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Old 10-12-2021, 01:21 AM   #1
AllGoNoShow
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Enlarging driveshaft hole in stock crossmember?

So I have a c-notch on a long-bed C10 and while measuring for the 4” one piece driveshaft that I want to run, I realized the driveshaft will be hitting the top of the trailing arm crossmember before the rearend hits the bump stops.

Has anyone just enlarged the hole on the stock trailing arm crossmember to fix this? Looks like I would just need 1/2 inch, which I could obtain just by cutting the bent lip of the existing crossmember and maybe even sectioning it and welding it back on?

I know there are some aftermarket options here but I think some of them would interfere with the bottom of the cab on a long-bed because of the placement of the crossmember in relation to where it sits on a short-bed (and I am on a bit of a time crunch). I had a 3.5 one piece driveshaft in it with no c notch and stock bump stops and it hit, but it’s getting lower and I want to upgrade to a bigger shaft after learning about and calculating the “critical speed” of a driveshaft that needs to be this long for a LWB.

Nick
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Old 10-12-2021, 12:39 PM   #2
cab4word67
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Re: Enlarging driveshaft hole in stock crossmember?

Interesting. I have a 4" driveline in my short box with leaf springs so I dont have that crossmember yet. Going to change all out to the CPP coilover kit witch runs the lower axle arms and that crossmember like a Chevy coil would have. I am very close to the bottom of the cab in your picture and wonder just what I will now have to do also. Likely modify the new crossmember.
Always liked taking brand new custom parts and cuttin them up.
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Old 10-12-2021, 01:25 PM   #3
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Re: Enlarging driveshaft hole in stock crossmember?

I would just make a clean vertical cut on both sides and remove the entire upper arch section. Then weld in a new half steel pipe section on top with whatever diameter would match the existing opening width. Then maybe some additional some additional triangular bracing for rigidity.
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Old 10-12-2021, 01:43 PM   #4
Big Kev-O
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Re: Enlarging driveshaft hole in stock crossmember?

I have never seen anyone modify that hole. Doesn't mean it cant be done but that is one of the main supports for the frame.

I know you can flip the entire crossmember on a 67-72 short bed. It will raise the trailing arm pivot points 3-1/4" and add an additional 1-3/8" driveshaft clearance. It should clear the bed floor by 3/4". Details here:
http://67-72chevytrucks.com/vboard/s...d.php?t=362464

Judging by your picture I doubt you can flip the factory member on a long bed. IF it fit it would be so close it may hit when the truck flexes. No hurt in trying since you are going to have to remove it anyways if you end up needing and aftermarket dropped trailing arm cross member. I am not sure if the ones Brother or POL sell will clear the cab. Brothers tech guys are pretty helpful. Give them a call and they can probably tell you the answer. All of the dropped longbeds I have seen look like they have tubular cross members. The PB Fab tubular trailing arm cross member looks like it should fit. Might want to reach out to PB.


https://pbfab.com/1963-72-trailing-a...ece-driveshaft
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Old 10-12-2021, 04:38 PM   #5
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Re: Enlarging driveshaft hole in stock crossmember?

On my 68 I ran into the same issue.
I have a plasma cutter so I cut out the upper radius. The reusing the piece I cut out and welded it back in a bit (maybe 1/2") above the cross member. Then made I made two vertical pieces to attach the lower cross member opening to the reused and moved up upper piece.
Then I used a piece of 3/16" steel to "plate" across the top of the cross member.
Also I ran two support tube brackets from the cross member up to the trans cross member. Basically additional support for the trailing arm mounts.
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Old 10-13-2021, 01:28 AM   #6
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Re: Enlarging driveshaft hole in stock crossmember?

Quote:
Originally Posted by AllGoNoShow View Post
So I have a c-notch on a long-bed C10 and while measuring for the 4” one piece driveshaft that I want to run, I realized the driveshaft will be hitting the top of the trailing arm crossmember before the rearend hits the bump stops.

Has anyone just enlarged the hole on the stock trailing arm crossmember to fix this? Looks like I would just need 1/2 inch, which I could obtain just by cutting the bent lip of the existing crossmember and maybe even sectioning it and welding it back on?

I know there are some aftermarket options here but I think some of them would interfere with the bottom of the cab on a long-bed because of the placement of the crossmember in relation to where it sits on a short-bed (and I am on a bit of a time crunch). I had a 3.5 one piece driveshaft in it with no c notch and stock bump stops and it hit, but it’s getting lower and I want to upgrade to a bigger shaft after learning about and calculating the “critical speed” of a driveshaft that needs to be this long for a LWB.

Nick
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What brand arms are you using? and the stock cross members have heavy duty exhaust holes?
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Old 10-13-2021, 06:44 PM   #7
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Re: Enlarging driveshaft hole in stock crossmember?

So I did pretty much what LS Short box did. Zipped off the upper lip with a cut off wheel, enlarged the hole behind it with a carbide bit on a die grinder, and sectioned in two small pieces (a hair over 1/2), which moved the lip up that much. Beveled the edges, MIG welded it all back in both from top and bottom, then dressed it all with a carbide bit and small drum sanders (would post pictures but now I don’t see a link to do so on my phone?)

I have to get suspension all back together but I think the geometry here works in my favor (a 1/2 inch more space here will be more then that at the pinion yoke), but we will see. With how little metal was taken out I don’t really feel the need for any extra bracing or anything.

Cab4word- They are qa-1 arms and dead mans garage exhaust cut outs.
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Old 10-13-2021, 09:54 PM   #8
AllGoNoShow
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Re: Enlarging driveshaft hole in stock crossmember?

Here are the pictures. With some paint, I imagine it will be near impossible to distinguish it was raised. You could raise it another 1/4, which would put it about even with the lowest point on the rear of the cab.
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Old 10-13-2021, 11:01 PM   #9
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Re: Enlarging driveshaft hole in stock crossmember?

Good job !
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Old 10-14-2021, 12:24 AM   #10
cab4word67
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Re: Enlarging driveshaft hole in stock crossmember?

looks like it was made that way. I like how people think outside the box and get stuff done.
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Old 10-14-2021, 08:36 AM   #11
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Re: Enlarging driveshaft hole in stock crossmember?

LWB here, but 4wd, & went to one piece driveshaft. Cut it all up & rebuilt with heavy wall square tubing.
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