehow I had a gut-feeling to stay away from to many electric-helpers........ I liked the manual engaged drive systems better...less fuzz...but my wife liked the newer design on the interiour.....

Thanks guys,
cheers
Michael

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[swathdiver]

The faster you go in 4LO, the quicker you'll wear out your drivetrain, that's in the manual btw. Also in your manual is the recommended top speed while driving in 4LO. For MY 2009 GMT932 it is 39 mph. I don't even think it will shift into 3rd or 4th, I remember it stopping. Again, my manual says I can do it but at the expense of longevity.

 

[Michael1972]

Thanks,
have read my manual 2 times regyrding the different modes, however have not found any specifics, nor max speeds. It seems to be differnet on yours....but it is a different model...

If the shift algorithm is different ftom HI and LO it migh make sense. If the gears shift identically however, it does not, unless the 2:1 gearing has a lower quality than the 1:1 ....

As soon as I have the Tahoe I will post the results here. Or, maybe there is one owner who can tell?
Secondly, I have 2 different replies to the cluk noise...i. this thread it says it is normal.....in my intro post it was said that no sound should come at all....... hmmmmm......
Does someome know how the front hub locks? Pinlock...claw lock? Than I could figure it out myself...what and if a sound might or might not be right...

Thanks folks,
Michael

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[swathdiver]

For mine, it's a clunk into 4LO and the manuals mention this. Your manual doesn't mention a clunk and neither does the detailed vehicle brochure. We have different transfer cases. In addition, neither mentions the maximum speed for driving in 4LO so one would assume there isn't one.

 

[Michael1972]

I,ll keep diggjng.....anything that I come up with... I will post here, hopefully it will help someone else eventually.
As soon as I get my workshop manual... I will be in for some serious reading... :~o
Currently I work based on some assuptions....we,ll see.

Have a great 25th....
Michael

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[Michael1972]

@Chubs
good call on the pump rub...... quite some information out there.
Will keep my eyey open on that one ....

I hope to tget the Tahoe within the next 5 weeks. Currently I sink xome serious cash in conservation...underbody work, corrosion work and prevention, cavity protection...... and some killer glas pack custom exhaust loud pipes...save lifes.... uxually I ride dirt bikes

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