Right, so I've put my toe in the water now.
First question, it's a 24v starting system right? now I have 2 x good 12v batteries on in series with the positive side on the right hand side appearing to come up on the starter body, the negative side on the l.h. battery comes up in the dash on the start switch, then onwards to the starter solenoid.....but you know its not exactly lively at swinging the machine over, in fact it struggles to turn one rev. Yesterday we managed to shift it with a digger on jump leads to it, then some heat and then finally a little sniff of easy start.
I realise these need a lot of heat but it doesn't even seem to get to the stage of swinging over.

Would it be a lazy starter causing this or voltage drop somewhere......is it positive earth or neg. earth?

Yes, it is a 24v system, negative ground. Check and clean all your connections. Are the cables or connections getting hot? Takes two good heavy duty 12v batteries in series, at least 1000 amp capacity ea.
If it still doesn't spin you've got starter issues.......or something in the engine/drive line is causing excessive drag.

You might want to check out the starter too. I had oil leak through the seals into the starter solenoid on my d47u. The solenoid alone would draw 100A. That starter got a lot more lively once that was replaced.

the three D's i have been around were built in the states and were negative
ground. your english built D sounds like it is a posative ground? the D's here
had four six volt batteries piped to 24 volt. the D's i worked on i junked the
six volts as you always had one drawing the others down and installed two
big 12 volts in each arm rest, i think they are group 31.

you say the left negative comes from battery to the start switch then to
the solenoid. on the switch are the battery cables on the same stud or
two different studs. they would have to be on the same studs as the amp
load would cause you to turn loose of the switch real quick if they were on
different studs.

i cannot believe cat built this thing without a disconnect on the ground side.
the D4D's here in the states had a disconnect switch just under the right
side of the seat bottom. you were always hitting it with your right foot, just
to the right side of the shift tower. i think they grounded under the seat, i do
not remember them having grounded at the starter. i do not remember the
power side going up into the dash, i think they went straight to the solenoid
and had 8 gauge wire going back to the dash. does your tractor have a
generator or alternator? i dont think i have ever seen a positive ground
alternator?

Hello Richard
Looks a tidy machine,I bet you will be spending your well earned leave days working on it.
Martyn

Hi Martyn, yes, I took the blade & cab off it yesterday to make it a bit easier to work on.....should get to it again this afternoon

"Old wrote:

Yes, it is a 24v system, negative ground. Check and clean all your connections. Are the cables or connections getting hot? Takes two good heavy duty 12v batteries in series, at least 1000 amp capacity ea.

Thanks OM, I reckon you've got it.....I just looked, one battery is 680cca, the second is 760, so that will be. No.1 job tomorrow morning - we live and learn!

Richard those two batteries should be able to turn her over. A little tip, pull throttle open to excess fuel, spin her over a couple of times, even slowly will deposit a little fuel into the cylinders, then hold the heat on for a good five min plus, then switch to start position, if the plugs are working properly even half a slow crank will have her fireing. Over the years we've used that method many times. Ive even seen a low loader driver sit for fifteen mins with the heat on a tractor we had given up for dead she roared into life. I think your D4 may have had 4 six volt batts originaly. Two 629 or 644 should be ok.
Gordon.

Good fully charged Batteries and plenty of heat and she will be ok.Make sure all you battery connections and cables are good.
Good luck.Had a chap phone me yesterday about a D2 dozer he is trying to revive.Its a 3j number 6721sp.As you can see, he has a lot of work to do.
Keep us posted Richard.

i have two 154ah JD battery's on my D4c give it two minutes heat and it will go eventually
mine needs some head work ,valves/seats
i recently put all new leads terminals etc on mine as the old ones had gone brittle and the case,s were splitting
the battery,s are a good fit in the battery boxes ,i could do with two box tops if anyone knows of any
cheers graham