Crack in fender

[bosco659]

Since I’ve owned my ‘76, it’s had a small crack at the bottom of the rear fender. It can be seen in the attached picture. I’m pretty sure this is being caused by vibration and unfortunately it seems the crack is growing longer. I’d like to stop this from spreading further, but at the same time I know that a proper repair would involve welding an a repaint and I’m not prepared to do that yet.

Here are a few ideas I’ve had and am looking for others’ opinions.

1. Drill a hole at the end of the crack. Fill it with a pliable material and stick a red vinyl dot over the repair (I have red vinyl that was used to make the stripe). Or I can go to Walmart and buy a vinyl “bullet hole” sticker. Lol
2. Reinforce the back of the fender, covering the crack with JB Weld or body panel adhesive, including a small reinforcement plate.
3. Since the crack was probably caused by vibration at a certain, unknown frequency, try to change the resonance frequency by altering the mass of the rear of the fender. May sound silly but I thought about sticking lead tire weights on the underside of age fender.
4. Perhaps the best “temporary” repair would be a combination of 1,2,3.

Any comments or ideas would be appreciated!

 

[Jim]

I'd stop drill it and leave it exposed for a while to see if it stops the crack. Remember to go past the crack and start your hole. If you don't the crack might still be there... somewhat invisible, but still there.
The problem with adding weights is you might actually make the vibes worse.... it's kind of a crapshoot.

 

[bosco659]

How big of a hole would you drill?

 

[bosco659]

How big of a hole would you drill? I’ll hold off on the weight idea.

 

[Jim]

Somewhere's around 3/16" to 1/4" is what I normally do for thin sheet such as the fender.

 

[bosco659]

K thx Jim.

 

[Vincenthdfan]

I'd stop drill it and leave it exposed for a while to see if it stops the crack. Remember to go past the crack and start your hole. If you don't the crack might still be there... somewhat invisible, but still there.
The problem with adding weights is you might actually make the vibes worse.... it's kind of a crapshoot.


View attachment 238613

What Jim said 100%.

Its what we always did to military aircraft when they'd shake themselves apart...very common repair.

 

[Jim]

Its what we always did to military aircraft when they shake themselves apart...very common repair.

On the F-111's, stop drilling was a daily occurrence. If I did a BPO on one and didn't stop drill a crack... I felt like I didn't do a very good inspection.

 

[bosco659]

Had a look underneath the fender today and realized there’s a substantial reinforcement piece in there already from factory. I’m surprised it would crack with that intact. Perhaps it’s not firmly attached to the fender? Is it just spot welded in? Seems to be a bit of a gap at the bottom. Maybe I can squeeze in some adhesive. Downside of that is if I decide to fix it properly by welding it, the adhesive will contaminate the weld joint.

Will still drill but finding the ”end” of the crack will be challenging because it’s under the vinyl stripe. If I feel motivated enough and make time, I’ll remove the fender and inspect it from underneath. There’s also a strong possibility the end of the crack will be covered by the reinforcement plate underneath. I’ll look this evening.

 

[gggGary]

2 part bumper epoxy with something crossing the crack a couple times worked into it, some soft steel wire, or a bit of fiberglass cloth, stiff window screen, a couple ideas.

 

[bosco659]

Had a closer look tonight. Seems the po knew there was a crack and thought if he put down a layer of bondo in the back, the repair would be complete. . I think the reason the crack is getting longer is the material that’s cracking probably isn’t metal but is bondo. I’ll do something to it but will most likely fix it properly at the end of the season.

@gggGary if I feel motivated I might dig out the bondo and try one of your ideas. Gotta get it to bare metal in the back first.

I hate it when people do these bandaid repairs. Wouldn’t have taken much to fix it properly.

 

[gggGary]

Bumper epoxy is worth having in the shop, it's a strong 2 part slightly FLEXIBLE "Bondo" The "give" helps keep it from cracking.

 

[Jim]

If I was just trying a temp fix 'till the end of the season... just stop drill it and keep an eye on it. If your plan is to weld and repaint at the end of season, whatever "extras" you throw at it now, will make welding that much harder later on.

 

[650Skull]

+1 on the drilling a hole.

 

[bosco659]

If I was just trying a temp fix 'till the end of the season... just stop drill it and keep an eye on it. If your plan is to weld and repaint at the end of season, whatever "extras" you throw at it now, will make welding that much harder later on.

Bike is headed to a bike show next weekend. Once it’s back I’ll get the drill out.

 

[TX650A Van Islander]

@bosco659, love your license plate!
Hope the crack stops with the hole drilling. What show are you going to?

 

[bosco659]

In Toronto next weekend. Not a show full of vendors or new bike dealers but a show where owners display their personal bikes. Modern, vintage, stock, custom bikes, people selling parts etc. should be good. My bike will be displayed in the vintage section. Didn’t want to leave my actual plate on the bike so the printer / laminated version was created.

 

[magoo66]

In Toronto next weekend. Not a show full of vendors or new bike dealers but a show where owners display their personal bikes. Modern, vintage, stock, custom bikes, people selling parts etc. should be good. My bike will be displayed in the vintage section. Didn’t want to leave my actual plate on the bike so the printer / laminated version was created.


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Enjoy!