Construction Forklift

QUESTION:

I've had a couple of forklifts, and they all have had the same problem, they get stuck in gravel, mud, etc. It seems that I've spent more time pulling forklifts out of mud than machines off trucks. So I finally decided to get some advise from this (very helpful) newsgroup.
It seems that the forklifts get stuck for a number of reasons:
The rear wheels buery themselves due to sharp steering. Solution: don't steer sharply or increase wheel size.
Whe the forklift is on uneaven ground, one of the front wheels lifts up and the forklift rests on the other three. Solution: make the free wheel stop spinning by applying brake to that wheel only. Or use very soft wheels so that the forklift won't balance itself on three wheels (ie. replace the hard rubber tires whith pneumatic tires).
When driving into the shop, there is a 3" ledge to go over. The undercarriage hits it and lifts the forklift up. Solution: increase ground crearance with bigger tires or use a ramp.
Right now the forklift (a 4000Lbs Allis Chalmers that weights 7700 Lbs) has 18 x 8 x 12 1/8" front tires, that, due to wear, are only 14" in diameter. I'm wondering if replacing them with new 18" tires will help the problem. I have enough room for 18.5" tires, can I get some that size? And who sells forklift tires, anyways? Also, how does one remove the tires off the rims, and how does one remove the wheels? I unbolted all the bolts, but I can't seem to be able to get the wheels off. Maybe a manual would help, but since Allis-Chalmers is out of business, where do I get one?
I there any way I can put pneumatic wheels on this forklift?
As for the selective braking (locking up the wheel that's lost traction), it seems like a pretty simple idea that might work. All I need is two valves in the hydraulic lines to each wheel, and I can prevent the wheel with traction from receiving brake pressure. What kinds of valves should I use, and do you think this idea will work? It's so simple, I wonder why none of the forklift manufacturers use it.

ANSWER:

One of the used farm equipment dealers here in Redmond, Oregon has what you need. It is a forklift based on a crawler tractor. No wheels, tracks like a small bulldoser. Was still on his lot the last time I drove by.

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