Educate me: why all the rusty fenders? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Mossbeard · 05-01-2014, 02:50 PM

I've recently acquired my first truck; a '66 C20. I've been learning a lot here but I'm wondering what causes the rust patches I've seen on so many front fenders (lower edge behind wheel)? Is there a design flaw? More important, after repairing the rust, what can be done to prevent recurrence while still keeping the truck looking original?

LostMy65 · 05-01-2014, 02:57 PM

There's a drain hole that wasn't made big enough to allow the silt that builds up in there from draining. Moisture and dirt gets trapped in there and it rusts away.
Some here have made the drain hole bigger.
One just needs to blast some water in there to flush it out from time to time.

NEWFISHER · 05-01-2014, 02:57 PM

Design flaw that traps moisture at the lower section. Same with the cab corners on GM trucks all the way into the late 70's. When you come across an original cab corner in good shape, it most likely has a 3/8 hole drilled in it to let the water run out. That was a mod done by an owner who was aware of the issue many years ago.

Improbcat · 05-01-2014, 02:59 PM

There is a bad design that traps water/dirt in the fender brace attached there and causes it to rot out.
Things that help are to drill a decent sized drain hole at the bottom of the brace and to seal the edges & top of the brace with seam sealer to keep the water/dirt out in the first place.

Mossbeard · 05-01-2014, 03:14 PM

Thanks everyone! That's exactly the info I was looking for. Very helpful.

1963c-10 · 05-01-2014, 03:56 PM

Don't forget the rusty hoods, floor pans, rockers (inner & outer) and inner fenders.

Mossbeard · 05-01-2014, 04:02 PM

Quote:

Originally Posted by 1963c-10

Don't forget the rusty hoods, floor pans, rockers (inner & outer) and inner fenders.

Yeah, I get a trickle of water from behind the dash on the passenger side when it rains. If I don't find the leak soon I'll have rusty floorboards.

1963c-10 · 05-01-2014, 04:11 PM

Quote:

Originally Posted by Mossbeard

Yeah, I get a trickle of water from behind the dash on the passenger side when it rains. If I don't find the leak soon I'll have rusty floorboards.

Check the roof seal....and the firewall where it meets the cab. Also check the windshield gasket as sometimes they get loose and I've seen water come in there also.

WhippinSaw · 05-01-2014, 04:37 PM

I want to power wash my lower front fender after watching this youtube video on 1960 to 1966 front fender rust repair . It shows why the fender rust at the 7 minute marker https://www.youtube.com/watch?v=oydlEWgNths#t=293

BR3W CITY · 05-01-2014, 04:03 PM

Mine rusted there as well, but strangely it did so in a very concentrated manner. I actually had about a quart of sand in that area, which held the moisture and caused it just to rust there.

markeb01 · 05-01-2014, 08:06 PM

IMHO the drain hole is big enough, if nothing is allowed in to begin with. Unfortunately GM designed the fenders to collect debris and form a compost pile in the lower fenders until the sheet metals bursts open on the front side. The only way to prevent it in the future is to close all the openings into the fender brace. Here’s how I permanently fixed mine:

05-01-2014, 02:50 PM	#1
Mossbeard Registered User Join Date: Mar 2014 Location: Porterville, CA Posts: 22	Educate me: why all the rusty fenders? I've recently acquired my first truck; a '66 C20. I've been learning a lot here but I'm wondering what causes the rust patches I've seen on so many front fenders (lower edge behind wheel)? Is there a design flaw? More important, after repairing the rust, what can be done to prevent recurrence while still keeping the truck looking original?

05-01-2014, 02:57 PM	#2
LostMy65 But Found Her 25yrs Later! Join Date: Oct 2010 Location: Oregon City, Oregon Posts: 10,530	Re: Educate me: why all the rusty fenders? There's a drain hole that wasn't made big enough to allow the silt that builds up in there from draining. Moisture and dirt gets trapped in there and it rusts away. Some here have made the drain hole bigger. One just needs to blast some water in there to flush it out from time to time. __________________ I lost my 65 - Found it 25 years later: http://67-72chevytrucks.com/vboard/s...d.php?t=426650 66 C20 Service Truck: http://67-72chevytrucks.com/vboard/s...d.php?t=428035

05-01-2014, 02:57 PM	#3
NEWFISHER Registered User Join Date: Sep 2012 Location: Oregon Posts: 3,303	Re: Educate me: why all the rusty fenders? Design flaw that traps moisture at the lower section. Same with the cab corners on GM trucks all the way into the late 70's. When you come across an original cab corner in good shape, it most likely has a 3/8 hole drilled in it to let the water run out. That was a mod done by an owner who was aware of the issue many years ago. __________________ GOD BLESS AMERICA!

05-01-2014, 02:59 PM	#4
Improbcat Registered User Join Date: Jul 2012 Location: E Providence RI Posts: 238	Re: Educate me: why all the rusty fenders? There is a bad design that traps water/dirt in the fender brace attached there and causes it to rot out. Things that help are to drill a decent sized drain hole at the bottom of the brace and to seal the edges & top of the brace with seam sealer to keep the water/dirt out in the first place. __________________ 1964 C/10 Longbed Fleetside, base model. (build thread) (pictures) SOLD 1964 C/10 Shortbed Fleetside, Deluxe. (pictures) SOLD

05-01-2014, 03:14 PM	#5
Mossbeard Registered User Join Date: Mar 2014 Location: Porterville, CA Posts: 22	Re: Educate me: why all the rusty fenders? Thanks everyone! That's exactly the info I was looking for. Very helpful.

05-01-2014, 03:56 PM	#6
1963c-10 Registered User Join Date: Nov 2011 Location: fayetteville nc Posts: 10,338	Re: Educate me: why all the rusty fenders? Don't forget the rusty hoods, floor pans, rockers (inner & outer) and inner fenders. __________________ 1963 Short bed step side SBW 427 big block and borg warner T-16 HD 3 speed manual http://67-72chevytrucks.com/vboard/s...d.php?t=519869 1963 Short bed fleetside BBW 348 1st gen big block w/Powerglide http://67-72chevytrucks.com/vboard/s...d.php?t=619024 1964 Short bed trailer

05-01-2014, 04:37 PM	#9
WhippinSaw Registered User Join Date: Aug 2012 Location: Lisle Illinois Posts: 602	Re: Educate me: why all the rusty fenders? I want to power wash my lower front fender after watching this youtube video on 1960 to 1966 front fender rust repair . It shows why the fender rust at the 7 minute marker https://www.youtube.com/watch?v=oydlEWgNths#t=293 __________________ 1963 Fleet Side cab, Converted Fleet Side Barden bumper, Step Side in the middle.

05-01-2014, 04:03 PM	#10
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: Educate me: why all the rusty fenders? Mine rusted there as well, but strangely it did so in a very concentrated manner. I actually had about a quart of sand in that area, which held the moisture and caused it just to rust there. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

05-01-2014, 08:06 PM	#11
markeb01 Senior Enthusiast Join Date: Feb 2007 Location: Spokane Valley, WA Posts: 8,356	Re: Educate me: why all the rusty fenders? IMHO the drain hole is big enough, if nothing is allowed in to begin with. Unfortunately GM designed the fenders to collect debris and form a compost pile in the lower fenders until the sheet metals bursts open on the front side. The only way to prevent it in the future is to close all the openings into the fender brace. Here’s how I permanently fixed mine: __________________ My Build Thread: http://67-72chevytrucks.com/vboard/s...d.php?t=444502



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