"Screeching" sound

arlen4720 · Apr 10, 2015

It is absolutely the relief valve. That's the way they sound. I was surprised too when mine first did it. They crack open at almost 5500 psi so it has a different sound than a typical 2500psi hydro relief. I don't believe that they are adjustable...At least there is no mention in the service manual about it. There are test ports to check the pressure with a 10,000 PSI gauge.
The procedure to check it is to put it in C range, then set the parking brake, rev to full throttle, then push the pedal. It should screech, and you take your reading. Repeat for reverse (2 separate relief valves, 2 test ports)

Are you in C range when you are doing this? I have a real hard time making mine relieve in B range, and darn near impossible in A range, but it will relieve at the drop of a hat in C range.

Sysop · Apr 10, 2015

He said the video example was in high gear, you may be onto something. :thumbsup:

JMER817 · Apr 10, 2015

Yes C Range. Do you have a 4000 series John Deere? I had an older 4310 (same as 3320 now) and also rented a 3320. Neither of them did this.

andy1981 · Apr 10, 2015

I have 2 4720's they both do this and have since they were new, it's usually in high gear with a heavy load going up a hill, or starting out when I should be in mid range

arlen4720 · Apr 11, 2015

JMER817 said:
Yes C Range. Do you have a 4000 series John Deere? I had an older 4310 (same as 3320 now) and also rented a 3320. Neither of them did this.

Yes , I have a 4720, which probably would do it worse than yours because it has more power to overwhelm the relief valve.
In my opinion, C range is not for doing any useful work, just transporting.

You could check the pressures if you think they may be weak. I did have the dealer check mine, and they were fine.

JMER817 · Nov 6, 2015

Update,

Dealer found hydro pressure to be at 3200psi from the factory. Spec is 2500psi. Checked and adjusted under warranty. No more screeching.

arlen4720 · Nov 7, 2015

JMER817 said:
Update,

Dealer found hydro pressure to be at 3200psi from the factory. Spec is 2500psi. Checked and adjusted under warranty. No more screeching.

Which pressure? The implement circuit is supposed to be 2500, but that doesn't have anything to do with the hydro tranny. The tranny circuit itself is set north of 5000psi.