I bought a 2003 Avalanche Z71 with 165,000 miles, fully loaded for only $3250. It has a couple things the previous owner let me know about and now I'm trying to fix them. I have AAA free 100 mile towing so a quick call to AAA had them tow it home with only a white lie about not trusting it got it home without making my pregnant wife and 2 year old help me get it home.





The PO was an older gentleman and said the trans was replaced in 2011 at 130k miles right before he bought it. I crawled under it and the paint pen marks and darker painted trans case verify that. However he said that 4wd doesn't work. When I put it in 4hi, the lights do go to 4hi, and I can hear it make the noise as it shifts, however if you go to hit the gas or turn slightly (just feeling for the expected bind to verify its engaged, not enough to really bind it) you get a slipping, grinding kind of sound, like the front driveshaft isn't fully engaged and the teeth are slipping. In 2wd I can spin the front driveshaft freely, and in 4wd or Auto it can't spin by hand, verifying the front diff is engaging, but it's not fully engaging at the T case. If I go to 4lo, it's definitely in low range, but if I turn I can tell it's not engaged with the front and it's not in 4wd. Is that the actuator motor not fully going through the full range of motion? My first guess is to replace the actuator for $100 but I wanted another opinion on what to look for or test before I throw money at it. I'm going to try changing the front diff fluid tonight to see if there are any shavings. I'm kind of thinking that someone drive it in 4wd AUTO too much on dry surfaces, I know from my Tahoe and old burben that in AUTO if you take a tight turn the T case tries to engage sometimes, maybe it bound too much and fucked something up, or the T case chain is stretched. Any insight here?

Someone tried to break into the truck at some point and jacked up the key hole in the drivers door so you can't get a key in it. Not a big deal, I use the fob, but I want to replace the key lock. How do I get a new key lock to match my key? Dealership?

It has some sort of road noise that is 100% dependent on speed. It doesn't matter if it's on different surfaces (old vs new asphalt), isn't dependent on throttle input, and doesn't change if I put it in neutral at 60. I'm thinking this could be tied to the 4wd not working. It doesn't sound like gear noise, and I put a temp gun on the T case and front diff after a drive and neither were hot, but it was only about a 5 mile drive at 70. Anything else I should look at?

The oil pressure gage is pegged at 80, even key on engine off. My 05 Tahoe has the same problem, and I've been reading it probably needs a new oil pressure sensor and it's not the gage. It goes to 0 key off, so I don't think it's the stepper motor.

Other than that it feels just like my 05 Tahoe, and should be a great truck. It has a ton of hours on it, 6300 at 165k miles, vs only 3300 at 130k on my Tahoe, so I'm guessing it spent a lot of its life as a short commute DD, explaining why the trans went at 130k. It sounds perfect though, the PO used only Mobil 1, and the motor is great.

 

I think you're on the right track. I would start out by changing all of the diff fluids and the transfer case fluid. It could be something simple like the transmission shop filling the transfer case with gear oil and not trans fluid or the front fluid being really bad with shavings.

Key hole would be hard to replace, if they tried to break in the cylinder should still be in the door, if you remove it you might be able to bend the outer casing back into place or try to rebuild that old one using a new one from a parts store.

 

I did the front diff and the fluid was clean so I'm thinking someone else has tried to chase the noise too, and it didn't change the noise. Next guess is the transfer case since I read it needs Auto Track II fluid, maybe someone accidentally put tranny fluid in it, since that's old practice on non Auto Trak cases.

Another weird one is the trans shifts different than the Tahoe. My old 2000 suburban did this too so I'm wondering if it's on purpose for the heavier avalanche/suburban vs the Tahoe. It seems to shift up a touch later, and downshifts a touch later. Like it will kind of lug at 1500 rpm for longer than I feel like it should rather than unlock the converter or downshift. I need to change that fluid too just to see if that helps.

 

My my 06 silverado hd with the 6.0 always felt flat right before a shift point, I decided to swap out my iridium plugs for copper plugs and noticed an increase in torque in the mid range. It seemed to help the feel of the truck, instead of feeling like there was only a flat power band the truck seemed to gain torque as it should and the shifts felt more meaningful especially when towing. So on the trucks I always reccomend copper plugs

 

Someone broke into my truck too and damaged the lock cylinder. On mine (yours is probably similar), the lock cylinder is mounted to the plastic door handle, and it cracks inside and needs to replaced as well. I got a used GM one from ebay that came with the lock cylinder. You can take them apart and swap the tumblers from your old lock to the new one.

Also consider getting some anti-theft door plates, fairly cheap insurance since these trucks are so easy to break into.

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