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This is just a thought. I'm fresh off the leaky shark fin antenna problem.  Dealer wanted $450 to replace it.  I honestly contemplated karate chopping him in the throat.   Anywho, all that to say...

 

I did the repair myself and reused the OEM shark-fin since I was fortunate enough not have any GPS issues yet.  One thing I'll point out is this, don't get to aggressive when tightening down the bolt under the antenna because you could actually end up creating a divot in the roof, thus voiding the curved design of the antenna seal to not seat correctly to the curvature of the roof. This would obviously introduce more water and drive you nuts thinking you've sealed it really good and tightened it down real tight.   Take off your antenna and start over.  Be sure to remove all the gunk/silicon/adhesive, use a small amount of rubbing alcohol to clean any residue before you reseat the antenna. Look for any kinks or divots in the roof from it being over tightened. Next, use a very small amount of windshield adhesive on antenna seal. If you're putting adhesive or sealant on the perimeter of the antenna then you also will need to apply an equal amount onto the seal that covers the hole.  Once you have equal amounts of adhesive underneath, slowly set it down in its final resting place being cautious not to allow it to slip or move around.  Before you tighten the bolt from underneath, put a very small dab of blue loctite on the threads to prevent the antenna from loosening down the road... don't forget, all cars vibrate and overtime bolts will loosen, especially the ones that can't be tightened down to much (the further away a bolt is from the vibration source, the greater the vibration.) When you do tighten down the bolt, just be cautious not to overtighten.  You can this by how much adhesive is being squeezed out.  NOTE:  If by chance you had over tightened the bolt during the first repair and it did create a kink in roof,  its very likely for the kink to happen again because there is now a weakness in the metal.  Just go slow and watch the antenna seal as you tighten the bolt down.  Wash rinse repeat for any rooftop device that's bolted through the metal.  

 

Afterthought,  you might want to skip the loctite step until later.  Put the bolt in and just tighten it so it's snug.  Let the adhesive dry for several hours.  then, go back and carefully remove the bolt trying your best not to move the antenna around breaking the bond. Now you can add the loctite to the bolt and continue from there.  This step might create less adhesive bleed.

 

Anywho...Just my thoughts. 

 

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I'd also like to point out that its unlikely your windshield is the source of the leak.  You would have noticed a faulty windshield leak long before and certainly right after it was installed.  I have had my windshield replaced and I also was suspect to this being the possible cause.  But Its been 3 years since it was replaced and would have certainly noticed a leak long before now, especially in my rain soak region of the U.S.   

 

Also, not as prevalent as the shark-fin antenna leak, but the 3rd brake light has also been talked a lot about from other members as a possible leaky source...food for thought 

Edited by BrianBrianBrian
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my 03 tahoe had the windshield replaced and it was fine for a few months and then randomly got a leak couldnt pinpoint it and swore it was the XM antenna but ended up finally calling safelite to come back out and check the windshield and sure enough it was a bad seal job by the previous technician. thats where i would start. couldnt find the leak with a hose either and no noises.

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Hello everyone, just signed up and hope to find great help here ... I've used other forums for other vehicles, and always find great points & help from fellow members, and hope to return the favor as well.
 
I bought a 2016 Silverado / Duramax LTZ two years ago, just out of bumper-to-bumper warranty at 40K miles, still going strong on the 5-yr engine warranty.  My problem is a persistent roof leak, driving me crazy.  First world problem, but absolutely should not be happening on this truck.  I've chased shark-fin possible source, and have no indications that it's the other common leak area, the rear mount center light.
 
Much research led me to the XM antenna; I was sure this is the problem, because I've lost GPS/XM/wifi when I started noticing a leak showing up at the front & sides of the overhead console, wet headliner.  This was Sep, 6 months after I bought it in March '18, so I didn't even try to go back to my dealer & complain, figured they'd respond like I've seen others report "oh no, on you to fix".  I just lived w/ no GPS, use my phone anyway.  I waited all the way to Aug 2019 (had very few leaks thru summer 2019) to buy the updated design shark-fin model & replaced it myself, first trusting the rubber seal & new design.  This did not fix the XM feed, so I finally got in touch w/ GM Customer Service, and after two trips into a different (local GMC) dealer, they only did minimal diagnostics on the electronics side, didn't do anything else with the antenna mounting or leak check.  So I gave up again, pulled the shark-fin off & used a good automotive sealer to supplement the new-design antenna; remounted it.  Still no electronics, but now hoping the water stops ... but no, rain storms still wet the headliner.  My last effort has been to use the same sealant around all of my cab-lights, and at the seals of the rear-center high-mount light.
 
Just moved my truck after a day of light drizzle here, it was dry at first touch, but after reshuffling in the driveway, drips from the low-point sides of the overhead console, at the front.  No water stains at the back window.  Maddening - I did a very solid sealing job around all the penetrations in the roof, cab-lights, rear-light, & antenna.  And still water.
 
Has anyone else dealt with anything close to this?  or have any insights?  Could there be a leak along the top of the windshield?  It doesn't apppear that could dribbling into the console area of the headliner, but who knows?
 
Appreciate any pointers - I have always been a GMC guy, put same faith in this truck, but this is such a maddening issue I'm just at wits' end.  Obviously, I could take it in and pay god knows what for hours of diagnostic/fix out of warranty, but just eats me up that this just should not be happening at all.
My antenna was replaced 5 times until they,,, dealer, and gm finally responded to mold and health issue lawsuit. Then, they said they put their best tech on it 39000 miles later its finally fixed. First leak was at 257 miles, last of 5 replacements and about 15 leaks later 38,589 miles its fixed. They said gm finally approved of new design. Wtf......

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On 2/21/2020 at 9:05 AM, BrianBrianBrian said:

This is just a thought. I'm fresh off the leaky shark fin antenna problem.  Dealer wanted $450 to replace it.  I honestly contemplated karate chopping him in the throat.   Anywho, all that to say...

 

I did the repair myself and reused the OEM shark-fin since I was fortunate enough not have any GPS issues yet.  One thing I'll point out is this, don't get to aggressive when tightening down the bolt under the antenna because you could actually end up creating a divot in the roof, thus voiding the curved design of the antenna seal to not seat correctly to the curvature of the roof. This would obviously introduce more water and drive you nuts thinking you've sealed it really good and tightened it down real tight.   Take off your antenna and start over.  Be sure to remove all the gunk/silicon/adhesive, use a small amount of rubbing alcohol to clean any residue before you reseat the antenna. Look for any kinks or divots in the roof from it being over tightened. Next, use a very small amount of windshield adhesive on antenna seal. If you're putting adhesive or sealant on the perimeter of the antenna then you also will need to apply an equal amount onto the seal that covers the hole.  Once you have equal amounts of adhesive underneath, slowly set it down in its final resting place being cautious not to allow it to slip or move around.  Before you tighten the bolt from underneath, put a very small dab of blue loctite on the threads to prevent the antenna from loosening down the road... don't forget, all cars vibrate and overtime bolts will loosen, especially the ones that can't be tightened down to much (the further away a bolt is from the vibration source, the greater the vibration.) When you do tighten down the bolt, just be cautious not to overtighten.  You can this by how much adhesive is being squeezed out.  NOTE:  If by chance you had over tightened the bolt during the first repair and it did create a kink in roof,  its very likely for the kink to happen again because there is now a weakness in the metal.  Just go slow and watch the antenna seal as you tighten the bolt down.  Wash rinse repeat for any rooftop device that's bolted through the metal.  

 

Afterthought,  you might want to skip the loctite step until later.  Put the bolt in and just tighten it so it's snug.  Let the adhesive dry for several hours.  then, go back and carefully remove the bolt trying your best not to move the antenna around breaking the bond. Now you can add the loctite to the bolt and continue from there.  This step might create less adhesive bleed.

 

Anywho...Just my thoughts. 

 

Great feedback - I was sensitive to the question of over-tightening, I could see how soft the metal is around the hole when I had it out, I feel pretty good about the tension & put into it, but the locktite is a good put that I didn't do & will on my next change of the antenna if I still need another one--through all of this, still have no compass/GPS.  I think I got to the bottom of my problem yesterday, post below.

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99% SURE I HAVE FOUND THE PROBLEM:  This is a bit embarrassing, but it's amazing what a new set of eyes can see;  I stopped by a Safelite shop (Alton IL, praise to the tech who helped me).  He took a look at the windshield seal and of course, not finding anything with the seal, he saw a hairline crack in the center cab light.  I completely missed this, never saw it while doing all my seal work; if you push on either side of the crack there's a reveal big enough for water to get thru.  For a test repair, I've done another short-term silicone bead worked into that crack & another over it to see if the heavy rains we have predicted tonight/tomorrow put it to the test.  I'm sure this is it - likely changing out the whole fixture as soon as we get some decent working weather.

 

If this is the final source of water leak, then I"m just left with whatever damage it did to the compass/GPS/XM module.  Thanks to all of you for points & feedback.

Edited by PapaBear7
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100% SOLVED.  We had extended rain this week that would have certainly leaked before the silicone I used to cover the crack line.  Really helped talking it out through here, the windshield quizzing sent me to the glass shop, and there's where a good set of eyes found the issue.  Thanks everyone.

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On 2/21/2020 at 10:05 AM, BrianBrianBrian said:

This is just a thought. I'm fresh off the leaky shark fin antenna problem.  Dealer wanted $450 to replace it.  I honestly contemplated karate chopping him in the throat.   Anywho, all that to say...

 

I did the repair myself and reused the OEM shark-fin since I was fortunate enough not have any GPS issues yet.  One thing I'll point out is this, don't get to aggressive when tightening down the bolt under the antenna because you could actually end up creating a divot in the roof, thus voiding the curved design of the antenna seal to not seat correctly to the curvature of the roof. This would obviously introduce more water and drive you nuts thinking you've sealed it really good and tightened it down real tight.   Take off your antenna and start over.  Be sure to remove all the gunk/silicon/adhesive, use a small amount of rubbing alcohol to clean any residue before you reseat the antenna. Look for any kinks or divots in the roof from it being over tightened. Next, use a very small amount of windshield adhesive on antenna seal. If you're putting adhesive or sealant on the perimeter of the antenna then you also will need to apply an equal amount onto the seal that covers the hole.  Once you have equal amounts of adhesive underneath, slowly set it down in its final resting place being cautious not to allow it to slip or move around.  Before you tighten the bolt from underneath, put a very small dab of blue loctite on the threads to prevent the antenna from loosening down the road... don't forget, all cars vibrate and overtime bolts will loosen, especially the ones that can't be tightened down to much (the further away a bolt is from the vibration source, the greater the vibration.) When you do tighten down the bolt, just be cautious not to overtighten.  You can this by how much adhesive is being squeezed out.  NOTE:  If by chance you had over tightened the bolt during the first repair and it did create a kink in roof,  its very likely for the kink to happen again because there is now a weakness in the metal.  Just go slow and watch the antenna seal as you tighten the bolt down.  Wash rinse repeat for any rooftop device that's bolted through the metal.  

 

Afterthought,  you might want to skip the loctite step until later.  Put the bolt in and just tighten it so it's snug.  Let the adhesive dry for several hours.  then, go back and carefully remove the bolt trying your best not to move the antenna around breaking the bond. Now you can add the loctite to the bolt and continue from there.  This step might create less adhesive bleed. 

 

Anywho...Just my thoughts. 

 

I am 99% sure this is the issue I am encountering and about to tackle this job myself as well. To be clear you just dropped the corner of the headliner, removed, cleaned and re-sealed the original Antenna? Thanks!

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On 3/4/2020 at 1:21 PM, GMC8810 said:

I am 99% sure this is the issue I am encountering and about to tackle this job myself as well. To be clear you just dropped the corner of the headliner, removed, cleaned and re-sealed the original Antenna? Thanks!

I'm glad you asked.  Yes, I did do that but next rain we had it was leaking again.  My head was spinning cause i knew i had sealed it.  I triple checked to make sure it wasn't the sunroof, 3rd brake light, or the windshield.  So I went on amazon and purchase a new antenna ACDelco 84346784 GM Original Equipment GPS Navigation System Antenna.

 

The new antenna will have weeping hole in the front, as opposed to the old one which is in the back of the antenna.

 

As per removing it, there are a few youtube videos of others doing the replacement you might want to check out.   HOW TO Fix Replace chevy shark fin OnStar antenna water leak Chevy GM GMC Cadillac

 

Remove the 3 screws from the visor and the single screw from the visor clip.  then remove the two bolts from the handle (Oh-shit handle).  The take the A-column off, I removed mine because if kept getting in the way.  You can then pull the headliner down just enough to get your hand in there to turn a sockett 10ml.  By accident, one cables from the headliner running down the A-column came unglued, I'm glad it did because if was a PIA..  I would recommend prying it off so you drop the headliner a little more.

 

Anywho... We just had a pretty good rain and no leaks.   Just as a precaution, I added a little clear silicone around the perimeter after I had it installed.  Use some painters tape.

 

Good luck

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