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Old 04-06-2013, 05:38 AM   #1
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Class 8 Motorhome... Need some opinions...

Hey guys and gals...

Like the title says... I am in the planning stages of building a custom class 8 motorhome.

So far here are a few of the details.

It will be max length of 45 feet, per Idaho maximum single vehicle length.

I want a custom rig, but I am a bit torn on the specific body. Here are the few I'm trying to choose on, a 50's GMC 630 hood and cab on a newer heavier frame, a W900A Kenworth, 60-70's Autocar or a 50's Mack. The diesel will be a Celect + N14 Cummins Red Top and the new TC-10 Allison 10 speed trans.

I know most motorhomes tow a car, but I am planning on mine riding inside the rear garage area so that I can tow a trailer with toys. The back will have barn doors with ramps for the car.

Here is where I need some opinions....

With a big long rig like this, and a Monster Diesel up front, I'm probably going to need a heavier axle than the typical 12k. I am thinking a 16k or 18k would be safe. I would prefer to not run a 385 or 425 if I don't have to and completely kill my turning radius.

On the back I am thinking a single drive axle with duals 20-30k, maybe 20k with a 13.5k tag axle. My crazy thought was with a single rig this long, how can I possible make it turn a bit better and not take a football field to turn around in, so why not add a tag steering axle? What do you guys think? I want at least a bogie axle in the back to help with the weight, but having a steering axle seems like a much better idea. Then in my research last night I was looking at drop axles and thought that would be perfect. Have it help steer when I am going forward, and then when I back up, it will lift and I have a single pivot point, therefore helping to turn better in reverse as well.... Thoughts??

I was planning on finding a salvage truck that the body was smashed but the frame still intact at straight. I have good welding skills and equipment but I'm still a bit uneasy about cutting and stretching the frame. Where the frame will be mated, I am going to weld and bolt them together just to be on the safe side. Also with a newer frame it will be easier to find a matching frame for the stretch.

My last question is for the rear pintle hitch. I am building a custom rear bumper that is the full 102 inches wide. It will be very reinforced, so do you think I would be alright with a 1/2 inch plate that has multiple trusses tying it to the frame along with the plate itself being welded to the frame?

This will only ever haul a 16 foot trailer with toys or an additional car so not a ton of weight.

Any more input on anything would be appreciated.

Jake
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Old 04-06-2013, 01:30 PM   #2
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Hey Jake,

Sounds like a challenging project, but it is totally doable. I will let others answer your specific questions since I have no HDT experience. So, I can only suggest that you look at Toterhomes and other mfgt'd HDT motorhomes for ideas.

About the toyhauler back-end, I submit that unless you engineer a rear drop frame like the Thor Outlaw and Newmar Canyon Star Class A Toyhaulers, then you will need l-o-n-g ramps...but probably need a rear-end lift like NASCAR guy use to get the car in and out.
See: Class "A" Toyhaulers

Thank you for your service and Best of luck
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Old 04-07-2013, 12:06 AM   #3
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Yes I know I will need long ramps. I was planning on getting a set from Discountramps.com. On my computer I figured I would need 12-16 ft ramps. I have already planned for storage of these long ramps.
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Old 04-07-2013, 12:56 AM   #4
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Quote:
Originally Posted by Nklpltd View Post
Hey guys and gals...

Like the title says... I am in the planning stages of building a custom class 8 motorhome.

So far here are a few of the details.

It will be max length of 45 feet, per Idaho maximum single vehicle length.

I want a custom rig, but I am a bit torn on the specific body. Here are the few I'm trying to choose on, a 50's GMC 630 hood and cab on a newer heavier frame, a W900A Kenworth, 60-70's Autocar or a 50's Mack. The diesel will be a Celect + N14 Cummins Red Top and the new TC-10 Allison 10 speed trans.

I know most motorhomes tow a car, but I am planning on mine riding inside the rear garage area so that I can tow a trailer with toys. The back will have barn doors with ramps for the car.

Here is where I need some opinions....

With a big long rig like this, and a Monster Diesel up front, I'm probably going to need a heavier axle than the typical 12k. I am thinking a 16k or 18k would be safe. I would prefer to not run a 385 or 425 if I don't have to and completely kill my turning radius.

On the back I am thinking a single drive axle with duals 20-30k, maybe 20k with a 13.5k tag axle. My crazy thought was with a single rig this long, how can I possible make it turn a bit better and not take a football field to turn around in, so why not add a tag steering axle? What do you guys think? I want at least a bogie axle in the back to help with the weight, but having a steering axle seems like a much better idea. Then in my research last night I was looking at drop axles and thought that would be perfect. Have it help steer when I am going forward, and then when I back up, it will lift and I have a single pivot point, therefore helping to turn better in reverse as well.... Thoughts??

I was planning on finding a salvage truck that the body was smashed but the frame still intact at straight. I have good welding skills and equipment but I'm still a bit uneasy about cutting and stretching the frame. Where the frame will be mated, I am going to weld and bolt them together just to be on the safe side. Also with a newer frame it will be easier to find a matching frame for the stretch.

My last question is for the rear pintle hitch. I am building a custom rear bumper that is the full 102 inches wide. It will be very reinforced, so do you think I would be alright with a 1/2 inch plate that has multiple trusses tying it to the frame along with the plate itself being welded to the frame?

This will only ever haul a 16 foot trailer with toys or an additional car so not a ton of weight.

Any more input on anything would be appreciated.

Jake
There's a guy building a 379 Pete' on Frame Welding - Truck Conversion & Toterhome Community
Quite in depth with lots of pic's.
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Old 04-07-2013, 11:22 PM   #5
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i wouldn't think it would turn that bad as a single axle or a tandem. depends how much off road or close driving you do.
you could do like i did and put a tag axle behind cab. i have a 20 foot garage on mine. just wish it wasn't so high off the ground. could have sloped floor but i didn't want it that way. if i ever get alot of money would like to put on a lift door.
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Old 04-08-2013, 01:26 AM   #6
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I bought a air ride rear axle cut off For my 94 F-700. My Ford has a 22K spring rear axle.
I'm converting this year. The axle and suspension I bought is the Very common Freightliner 20K "airliner suspension" out of a 94 OTR truck.
Because my box is so close to the tires I run 255/70R22.5 low profiles on the back and slightly taller low profiles on the front.
If I was in your shoes I'd just find a used OTR truck (with air ride) and get the Tandems out of it. The latest school bus have air ride axles as well. That is the frame you would use as well.
You could chuck the front diff. Rebuild the rear one with the ratio you want and stick it in the front axle. Then just use the rear axle as a tag axle.
For tight turns you could just let all the air out of the rear axle bags.
For unloading you dump air from both front and rear axle bags.
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Old 04-09-2013, 02:08 PM   #7
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Quote:
Originally Posted by volvoman View Post
i wouldn't think it would turn that bad as a single axle or a tandem. depends how much off road or close driving you do.
you could do like i did and put a tag axle behind cab. i have a 20 foot garage on mine. just wish it wasn't so high off the ground. could have sloped floor but i didn't want it that way. if i ever get alot of money would like to put on a lift door.
Like the man on the radio said: "And now the rest of the story"...
See: Pictures of conversion motorhome

Volvoman is "The Man"

If I had the skills and the shop, I would be doing this too, but alas I have to live with my Outlaw
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Old 04-10-2013, 09:22 AM   #8
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My 45 foot Dynamax has a Tag/Drive axle that lifts. I've been in some pretty tight campgrounds and am able to manuever just as well as any 45' class A with a tag. My turning radius with the freightliner columbia front end is a bit less but I've never noticed a big problem when I lift the tag.
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Old 04-11-2013, 12:12 AM   #9
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My 45 foot Dynamax has a Tag/Drive axle that lifts. I've been in some pretty tight campgrounds and am able to manuever just as well as any 45' class A with a tag. My turning radius with the freightliner columbia front end is a bit less but I've never noticed a big problem when I lift the tag.
Do you mean that your 45 ft WITH the tag axle can go everywhere that one WITHOUT the tag can go?
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Old 04-11-2013, 12:46 AM   #10
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Do you mean that your 45 ft WITH the tag axle can go everywhere that one WITHOUT the tag can go?
I think what he was saying is that with the tag axle with a normal load on it it will increase the turning radius. And when he dumps the air off the tag suspension the piviot point of the two rear axles Now changes forward to the front drive axle and it turn much sharper.
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Old 04-11-2013, 01:05 AM   #11
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That makes sense...
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Old 04-11-2013, 07:08 AM   #12
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I think what he was saying is that with the tag axle with a normal load on it it will increase the turning radius. And when he dumps the air off the tag suspension the piviot point of the two rear axles Now changes forward to the front drive axle and it turn much sharper.
Exactly, I can basically go where any class A 45' bus can go in campgrounds. Tight corners, backing into a tight site ect.....just lift the tag and the pivot point changes. BTW, We just spent 3 months in Florida. I filled the coach with a full tank of water, full fuel and 3 months worth of our stuff. Weighed it at the scales and we still had almost 10,000 pounds of weight we could have added. Love that about the big class 8 conversions.....so much capacity and power.

Going thru the mountains of Tennessee and Kentucky with my jeep tow and I could pass semi's and other motorhomes like they where standing still.
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Old 04-18-2013, 11:31 PM   #13
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I just happens to the see the air spring I bought for my "new to me" axle.
It has 14.25 inches of travel. so If i dump all air off bags it should drop about 7 inches at the axle and about 9 at the rear bumper.
Ordered a used 3.58 ratio gear set for $300 for it today as well. Beats the heck out of $1000 for a new set.

One thing I have heard some dodge pickup owners complain about with tuned 5.9s is that they are hard to keep cool. My truck uses the same radiator as a F800 with a 8.3 Cummins. No way does it ever get hot.
That is the another good part about the class 8s
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Old 04-25-2013, 01:01 PM   #14
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You should probably start with a chassis/cab that has the right capacity front axle so the title and door sticker reflect the heavy axle from a liability stand point, also if you find a heavy chassis it might have a double frame that will help to stiffen the long frame and also make splicing the frame to lengthen it easier, find a donor double frame cut off, (hopefully with the desired rear axle and suspension combination) with matching frame rail dimensions height width and thickness then you can trim them up so that you have some overlap, approx. 2' or more so that the inner and outer frame splices are staggered, then bolt the overlapped sections together and weld the splices
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