953A transmission help.

[Junk runner]

I have a 1986 953 I hadn’t used in awhile because it wouldn’t move. I finally got around to working on it and checked the pressures. I determined it needed a filter so I changed the filter and oil. When I started it it wouldn’t move but the transmission whined when trying to go forward or backwards. I checked the pressure at the brake check port and it was 0 sitting or engaging forward or backwards. I put charge pressure straight to the brakes and the machine goes forward and backwards but very slow. I would appreciate any information on what to do next. The cab is up and the brake lever is pinned with a 5/16th bolt. The machine worked fine before the filter issue and there wasn’t any metal in the filter.

 

[Dave Neubert]

If you have the brake pinned that applies the brakes zero pressure is brake applied are you using 10 wt oil

 

[Junk runner]

Yes I put 10 wt in it. Im not sure what it had before that’s the first time Iv had to service this machine. I thought my manual said to pin the lever but I’ll check the pressure with it unpinned. Thanks

 

[Dave Neubert]

Well they tell you to pin it when the cab is tilted so you don't run yourself over doing tests

 

[Cmark]

Wrong way round. When the cab is tilted, the geometry of the brake pedal linkage automatically moves the lever to Brakes On for safety. To carry out tests, the linkage is disconnected and the lever is pinned in the Brakes Off position.

 

[Junk runner]

Ok I have it pinned. Any suggestions what may be causing the brakes not to disengage unless I put charge pressure to them and why the machine moves slow?

 

[Cmark]

You say you have the manual? All of it or certain parts?
Have you read and understood the sys op for the seven systems?
Have you removed the top cover yet? If not, do that and;
A. Disconnect the hose to the brakes. Leave the end to the brakes open and put a cap on the end going to to the transmission. Attach a pressure gauge to the brake pressure test port.
B. Run the engine at high idle.
C. Slowly move the FNR lever each way.
D. Watch to see if the underspeed valve (the thing with the big coil spring) moves up and compresses the spring and report back. Better still, post a video with sound.

 

[Junk runner]

I have the entire service manual and read through it although hydraulics are not my strong point if I even have one. I hadn’t taken the cover of yet because I wasn’t sure if it was more likely an issue under there or in the valve body but I will do that this weekend and report back. Thanks for your assistance.

 

[Cmark]

I'm pleased that you have the full manual, it will give you a good grounding so you won't need the basic points spelling out.
Have you already been through the troubleshooting chart and recorded venturi upstream and downstream pressures etc?

 

[Junk runner]

I went through the chart and it mentions a plugged orofice in the valve body but when I pulled the plug they said to pull out and check for pressure I had it which indicated it wasn’t plugged. I tried backflushing it anyway while I had it out. I haven’t checked the other pressures yet but will be doing that and reporting them all back to you. Do I check all pressures on high idle?

 

[Cmark]

Yes. And the actual high idle speed matters. Probably not so much just yet until you get the machine moving, but it's important for the correct operation of the transmission.

 

[Junk runner]

I tested some pressures today ill list them as the ports were numbered in my manual.
1 underspeed valve throat. 255 in park 225 slow and 200 fast.
2 underspeed valve upstream 255 it would slowly rise to 355 when forward or reverse were engaged
3 brake pressure 0 at park 175 forward or reverse. I had 0 brake pressure no matter what till today.
4 servo supply 250 park forward or reverse.
5 venturi throat 235 park 200 forward or reverse
6 venturi upstream 360 park 325 forward or reverse
8 charge pressure past filter. 185

I hooked the brake line back up and now brakes disengage and machine runs much faster than before although it was a very short test since the cab is up. If im reading it right which i sure wouldnt guarantee according to my book some of these pressure arent right even though its actually moving now. I havent pulled the top off the unit yet because I need to do some serious cleaning before I do so I dont get dirt in the system. Now that it moves if we get another warm day I can get it to the hydrant and do that.

The aerial number of the machine is 76y01500.

 

[Cmark]

Before you get much further into it, you should also check the motor case drain pressures. You'll need a low pressure gauge, something like 0-25 psi.

 

[Junk runner]

Ok I’ll get my book and see if I can figure it out. It looked like they were taking the front off the transmission to check that bit that’s the one test I didn’t read much about because I didn’t realize it was important or what it meant. I have a 0 to 100 gauge for my lowest right now I’ll grab another gauge to check that.

 

[Cmark]

It's the drive motors, not the HPCU. You'll see a test port on the case of each motor. If you have a large internal leak in the motor, it will take so much oil flow from the charge circuit that the rest of the systems can't function properly. Anything more than 2 or 3 psi on either motor and you have a problem.

 

[Junk runner]

All I had today was a 0 to 100 pound gauge but put it on the drive motors and the needle didn’t move at all. I adjusted the servo relief valve and got the servo pressure up to specs and didn’t do any other testing I do hear a fairly high pitch whine from the transmission I don’t remember hearing when it quit moving a year ago so I’m sure that can’t be a good thing.

 

[Dave Neubert]

I have had the metal lines on the servos leak at the fittings had to replace the fittings they are a compression type. But normally it will move and then quit moving as it warms up

 

[Junk runner]

I’ll check that when I pull the top could you visually see them leaking?

 

[Dave Neubert]

I would
say yes