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Chevy Silverado and GMC Sierra Undercarriage Rust

5 messages,  Last post on Jun 06, 2009 at 5:27 AM

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What is this discussion about? Chevrolet Silverado 1500, GMC Sierra 1500, Chevrolet Silverado 2500, Truck

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#1 of 5 2008 GMC 1500 Undercarriage Rust by blurry25 Apr 15, 2008 (11:26 pm)
I purchased a 2008 GMC Sierra this weekend and after I got it home I noticed that the undercarriage had quite a few areas with surface rust. The rearend housing also has a bit of rust and the backs of the front spindles are rusted. It is all just surface rust, but it still kind of bothers me. I took the truck in to get detailed at the GMC dealer today and asked about the rust. They said that there was a technical service bulletin for this issue and proceeded to spray a little flat black paint of areas that are easily seen. I guess they thought that I would look under the truck. I would prefer something a little more factory like the rubberized black paint normally used on the undercarriage.   Are areas of surface rust on the undercarriage normal on a new truck? Should I even worry about it? Lastly, what if anything does the dealer have to do for a technical service bulletin?   Thanks in advance. Replies to this message: obyone (Apr 15, 2008 11:57 pm) bensierra (May 22, 2009 7:04 pm)
#2 of 5 Re: 2008 GMC 1500 Undercarriage Rust [blurry25] by obyone Apr 15, 2008 (11:57 pm)
Replying to: blurry25 (Apr 15, 2008 11:26 pm) A TSB is information regarding procedures or changes in procedures for repair or parts. Basically it is a way for the factory to communicate changes to the dealer whether it be tools, service procedures, upgraded parts, etc.   If there was a tsb regarding surface rust, I ASSURE you that spraying flat black paint on unprepped surface rust IS NOT part of any TSB. There are sites like alldatadiy.com where you can get a detailed list of the TSBs available for your truck. The manufacturers really don't like you doing this as you may find problems with your truck that you never really noticed in the past but because of a description in the TSB suddenly you need to make a warranty service appointment.
#3 of 5 Re: 2008 GMC 1500 Undercarriage Rust [blurry25] by bensierra May 22, 2009 (7:04 pm)
Replying to: blurry25 (Apr 15, 2008 11:26 pm) My dad purchased a 2008 Sierra 2500 HD last year and asked me to rustproof the frame last fall. I went to my local NAPA store and bought a 5 gal.Rustproofing Undercoat...can remember the brand but I'll check. We put it on the hoist and I noticed the same thing as you. Control arms and rear end were starting to rust. I undercoated the complete frame in and out without any misses. I used about half the pail. I also did doors, rockers, box sides etc....Here's were it gets interesting, 2 months down the road he stopped at the local carwash to clean the winter salt of the truck. The factory undercoating was peeling off like you wouldn't believe!!! The rustproofing totally destroyed the SOFT, STICKY factory undercoating. We are currently trying to clean that stuff off. Never seen anything this hard to clean in my 12 years of Auto Body Repair. Pressure wash, degreased, scrape off, wire brush, degrease again, pressure wash and finally sand blast to finish it all off before epoxy/paint. Nightmare!!!! Wondering if anyone else had or heard of this happening to someone??
#4 of 5 for the frame by ntsmith69 May 30, 2009 (10:19 am)
i am in autobody as well. and what i found that exp on frames and the under carrage is to clean it as best as you can. then use rust converter on the whole area thats needs to be painted. after that dries spay an etch primer on it. you can buy this in cans called ONE STEP self etching primer. this will help bond the new paint to the frame. i have done this to many vehicles and never had a problem. even on the factory coating just add the etch primer and you should not have a problem. it is all in cans so no need of spray guns. and for the top coating i use rock guard in cans. the paintble type . i found the other ones do not harden as much and if you want to touch it up down the road it is easier. but spraying black paint over it will just come off and is just for looks till you get out of the garage. Replies to this message: bensierra (Jun 06, 2009 5:27 am)
#5 of 5 Re: for the frame [ntsmith69] by bensierra Jun 06, 2009 (5:27 am)
Replying to: ntsmith69 (May 30, 2009 10:19 am) The thing is that rust converter needs rust to work. When you peeled the soft coating off where it hadn't peel yet, the frame was clean bare steel. The rust proofing had melted the factory even softer than it was.Check the new generation GM and no paint or primer will stick on that frame undercoating. You can't blast it or sand it. Stick your fingernail in it and you'll scrape it down to bare metal. It's almost like a grease.

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