what size sub soiler would the D4 6U 1953 model pull?   i have a slusser McLain three shank pull type with the long point that lifts the soil.  probably won't be any deeper than 20 inches sandy loam

Two shank probably, three might be really lugging it.

modern they say 30hp per shank

i found a sales brochure for a similar madel same mfg that says 50 hp 5 shanks

Depending on your soil type and conditions, I say begin with 1 and try adding shanks. Around here, a single going 24" in compacted soil will make a 7U grunt and spin out.
I can go shallow with chisel shanks and use 5-7 of them. JM

Gee, you are spot on! Here in the parched plains of NW Kansas we rip our terrace channels to keep water from a heavy rain from pooling in the channels. It takes a 250 to 300 HP 4WD tractor (with duals) to pull a 5 shank ripper at about a 24 to 30" depth in soil, no rocks.

i did some measuring. tthree shanks from tip of shank to ripper frame 20 inches. the shank design is interesting with the tip being about 8 inches long and lays at about a 15 degree angle off of flat. total width is 57 inches. there are pockets for five shanks but only three in the frame. i think the extra pockets are so you can pull two shanks at different width.

Hi. D4Jim.
It has been recognized for a long time now that it takes only about 2/3 the weight and horsepower in a crawler tractor to pull the same load that wheel tractor will pull. Or, to put it another way, it usually only takes a 100 hp crawler to pull the same load that a 150 hp wheel tractor can pull. Yes, it will pull it slower but it will usually pull it with less slippage than the wheel tractor.

Back in my younger days, back just after Noah landed his canoe and turned all the animals lose again, I worked onna wheat farm which hadda 80 hp wheel tractor with dual tires on the rear and a 2T series D4 at around 36 drawbar hp. There was one field that I worked with both tractors which had a shallow creek, dry but with deep washed sand in the bottom. This was back in the days when hydraulics were just starting to show up on farm implements - this farm DIDN'T have 'em..

When pulling 2 X 14-disc one way plows with the 80 hp wheel tractor, I had to stop and lift both plows almost out of the ground to be able to plow through that creek. With the little ol' 36 hp D4, all I had to do was change down a gear, 4th down to 3rd, until the first plow was out of the creek..

Just my 0.02

i'll give it a try with the D4 and let ya'll know. the shank design is not really the ripper type anyway.

ah so its more a cultivator than a ripper.