L3901 HST filter seal keeps blowing

[HyenaAlley41]

I recently bought an L3901HST with about 80 hours on it. I was out mowing yesterday and the filter under my left foot started spraying hydraulic fluid everywhere. As soon as it happened, I immediately shut the tractor down. I noticed the the seal for the HST filter had blown out. The filter was all gray without any part numbers. I thoughts are that it's original to the tractor and the tractor did not have the filter replaced at 50 hours. Continuing my thoughts, I figured the filter seal was old and hardened and couldn't hold pressure anymore. This morning I went down to my local dealer and picked up the two HST filters and some UDT2. I cleaned the filter area, checked for any issues before replacing the filter and topping off the hydraulic fluid. No I didn't double gasket the filter. I then cranked up the tractor and let it idle at low RPM for a few minutes to circulate the fluid before I continue mowing. After idling about 5 minutes, I brought the RPMs up and the seal on the new filter rupture again. Ok, so it isn't a 'old hardened seal' problem. I searched these forums and chatted with some more mechanically inclined folks I know. I took the pressure relief valve out, cleaned it off with brake cleaner, put it back in and still the seal blew out again.

As of right now, I'm stumped. Could it be that the pressure relief valve is broken and I didn't notice? The spring is fine, there are no shims on the bottom like someone was trying to hotrod the hydraulic system. Is there an easy way to check the pressure relief valve? Or is there something else that I can check/clean/adjust. I'm open to suggestions. Thanks!

 

[ruger1980]

Are you absolutely certain that it is the filter leaking and not the tubes and o-rings to the filter mount? Is the mount and bracket all straight and no signs that it has been tweaked?

 

[HyenaAlley41]

Yes, the o-ring on the filter was outside the the filter body. When I unscrew it and re-seat it properly, I can turn the tractor on and let it idle and no oil is going anywhere. As soon as bring the RPMs up, there's a small 'pop' sound and fluid spewing everywhere again and the filter seal is again, on the outside of the filter.

As far as I can tell, this tractor hasn't been messed with, to include the mount/bracket the filter is on. I did look witness marks on bolts/hoses, etc and I can't seem to see anything 'off'.

Thank you for your reply.

 

[Russell King]

Are you sure you have the correct filter in the correct location?

Can you compare the old filter to the new filter to see if there are differences between old and new?

 

[HyenaAlley41]

Yes. When I pulled the filter off I double checked that they looked the same, same seal, etc. When I pulled the old one off, I was hoping that the seal was noticeably hardened, it was not. The replacement of that filter, the one under my left foot that keeps blowing out is a HHK70-14073.

The one on the right side is a TC422-82620 and much larger.

 

[whitetiger]

1. Install a new HST filter and check HST charge pressure at the P port per WSM, but shut down immediately if the filter seal starts to extrude before completing the test. [1]
2. If charge pressure rises above the WSM factory specification of 0.5 to 0.6 MPa / 5 to 8 kgf/cm² / 80 to 90 psi, re-open the charge relief area and inspect the bore, seat, port passage, and outlet path—not just the poppet and spring. [1]
3. Blow/flush the oil path between the HST filter outlet and charge relief valve, then inspect the HST filter base/inlet pipe and cooler-related return passages for restriction or debris. [2]
4. Cut open the failed HST filter and inspect for collapsed media, yellow/tan filter adhesive, silicone, plastic, or water-contaminated/milky oil.
5. If pressure is not high but the filter still deforms or blows the seal, inspect the suction hose/pipe to the filter housing for deformation, twist, kink, or internal collapse; replace if questionable.
6. If no external restriction is found, inspect the HST port block/passages and case relief path for blockage before returning the unit to service. [2]

(1)


(2)

 

[HyenaAlley41]

Thank you for this. This is probably what I am going to have to do. I was hoping that someone had run into this before and it would be a 'quick fix'. Is there a pressure tester you recommend for this job? Thank you.