Frame straightening

[Bigsweet75]

Good afternoon to all,

The 1931 Briggs four-door I purchased had what appeared to be a restored chassis, including a rebuilt engine with 1500 miles on it most of the hydraulic brakes set up, but the body was original. I replaced all the wood in the floor of the body including the two main runners and cross sections. I had the body sandblasted then I primed and painted it. I attached the splash aprons and front fenders to the chassis put the rear fenders on the body started bolting everything down, but things didn’t seem to be lining up quite right. I set the body on the chassis and put the 4 doors on. I realized as you can see in the pictures that I should run a string line along the underside of the driver side rail. Each end the string is set 1 1/2” away from rail. Though at about the rear motor mount section of the driver side rail there is only 3/8” gap. My math says she’s sagging 1 1/8”! I’m guessing I’ve got to take the body off again then remove splash, aprons, and fenders. I just read about a method to straighten the frame by putting heavy timbers or railroad ties on the ground with chains around them and bottle jacks position at the rear motor mount location of frame to remove the sag.
Curious if anybody has any advice?

[Keith True]

That frame is tapered,not straight.you need to put the string on TOP of the frame,not the bottom.The top is flat front to rear,the bottom is not.You can do it with the body propped up a bit.

[nkaminar]

If you do need to straighten the frame, you will have to have a frame alignment jig or take it to a shop that has one. Or you can chain the frame down to a concrete pad with heavy duty anchor bolts in the concrete and use a 20 ton hydraulic bottle jack. Or you can try the heavy timber route.

Some people will use heat and quenching to straighten the frame, claiming that it does a better job and does not stretch the frame like a jack will, although the jack will stretch the frame very slightly.

It is typical for the frame to be hour glass shaped at the rear engine mounts. Lots of people have a jack that spreads the frame there to install the engine.

[Bigsweet75]

I just assumed I could use the bottom of the frame, I didn’t know it was tapered.
I will raise up the body and check the topside of the frame.

[Keith True]

The frame is tapered up at the rear,and it is tapered up at the front.You can see it clearly in your picture of the front half.You just need to put your string and blocks on the top side.They do straighten pretty easily,if you use a bottle jack don't just put the post against the frame.You will kink it if you do.A piece of steel,about 2 inches wide,6 long,and 3/4 thick on top of the post will spread the pressure.If it is a severe bend there are ways to heat/cool/shrink the bottom chord of the rail,but first see how serious it really is.

[kenparker0703]

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I have a"jig" made from a 8 ft long 8" H beam. A set of clamps are made to clamp to the frame (even with the body on), then chains go from clamps to H beam. A 20 ton bottle jack does the lifting.


Your frame is tapered at the front and rear, so, place your 2 x 4 blocks, front and rear, under the frame where the frame is EXACTLY 3" deep. The frame will be 4" deep at the motor mount. Measure the 'frame sag" from the top rail - not the bottom rail. Top rail is originally straight.


When you start lifting place a steel block or spacer inside the frame at teh point of the jack. You want to prevent the flange of the frame from bending upward leaving the web of the frame crooked. Web and flange must move together.


It will take several "lifts". one 8-10 inches in front of the motor mount, two at the motor mount, three 8 - 10 inches behind the motor mount. The maximum sag on your frame will be at the motor mount.


Keep in mind, as the frame has sagged it has also stretched in length. Your unsagging it will not return the length to factory. We are talking about maybe a 1/32" to 1/16" stretch - no big deal.\


The alternative is to use heat and alternate cool to unstretch the metal. Not an easy task. good luck, ken

[Ordsgt]

As far as your car has been disassembled I would recommend you take the frame to a body shop to check it. I was in a minor accident and found the frame had some bending. The frame bent back fairly easy with no heating

[ratamahata]

Henry designed the model A frame like the model T... both riveted, so the frames would flex easily on early dirt roads...Take note if the front ot rear suspension were not equally side by side for some reasons or the car is not seat very well on the ground all the meditions would change...

[Chuck Dempsey]

You might have seen these already, but here are some 'Barn threads from the past -

https://www.fordbarn.com/forum/showt...+straightening

https://www.fordbarn.com/forum/showt...road&showall=1

https://www.fordbarn.com/forum/showt...245#post146245

...and one youtube...

https://www.youtube.com/watch?v=eqIK7yMtlsE

[rotorwrench]

The bottom rail flange is the one that stretches. The upper rail flange compresses in the average front rail sag deviation. Heat the stretched side during the straightening process and it will remove the stretch by compressing it back to shape and helping the compressed side stretch back to normal. It may grow a little but it depends on how a person goes about straightening things.

The only good way to straighten a frame is with the body removed. A bare frame is easier to handle so that makes it a lot easier. Wreck damage is more difficult to repair than normal sag deviation but smooth bend damage can generally be repaired. Frame rails can be patch reinforced in problem areas but purists usually avoid splicing or patching frames. Good frames are a lot harder to find now than they were twenty or thirty years ago. It also leads to title difficulties if the left rail or frame is replaced.

[BRENT in 10-uh-C]

Originally Posted by Bigsweet75

Good afternoon to all,

The 1931 Briggs four-door I purchased had what appeared to be a restored chassis, including a rebuilt engine with 1500 miles on it most of the hydraulic brakes set up, but the body was original. I replaced all the wood in the floor of the body including the two main runners and cross sections. I had the body sandblasted then I primed and painted it. I attached the splash aprons and front fenders to the chassis put the rear fenders on the body started bolting everything down, but things didn’t seem to be lining up quite right. I set the body on the chassis and put the 4 doors on. I realized as you can see in the pictures that I should run a string line along the underside of the driver side rail. Each end the string is set 1 1/2” away from rail. Though at about the rear motor mount section of the driver side rail there is only 3/8” gap. My math says she’s sagging 1 1/8”! I’m guessing I’ve got to take the body off again then remove splash, aprons, and fenders. I just read about a method to straighten the frame by putting heavy timbers or railroad ties on the ground with chains around them and bottle jacks position at the rear motor mount location of frame to remove the sag.
Curious if anybody has any advice?

It is yours to do as you wish however that is NOT how I would, -or do it. My reasoning is your frame has already been bent in one area causing the sag. Now you are going to take a jack and force the frame rail where it bends in another area?? If so, now you have a frame bent in two areas. If your frame is bent in three areas and you use a jack, now you have six bent areas!

If you study the metallurgy, you will realize that metal can stretch or shrink using heat however it will not shrink when it is cold and then stay at the shrunken dimension when the temps normalize. So why not just use heat to shrink the stretched area(s) on the frame??

[daveymc29]

If you study the metallurgy, you will realize that metal can stretch or shrink using heat however it will not shrink when it is cold and then stay at the shrunken dimension when the temps normalize. So why not just use heat to shrink the stretched area(s) on the frame??

Is this exactly what you meant to say?

[Oldbluoval]

It’s Brent’s statement so he’ll have to respond but……
My experience with sheet metal is exactly as he states. I’ve found you do have to quench metal while hot to shrink
I have little experience with shrinking metal the gauge of frame however

[rotorwrench]

I recently read a lot of Pluck's Model A Frame Study. It is a complicated history so it is not an easy read. In a previous discussion on frames, the condition and thickness of the frame material came up and it was mentioned to be 8 gage thickness which is confirmed by the study. It actually falls withing a decimal range that is nearest to 8 gage (US Standard Revised Gage). The study shows that the range changed at least once during production in reference to the rails specifically but it wasn't a major change. I measured my 1929 frame rails and it is very close to the 0.1644" but varies a little. A person has to remember that these frame rails were stamped with a relatively deep draw and that tends to stretch the metal in the bend area of the stamping. It was most likely a 1008 cold rolled steel with at least some draw qualities. Draw quality steel is usually aluminum killed or referred to as something like AKDQ. This steel is not especially strong but receives a lot of its strength by the way it is formed into a structural U- channel member. It also gets some work hardening by the way it is formed with huge presses and dies so it was determined to be strong enough to get the job done with reliable long term service under moderate road conditions such as were the norm in 1927/28.

This is basically what we have to work with after adding 90+ years of both service and sometimes harsh environmental conditions. A rusty frame is going to be weaker than a clean rust free one so a lot depends on condition of the frame to be straightened. Steel can be worked, normalized, and shot peened to restore it's integrity so application of heat is not that big a problem but the amount of heat applied is a learned skill that will have an effect on the overall outcome of the process. A person should learn all they can about a process like this before trying to tackle it.

[daveymc29]

Originally Posted by Oldbluoval

It’s Brent’s statement so he’ll have to respond but……
My experience with sheet metal is exactly as he states. I’ve found you do have to quench metal while hot to shrink
I have little experience with shrinking metal the gauge of frame however

Thanks, I reread it. This time seems correct. Sorry.

[Tinbasher]

Brent way of repairing the frame works really well. I've done 4 that way and had great success with it. One thing I've learn't over the years is there many different ways to get to a finished product. The trick is to find the best one for you. JP

[goodcar]

OK, two ways of straightening the frame, heating and bending have been discussed. So exactly how does one do it with heat. Raise the body?? What do you use for heat, acetylene, propane, what?? Do you somehow then measure to get to a certain temp? Then spray with cold water?

[Oldbluoval]

Ok…guilty of assuming. We all know what happens when we “assume”
I was assuming the body was off. I know older frame shops, before unibody, straightened on a machine that basically bent them straight.
I couldn’t straighten a Model A frame with the body on…….easily as I now perceive it.

[rotorwrench]

Every disfiguration or deviation from original shape is going to be different in how a person goes about straightening. The frame is a C-channel so it has two flanges and a web in between. Which part of the C-channel is affected is what determines a course of action. Very minor deviations can be corrected cold but a person needs to look for bends & puckers after it is back to it's original dimensions. If they are minimal, that's a good thing. When things are bent beyond cold straightening the a course of action may require heat to bend and shrink.

The low phase transition temperature is around 1200 degrees F. This is basically the never exceed temperature. Steels start to turn a dull perceptible red color around 900 degrees F so it would be safe not to heat things too much above that with out close monitoring with infrared temp sensing equipment. Only apply heat to the affected area. Try bending before it gets red and see if it yields or not. When shrinking, a person should apply the same logic but application of air blast to cool should be done at a lesser temperature to prevent crystallization. I wouldn't use water on something that thick. In other words let it cool down to 500 degrees F or less depending on the steel type. A person can hammer a pucker a little bit as long as there is no dolly involved. This is hot shrinking and it has to be done with minimal blows and limited hammer force. All I can say about experience level is that a person should experiment with something similar before attempting any of this stuff. Folks that do it for a living know what they can and can't do.

The model A rails could be 1008 or 1010 cold rolled but I don't know what it is for certain. Hot correction is limited on steels like this. It will lose strength if worked more than once. A person should be prepared to install a fish plate made from an old culled out frame rail to get reinforcement for weakened members. If this is not wanted or not possible due to interference then find another good frame somewhere.

[goodcar]

Thank you.