Cat 973 wont move

Hi all. It has been a while since I posted here. Anyway after much work need assistance on a problem I am having. I purchased a cat 973 s/n 86G
which was sold because it would not move. We have been troubleshooting and have now found out we are unable to get charge pump pressure to the brakes. We ran a line from charge pressure test point to the brake line directly and then the machine moves only in front. We have change filter, using SAE10. We took out the spool valves in the main control valve and cleaned, eventhough looked OK. Any ideas would be appreciated.

Start by trying to travel with throttle at half position, then look at the main filter. Drain the filter housing before removing filter, then cut filter open and look for metal.
Later Bob

Bob/Ont said:

Start by trying to travel with throttle at half position, then look at the main filter. Drain the filter housing before removing filter, then cut filter open and look for metal.
Later Bob

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Thanks Bob. We actually had to change filter. We also cut filter and saw no metal. Because the machine had been sitting for a few years we drained all the oil in the hydrostatic pump, took off bottom to clean strainer, No metal in system. For some reason we are not getting any oil pressure to the brake side of the main control valve. On the test ports on the top of the control valve, there is only pressure on the 2 ports on the right, but none to the left which is for brakes.

On the test ports on the top of the control valve, there is only pressure on the 2 ports on the right, but none to the left which is for brakes.

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Any chance of posting a photo so that we can see exactly which test ports you are referring to..?

What did you use for oil? It needs to be Hyd oil 10 and have the proper filter. Cat filters are now a finer micron and require a long warm up, the last I used were Donaldson but that was a long time ago. Oil too heavy10w30 or filter too fine will result in pump flow bypassing filter into the sump and the machine will not move. Try half throttle and see if the underspeed override will make it move.
Later Bob

Nige said:

Any chance of posting a photo so that we can see exactly which test ports you are referring to..?

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Nige I will try and get a pic tomorrow. However it is the brake pressure test point with zero pressure.

Bob I have 3 other 973 machines. We use 10W in all of them. We use the same type filters in the other machines no problem. Something is causing the oil to the brakes to shut off. Not sure how the control valve would do that. On the other machines as soon as you start, pressure goes to the brake line, unless you have foot on brake. This is not happening with this machine.

Brake pressure is Charge Pressure so what are you getting for Charge Pressure? Glad you have a few machines, you know about them.
Later Bob

Bob/Ont said:

Brake pressure is Charge Pressure so what are you getting for Charge Pressure? Glad you have a few machines, you know about them.
Later Bob

Click to expand...

Bob, that is the strange thing..there is charge pressure on part of the main control valve. As a test we have run a line from a charge pressure tap directly to the brake line. Brakes free up and motors work. However getting no pressure from port on the main control valve

Have you checked the brake lever under the cab to see if it is in the full brake off position with the pedal up .

Does the engine lug down when you move the FNR to the drive position?

For now we have the cab up for easy access. So we are controlling the level manually.

Cmark the engine does not lug down inits present condition with no oil pressure to brakes. When we did the direct connection to brake line from charge pressure port we hear engine and pump working.

Do you have the speed/brake control lever locked in the run position with a 5/16 NC bolt? What happens to your Upstream and Throat pressures when you pull or push the travel control fully? What are the pressures?
Later Bob

Nige the port being pointed at doesn't have pressure no matter what.

Update we again applied charge pressure directly to the pointed to port from a charge pressure test port. The pressure goes through to
the brakes and the machine is able to move front and back. We found that 2 hoses to the servo were misplaced.

When we connect everything we are not getting any charge pressure though the main control valve to the brakes. And the brake control
lever is in the brakes off position.

You do know that in your photo the brake lever to the left of the picture is in the brakes on position?

That's what I said to him in post #14 Mark. Position the lever and lock with 5/16NC bolt then take off he brake hose and cap fitting and try it again. Should load up the pumps. If not check the drive motor case pressure.
Later Bob

Mark I do realize in the picturethe lever is in the brakes on position. Bob I did in fact take your advise and locked the lever with the 5/16 bolt. However just before the picture I removed the bolt troubleshooting to see if the spool valve might be offcenter or something. I have locked it again. The hose from the main control valve to the divider/valve(brake) I removed at the divider, no oil pressure there in the brake off position. Seems to me for some reason the charge pressure is not passing through the main control valve to the brake section of the main control valve. I have read in a post of something causing the machine to vent???? Could this be happening?

If the charge pressure gets below 95Psi app the vent spool will move and the underspeed valve will fall bringing the pumps back to neutral. The main reason for he charge pressure drop is loss of oil from the drive loops' This can be confirmed by measuring he cooler flow during operation, should be more than 16 GPM under load with oil at 175 Deg F. If you have good cooler flow and lose charge pressure oil can be lost from a faulty aluminium plate behind the control valve. I have only had his happen once but it is common as these machines age. Also check that the woodruff key in the speed control valve spool is in place or the lever might be out of position and causing the trouble.
Later Bob

Hi Guys,
Not sure if this is the appropriate place to start a new thread, but it is the same issues as above.
I have a Caterpillar 973, serial number 86G032XX, 07/97 in NSW, Australia. It is the second series of machines made in France. The previous owner had it sitting in a quarry for many years after a mechanic adjusted/serviced the hydrostatic transmission. They reversed the machine up and then it wouldn't go forward. It sat there for 5-10 years. A few people have had a go fixing it, to no avail. I picked it up for a bargain as the owners has lost interest. I want to bring it home and sort out the hydrostatic transmission. The motor runs okay and the implements and associated hydraulic pump works okay (except for some burst perished hoses).
At the time I didn't realise that the hydrostatic transmission had been drained (to use the oil elsewhere), but I only ran the engine for a few minutes to see how it sounded. Reading the owners manual, it appears I'll have to get the brakes off to move it onto a loader and get it home. I understand this can be done in 2 ways: by pressurising the hydraulic lines to the brakes, typically from the distributing manifold (on the left side of the machine ?) with a hand pump; OR taking the centre shaft out of the final drive sun gears.
My question is: can I take a simple hydraulic pump like a portable-power pump and attach it to the hydraulic lines to disengage the brakes? What sort of oil volume will I need to pump, to get both the brakes off ? I plan to put oil back in the hydrostatic transmission - Caltex Delo Gold Ultra - a multigrade 15W-40 oil, same as the engine oil, recommended for the 86G3000 and up. It'll be working in 10° - 40°C temps.
However can I get the brakes off by pumping oil into the brake lines regardless of the hydrostatic oil status - drained or otherwise ?
I'm hoping Bob/Ont and you other experienced CAT 973 guys, will pick this up quick.