Countersunk bolts in trans crossmember -
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Unread 08-13-2014, 06:00 PM   #1
Web Wheeler
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1996 ZJ 
Join Date: Nov 2012
Location: Cupertino, CA
Posts: 8,871
Countersunk bolts in trans crossmember

Still new to working with metal so probably a newb question.

I'm prepping my clayton crossmember for my long arm build and getting the poly trans mount put in it. Clayton expects you to use the standard bolts from the trans mount which means the heads of the bolt protrude from the bottom of the crossmember. Based on the state of the bolt heads on my current crossmember I don't really want that.

Is there any reason I shouldn't use 3/8 countersink bolts in place of the standard ones? I have the bit to drill the countersinks, the crossmember is 1/4" thick so I feel like there's plenty of material there.

I know there's a slight decrease in strength with a countersunk head vs standard but will it matter?

1996 ZJ Green Laredo V8, 2.5" OME and Bilsteins, 33's, Holes drilled in the roof.
1984 F250, 460 BB, T19, work truck/future tow pig
1987 Mercedes 300D Turbo, the diesel daily, 30mpg in style

Originally Posted by Texas ZJ1 View Post
I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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Unread 08-16-2014, 03:52 PM   #2
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1991 YJ Wrangler 
Join Date: Dec 2003
Location: Hale'iwa, Hawai'i
Posts: 5,092
1/4" really isnt that much meat to countersink in this application. Are you more concerned with damaging the bolt heads or that they will get hung up on things?
-insert meaningless out-of-place political diatribe-
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Unread 08-16-2014, 09:07 PM   #3
2004 TJ Wrangler 
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Or a button head screw?
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The one I miss most is my mind

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Unread 08-17-2014, 04:24 AM   #4
jason m
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Location: Holland mass USA
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Two problems, first as its all been said 1/4" is not a lot for a countersink bolts, second with a countersink bolt you use Allen type wrench to tighten them, you won't get them hold as tight as a normal fixed head bolt would.
There bolts, buy good quality bolts like caterpillar use's and they will last a long time.or just replace them every few years once they get gouged up. I have the same bolts on my cross member for 10 years now, yes they are so worn down the zinc is gone and gouged to the point a socket fits hard.
But I bought Cat bolts and they have a larger head and made to a higher quality standard.

1993 YJ 4.0 60 Front, Rear steer 60, bolth spooled, 5.38's, 700r/241 39.5 iroks and beating it like it owes me money.

And on the 8th day, God created the 14 bolt....
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