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bcarlson
02-15-2004, 06:28 PM
I've been wondering about this for a while, and now that we have a category, thought I'd ask about it. My girlfriends dad runs a few dump trucks, and is thinking about stretching the frame on one to add an axle. How accurate do the rails have to be to keep the truck tracking straight?

I guess what I'm asking is this: assuming you chop your frame in two, add a section, then weld it back together, do you just get it close then adjust your alighnment, or do you just get the cut and reassembly perfect to begin with? Thanks!

Ben

SecaTim
02-15-2004, 06:32 PM
I guess what I'm asking is this: assuming you chop your frame in two, add a section, then weld it back together, do you just get it close then adjust your alighnment, or do you just get the cut and reassembly perfect to begin with? Thanks!

Ben
You want to keep the frame as square as possible. This will aid in the final alignment. This is assuming that the strech will occur before the existing axle. If adding to the frame after the axle then you would be able to align any new suspention as needed .

Tim 8)

bcarlson
02-15-2004, 06:48 PM
Hi Tim,

yes, the cut would be made between the front and rear axles. I guess maybe what I'm asking is what is the margin of error? If I have a 24' frame 1/8" off in square, corner to corner, is that close enough? What is the error on trucks from the factory?

Can I make up for being off 1/8" in alignment?

Thanks

Ben

BRENT in 10-uh-C
02-15-2004, 06:50 PM
Stretching a frame rail is not that hard nor difficult to lay out. There are several ways to execute the process. BTW, if you ever have the need to splice two frames to make one, just cut through the middle of a bolt hole to give you a reference. Two half-circles from each side make a complete circle when the two frames are mated together.

Back to the truck frame. You can actually be off by approximately a 1/4 of an inch and still have enough movement in the tie-bolt of the spring to the spacer block and the housing pin. The same kinda applies with the front end especially if wedge plates are used when adjusting caster. Just as Tim said, a complete alignment should be performed to cover liability.

I hope that helps...

Boogiemanz1
02-15-2004, 09:25 PM
I have done this in the past. The bolt hole will work on both sides of the existing frame, but it is seldom your added section comes from the same vehicle. Of course you want it as accurate as possible, and X-ing the frame with a tape from the tie bolts of the rear end to the spindle of the frontaxle before and after will give you a way to square it. As for the frame cut, make it on an angle usually more than 45degree. The weld will be much stronger than a square cut. After the frame is stretched and welded together make a "fish plate" to fit on the inside or outside of the frame, longer than the addition by a foot on each end. drill holes thru the frame and the plate and bolt it on, careful to hold both ends and the addition. This will add lots of strength......John

Byron
02-16-2004, 03:36 AM
Technically if you are 1/8 (3mm) out on a corner to corner measurement you are only 1/2 the measurement out of square ie to bring the frame back to square you only need to pull the frame 1/16 (1.5mm) to make it square. This amount of movement is well within tollerance for any truck chassis. If the measurement is larger it is possible to "move" the frame into tolerance by using weld shrinkage to pull the frame to the required measurement. With metalshaping shrinkage from welding is the enemy but even the enemy can be put to use with experience.

Byron.

Dutch Comstock
02-17-2004, 07:21 PM
Car frames made untill the 1980`s were only made within 1/4 inch total runout end to end.The heavier trucks are no closer and can work well with less tolerance than this.String lines or clamped angle irons on your truck frame will keep it as close as it was made or closer.When stretching the frame you have to determine the gross weight you will be hauling versus the listed grose weight of the truck capacity.You sometimes have to fish plate a section of the frame double the length of the stretch to keep the load carring capacity the same. You also have to be carefull about the method of welding the frame.The mig weld does not penetrate well and will easily break if not done correctly.Stick welding with 7018 rod is the best.You also grind the weld bead flat so that a crack does not start at the raised weld bead. Dutch