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.

 

[J_J]

I have never seen a fitting go into an elbow like that. That hose you point to is a 3000 psi hose, but why an extra hose would be connected to the flow is puzzling.

If I remember right, those wheel motors are 1500 psi motors, and the pump is a 3000 psi pump, pushing fluid through both motors in series and develops 1500 psi across both motors. You should have a hose connecting the two motors in series. A hose should go to a tee and then go to each motor, and then back to pump. I am not sure if you have a two section pump or not, otherwise, one section feeds the rear, and the other section feeds the front, in a series /parallel setup.

Do you have a clear hyd schematic of the drive system that you can post?

 

[Clumber]

JJ, see post #1 of this thread.

 

[J_J]

Thanks. That tells me the left side front and left side rear wheel motor are in series, and the same for the right side. It also shows that the pressure hose from the pump goes to a tee.

Don't see a hose for the third hose on the shematicc , which I now believe is not a case drain. My case drain comes directly off the motor casing.

I will bet that if you call Terry, he will say that it is a so and so, we just forgot to draw it in the schematic.

 

[3238dpw]

Ok, it has got me wondering. Is there one on the front too?

 

[BobRip]

I will now take a wild guess (my sincere apologies)

1. It might be an equalization hose between the two circuits to keep too much pressure off of one wheel motor if the other one slips.

2. It might balance torque if one side is spinning. (this is crazy).

Just throwing out stupid ideas here.

 

[Clumber]

Ok, it has got me wondering. Is there one on the front too?

No, only two 1/2" hoses going to the wheel Motors plus the parking brake cable.

 

[FAZTRAC]

Clumber
I gave you a bum steer on the third line. They are not motor case drains in this application, far from it. I looked at it closely and mine is also T'd into one of the pressure lines on both sides of only the rear wheel motors, but not on the front. The single hose links the two motors together when in forward direction, and equalize the pressure between the two rear motors acting presumably like a crude form of positraction without clutches. The pump always sees the sum total of the imposed resistant load from the four combined wheel motors trying to work.
The explanation of case drains in the previous post is valid, just not for the application on this machine. Sorry about that, didn't look at it close enough on first pass.

 

[Clumber]

Clumber
I gave you a bum steer on the third line. They are not motor case drains in this application, far from it. I looked at it closely and mine is also T'd into one of the pressure lines on both sides of only the rear wheel motors, but not on the front. The single hose links the two motors together when in forward direction, and equalize the pressure between the two rear motors acting presumably like a crude form of positraction without clutches. The pump always sees the sum total of the imposed resistant load from the four combined wheel motors trying to work.
The explanation of case drains in the previous post is valid, just not for the application on this machine. Sorry about that, didn't look at it close enough on first pass.

I have been saying that the third line goes from wheel motor to wheel motor, but the hose actually connects to the elbow fittings of the hoses that connect the front and rear motors on one side of the tractor. So the third line appears to join the left and right side drive wheels (not just the rear wheels). See the CAD diagram in Post #1 of this thread.

Also, I thought that each wheel spins independently anyway creating a positratction effect due to the series/parallel configuration. :confused2:

 

[ponytug]

I asked Terry about this connection on my 1445. He said, I paraphrase here, that it provided a flow relief to allow turns (i.e. differential like behavior), since the amount of fluid moving through the inside motors was less than that moving through the outside motors. Since it just equalizes the differential in the two flows, it can be a small hose. I have been tempted to wonder if valving it would result in a locking differential like behavior, but I haven't wanted to get the wheel motor circuits dirty by opening the line.

I hope that this helps.

All the best,

Peter

 

[cqaigy2]

ok i'll buy the "differential" idea.

That seems like a good explanation especially since Terry said it.