CAT 973 Steering issue

[jacobkoch]

We recently acquired a 2000 model 973 for our farm to do some clearing work. After working the machine for about 8-10 hours (not at one time but across several days for a couple hours each day) I noticed the steering on the right side begin to have a slight delay when pressing the pedal. Shortly thereafter I lost steering on the right side, and when trying to steer left, the machine would instantly reverse rather than steer left. What could be the cause here or what is the best way to approach this?

 

[Nige]

a 2000 model 973

Doesn't help much when looking for information. A Serial Number is required. Once that is supplied we can move forward.

Question: Does it have three switches under the RH seat armrest.?

 

[jacobkoch]

SN 86G01338

And no switches under the arm rest to my knowledge

 

[Tyler d4c]

If im not mistaken a 86g model is still old school mechanical. Cmark or pittsburg cat man is the knowledge for this!

 

[pittsburgh cat man]

I would start by checking case drain on motors. First you need to cap the brake line, to lock the brakes,But be careful 973s are the only ones that Ive seen that will try to move a little when you put it in gear after you cap the brakes. Their are two taps on top of each motor the one closest to frame is to shift the motor you do not want that one the other one closer to middle of tractor is case drain spec is 0-2 psi You take the reading with tran lever pulled all the way back after your sure it's not going to move. In your case I would not worry about warming tran up. Finally do not hold tran at stall for more than 30 seconds as it will destroy the port plates after every 30 seconds at stall it needs 30 seconds in nuetral attachment below will help

 

[Nige]

SN 86G01338

And no switches under the arm rest to my knowledge

A pre-electronic machine. I was just trying to skip a step in case it was and we could look at electronic faults but that's not the case. Win some, lose some.

How are you equipped with pressure gauges for testing.?

If im not mistaken a 86g model is still old school mechanical. Cmark or pittsburg cat man is the knowledge for this!

1. What grade of oil is in the hydrostatic transmission and the splitter box.? This is important.
2. Do you have an Operation & Maintenance Manual.? If not then you need to get hold of one ASAP. SEBU5848 is the Cat Publication reference. There might be one on eBay but check out the prices of a new one first.
Parts Manual is SEBP1387. Here's what looks like a good used copy on eBay.



If the tractor is losing function after some hours of operation when it gets really hot I'm wondering if the HPCU and it's associated pipework/tubes might have some tired seals.? it's not an unknown problem. Thing is I can't upload any illustrations right at this moment to show what I mean.

 

[pittsburgh cat man]

I was just wondering if the serial number you listed is right. I kept thinking that number sounded very Familiar I modifed 86g 1337 for the steelmill in 1991

 

[jacobkoch]

I was just wondering if the serial number you listed is right. I kept thinking that number sounded very Familiar I modifed 86g 1337 for the steelmill in 1991

 

[jacobkoch]

A pre-electronic machine. I was just trying to skip a step in case it was and we could look at electronic faults but that's not the case. Win some, lose some.

How are you equipped with pressure gauges for testing.?

1. What grade of oil is in the hydrostatic transmission and the splitter box.? This is important.
2. Do you have an Operation & Maintenance Manual.? If not then you need to get hold of one ASAP. SEBU5848 is the Cat Publication reference. There might be one on eBay but check out the prices of a new one first.
Parts Manual is SEBP1387. Here's what looks like a good used copy on eBay.

View attachment 329419

If the tractor is losing function after some hours of operation when it gets really hot I'm wondering if the HPCU and it's associated pipework/tubes might have some tired seals.? it's not an unknown problem. Thing is I can't upload any illustrations right at this moment to show what I mean.

The day that I noticed the steering issue begin, the machine ran perfectly fine as it had before. Once I noticed the issue, I let the machine cool down and then shut it down. The center sight glass for hydraulic fluid was low at that time. The next day after getting fluid, I started the machine, and then re-checked fluid levels and added around 2 gallons back to get the fluid back into the operating range. The steering issues were the same as the day before even with the machine "cold" and with fluid levels all correct. I will get on ordering manuals for the machine like you mentioned. Thanks for the help with this!

 

[jacobkoch]

I would start by checking case drain on motors. First you need to cap the brake line, to lock the brakes,But be careful 973s are the only ones that Ive seen that will try to move a little when you put it in gear after you cap the brakes. Their are two taps on top of each motor the one closest to frame is to shift the motor you do not want that one the other one closer to middle of tractor is case drain spec is 0-2 psi You take the reading with tran lever pulled all the way back after your sure it's not going to move. In your case I would not worry about warming tran up. Finally do not hold tran at stall for more than 30 seconds as it will destroy the port plates after every 30 seconds at stall it needs 30 seconds in nuetral attachment below will help

Thanks for sharing that attachment. I read through and found the ACTION section that most closely aligns with the issue that I am having:

"c. Movement to the rear by pushing the steer pedal or pedals all the way down must not occur unless the transmission control lever is in the REVERSE position. Check for a broken oil line between the servovalve and servo cylinder on the right side or a problem in the servo cylinder."

 

[Nige]

If the tractor is losing function after some hours of operation when it gets really hot I'm wondering if the HPCU and it's associated pipework/tubes might have some tired seals.? it's not an unknown problem. Thing is I can't upload any illustrations right at this moment to show what I mean.

Now I can. All the small tubes in this illustration (example arrowed) have a set of seals at each end (photo) under the union nut. These seals deteriorate over time and usually leak when the machine is hot causing performance issues.

 

[pittsburgh cat man]

I would still check case drain first to make sure the problem is in the hystat 973s have been known to break the u joint in motor. If the motors are close to spec then i would check servo pressure it prob be low but can be adjusted usally The lines you mentioned for servo cylinders are not the ones with seals shown above they are a regular hyd line with jic fittings 1,2,3. in post above. the servo valves are under the top cover there are lots of things that can cause problems like yours a broken sync link,broken cardan joint or a pin came out of servo cylinder

 

[Nige]

The lines you mentioned for servo cylinders are not the ones with seals shown above they are a regular hyd line with jic fittings

I'm sorry I have to respectfully disagree with you. We had exactly the same problem of performance loss after operating for a few hours not long ago on a 943B and the cause was was damaged seals on those particular lines. That's where the photo came from. Attached the parts listing for this 86G machine. The big black seal on right of the photo above is 8T-9502. If any of the other three items in the left side of the photo are damaged it requires a 5P-8752 Nut Assembly because they are not available separately. There was alaso a Service Mag (attached) on the subject.

I'm not saying that your suggestion of checking the case drain is heading in the wrong direction. Simply that leaks in the HPCU lines could also be a possibility.

 

[pittsburgh cat man]

The man was talking about servo lines I was just trying to point him in the right direction.

 

[Mobiltech]

The fact that it backs up when trying to turn forward makes me think it’s only driving one track and the other is freewheeling like a broken joint or a planetary input shaft failure.

 

[jacobkoch]

Just wanted to update y’all on what the final result was. We ended up getting CAT to send a mobile tech who eventually located a leak in one of the servo lines just under the linkages under the top cover responsible for engaging the pump to deliver fluid to the right hand drive.

 

[jacobkoch]

Thanks again for the help with this. Learned a ton about these machines through this process.