Boomer 35 HST leaking hydro fluid.

mklingenmeyer · Jul 11, 2025

I recently picked up a 2011 Boomer 35 with 1230 hours from auction. Got it for a pretty good price but it looks rough and I knew it was leaking.
Topped off fluids and got some work done with the loader before I looked into this much. Seems to run and function good. whine from hst but could be normal from what I hear.
Theres a plate with weep hole at the bottom of the hst transmission housing and whoever had it before me decided to close the weep hole with a plastic plug and sealant. Maybe trying to hide the leak for auction? Maybe they thought they were stoping a leak. who knows. I knew it when I bought it though.
I pulled the weep hole plug and the whole plate. Some hydro fluid sitting there drained out. Also had quite a mouse nest packed in there probably from when the weep hole was open.
Anyways long story short. Looks like I have a leaky hst. Is it possible there’s a seal on these two Allen head bolts shown in the picture? I haven’t touched them yet.
I’m guessing I’m looking at splitting the tractor and taking the hydro unit to a shop for new seals unless it’s leaking somewhere else in there. Thoughts? Anything simple like those Allen head screws that I should be looking at before I take this apart? suggestions?

Waiting to get a service manual before I split it. It doesn’t seem too complicated.
I’ve restored some cars and done my share of wrenching but never dealt with Hydrostatic transmissions.
Thanks

oldnslo · Jul 11, 2025

I believe what you are considering Allen head bolts is actually plugs that would have seals on them but would definitely want a parts breakdown to confirm.

mklingenmeyer · Jul 11, 2025

You’re right. Looks like 11 and 12 on this diagram.
I doubt I’m lucky enough that it would be that easy but you never know. Could very well be coming above that but it sure seems like it comes from those plugs. I’ll clean things up and watch it.

If the plugs are suspect, think I need to drain hydro fluid to do that or would it just empty what’s in that pump if I took them off to replace the seals?

Mudfarmtruck · Jul 11, 2025

i would suggest checking the hst pressures before you go and start taking things apart. you must have somewhere to put a gauge/ hose and gauge.

oldnslo · Jul 11, 2025

mklingenmeyer said:
You’re right. Looks like 11 and 12 on this diagram.
I doubt I’m lucky enough that it would be that easy but you never know. Could very well be coming above that but it sure seems like it comes from those plugs. I’ll clean things up and watch it.

If the plugs are suspect, think I need to drain hydro fluid to do that or would it just empty what’s in that pump if I took them off to replace the seals?

I am not 100% certain what the drill paths under those plugs are connected to. Could just be a small amount of fluid from the pump or the drain the complete transaxle.

mklingenmeyer · Jul 11, 2025

Mudfarmtruck said:
i would suggest checking the hst pressures before you go and start taking things apart. you must have somewhere to put a gauge/ hose and gauge.

I’ll have to look into that. I think there’s a spot to test with removing the floor. Probably have to wait until I get a service manual to see. I’m not very familiar with the process.

mklingenmeyer · Friday at 7:19 AM

Looks like my only solution is to split the tractor to get the hydrostatic out and bring it to a shop or new holland dealer to have a seal kit put in it.
Anyone recommend a specialty shop in Wisconsin to bring the pump or is new holland dealer best?
I tried to inspect it with a little camera. I can’t see the exact leak but it seems to be somewhere in the middle on the hydro pump.
Feeling a little bummed about my auction purchase but I knew there was a chance I’d have to do this. Kind of expected it with an $8,500 tractor. Hopefully I don’t need a whole new pump that costs $2,700. It seems to work good just leaks so I’m hoping seals is all.
Could probably work the tractor through the summer with it dripping but I don’t like leaving hydro fluid all over my land. Plus my ocd makes me feel like I need to fix this.