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Drive shaft legnthening

sub3

New Member
Joined
Jun 5, 2017
Messages
21
Hello! Just took my bronco for the first drive after complete rebuild w/2.5" suspension lift. Had some mad vibration under acceleration, because i'm an amateur I thought I could get by without lengthening the driveshaft but after looking more closely, I think its necessary. See picture

Is it as simple as cut it in half, figure out the tube size and thickness, order tube, cut off the ends of the driveshaft, weld in new tube at longer length? (In my case I think I need about 4") then paint and install?
 

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DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Are you sure that's not the front shaft? You should never see that much extension for just a 2.5" lift.
I have a 3.5" lift and a stock shaft measures out perfectly.

The rear pinion angle is an important factor in driveshaft length too though, so don't measure for fitment until you are sure the angle is dialed in.
Basically you want the pinion pointing up into the drivesahft, about 1-2 degrees below the centerline.

Good luck.

Paul
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Sorry, should have looked at the pic closer. Your angle looks pretty much perfect from here, so I guess it's longer shaft time.

Just to be sure though, you should measure between the top of the axle tube and the bottom of the frame rail to make sure you're rocking 2.5" of lift at this point.
I know our springs sit high, especially in the beginning. And even have a problem sitting too high sometimes.
You'd be looking for approx 8 to 9 inches between the frame and axle.

Paul
 

sykanr0ng

Bronco Guru
Joined
Aug 11, 2014
Messages
5,363
You think you have vibration now, if you put an unbalanced driveshaft on it you will have a whole new definition of vibration.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
You think you have vibration now, if you put an unbalanced driveshaft on it you will have a whole new definition of vibration.

So true. I did a quick shorten for a ranch truck that got a divorced transfer case just for extra gearing while pulling a water trailer. I was a little off, thought good enough for a farm truck that won't see over 10 MPH. That was optimistic, shake was bad at 10. Max shake free speed was 5 MPH.

The driveshaft shop trues them to a couple of thousandths of being true and spin balances them. A little tack weld holds a washer in place for the balance weight. They are pretty touchy about getting them right.

Also the welds need to be spot on. There is a lot of torque, and a lot of speed. If it comes apart it will often take out other stuff besides itself. Exhaust, floors, brake lines, tailhousings, fuel lines, electrical, yokes, etc.
 
OP
OP
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sub3

New Member
Joined
Jun 5, 2017
Messages
21
Thanks for the help and i'll checkout 4xshaft.com! Next I need to stop being indecisive about my wheel options but thats a conversation for another thread :cool:
 

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sprdv1

Contributor
REBEL
Joined
Mar 8, 2007
Messages
81,734
Thanks for the help and i'll checkout 4xshaft.com! Next I need to stop being indecisive about my wheel options but thats a conversation for another thread :cool:

Lots of options.. don't get rid of them caps.. :)
 

Weevil

Full Member
Joined
Jun 13, 2011
Messages
314
You can go to a longer slip yoke and the big question is are the u joints lined up or is your spline off one tooth . That makes for ugly quick vibration
 
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