Fluid transferring to front diff through piston seals

[Cwalker7]

I have been working on a 950H(K5K) Cat loader that keeps transferring hyd oil from the brakes into the front diff. I have checked all pressures and tried new pistons but no luck. I believe the 325-3780 D ring brake seal is the issue. When this seal is in the housing, it barely protrudes out. When pressured up on the machine there is a steady but slow flow of hyd oil running out. Scratching my head at this one as 4 other mechanics in my shop have taken a look and don't know why it wont hold. Last possible problem I can see in the housing being worn as the machine has 20k hours on it but it shows no sign of obvious wear. Anyone seen something similar or know what I am missing? Thanks

 

[funwithfuel]

Ok, disclaimer, not a cat guy. Have you isolated which brake is leaking? When I'm faced with this problem, I rig up a port o power pump with a shut off valve. Pump the brake up to max and shut the valve. Observe the pressure for a leak off. Do the same to each side.
Another possibility for front axle oil gain is diff lock. I've had a vickers valve that allowed oil to apply to the diff lock all the time until the piston seal failed.

 

[heymccall]

Is you using backup ring?

 

[Cwalker7]

I am using the backup ring yes

 

[Nige]

That loader has separate circuits for the front and rear brakes.
What brake pressures did you measure in the front & rear circuits.?
The specification for the rear axle brake pressure with all machine systems at normal operating temperature is 1250 ± 50 psi. The specification for the front axle brake pressure is 30psi higher than what was measured at the rear axle.

Have the accumulator precharge pressures been checked yet.?

 

[Cwalker7]

Rear axle was measured at 1210 and the front measured at 1245. Brake accumulator pressure was confirmed at 1030 psi. I installed 2 new 470-3802 accumulators

 

[Nige]

Is the brake oil bypassing both front brakes or just one.?

 

[Cwalker7]

Through both at at the 325-3780 brake seal

 

[Nige]

At any point have the three brake retraction springs 293-3609 (Ref #24) been replaced.?
I came across a SMag regarding the introduction of a new brake piston seal 325-3780 & the backup ring 325-3781. There were 3 items to be replaced, the third of which was the spring.

All three parts mentioned above were introduced to the 164-3018 Brake & Planetary Gp at CHG06 on 11/11/2008. It would be interesting to date the machine and figure out if it was originally built with the former brake retraction spring P/N 112-0762.

Whether this is relevant or not I'm not sure, but asking anyway.

 

[Cwalker7]

Springs were replaced on both sides, standard practice to replace

 

[Nige]

In that case I would suggest getting hold of the measurements of the housing and checking it against specification. I don't have that information I'm afraid.

I get the impression though that, despite the piston seals not standing too proud of the housing when installed, they will move once brake system pressure is applied and should seal the space between the housing and the piston.

 

[Nige]

I could understand one piston seal leaking but to have it happen to both of them on the same axle at the same time is strange, despite the fact that the front brakes do more of the work than the rears.