M51a2 towtruck/rollback project

[Gmtblazer]

Hi guys. Need input/advice for my project. I have a m51a2 dump that I want to turn into a rollback with a knuckboom crane behind cab. I have a towing company and a couple times a year I get a freaky off road recovery job that my 4wd f550 just can't get to or handle solo. I've been collecting parts, I have the 10k knuckleboom, a 20' rollback body, a 12v cummins with an Allison auto. I am a good fabricator and diesel mech. Need the truck to be very good off road but on road capable for short runs. Should I stay with the multi fuel or swap the cummins? Would need longer wheel base for rollback so thinking about adding another axle or maybe two? I could just stretch the frame but 4 rear drive axles would look badass, if it would work? I would like to keep duels but I dnot think they would fit with the size tires I want to run. I was thinking about swapping to a late 40's cabover cab to get more room for the knuckleboom. What are your thoughts?

 

[red]

Asking the truck to do too many things. Tight turning radius or 20ft rollback bed, can't achieve both at the same time with a straight frame truck. A mk48 maybe since it pivots in the middle. With the short wheelbase the dump truck will not turn with that many axles in the rear unless they were steering. Getting rear steer approved for street use (as a retrofit) is difficult in more relaxed states when used as a hobby vehicle, as a commercial vehicle in the northeast?

What kind of terrain are you dealing with and what offroad vehicles usually? If you are looking at off camber trails carrying the disabled vehicle on the bed is a bad idea, too high of a center of gravity and will roll. Mud bogs it would be ok but still tippy.

If off camber trails then you are limited to a old Holmes type setup.
Wheel lift is out due to little ground clearance
Roll back is out due to very high center of gravity


With your vehicle/parts list. Install the knuckleboom, mount up a rear lift like a Holmes, and the tool boxes. Maybe add in a winch at the rear of the truck as well. 12v Cummins is much more reliable than the multifuel. Or sell the truck and get a 5 ton wrecker since that's what it is designed for.

 

[red]

Someone elses build with a short offroad wrecker idea




Military 5 ton wrecker (my m816). The M543 and M936 are the same length and use the same bed. It's a standard wheelbase 5 ton (same as the cargo), which is not much longer than the tractor/dump truck wheelbase.

 

[Gmtblazer]

Thanks for the reply red. Mainly flatland around here, I don't think high center of gravity would be a concern. With all the awd, 4wd, or a car so damaged it can't roll I'm really stuck on the flatbed part of it.I dint think about turning. What tires are on yours? Looks nice. How big can I go and keep the duells?

 

[74M35A2]

I converted a box truck to a rollback flatbed, by harvesting the Jerr-Dan aluminum rollback and slide frame off a trashed diesel F-Super Duty and moving it over to the box truck. Hydraulic wheel lift off the back was part of it also. It was a really easy task and works perfectly (and is for sale). Only thing there is to watch the frame height vs ramp angle. If you are building it onto a tall frame truck, you won't be able to easily load Corvette's and such. But, if you are focusing on off-road recovery (is there any money in doing this?), then it should not matter. On a heavier truck, you could transport things like forklifts, presses, sheds, and industrial equipment to help pull in additional $ if you are plated properly to do such (in MI, you are not supposed to use a standard "Wrecker" plate to move anything but automobiles). The truck I built it upon is a 1998 Chevy C7500 medium duty truck, because I wanted full size frame rails and chassis to handle MI terrible roads with a load on it. A lot of the standard flat beds had cracked frames after only a few years old, from our road conditions and operator abuse. This truck is 5 speed manual with a 2 speed single rear axle, dual wheels on rear. 22.5" semi rims all the way around. 4 wheel hydraulic/hydroboosted disc brakes.

It is easier to do than one even thinks. You would have room for the knuckle crane if your frame is long enough, they are 2 completely separate things. Remove the bed headboard to give more operating clearance for the crane, and you are off to the races. One PTO pump can run either one.

It will have a high center of gravity like red said, and same on the Cummins vs old multi-fuel engine, light years apart in mileage, power, and reliability.

If it is just for pulling out somebody stuck, I would go 932a2 with a winch on the rear also.

 

[red]

Thanks for the reply red. Mainly flatland around here, I don't think high center of gravity would be a concern. With all the awd, 4wd, or a car so damaged it can't roll I'm really stuck on the flatbed part of it.I dint think about turning. What tires are on yours? Looks nice. How big can I go and keep the duells?

Those are 395x85x20"s on my m816 (47" tall). If you stay with military surplus tires the largest tires to run as duals and not be overwidth are the 11x20"s. Could run civilian tires for a 20" wheel or swap out to 22.5"s.

If you are determined on the flatbed then cut it down to 12-14ft, long enough for the wheelbase of most full size trucks. Again wouldn't recommend the flatbed. If a vehicle is that badly damaged offroad then it's scrap anyways.

If a vehicle is unable to roll I'd just hang it from the crane while offroad. That lets you keep the short wheelbase for tight turning, center of gravity down low, and very versatile. Maybe mount the rollback bed onto a trailer chassis that can be towed by the offroad tow truck. Use a few hydraulic QD's run between the truck/trailer to power it.


Quick video of my m816 playing around offroad. This trail is easy and not tight. The bed is 13ft long from behind the cab to the end. With an extra 9ft of length (figuring 2ft for knuckleboom and 20ft of rollback) it wouldn't have made that turn due to the rear overhang swinging out into the trees, on a easy trail.

https://www.youtube.com/watch?v=nl1kEIg3cno

 

[grendel]

Yep. I had a wrecker... now building a 4x4 (bobbed) M932A2 to go into the woods and recover vehicles. We have a similiar contract with the police.

You know a set of 16R20's can handle 23K pounds and change? So can a single axle. I went with a 20k lb Peterbuilt air leaf when I bobbed it.

 

[Rescue101]

Have you seen your wrecker lately? Going under paint in the next 2-3 weeks,just waiting on the new towbar to finish it up

 

[grendel]

Have you seen your wrecker lately? Going under paint in the next 2-3 weeks,just waiting on the new towbar to finish it up

Glad you love it like I did