JD 455 snowblower won't stay raised

[Limoges 455 JD Owner]

Hello, new JD owner here. I recently purchased a 455 with 575 hours on it, and I noticed the 47" snowblower attachment doen't stay raised: after a few minutes (5ish? Haven't timed it, but I'll notice it's lowered to the ground.). This is an issue because I'd like to raise it to a specific level when clearing snow off my gravel driveway, but lower it when clearing snow from my paved driveway.
I haven't changed the hydraulic oil and filter yet: will be doing that in a while.
Also: I can push the lower lever forward, and the blower will actually lift the front of the tractor up, but this doesn't happen on its own.
Edit: I just tested the mower deck, and it too drops after a few minutes. So I assume this is systemic.

Thanking you guys in advance.

 

[beenthere]

Welcome to TBN

Lowers when tractor is running, or just when the tractor engine is turned off ?

Probably nothing wrong, just the way internal hydraulics is built/designed.

Maybe others have a better answer to offer.

 

[bigtiller]

I had the same setup in 2002.
That's the way they work, there's nothing wrong with it.
I used to watch the depth of the track that the front tire made, to judge how high/low the blower blade was.