Third Hose on PT-425 Rear Wheel Motor?

J_J · Jul 3, 2011

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 · Jul 3, 2011

JJ, see post #1 of this thread.

J_J · Jul 3, 2011

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 · Jul 3, 2011

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

BobRip · Jul 3, 2011

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 · Jul 3, 2011

3238dpw said:
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 · Jul 3, 2011

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 · Jul 4, 2011

FAZTRAC said:
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 · Jul 4, 2011

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