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Old 03-22-2012, 04:16 PM   #1
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Default How to stretch a Peterbilt 387 chassis- Questions

I read quite a few articles here that talk about stretching the frame. But I have simple question/s:

Obviously, how to stretch a Peterbilt 387 chassis? I mean, where to cut and stretch? Overall length should be 45 feet. Not concerned about wheel base length being long etc, longer the better.

Second, how much does a limo conversation company or any truck conversation company charge me for this stretch? This included chassis stretch, drive shaft, air lines etc. Basically, drive it out of there.
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Old 03-22-2012, 09:11 PM   #2
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I just got a quote for a local company to stretch my GMC 6500 4' between the cab and the rear axle of $2700. That is basically just frame, and add one section of driveshaft. Mine is hydraulic disc brakes, so lengthen the brake line and wiring. If anything the air brakes would be easier, nothing to bleed, but more money in fittings.

There are companies out there that specialize in that sort of thing, but I just found a local company that builds new roll backs and tow trucks and they can do it. I would think in any major metropolitan area there would be a company that is a body installer that can handle a frame stretch. I would think a limo company would not be my choice, they don't deal with anything as heavy duty as a class 8 truck.

I found a company a while back on racing junk that was advertising a 14' toterhome body built on your chassis for about 17k if I remember correctly. I could not find them when I looked just now. I'll post a link if I find them.

Good luck!
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Old 03-22-2012, 09:29 PM   #3
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Quote:
Originally Posted by vijay View Post
I read quite a few articles here that talk about stretching the frame. But I have simple question/s:

Obviously, how to stretch a Peterbilt 387 chassis? I mean, where to cut and stretch? Overall length should be 45 feet. Not concerned about wheel base length being long etc, longer the better.

Second, how much does a limo conversation company or any truck conversation company charge me for this stretch? This included chassis stretch, drive shaft, air lines etc. Basically, drive it out of there.
Search Hawk Engineering, they can help you out. I agree with the comments on the limo conversion company. I was involved in my Dad's hearse rental business for a while. The hearse builders also build limos. I've been to two factories ... I don't think the hearse/limo companies are capable of doing a class 8 stretch. Even if they do Hummers, Suburbans, and Excursions ... they aren't like big Pete.

"Not concerned about wheel base length being long etc, longer the better." Be very, very careful with the wheelbase, especially if you're going to 45 feet. Look at the capacity of your front axle. If its only 12,000#, you could exceed that very quickly with a long wheelbase that doesn't have much weight behind the rear axles, especially if you have two huge fuel tanks (like 150 gallons) under the cab doors (as far forward as possible) and have batteries, generator, and water tanks forward. You need to think about weight and balance, just like an air plane to make sure you don't overload your front axle.

Good luck. Keep us posted.
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Old 03-22-2012, 11:46 PM   #4
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Originally Posted by hot rod View Post
I found a company a while back on racing junk that was advertising a 14' toterhome body built on your chassis for about 17k if I remember correctly. I could not find them when I looked just now. I'll post a link if I find them.

Good luck!
Thanks you, if you find that company info please post back.
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Old 03-22-2012, 11:50 PM   #5
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Originally Posted by #90-GTSC View Post
"Not concerned about wheel base length being long etc, longer the better." Be very, very careful with the wheelbase, especially if you're going to 45 feet. Look at the capacity of your front axle. If its only 12,000#, you could exceed that very quickly with a long wheelbase that doesn't have much weight behind the rear axles, especially if you have two huge fuel tanks (like 150 gallons) under the cab doors (as far forward as possible) and have batteries, generator, and water tanks forward. You need to think about weight and balance, just like an air plane to make sure you don't overload your front axle.

Good luck. Keep us posted.
Yes, that makes sense, very good point. However, I need this project to be able to go a little off road. So, I really cannot have too much overhang.
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Old 03-23-2012, 01:01 AM   #6
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Wheel base will play into it just as much as rear overhang for off pavement use. The longer you stretch a frame and extend the wheel base, the more likely you are to high center, turning radius exceeds that of a battle ship, and stress on the frame rails increases exponentially. #90-GTSC is right on about front axle weight, Class 8 trucks are designed to carry their weight centered between the rear axles, and the majority of front axle weight comes from the tractor itself. Does not take to much to overload the axle on a conversion. Heavier axles are available, but expensive, ride hard and require wider wheels and tires to carry the weight. I am trying hard to keep my design for my conversion right at around 40' with probably 8-10 feet behind the rear wheels. This should give a better ride, improve maneuverability in campgrounds and on mountain roads here in the northwest. There are some very knowledgeable folks on this site that are happy to share what they know. Good luck with your project.

Dave
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Old 03-23-2012, 06:01 PM   #7
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I am trying hard to keep my design for my conversion right at around 40' with probably 8-10 feet behind the rear wheels. This should give a better ride, improve maneuverability in campgrounds and on mountain roads here in the northwest. Dave
Dave: Are you making any weight and balance calculations on your build? I not, I'd be willing to start a thread dedicated to weight and balance and use your build as an example. I've got experience from the airplance biz (hold commercial pilot's license) and have put together an Excel spreadsheet for this; but so far no truck to have numbers to play with. We can exchange posts here or emails.

Dick
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Old 03-24-2012, 12:51 AM   #8
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Dick, thanks for the offer, as I get closer I may well take you up on that. I am heading east to meet with some of the conversions builders in May, and trying to narrow down the buy, build, or somewhere in between options. I have pretty much worked out what we want in a coach, and now need to find if someone can build it for a reasonable price, or at least a weather proof shell, or if i will go at it alone..lol. Its now time to take my list of specifications and all my sketches and get serious about getting a design done on the computer. I am planning on modeling the entire project in 3d on my computer, including structural steel and all components. That way I can do a "walk through" of the design, and run a structural analysis of the framing to make sure i do not have any weak or overbuilt areas. I should be able to get a pretty good idea of the vehicles CG from the computer model, and it would be great to compare my results with your spreadsheet when i get to that point. I am planning on posting renderings and images of my electronic model as it progress to get some input from folks on the site. My upcoming trip to the conversion factories, along with all the kids moving out has given me a serious push to "officially" get this project started. Look forward to chatting with you,.
Dave
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Old 03-24-2012, 10:09 AM   #9
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I am heading east to meet with some of the conversions builders in May, and trying to narrow down the buy, build, or somewhere in between options. I have pretty much worked out what we want in a coach, and now need to find if someone can build it for a reasonable price, or at least a weather proof shell, or if i will go at it alone..lol.
As you talk to the coach builders, ask them what they do about weight and balance when they design a coach. I have never used any of the CAD software, but it would make sense to me that there be a feature in CAD software to automatically do the weight and balance as the various components are added to the design. You'd probably have to build a library of components and their weights (which is half of W&B), and of course the CAD system knows were you drop everything.
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Old 03-24-2012, 11:18 AM   #10
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I am also a pilot (ATP), I also have some experience with sail boat design, where centers of forces are equally important. I also know that weight distribution on performance cars has a direct impact on handling. So, aside from the risk of overloading the front axle, I would also think that rear axle placement has a direct impact on handling characteristics. Now I know that we don't do .9G turns with our recreational vehicles, but discovering that you have an inordinate amount of over/under steer, or to have the tail snap out when you suddenly try to avoid that moose in the road would be a rude awakening, to say the least. You will also be looking at affecting the load and wear of tires. All in all if it were me I would do a careful analysis of cg and place the rear axle as accurately as possible to achieve a desired weight distribution.
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