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Mack Frame Rail Questions.


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I got to get the frame on my B81 streched 2 foot. Was thinking of taking all the rails apart cleaning them and paitning them.

1 Has anyone done this?

2 What did you do with the rivets that hold the rails and cross members together?

3 Im going to weld the new section of rail into the center. Good or bad idea?

( center 2 ft, outside 3 to 4 ft piece and then cap that with a longer pice bolted threw the other 2)

Cab cross members cracked.

The cross member behind that is a I beam with a 1 inch thick flange (who ever built it did one hell of a nice job).

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In order or your questions:

1: Yes, I have performed this operation.

2: I used a slice disc and take the heads off flush with the frame.

3: Most will tell you to graft onto the end of the frame rails, then roll the axles back to the location needed. I've done it this way, and

just grafted the section into the middle both without problems. If you add to the middle, you have twice the welding to do.

I would weld up the cracked crossmembers myself.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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What did you replace the rivets with?

I was going to add on to the end but the rails cracked in 2 spots on one side a one on the other in the center.

Thanks rob and david.

Was going to start on the LJ but i need to get the 5 ton wrecker off to its new owner soon. So i might as well put the wrecker body right on the frame its going on.

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What did you replace the rivets with?

I was going to add on to the end but the rails cracked in 2 spots on one side a one on the other in the center.

Thanks rob and david.

Was going to start on the LJ but i need to get the 5 ton wrecker off to its new owner soon. So i might as well put the wrecker body right on the frame its going on.

I use grade 8 fine thread bolts and either lockwashers and nuts, or Nylock nuts, (hardened). You want these tight.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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I agree with what's been said here already. As far as replacing the rivets, you really don't have a choice, grade 8 bolts into ream-to-fit holes. For what you're going to do on a truck like that, I think to weld the cracks would be acceptable, cut the inner frame back farther so as to stagger the joints, and to get weld inside and outside of the outer rails.

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What did you replace the rivets with?

I was going to add on to the end but the rails cracked in 2 spots on one side a one on the other in the center.

Thanks rob and david.

Was going to start on the LJ but i need to get the 5 ton wrecker off to its new owner soon. So i might as well put the wrecker body right on the frame its going on.

you are making the b-81 into a wrecker?

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