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View Full Version : Lengthening a Semi Frame (single to tandem axle)



72sporty
03-02-2007, 09:59 PM
Just curious if anyone has any info, or does this professionally. I'm interested in the various methods employed. ie: tips, trick, & suggestions. I understand both the liabillty, and my capabilities. I also know it get's done all the time, and with the proper procedures it is not only do-able, but just as safe as at least 95% of the trucks running down the road today. I have a bad feeling a may have just opened the proverbial "can of worms" here, but this forum sees like a good place for a lively discussion. All opinons, comments, and advice, are welcomed and appriciated. Thanks, Adam

DetailerDave
03-02-2007, 10:23 PM
I used to work for several different companies that did frame mods. If we lengthened them, we doubled the frame at least 2 feet each side of the splice. We used formed hot-rolled plate channels inside the original frame.

72sporty
03-02-2007, 10:33 PM
Thanks Dave, Is it safe to assume the H.R. plates were bolted to the factory frame in front of, and behind the welded connection? Mag Drill, Frame bolts & Lots of torque? I'd hate to create a H.A.Z., and a stress riser in front of my plates, seems like it might defeat the purpose.

DDA52
03-02-2007, 11:50 PM
I did one for my mechanic. He did all the setup and I did all the welding. Basically, I did all the good stuff.:laugh:

It was done a little differently and quite a bit stronger than most. He had a steel fab company break two rails to match the frame rails and then break another set that fit inside the first rails and ran the length of the frame behind the cab. It was then stagger bolted every foot where there wasn't an axle hanger, spacer, suspension mount, etc. Lots of bolting and double framed = very strong.

I did all the welding with .045 Linc Outershield 71M and C-25. That is a pretty good wire for that, IMO. Very hot and it will burn in deep.

This truck was originally a single axle with 8' behind the cab. It was stretched the first time for one customer who backed out and another stepped up, but wanted another 5' added on. The last pic shows it ready for a tank body...that is what the upper rails/beams are for.

denrep
03-03-2007, 12:52 AM
Adam, What's the application? Don't forget your adding weight. Be careful, sometimes, due to complex axle loading and spacing laws, combined with the extra weight of the tandem components, payload capacity is hardly increased by adding an axle.

If you're really good or lucky you can find frame rail height that will nest with yours. It's cheating a little. What you have to do is push the outside rails apart and pull it back together with the bolts. There is no way around this slight "wave" as all US frames are spaced on an SAE standard of 34" outside. For example, if you hope to push your cut-off suspension with frame and crossmembers intact, into the trucks rails, you will have to spread the receiving rails apart. With this method you'll have to make clearance holes for rivet heads etc. But it is strong and fast. You also can cut one flange off of a reinforcement rail, what really counts is the vertical web. For a simple splice, try to make it at a crossmember, for strength.

Cab to axle dimension, try to stick with 48 60 72 78 84 96 102 108 120 126 138 144 or 156 inches, saves grief with body and hoist mounting. If the application is something like a dump truck try to double the rail all the way up close to the front (steering axle) spring hanger. This involves a lot of extra work to remove fuel tanks battery box and so on but makes for a much stronger frame. I have seen the cuts staggered from one rail to the other as well as a "step" rather than a simple square cut. I don't know if that helps or is necessary, add the overlapping rail instead.

Plan your cut carefully. You may be able to use lots of rail from the donor suspension assembly. Don't forget about driveshaft and hangers. They will be a big part of the stretch, try to plan so you can reuse as much as possible. Again, keep in mind body or hoist operating clearance. Sometimes this requires modifying or relocating crossmembers.

As mentioned; Lots of drilling and bolting. Try to avoid modifications at the tandem, there's probably an extra "H" in there plus lots of bolts and brackets. Don't overbuild your stretch.There is something to be said for a trucks ability to absorb twist and flex evenly.

Now, about brakes, tire size, driveshaft, and axle ratio, they have to be compatible.

Good Luck

72sporty
03-03-2007, 05:22 AM
Hey, Thanks for the info. Basically what we have is a KW origianally built to pull house trailers. I generally do fabricating work on thr Hyd. hitches, wheel lifts, escort ramps ect. Lately the trailer markets been slowing down around here, and I've been torchin apart fancy tool box/car ramp outfits to mount air slide fifth-wheel plates. Remounting mudflaps, tailight, and whatever else it takes to be able to haul houses & freight with the same truck. This truck inparticular was origianlly built for houses, not so much as air even being plumbed for trailer brakes. Because of the short wheelbase (more desirable for a shanty shaker) of the truck, with a single rear axle, and large sleeper you quickly run out of room for turning clearance with the 5th wheel. The plan is to buy a set of tandems at the salvage yard, torch the old & weld the new. This should give him alot more adjustment for his air-slide. My theroy is with a Smith torch set & a TB 302, almost anything is possible. Thanks for the replys, Adam

David R
03-03-2007, 06:10 AM
A few notes. Cut the side of the frame on a 45* (\) angle. Weld the pieces together with full penatration both sides. I use 7018. Plate top bottom and sides at least an extra foot past the joint. DO NOT weld the ends of the plates. This will create a place for the old frame to crack and not let the frame twist. I have done it many times. Use fine thread grade 8 bolts to hold the suspension to the truck. If you don't know how to sharpen a drill bit, this is when you will learn. A mag drill makes it easier, but you don't have to. Find a commom point on both sides of the frame and make all measurments from there.

Have fun
David

72sporty
03-03-2007, 08:41 AM
Thanks David, sounds like were on the same page. Adam

zapster
03-03-2007, 03:35 PM
Maybe you would like to box the frame at the meeting point by about a foot.. and have halfway be over the center of the meeting point??

Just a thought..

...zap!

lorenzo
03-03-2007, 04:47 PM
7816

This is pretty much how I would cut the frame for splicing. The gold sections represent the original OEM frame.... the blue is the section that will be bent to fit inside the OEM frame. I only had a few mins to do this so it's not too detailed. I left the gap large for ease of viewing. Also the bolt holes I placed didn't come out for some reason, I'll play with that after and re post if you'd like.

There are several things you may want to consider when doing this....

1. If you are buying a set of tandems out of the bone yard. See it you can have them cut the frame and several feet before the first axle. The advantage of buying a section of rame with the tandems already attached is that you can use pre-drilled O.E.M. holes on the Kenworth frame and pre-drilled O.E.M. holes on tandem frame to accurately measure the distance of the spread.

2. DO NOT splice the frame in the immediate area of the suspension and do not cut it where a cross member bolts up.

3. Depending on how long of a stretch you do you will also need to consider the fabrication of a new cross member to support the drive shaft

denrep
03-03-2007, 07:43 PM
It's interesting to see all the different theories on frame stretching and splicing. All of them will work and any argument of greater strength is probably mute, but I'm curious about the angle and step cut theories.

When I worked at a shop that did lots of them, all cuts where 90 degree. The goal would be to splice where a crossmember would end up. I think the reasoning was that this would be a rigid spot in the frame. I'm not sure. Regardless of truck make, we would use a new crossmember (Ford I think) that had a large flat flange that would bolt on each side of the splice.

Shop bent steel, even though readily available, was always a last choice, and used as reinforcement only. Frame rail, new or used was preferred. This was 30 years ago, the high strength (100,000+?) rails where just coming on. I remember a heavy Dodge that had been stretched at a welding shop. The workmanship was excellent, but they used HR plate, shop bent, chassis failed during a dump cycle.

When I wrote I was thinking about a dump truck stretch. That's a whole different animal, than on highway use. Your talking about rough terrain operation and then all the weight on the rear hinge, shaking, jerking and twisting while trying to dump the load.

The worst jobs where changing light highway tractors to dump trucks. That's when we would double, (or triple!) the rails way up to the front springs. This kind of radical reworking of trucks, like a lot of things, seems to have passed.

By the way, does your KW have a hand valve and TPV (tractor protection valve) installed? If not, your in for some plumbing too.

We're anxious to see it hooked to some paying freight, carry on!

DDA52
03-03-2007, 07:50 PM
The Sterling I did has a huge tank on it. IIRC the weight will be around 70,000# when fully loaded( no it is not road legal;) ). It spends 95% of its time getting the snot beat out of it off road and loaded. The frame cuts are all 90°. So far, no issues whatsoever.

David R
03-03-2007, 08:23 PM
I don't think there is anything wrong with 90* cuts, but I was taught in school to use the pic lorenzo posted. I have always done it this way. it spreads the load and gives a longer area for the stress to spread out. by the time you plate it one foot past, you end up with at least 3' of plate on each part. If it is reinforced, I doubt any thing done with good sound practices would have a problem.

David

72sporty
03-03-2007, 09:45 PM
Thanks to all, this virtual round is on me:drinkup: :drinkup: :drinkup:

It seems to me everone is reading the same play-book for the most part. That means alot in my book. I like the angle cut myself, but stopping the angle a liitle before the radius is pure genius. Seems like a wonderfull plan and well worth posting the question in this forum. I think it will make for an easier fit-up, and the end result will be a better weld joint.

In a perfect world the splice will be at least 18 to 24 in. in front of any suspension components, and the origianal driveshaft length will be maintained. Basically we will be adding length to the back of the truck only for the tandems.

The bonus prize will be if I can remount the hyd. hitch to the new back half so he can pull whatever his heart desires. Not that I'd try to convince him to spend a little extra money why were at it.;)

Any other thoughts or opinons are more than welcomed and appreciated, maybe someone else down the line will get some good info from this thread.

Thans again, Adam:cool2:

DDA52
03-03-2007, 11:29 PM
I don't think there is anything wrong with 90* cuts, but I was taught in school to use the pic lorenzo posted. I have always done it this way. it spreads the load and gives a longer area for the stress to spread out. by the time you plate it one foot past, you end up with at least 3' of plate on each part. If it is reinforced, I doubt any thing done with good sound practices would have a problem.

David

Of course, the way that Sterling was done, the weld was purely cosmetic.......what with 24' of inner liner/plate.:p :D ;) With that much inner liner, joint design isn't really a factor.:cool:

wello
03-04-2007, 05:10 AM
thanks lorenzo hope you don't mind i had a lend of your picture

heres another way of doing it
its the way we do all our chassis Lengthening at work
we do all cuts at 45 never any 90's and always put another rail inside
don't forget before cut or move anything make a mark on each rail from a square
section on chassis so you have a even point each side to work from

another tip if you have the old rail the suspension come off is to fold a piece of sheet and make a drilling template with the marks you do on the chassis for the centre of the suspension using a template saves alot of marking out



7840

lorenzo
03-04-2007, 09:49 AM
thanks lorenzo hope you don't mind i had a lend of your picture

:nono: How dare you....... go get your own sofware!!!!!!!!:nono:

:mad: The nerve of some people!!!:mad:

:laugh: :laugh: :laugh: :laugh: :laugh: :laugh:

Disclaimer, the author of this post would like to indicate that any feelings of anger, outrage or irritation that may have been conveyed to the readers of this forum, registered user(s) or guest(s), especially to the user named author of the quote contained here within this post, were and are done for humor value and not as an actual indication of one of the above fore mentioned negative feelings.

Disclaimer of the disclaimer, The author of this post as well as the author of the above disclaimer, whom are for all legal purposes one in the same person(s), but not the author of the quoted post written by the subject identified through the user name of "WELLO", would like to add that not only where all of the disclaimers contained here within this post added for the value of humor, they were also added with the sole intention of preventing any negative backlash which may have ensued the reading of a reply post with negative content that the author tried to offset with the use of icons, provided by the host to the user as a means of expression, yet ignored or not taken for face value by said reader(s) who as a reaction to the negative message of the original mentioned reply post by the author identified as "LORENZO" may respond in a negative manner his or herself, themselves, therefore setting off a long chain reaction of hate and anger filled reply post(s) to which more reply posts would be created, creating a snowball effect which could potentially lead to a nuclear war ending civilization as perceived by any individual(s), registered user(s) or guest(s) that may read this reply post.

DDA52
03-04-2007, 11:09 AM
dang....where is my magnifying glass??? Maybe I should have my legal dept check that out before I read it.:rolleyes: :laugh: :laugh: :laugh: :waving:

Sandy
03-04-2007, 11:33 AM
dang....where is my magnifying glass??? Maybe I should have my legal dept check that out before I read it.:rolleyes: :laugh: :laugh: :laugh: :waving:

Really tuff to read but looks like it says "end of life as we know it , because wello used his pic".

Wow, that's harsh.. :laugh:

denrep
03-04-2007, 01:20 PM
...Basically what we have is a KW origianally built to pull house trailers... with a single rear axle...The plan is to buy a set of tandems at the salvage yard...

Adam, Have you thought about frame lengthening and adding an air lift axle?

72sporty
03-04-2007, 01:35 PM
Yes, Thats an option, but not one the owner is real fond of.

wello
03-05-2007, 01:36 AM
:nono: How dare you....... go get your own sofware!!!!!!!!:nono:

:mad: The nerve of some people!!!:mad:

:laugh: :laugh: :laugh: :laugh: :laugh:

Disclaimer, the author of this post would like to indicate that any feelings of anger, outrage or irritation that may have been conveyed to the readers of this forum, registered user(s) or guest(s), especially to the user named author of the quote contained here within this post, were and are done for humor value and not as an actual indication of one of the above fore mentioned negative feelings.

Disclaimer of the disclaimer, The author of this post as well as the author of the above disclaimer, whom are for all legal purposes one in the same person(s), but not the author of the quoted post written by the subject identified through the user name of "WELLO", would like to add that not only where all of the disclaimers contained here within this post added for the value of humor, they were also added with the sole intention of preventing any negative backlash which may have ensued the reading of a reply post with negative content that the author tried to offset with the use of icons, provided by the host to the user as a means of expression, yet ignored or not taken for face value by said reader(s) who as a reaction to the negative message of the original mentioned reply post by the author identified as "LORENZO" may respond in a negative manner his or herself, themselves, therefore setting off a long chain reaction of hate and anger filled reply post(s) to which more reply posts would be created, creating a snowball effect which could potentially lead to a nuclear war ending civilization as perceived by any individual(s), registered user(s) or guest(s) that may read this reply post.
wow how long did it take to think up that Disclaimer Lorenzo its very well done
you have a great sense of humor :cool2:

littlefuzz
03-05-2007, 02:01 AM
geez, that's a he!! of a disclaimer LOL

lorenzo
03-05-2007, 05:00 AM
wow how long did it take to think up that Disclaimer Lorenzo its very well done
you have a great sense of humor :cool2:

:waving: Thank you for understanding my humor, it's all in good fun:waving:

wello
03-05-2007, 05:04 AM
:waving: Thank you for understanding my humor, it's all in good fun:waving:
thats what is all about learning and havin fun :waving:

wello
03-09-2007, 03:51 AM
here are some pics of how it can go wrong we got this truck in this with a bent and broken chassis all because of a job done lenghting the chassis
the 2 rails you'll see are the new inner rails were going to fit after we straighten the and repair the chassis
this is the bend in the rails a little hard to see
7938
this the crack from the bad job in the first place and also from having the pivot point to far back on a tipper
7939
7940
7941
and these are the rails were going to fit inside after repairs are done
7942