F600
Super Moderator
Joined: Apr 2004
Posts: 34,472
Likes: 2,799
Welcome to FTE.
What kind of help do you need?
You making a pickup out of an F600?
You a welder and wrench turner? Got 12 ton jacks, HD jack stands, plasma cutter, place to work out of the rain and mud?
You will find OEM F600 rear suspension to be quite "firm" when the truck is converted this way. I suggest you shop for an air ride suspension along with your other shopping.
What kind of help do you need?
You making a pickup out of an F600?
You a welder and wrench turner? Got 12 ton jacks, HD jack stands, plasma cutter, place to work out of the rain and mud?
You will find OEM F600 rear suspension to be quite "firm" when the truck is converted this way. I suggest you shop for an air ride suspension along with your other shopping.
Thread Starter
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New User
Joined: Feb 2017
Posts: 2
Likes: 0
F600
i was told it cud be cheaper to shorten the chassis and then existing driveshaft, than to cut a 8ft bed and ad 3ft more and weld it together. ..i dont know wut to do. I have a ex At&T truck that stil have a utility box with boom lift...that im giving it away... Freeeee
Laughing Gas
Joined: Jul 2000
Posts: 851
Likes: 15
From: Elkton, MD
if your worried about welding the frame, best bed is to move the suspension and related crossmembers forward and cut the extra length off the back of the frame, just make sure it's all square. I've had a few where they did this.
Laughing Gas
Joined: Jan 2008
Posts: 1,027
Likes: 4
There are excellent resources for frame shortening
But it is also a technique that requires a strong understanding of the right way asnd wrong way... where and how to cut and where and how to weld and where and how to reinforce
Safety is paramount and just cutting a frame apart and welding it back together without proper planning is a recipe for disaster
How and Why to Stretch or Shorten A Truck Frame -
How to properly shorten a frame on big truck??? - The Garage Journal Board
there are many threads on this out there..lots of research saves lots of headaches
This is an article I wrote about 15-20 years ago on frame modification... I hope you might find it helpful
Lately there have been some questions about frame lengthening/shortening and splicing. This thread is a compilation of what I know and some research I did. Please add your experience to it and Ill try to get it cleaned up and into the tech section eventually... As always with any modification it is the end users responsibility to make modifications that are safe.
Any frame modification not done by a certified company voids any manufacturer's warranty//// like we care after what we do to our trucks
Truck Frames
The frame is the "backbone" of the truck.. The frame supports engine, cab, transmission, fuel tanks, and all other components, including the payload. It is also the bridge that connects the front and rear axles, allowing a useful tool for transportation.
The two basic requirements of a truck frame are sufficient strength to perform the intended job and the rigidity to provide a platform for the truck. It should also provide stability, safe operation, and operator comfort.
Truck frame strength is the structure's ability to resist yielding, buckling, fracture, and fatigue.
The section modulus (SM) is an engineering term that indicates the strength of a frame by the shape of its section. The SM in truck frames relates to vertical loads on the frame rail, and is expressed in in3. The SM of a typical frame section is calculated by this formula:
SM=(BxH3)-(bxh3) 6H
SM= section modulus B=outside flange length H=outside web length b=inside flange length h=inside web length
RBM (resisting bending moment) is the product of the material yield strength and the section modulus of one side member. RBM is used as a means of comparing the relative strength of side members with different geometry and fabricated from different materials. RBM equals SM multiplied by yield strength of material.
Frame Modifications Frames are modified to change wheelbase, alter the use of the vehicle, and to repair damaged areas.
Before modifying a frame, certain facts should be known: what the vehicle will be used for, front and rear axle ratings, wheelbase, CA/CT, frame dimensions, frame specs, frame condition, and whether the frame is straight or tapered, or a single or double. It also must be determined what should be done to make the truck fit its vocation, and how will the modifications affect the truck. Safety factors also must be taken into account.
Before modifying a vehicle, it should be inspected. The vehicle should be driven to detect vibrations, handling problems, and whether it turns equally left or right. The alignment of the rear axle or axles should be checked. Inspect the frame to see if it is straight, damaged, level, and assess its overall condition.
Wheelbase Increase/Decrease The load on the frame can increase directly with an increase in wheelbase if there is no change in axle rating or vocation. A 10% increase in wheelbase will likely increase the frame loading (bending moment) by the same amount..
Tapering, Staggering Essential in Frame Splicing
Which frame splice is the strongest: Straight butt joint? Staggered butt joint? Or tapered butt joint?
There is no correct answer. They're all the same based upon all factors being equal, skill of weldor, type of frame on and on...
If the frame is not properly reinforced, it doesn't matter which type of splice is used because the joint on the bottom of the frame will fail from fatigue.
The bottom rail is in tension... It's being pulled apart. The weld we put on the bottom rail is going to fail first. That's why it doesn't matter what kind of butt joint you put in.
The general rule is that reinforcements should taper a minimum of two times the frame height - which fits into Volvo's,(heavy duty tractor trailer formula but a good one for us to look at), recommendation of 20-30 degrees, 20 being 2.7 times the frame height and 30 being 1.7 times the frame height. So for a 9" frame, you go 18" each way and taper from there.
Stiff to flexible is bad... You want to spread the stress out as much as you can. Any kind of tapering you can put on is good. Sometimes you have to take off cross members and shorten them. Sometimes you get away without it.
The Seven Commandments
Frame-splicing commandments:
Don't go from stiff to flexible. Taper and stagger reinforcements. If you're in a situation where you're putting an inside reinforcement on and an outside reinforcement on, stop them in different places. Taper, taper, taper. Stagger, stagger, stagger.
Stay out of high-moment areas or extend reinforcement to a lower-moment area. That's when you're working on a straight truck and you know you're going to have to do something behind the cab. Get as far up under the cab as you can. It's amazing how frame moments drop off when you get under the cab.
Match steels for yield strength as closely as possible.This isn't always easy to do.. so as a rule of sum plain mild steel has about 1/2 the strength of more specialized available steels,,, just make sure its weldable and if so..how.
Extend reinforcements a minimum of twice the frame height past the splice before beginning the taper.
The strength of a frame rail is in the flanges. I can't repeat that enough times.
More steel is stronger than less steel. If there's a question, increase the gauge. Increase something. When you're putting a reinforcement on a truck, the difference between, say, 1/4" steel and 3/8" steel weight wise is next to nothing. If you're putting a 3' piece on, the weight change is nothing.
Using a straight cut at the splice is acceptable if you stagger fish plating and/or secondary frame pieces...
Body Mounts
The purpose of body mounts is to attach the body to the truck frame and prevent the body from moving on the truck frame in a horizontal direction - forward, rearward, and laterally. Rear mounts could be shear plates or some other rigid configuration that prevents movement. Front mounts should be flexible or placed to avoid stress concentrations in high-moment areas.
Mounts can be combined to take advantage of the best features of more than one type. Spacer strips used between the body and truck frame perform multiple functions: cushioning member, sacrificial wear member, and stress-spreading member. Rigid mounts should be used at the rear and flexible mounts at the front. The front mount should not be at the front of the body.
If U-bolt body mountings work, such as in a custom flatbed... use them. But a strong caution.
I've seen more damage done to truck frames with U-bolts than any other single type of mount, A mechanic gets under there and says, ‘That looks loose.’ He puts the air gun on it and torques it until he collapses the frame rail.”
Even though U-bolt body mountings are popular, they are among the least effective mounting systems. If they are used, proper frame spacers must be used. Some of the problems: loosening, not preventing forward movement of the body, and frame damage.
Sometimes they don't have the right size U-bolt, so they notch the frame flanges. As you can imagine, there aren't many ways you can concentrate stress better than that. If the truck lives its life driving around the city at 30mph never fully loaded, that will probably live. Off road doing the Rubicon with the bed rubbing every rock may be another story entirely
On stress concentration the 6th Power Effect holds that doubling the stress decreases the truck's life by a factor of 64. Therefore, a 300,000-mile truck becomes a 5,000-mile truck. Reducing the stress by 10% doubles the life, and increasing the stress by 10% halves the life.
That 10% change is not a lot.
Most ford trucks use ladder-type frames with side rails and cross members. Frames are subjected to three types of loads: vertical, torsional, and side.
Side rails support vertical and side loads such as engine, transmission, fuel tanks, battery boxes, suspensions, bodies, work equipment, and cargo. The cross members provide torsional rigidity and support components such as the engine, transmission, and radiator. In addition, the cross members prevent the side rails from twisting with side loads such as the fuel tank and battery boxes.
Frame strength is described through yield strength, section modulus, and Resisting Bending Moment (RBM). Yield strength defines the material and is the maximum stress, in pounds per square inch, that the material will sustain without permanent distortion. Typical values are 35,000 psi for mild steel, 80,000 for alloy steel, and over 100,000 psi for heat-treated steel. Section modulus defines the shape of the frame material in inches cubed and is related to frame stiffness and flexing. Chassis manufacturer-published section module literature can be as much as 30% too high. RBM is the product of the section modulus and yield strength in inch-pounds, which describes the ability of the frame to carry loads.
part 2 to follow..................
PART 2
From American Trailer Builders Association
FRAME LENGTHENING OR SHORTENING
SUGGESTED CUTTING AND SPLICING PROCEDURES
1. Be sure the frame to be modified has been checked and is straight.
2. Preferred cut of frame rail is 45 degrees, but vertical cuts are often used.
3. Clean up and grind each side with a slight chamfer.
4. Match up two mating pieces and make sure frame is being held straight length ways and side
ways
5. Before welding pre-heat frame rails on both sides of splice 6 to 10 inches, keeping heat from 75 to 175 degrees.
Also to track the amount of heat being placed on the frame rail you can use a 125 to 175 degree Temp Stick, if you want to do it the lo-buck FTE
way then
drop a few drops of water on the rail and when it sizzles the temp should be about right.
6. Weld frame rail web by starting at the center and moving up or down, which will help keep the
joint warm. Weld flange by starting at the flange radius moving towards the inside edge. Weld both sides of
web and flange. The bottom of lower flange should be welded before the upper part. Also keep the inner and
outer weld bead equal, this will minimize stress and possibility of cracks around the small web.
7. Grind down welds inside and outside. Then warm up rail as was done in pre-heat so as to
relieve all welding stress that was built up. Post heating does not require as much heat as pre-heat.
8. Reinforce weld with channel, “L” or plate. Weld reinforcing on the vertical plane. When using
channel or “L” as reinforcing it is not necessary to weld horizontal. One of the main reasons for reinforcing the
weld especially when lengthening is that sometimes it is hard to find the same type of materials that is in the
frame. Therefore material that is very close to what is on the truck has to be used. This can cause the
penetration of the weld to be slightly different from one side to the other. The reinforcing is also an insurance
for the weld.
Thats what I know...
Ultra shorty F600s are cool.. but as Sam said they get stiff at an 8 foot bed.. which means an even shorter C/A.. like 72"... I think his idea of air suspension would be right on
But it is also a technique that requires a strong understanding of the right way asnd wrong way... where and how to cut and where and how to weld and where and how to reinforce
Safety is paramount and just cutting a frame apart and welding it back together without proper planning is a recipe for disaster
How and Why to Stretch or Shorten A Truck Frame -
How to properly shorten a frame on big truck??? - The Garage Journal Board
there are many threads on this out there..lots of research saves lots of headaches
This is an article I wrote about 15-20 years ago on frame modification... I hope you might find it helpful
Lately there have been some questions about frame lengthening/shortening and splicing. This thread is a compilation of what I know and some research I did. Please add your experience to it and Ill try to get it cleaned up and into the tech section eventually... As always with any modification it is the end users responsibility to make modifications that are safe.
Any frame modification not done by a certified company voids any manufacturer's warranty//// like we care after what we do to our trucks
Truck Frames
The frame is the "backbone" of the truck.. The frame supports engine, cab, transmission, fuel tanks, and all other components, including the payload. It is also the bridge that connects the front and rear axles, allowing a useful tool for transportation.
The two basic requirements of a truck frame are sufficient strength to perform the intended job and the rigidity to provide a platform for the truck. It should also provide stability, safe operation, and operator comfort.
Truck frame strength is the structure's ability to resist yielding, buckling, fracture, and fatigue.
The section modulus (SM) is an engineering term that indicates the strength of a frame by the shape of its section. The SM in truck frames relates to vertical loads on the frame rail, and is expressed in in3. The SM of a typical frame section is calculated by this formula:
SM=(BxH3)-(bxh3) 6H
SM= section modulus B=outside flange length H=outside web length b=inside flange length h=inside web length
RBM (resisting bending moment) is the product of the material yield strength and the section modulus of one side member. RBM is used as a means of comparing the relative strength of side members with different geometry and fabricated from different materials. RBM equals SM multiplied by yield strength of material.
Frame Modifications Frames are modified to change wheelbase, alter the use of the vehicle, and to repair damaged areas.
Before modifying a frame, certain facts should be known: what the vehicle will be used for, front and rear axle ratings, wheelbase, CA/CT, frame dimensions, frame specs, frame condition, and whether the frame is straight or tapered, or a single or double. It also must be determined what should be done to make the truck fit its vocation, and how will the modifications affect the truck. Safety factors also must be taken into account.
Before modifying a vehicle, it should be inspected. The vehicle should be driven to detect vibrations, handling problems, and whether it turns equally left or right. The alignment of the rear axle or axles should be checked. Inspect the frame to see if it is straight, damaged, level, and assess its overall condition.
Wheelbase Increase/Decrease The load on the frame can increase directly with an increase in wheelbase if there is no change in axle rating or vocation. A 10% increase in wheelbase will likely increase the frame loading (bending moment) by the same amount..
Tapering, Staggering Essential in Frame Splicing
Which frame splice is the strongest: Straight butt joint? Staggered butt joint? Or tapered butt joint?
There is no correct answer. They're all the same based upon all factors being equal, skill of weldor, type of frame on and on...
If the frame is not properly reinforced, it doesn't matter which type of splice is used because the joint on the bottom of the frame will fail from fatigue.
The bottom rail is in tension... It's being pulled apart. The weld we put on the bottom rail is going to fail first. That's why it doesn't matter what kind of butt joint you put in.
The general rule is that reinforcements should taper a minimum of two times the frame height - which fits into Volvo's,(heavy duty tractor trailer formula but a good one for us to look at), recommendation of 20-30 degrees, 20 being 2.7 times the frame height and 30 being 1.7 times the frame height. So for a 9" frame, you go 18" each way and taper from there.
Stiff to flexible is bad... You want to spread the stress out as much as you can. Any kind of tapering you can put on is good. Sometimes you have to take off cross members and shorten them. Sometimes you get away without it.
The Seven Commandments
Frame-splicing commandments:
Don't go from stiff to flexible. Taper and stagger reinforcements. If you're in a situation where you're putting an inside reinforcement on and an outside reinforcement on, stop them in different places. Taper, taper, taper. Stagger, stagger, stagger.
Stay out of high-moment areas or extend reinforcement to a lower-moment area. That's when you're working on a straight truck and you know you're going to have to do something behind the cab. Get as far up under the cab as you can. It's amazing how frame moments drop off when you get under the cab.
Match steels for yield strength as closely as possible.This isn't always easy to do.. so as a rule of sum plain mild steel has about 1/2 the strength of more specialized available steels,,, just make sure its weldable and if so..how.
Extend reinforcements a minimum of twice the frame height past the splice before beginning the taper.
The strength of a frame rail is in the flanges. I can't repeat that enough times.
More steel is stronger than less steel. If there's a question, increase the gauge. Increase something. When you're putting a reinforcement on a truck, the difference between, say, 1/4" steel and 3/8" steel weight wise is next to nothing. If you're putting a 3' piece on, the weight change is nothing.
Using a straight cut at the splice is acceptable if you stagger fish plating and/or secondary frame pieces...
Body Mounts
The purpose of body mounts is to attach the body to the truck frame and prevent the body from moving on the truck frame in a horizontal direction - forward, rearward, and laterally. Rear mounts could be shear plates or some other rigid configuration that prevents movement. Front mounts should be flexible or placed to avoid stress concentrations in high-moment areas.
Mounts can be combined to take advantage of the best features of more than one type. Spacer strips used between the body and truck frame perform multiple functions: cushioning member, sacrificial wear member, and stress-spreading member. Rigid mounts should be used at the rear and flexible mounts at the front. The front mount should not be at the front of the body.
If U-bolt body mountings work, such as in a custom flatbed... use them. But a strong caution.
I've seen more damage done to truck frames with U-bolts than any other single type of mount, A mechanic gets under there and says, ‘That looks loose.’ He puts the air gun on it and torques it until he collapses the frame rail.”
Even though U-bolt body mountings are popular, they are among the least effective mounting systems. If they are used, proper frame spacers must be used. Some of the problems: loosening, not preventing forward movement of the body, and frame damage.
Sometimes they don't have the right size U-bolt, so they notch the frame flanges. As you can imagine, there aren't many ways you can concentrate stress better than that. If the truck lives its life driving around the city at 30mph never fully loaded, that will probably live. Off road doing the Rubicon with the bed rubbing every rock may be another story entirely
On stress concentration the 6th Power Effect holds that doubling the stress decreases the truck's life by a factor of 64. Therefore, a 300,000-mile truck becomes a 5,000-mile truck. Reducing the stress by 10% doubles the life, and increasing the stress by 10% halves the life.
That 10% change is not a lot.
Most ford trucks use ladder-type frames with side rails and cross members. Frames are subjected to three types of loads: vertical, torsional, and side.
Side rails support vertical and side loads such as engine, transmission, fuel tanks, battery boxes, suspensions, bodies, work equipment, and cargo. The cross members provide torsional rigidity and support components such as the engine, transmission, and radiator. In addition, the cross members prevent the side rails from twisting with side loads such as the fuel tank and battery boxes.
Frame strength is described through yield strength, section modulus, and Resisting Bending Moment (RBM). Yield strength defines the material and is the maximum stress, in pounds per square inch, that the material will sustain without permanent distortion. Typical values are 35,000 psi for mild steel, 80,000 for alloy steel, and over 100,000 psi for heat-treated steel. Section modulus defines the shape of the frame material in inches cubed and is related to frame stiffness and flexing. Chassis manufacturer-published section module literature can be as much as 30% too high. RBM is the product of the section modulus and yield strength in inch-pounds, which describes the ability of the frame to carry loads.
part 2 to follow..................
PART 2
From American Trailer Builders Association
FRAME LENGTHENING OR SHORTENING
SUGGESTED CUTTING AND SPLICING PROCEDURES
1. Be sure the frame to be modified has been checked and is straight.
2. Preferred cut of frame rail is 45 degrees, but vertical cuts are often used.
3. Clean up and grind each side with a slight chamfer.
4. Match up two mating pieces and make sure frame is being held straight length ways and side
ways
5. Before welding pre-heat frame rails on both sides of splice 6 to 10 inches, keeping heat from 75 to 175 degrees.
Also to track the amount of heat being placed on the frame rail you can use a 125 to 175 degree Temp Stick, if you want to do it the lo-buck FTE
way thendrop a few drops of water on the rail and when it sizzles the temp should be about right.
6. Weld frame rail web by starting at the center and moving up or down, which will help keep the
joint warm. Weld flange by starting at the flange radius moving towards the inside edge. Weld both sides of
web and flange. The bottom of lower flange should be welded before the upper part. Also keep the inner and
outer weld bead equal, this will minimize stress and possibility of cracks around the small web.
7. Grind down welds inside and outside. Then warm up rail as was done in pre-heat so as to
relieve all welding stress that was built up. Post heating does not require as much heat as pre-heat.
8. Reinforce weld with channel, “L” or plate. Weld reinforcing on the vertical plane. When using
channel or “L” as reinforcing it is not necessary to weld horizontal. One of the main reasons for reinforcing the
weld especially when lengthening is that sometimes it is hard to find the same type of materials that is in the
frame. Therefore material that is very close to what is on the truck has to be used. This can cause the
penetration of the weld to be slightly different from one side to the other. The reinforcing is also an insurance
for the weld.
Thats what I know...
Ultra shorty F600s are cool.. but as Sam said they get stiff at an 8 foot bed.. which means an even shorter C/A.. like 72"... I think his idea of air suspension would be right on
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