5th wheel placement

[Bacsy]

I haven't found a thread on this maybe I missed it, but here goes i'm building a MDT 1985 S Model i've installed a 70" sleeper from 93 Peterbilt, i'm going to pull a 35' toyhauler nuthing huge. My question is I have 5 and a half ft of space to install the 5th wheel, I know I have several options but the easiest is to install the 5th wheel behind the rear wheels. Has any one done this ? any suggestions ?

 

[Bob86ZZ4]

Most of the trucks I've seen converted to haul a 5th wheel camper they put the hitch behind the rear wheels. They all say it makes it much better for steering and backing and stuff. I wouldn't worry about moving the hitch way back.

 

[Bacsy]

Thanks for the input I saw pictures on anouther site and they had the wheel way back, i"m just starting my build and was always told that it would sway but doesn't appear thats always so.

 

[hot rod]

check out the escapees forum and the hdt rally. Those are geared more towards class 8 trucks converted to tow big 5th wheel campers.

I just got done converting my mdt to tow a fifth wheel trailer. I put my fifth wheel right where it is supposed to be, just an inch or two ahead of the center line of the rear axle. Then built the box to be 5' ahead of the hitch center line to allow plenty of clearance to turn the truck 90 degrees to the trailer. You have to figure a 102" wide trailer is 51" from the center to the edge, then allowing a few extra inches for clearance. 23000# trailer tows great like that. Backing is far easier than with my dually as the turning radius of the mdt is far shorter, even with the much longer wheel base. I wouldn't consider moving the hitch back just for ease of backing, it can't help that much and if a guy can't back up with a standard fifth wheel location, he needs practice, not the hitch moved back.

Most of those trucks you see with the fifth wheel way back are done purposely to improve the weight distribution for ride and balance of a full class 8 semi that is has a way longer wheel base than your truck, and a much heavier unloaded front axle weight. Those guys have done careful calculations to figure out exactly where that hitch should be to get the front axle weight where they want it with the trailer hooked up and fully loaded. Just making an educated guess from looking at your rig, but you have a relatively short wheelbase, and the added sleeper is so far back that the extra weight is already more on the back axle than the front. I suspect your truck is already light on the front end and having the hitch behind the rear axle will only make that worse. My Kodiak has a longer wheel base than yours, approximately 12' from the cab to the axle, and with my 7' box built and the trailer hooked up (with the hitch just ahead of the axle) the front end was still light and rode really rough. When I stash about 1800# of cargo in the box the ride smooths out real nice. Which just confirms to me that the hitch has to go inline with the axle on an mdt like ours.

Of course on your truck it is not possible to put the hitch at the rear axle with as far back as your sleeper goes, you'd never be able to turn. So you are going to end up with the hitch at least 5' behind your sleeper, but my advice would be not an inch farther than you have to. No other choice. So the question becomes are you willing to stretch the wheelbase if the balance does not come out right? And you should try to do those calculations before it gets to that point. There are some threads on escapees that talk about that issue.

Here are some pics of my truck before I built the box, and under construction to give you an idea of the wheelbase and hitch location:

 

[Bacsy]

I had thought about converting to air ride and moving the axle back, also I had looked at sliding hitches, pullrite has one that unlocks automaticly but that limits me to only my trailer and not anyone elses because there is a plate that goes on the trailer that unlocks the hitch. I don't know how well they work.

 

[hot rod]

If you are going to do both air ride and stretch the frame, it is probably easiest to go to the boneyard and get the whole rear frame section and axle from a truck that already has air ride. Just cut it behind the cab and weld it to your frame wherever it needs to be to get the wheelbase you want. No mucking around with the suspension, brackets, air bags or anything. And you would need to stretch your frame to move the axle back anyway, so you are getting the air ride for no extra work. Then sell your old axle to recoup some of the money.

 

[hot rod]

Oh yeah, and the air ride is a great idea for towing your camper anyway. Those trailers are really not built strong enough to endure the rough ride of towing with a heavier truck and leaf springs. There are some horror stories out there on the internet of fivers with the frame collapsed in the hitch area towing with a class 8 truck. Most of those guys are running an air ride fifth wheel. I found a good deal on my Trailersaver hitch on ebay for about half the price of a new one and I couldn't be happier with it. Very nice cushy ride for the trailer, with the added bonus of being able to dump the air to unhitch/hitch. All I have to do is run the landing gear down until it just touches the ground then dump the air on the hitch and the trailer is already leveled. My trailer is 23000# and the hitch is rated for 30000#.

 

[Bacsy]

Thats good info grafting a frame is something I can do (I used to build race trucks from the ground up) I was looking into new toy haulers this weekend and certainly didn't realize that they had got that heavy.