Cat 955 Transmission Not Shifting

[flyman]

After putting everything back together on the Cat 955L the transmission will not shift. I tried uploading a video to show you. Instead attached a picture.

Running or not, use the shifting lever from 1st to 2nd to 3rd, and it is hard to pull. You have to give it a little force. Just it will not stay in that gear and go back to neutral each time. Like something preventing it to shift.

Any idea how to test the pressure of the transmission pump? Could this be it or what am I looking for???

A little history, I had to pull/float the transmission, to put the transfer coupler back into place.

 

[Nige]

You cannot upload a video direct. You have to upload it somewhere else like YT first and then link it.
What's the machine Serial Number.?

 

[flyman]

It's a 85j* series. The video shows the resistant in the shifting while holding the lever. It gets harder, and harder when shifting through all the forward or reverse gears. It springs back to neutral when releasing the knob at any of the gears. I also show the control linkage following the shaft; rod assembly connected to the transmission moving as I'm shifting. That looks normal.

Before shutting it down, there was no signs of the transmission failing. Cleaned out the transmission magnetic filter, which had some small debris that I figure was from the gear/cross-shaft bearings being broken when pulling and replacing the clutches. Changed the transmission filter, which is similar to the old one, just could not find the exact same one. Differences being the center shelf in the filer very slight smaller diameter.

When taking the transmission out, only disconnected, the transmission from the mount, rubber flange joints, and floated it to get behind it. Also, a black wire to the under neath side of the transmission with copper tip had to be discounted. (Is this a modulating valve???)

When putting it all back together, seems everything line up correctly. Running the engine, the rubber flange spins, and I'm able to push the machine with another machine. Also use the bucket to move it back and forth.

I’m asking how to test the pressure is because I found an older post references the transmission has a spring to force the shifter back into neutral when the pump pressure is low. Locking it in neutral. This is to prevent you starting in gear. It mentions when the trans gets low on oil it loses pressure and goes out of gear. Another post say check the pump pressure on the filter at the plug in cover. Should be 350 psi.

Uploaded diagram, trying to figure out is this where to hook up the pressure gauge on the filter cover assembly and if I'm going down the right path?

 

[flyman]

Another comment, I drain, replace the transmission oil with new with fluid at correct level. While the transmission was floated/lifted, it was slant to get it in/out. Could oil drain from the transmission oil pump, removing pressure from the spring? Possibility another reason why this is happening? Then how is it built back up?

Nige, I did find an older post, where you are saying that you checked the Service Manual for an early 85J machine and reference the pump pressure at Low Idle is supposed to be 310psi minimum and 355+/-12psi at High Idle. Until I hear from you, I'm going to start here.

 

[Nige]

My best suggestion is to get hold of a Service Manual. For an 85J-prefix machine there are two different publications depending on Serial Number.

S/N up to 10128 it is REG00634, S/N 10129-Up it is SENR7364. Used copies of both appear to be on sale in the usual internet marketplaces but in typical fashion appear to be priced higher than new ones......

Try clicking HERE, put in your Serial Number and click Search.

 

[flyman]

Test. The pressure gauge on the transmission pump reads 100psi at Low Idle and 150+/-12psi on High Idle. What does that mean, lost flow? What do you look at next? Did the pump run dry, if so, can it be primed?

 

[Nige]

Based on what you said regarding recent disassembly work I would think the most likely cause is an air leak on the pump suction side. When you replaced all the components did you use new O-Rings/gaskets and are all the hose clips on the pump suction line tight.?

 

[Welder Dave]

Why is it such a problem to post a full serial number? There have been multiple times when a serial number was requested and all that was given was the prefix. Is it that hard to go to the machine and write it down or already have it written down? You need it for parts anyway.

 

[flyman]

I'll start tracking this down and also purchased o-rings. Also found this on the internet describing the operations in how it works. Am I correct, is it "valve (13)" that has the spring that is pushing the level back to neutral because I do not have enough pressure?

https://epccat.com/doc-t4/45605-systems-operation-955l-track-type-loader-power-train/

Operation​

When the engine is started, with the selector lever in NEUTRAL, oil goes through a passage in pressure control valve body (3) to differential valve (5). The oil goes around the differential valve to modulation relief valve (9). Part of the oil goes out of valve body (3) to selector valve body (20). The oil goes into protective valve (13). Oil pressure increases in valve (13) and causes compression of the spring on valve (13). This permits the transmission to be moved out of NEUTRAL position.

 

[Mobiltech]

My first thought would be to make sure it’s going to neutral before you start it. If you start it in gear it will do what you’re saying because of the neutral safety built into the trans.
Did you possibly bend the linkage or hook it up wrong so it can’t get to neutral.

 

[Nige]

Attached the complete SysOp for a 955L 85J-prefix.

 

[flyman]

My first thought would be to make sure it’s going to neutral before you start it. If you start it in gear it will do what you’re saying because of the neutral safety built into the trans.
Did you possibly bend the linkage or hook it up wrong so it can’t get to neutral.

Not moving out of neutral, starting the engine multiple times and running it trying to switch gears. Ran the engine for 15 mins to see if pressure build up, but no luck.

Transmission linkage is straight, not loose. You can see it move the lever on top of the transmission into each of the gears. Feel the force that is snapping it back is directly coming from the transmission lever and there are no odd noises coming from the transmission.

Was a small leak on top of the transmission oil filter element, o-ring split and ordered a new one. Pretty sure this isn’t the issue. Put the old filter back in, since the inside flow holes were slightly bigger, just to confirm isn’t it as well.

 

[Nige]

Was a small leak on top of the transmission oil filter element, o-ring split and ordered a new one. Pretty sure this isn’t the issue.

I’d say you were correct. The leak is most likely to be on the suction side - i.e. before the pump.

 

[flyman]

Found two o-rings needed to be changed. It's back up and running

 

[Nige]

Found two o-rings needed to be changed. It's back up and running

Which two o-rings exactly.?