963a Cat won’t build drive pressure to right track.

[Mr94]

I have an early 80s 963 that will only build 800 psi to the right track.
I have good charge pressure, no case drain pressures, left track saw 2000psi just bumping the lever a bit. the loader also works well. I have a few very very small metal flakes in the filter. How can i tell whether i have a bad pump or just a leak in the servo circuit or something?
I pulled the hpcu cover, ran the machine to check for leaks under there, and manually pulled the lever to the right servo with the brakes locked.
11zn00191
I‘ve been lurking here for years and finally had a reason to post.
thanks

 

[Dave Neubert]

If it don't build pressure when you manually move servo I would think that it is a pump problem in the transmission

 

[Mr94]

Weird update today after being away. I screwed in the sync cut-off screw per testing instructions and my right drive pressure is sitting at 1200 psi with the engine revved and it backs down to about 1000 with the oil warmed up some. If I back that sync screw out the three turns to spec, I drop to proper ish charge pressure. I can’t make right drive pressure change when moving the servo arm under the hpcu cover. I can easily make left drive pressure build. I’ve also never seen these servos move the full 17 degrees they are supposed to.

 

[Mr94]

I showed the Guys at cat this filter junk after picking through the whole thing and they seemed very unconcerned. No gold, no big pieces.

 

[Mr94]

Top off the hpcu
the stickers are wrong but here she is

 

[Mr94]

I’m going to test servo pressure and charge pressure while trying to stroke the pumps and report back tomorrow.

 

[Cmark]

A couple of points/questions.

How are you moving the servo spool?

The brake lever (circled) needs to be moved to the brakes-off position. There is a hole in the lever which pins it to the valve body in the correct position using a 5/16" UNC bolt.

Have you got the parking brake hose disconnected and the outlet capped?

When you have done both these things you can run the engine at high idle and operate the FNR lever to stroke the pumps. Be careful at first in case the brakes are worn and it tries to drive through them.

When you move the FNR lever, the underspeed valve (big spring thing) should raise. Is it doing so?

You need to drain some oil out of the HPCU so that you can see the swashplate actuator cylinders and rotating groups.

Check the hoses to the cylinders for leaks.

You should be able to see the port plates on both pumps. Try and compare the amount of leakage from the port plates under pressure. It might get a bit messy.

The transmission serial number would be useful. Unlike other Cat machines, we can't link the machine serial number to the tranny on these.

What were the symptoms which brought you to this point?

 

[Mr94]

I have been reading your stuff for years, thanks for chiming in.

I moved the servo spool with my hand right there with the cover off, engine running.

I’ll look for the bolt hole for the brake lever.

I don’t have the parking brake capped, but I can do that. I’ve never worked on one of these but I’ve spent a few hours with the manual to at least know what some of the components are.

I don’t know that I’ve seen the underspeed valve raise.

I didn’t realize I could lower the oil that far. I guess as long as it’s above the suction screen, right?

I bought this machine as a project with what I was told was a weak right drive motor. I don’t have any case drain pressure and very minimal flow, so to the hpcu we go.

I’ll report back
many thanks.

Serial plate below

 

[Cmark]

I don’t have the parking brake capped, but I can do that.

To clarify. Disconnect the hose to the parking brakes at the transmission control valve. Put a cap on the fitting at the control valve end. Leave the hose open. I think the cap is 1/2" JIC.

I didn’t realize I could lower the oil that far. I guess as long as it’s above the suction screen, right?

Right.

 

[Mr94]

I lowered the oil level, set the brakes as instructed, and watched the swash plate cylinders while moving the FNR lever.

The left side moves fine. The right side doesn’t move at all.

I can’t get a very good look at anything else in there on the right side with that cover plate in the way up top

Something is spraying out down there and I can’t tell if it’s from the pump, cylinder, hoses, etc.

I know you said to compare the amount of oil coming out at the front of the pump but I don’t have a window to the right hand pump unless I move that cover. Is it just to prevent splashing?

My linkages did move the 17 degrees once that

 

[Mr94]

Sorry, phone locked up but it let me post what I had.

My linkages did move the 17 degrees once the underspeed valve raised properly.

 

[Cmark]

So both servo spools are moving the same amount? I'm suspecting the hose(s) to the servo cylinder or maybe the cardan joint.
If you need some tips on disassembly, post a birds eye view of the top of the tranny and I'll try and help.

 

[Mr94]

The servos are stroking fully.
I can’t even get the right cylinder to budge a bit. I have very little drop in servo and charge pressure even when I suddenly stroke the servos and it recovers very quickly unless I try to make it bog to vent out on the left one. The cover plate is shown better in the later pictures.

Is it worth hooking gauges to those outlets that the hoses hook to on the right servo to see what kind of pressures I’m sending to the cylinder?

Or shall I just work on removing that cover to examine things better?

 

[Cmark]

Personally, I would be taking it apart. Easiest to remove the entire servo valves and linkages as an assembly like this. Then you can get to the servo cylinders more easily.

 

[Mr94]

Before removing the linkages i unhooked one line at a time and put a pressure gauge directly on the servo. The gauge read 300 on both outlets. The cylinder does not hold pressure. It bypasses oil to sump as fast as you can send it.

Is that my whole problem? Piston seals in the swash plate cylinder are shot?

 

[Cmark]

If you're firm in your diagnosis that the cylinder is bypassing then yes, that's your problem. You could maybe compare it to the left side to be sure.

There's nothing special going on inside the cylinder.

 

[Mr94]

Will do. If I pull the hpcu and pump head to repair this, what else would you do to a 13000 hour machine with an excellent undercarriage but leaky old engine? I probably only need 200 hours from this machine.

 

[Cmark]

I would check the end-float on the shaft and swash plate bearings. If they were out of spec then new bearings would be in order. Obviously new hoses and seals.

After that it depends on what you find in the sump. If there's just dirt and bits of rubber from the perished hoses, then probably do nothing. If you find any signs of brass flakes then it would be wise to dismantle the rotating groups and inspect the slippers.

 

[Mr94]

 

[Mr94]

Time to make some progress