Re: Mercedes 2626 AK 6x6
Well, the Merkabah has a console, big and heavy, that is part of and holds the bogie to the main frame rails. It has a pointed bolting pattern on the vertical part of the rail -or soul of the rail, and the frame on that part has long inner rails as reinforcement. Pretty tough. The distance between the center of both axles is 1350 mm.
If, by any chance, I would want to extend the wheel base I would prefer to cut the frame in between the bogie and the front axle and stretch it using a donor frame piece, taking good account of all the considerations from MB on the subject. As you can see from the older but clearer pictures, the frame rails have a fish type form as the soul is reduced in height near the tail so it would be not possible to move the whole console and the bogie backwards. Moreover, I am not pretty sure I would be comfortable having to drill all those extra holes along the rail.
But if the frame of the truck is straight and has plenty of holes already bored, as in the newer models, and you do not want or need to extend the length of the truck, then I should strongly recommend to move backwards the bogie. This could be accomplished just by “simply” unbolting and bolting it back as far as you want depending on the availability of holes in the rails. You can drill more, of course, following the guidelines of the builder. Naturally, if you want to extend also the whole length of the frame you can weld a piece on the tail with much less strength and torsional considerations.
If talking about moving the bogie, you must consider stretching the cardan shaft, relocating the suspension spring hangers if they exist, the same with the hangers of the sway bar, and extend the electric wires and the air and hydraulic lines which is the easiest part.
If talking about stretching the frame you just have to extend the cardan shaft, the lines and the wires but you MUST have a qualified welder and be sure that the frame rails were not heat treated. If so you cannot weld them.
Extending the wheelbase could be of use to get you more departure angle without having to “bevel” the rear of the living cabin -or Box, or to allow for more overgang. The last could be a problem when you have a third axle. Why do you want to do it, and for which truck?