question about H.S.T. pressure relief valves

stubbornrichard · Nov 15, 2008

i am taking my older model b7100 kubota to the dealer on monday to run some pressure tests on the h.s.t. to see if they can figure out why it has low power, hopefully it will just be these pressure relief valves that i found out about on here, if so i was wondering if anyone has had these fixed and was it a big job or could i do it myself, or does the h.s.t. have to be completely dissembeled, any help would be great!! thanks.

alchemysa · Nov 16, 2008

Have you checked the metal mesh screen. Blocked screens are not uncommon and can bring a HST to a standstill. (Part 070 on the pdf).

john_bud · Nov 16, 2008

Four of the relief valves should be externally accessible.

There are probably 5. Charge pump relief, filter protecting relief, forward high pressure, reverse high pressure and case relief.

I think the case relief is NOT externally accessible. It can be any of them, the hst filter or the strainer. My WSM shows the HP relief should be set to 4836-5124 psi. That's for the L3410 hst, but should be similar to the B.

You would need a manual to find the ports and reliefs and a set of gages. 0-1000 psi and one to measure the high pressure. Not hard to do, just hard to guess where to measure with out a manual! On the L, the ports are under the drivers left foot behind the filter. Three hex head plugs verticlly in the outside edge of the HST.

Charge pressure is 342-370 psi. HP is 4836-5124 psi.

The three ports are P1 top (reverse), P2 middle (charge) and P3 bottom (forward)

You test the forward and reverse in high gear brakes locked maximum RPM and stall it for NO MORE than 10 seconds. Oil temp MUST be 120-140F before you start.

jb

stubbornrichard · Nov 18, 2008

i was not able to take it in on monday because they are busy untill next week but the guy told me it is atleast a few hundred dollars to run the tests, i guess its a fair price because i dont have the hydraulic pressure guages and i can only imagine how much those are, for a while i was thinking that i was over working the tractor with the front end loader plus the 4 foot brush cutter but i hear alot of people run the same attachments and there b7100 goes up hills just fine so hopefully i dont spend alot of money to just have the same problems with this little tractor, thanks for the info john i will be taking a look tomorrow to see if i can find a couple of these valves

john_bud · Nov 18, 2008

Check out places like surplus center (link from this site), or even NAPA. Gages are in the 20-30 dollar each range. Adaptors will probably set you back about the same. Price to do it your self is about $100 + the work shop manual to tell you what gives on your model. You should buy a manual anyway.

The estimate sounds high. The tests can be all done in about 30 minutes, including running the tractor into the shop. I would guess that he just took a butt covering pure wild guess. Now if that included taking the return line screen out and putting on a new filter, cleaning the fluid and putting it back, then it's a fair estimate. It could also include running the tractor around to heat up the fluid at shop rates.

jb

Rikchester · Jul 14, 2015

Hello Kubota experts. I am new to the orange tractor and this forum. I recently purchased a Kubota B20 but it doesn't drive forward or reverse. I did a lot of research but cant figure out exactly what is wrong with it. I think it might be one of the valves but not sure which one. Everything else works fine. Can anybody give some advice on what should I do and where can I find transmission parts for this model. E bay doesn't seem to have anything useful.
Thank you for any help.
God bless you.