Third Hose on PT-425 Rear Wheel Motor?

[Clumber]

While removing a rear tire I notice a third line on a rear wheel motor. See photo below. I traced it to the identical position on the opposite rear wheel motor. The CAD drawing does not show the a third line. Anyone know its function?

 

[BobRip]

It is probably a case drain to return leakage from the seals to the tank. Some PT have them, some, don't.

 

[Clumber]

It is probably a case drain to return leakage from the seals to the tank. Some PT have them, some, don't.

My first thought also, but the line does not go to the tank. the hose just taps into one fitting and goes to the same fitting on the other rear wheel. The tap my be on the fittings of the return hose...

 

[BobRip]

My first thought also, but the line does not go to the tank. the hose just taps into one fitting and goes to the same fitting on the other rear wheel. The tap my be on the fittings of the return hose...

Hmm, there is no really return hose. Sometime one is the supply sometimes the other. Is there a tap that you did not see somewhere in the middle of this hose that goes back to the tank. Or maybe you have mistaken which is the supply and which is the return. Hopefully others will join in as mine has only two hoses per motor, so I am speaking not from personal experience.

 

[J_J]

It is almost certain that it is a case drain. That case drain is used to lubricate the motor, and help take some of the heat from the hyd wheel motor.

There is probably a tee fitting that collects all the case drains and eventually routes them to the cooler, then tank.

On my earlier 90's 1445, the case drains collect into a manifold and goes to the case of the VSP pump, and then to the cooler and then to the reservoir/tank.

Some hyd wheel motors may also have another hyd hose used to release the spring applied brakes.

Did you actually follow the hose from start to finish, or did it disappear under the engine and appear at the other wheel motor?

Can you get a small camera up under the engine and take some pictures?

 

[Clumber]

I will try to get photos this weekend.

 

[FAZTRAC]

Clumber
I have an identical machine to you, probably only a couple of serial numbers away from yours.

The small third hose is postively what is called a "case drain". Almost all high quality high pressure, drive motors have them. They are also found on all piston type swashplate pumps and motors.
Most component manufaturers want these case drains routed directly back to the top of the reservoir. They drain the excess oil out of the motor and pump housings which leaks past pistons in pumps and gearolers in motors and cannot tolerate any back pressure or it can blow out the shaft seals that they are meant to protect.

Based on your level of curiosity, You might want to purchase one of the good textbooks put out by the Parker C. or John Deere or any of the Womack publications. They give good detail and illustrations of all of the innards of your PT tractor and attachments.

It will simplify your trouble shooting efforts, and give you a more holistic understanding of how this PT animal works. Cheers

 

[Clumber]

FAZTRAC, thanks for response. Can you trace the small hose back to the tank?

 

[cqaigy2]

Looks to me like the smaller hose is connected to the larger hose and not directly connected to the motor.

Hard to tell for sure from that single picture, but they could be connecting the input of both motors together, kind of like a series/parallel setup? Depending on which motor that stalled, the input pressure would rise and the output of the same motor would fall, starving the input of the second motor in series unless you provided a path to the second motor's input.

Looks good on paper. :laughing:

I wonder how well that would work if the flow was reversed, like say going backward?

And i don't see a return line going back to the tank shown in the schematic either so maybe that third line does go back to the tank somehow.

 

[Clumber]

It is almost certain that it is a case drain. That case drain is used to lubricate the motor, and help take some of the heat from the hyd wheel motor.

There is probably a tee fitting that collects all the case drains and eventually routes them to the cooler, then tank.

On my earlier 90's 1445, the case drains collect into a manifold and goes to the case of the VSP pump, and then to the cooler and then to the reservoir/tank.

Some hyd wheel motors may also have another hyd hose used to release the spring applied brakes.

Did you actually follow the hose from start to finish, or did it disappear under the engine and appear at the other wheel motor?

Can you get a small camera up under the engine and take some pictures?

Here are some new photos that show the third hose as configured on the rear Wheel Motors.

Pics 1 and 2 shows the Left Wheel Motor (drivers side of tractor). The third hose connects to the fitting and not the motor. There are only two ports on the motor as shown.

Pic 3 shows the third hose going from the Left WM to the middle of the tub.

Pic 4 shows a slightly different view of the hose at middle of tub. I can move the hose at this point and see movement at both wheel motors. The hose dose not return to the tank.

Pic 5, taken from the Right side over the right wheel motor. It shows the hose from the middle of the tub to the WM access hole in the tub. The hose is plain sight as it passes under the large hose under the pump. See Pics 3 & 4. I can run my hand underneath the hose. There is no T-valves anywhere on the hose. It just goes from WM to WM.

Pic 6, taken from the front of the tub shows the third hose going thru the tub side to the right WM.
I doubt that this is a case drain. But my knowledge of hydraulics is limited.