Frame Stretch

[mattb73lt]

I was looking for some imput on how to best do a frame stretch.

I have a fairly short wheel base 1960 B-73LT(L cab) and am going to stretch it into a car carrier for my antique cars. What I have for a body is a late 70's Jerr Dan roll back that was mounted to a Ford truck. I saved everything from the Ford from the cab back and it's all still mounted to the frame.

The Mack frame is about an inch shallower than the Ford frame and the outside measurements are about 1/4" less than the inside measurements on Ford frame. This would allow the two frames to slide together and by placing two 1/8" shims down the length of the joined areas, take up the difference.

I was thinking about doing the stretch in this manner, then using body bound bolts, bolt the whole thing together using the cross member patterns and a logical bolt pattern in-between for maximum strength.

The reasons for method were to simplify and speed up the mounting of the body, since it's already mounted to the frame and to create a double frame for more strength due to the increased wheelbase.

The dimensions of the two frames are so close to allow this. Once alligned,squared and joined, I would use all Mack components for the drive line.

In theory, it would seem the best way to proceed, but I'm also thinking safety and not creating something dangerous. Also, if I ever sold it, it would be very easy to separate and return to it's original configuration if so desired by the new owner, leaving the frame very unmolested.

Looking for some thoughts and possible alternate methods?

Thanks, Matt

[David]

Sounds like a plan. How much overlap will you have? Sounds like the Ford frame will come up to the back of the cab. Very easy place to hide the exposed end of the frame. Most important thing is to make sure it's square.

[mattb73lt]

About six feet of overlap. I was planning to bring the Ford frame as far up to the cab as possible. Trimming as neccessary to avoid interferance and remounting issues with fuel tanks. Geometry is a concern to keep it as square as possible.

[Freightrain]

Here's how I did mine:

http://www.bigmacktrucks.com/index.php?/topic/16282-adding-air-ridestretching-frame/

Bolted it together, with about 5ft of overlap. Got near two years on it now and no problems.

[mattb73lt]

Yeah, that's what I had in mind. Much longer wheelbase,though, due to the body length. I was going to demount the body, blast,prime and trim/repair the donor frame. Repair the B-73 frame, as it had tandems installed at one time, then mate the whole thing together as you did and remount the body to complete it.

[Vladislav]

What is a gear-to-axle bolt arrangement of tandems?

It there are 8 bolts and the ratio is about 7-8 I could be in interest for tandem gears.

Vlad

[mattb73lt]

It was a late 60's R model tandem, wedge brakes and about a 9:1 ratio out of a USAF fuel truck. Not very desirable, unless you needed about a 40 MPH truck. And they are long gone now, sorry.

[220cummins]

Yeah, that's what I had in mind. Much longer wheelbase,though, due to the body length. I was going to demount the body, blast,prime and trim/repair the donor frame. Repair the B-73 frame, as it had tandems installed at one time, then mate the whole thing together as you did and remount the body to complete it.

With a much longer frame and use of a roll off(high center of gravity when in use) I would recommend "z" cut, stagger joints, and weld (SMAW-ROD NOT MIG) the existing frame rails to desired length. Then slip an inner frame to the whole length bolted to the outer extended frame. Always bolt together inner and outer rails with grade 8 fine tread nuts and bolts. just my .02 cents