charge pressure

[dusty-t]

Hey Guys. I took the b7200 to my local dealer because I thought the hydrostat was weak. I called today and they said that they checked the charge pressure it dumped to nothing. They say I need to rebuild the hydrostat. I don't know if he was planning on doing further testing because he said that he had'nt tested the high pressure yet. I am confused. HELP!!

[Service Dept Vic]

Dusty-t,

It's not developing an initial pressure "build", or charge, required to advance the tractor. Once in motion, less charge or pressure build is required to keep it moving, so the pump merely maintains the charge up pressure.

This is why you couldn't make an incline or grade. Without the charge pressure building and holding the transmission will just slip when it encounters a slight to moderate resistance.

Sorry buck-o, it's HST rebuilding time.

[dusty-t]

Thanks for the reply Vic. I don't suppose there is a rebuild kit available. And yes I would rebuild it myself. Wengers in PA have a used one for a thousand bucks. But I don't need the tractor so I would rather take a crack at rebuilding it myself. But I need to Know I can get the parts I need before I start. Thanks again.:cool:

[eserv]

I would check the charge suction strainer before I committed to rebuilding the HST. Then overhaul or replace the charge pump. parts for the main part of the hst are very expensive and likely hard to get for your b7200

[dusty-t]

Thanks for the reply eserv. I gather the suction strainer is one of the screens that go through the hydro banjo fittings at the sides of the hydrostat unit. If so I have replaced both with new screens.

[eserv]

FYI A new HST to fit your tractor will sell for about 2300 Canadian. Kubota have one in stock at Markham.
Mount Forest Huh? My brother lives just north of Shelburne!

[ipz2222]

hst. Does that stand for hydrostatic transmission??

[eserv]

Yes, HST stands for Hydrostatic Transmission.

[eserv]

Hi Dusty-t
I didn't read your other thread until after i"d posted in this one so I didn't know you had changed the strainer.
The hst can be rebuilt easily enough, the problem is that kubota don't supply any parts for it anymore. That is not to say you cannot get parts from Kubota but you'll have to have a good partsman who is willing to take the time to source them from other models. probably it is rebuildable without any parts though!! if there is a good machine shop there who can resurface the valve plate (end cover in this case) and the rotating groups it might be all you need. This sealing surface gets scored and won't seal causing a "weak" hydro. This poor seal is where your charge pressure goes also.If it pulls smooth but lacks power and speed that is likely your problem. The check valves and high pressure relief valves, unless both of them are shot, will cause poor performance in either forward or reverse, but not both.
Could also be as easy as a broken spring in the pump or motor too.
You'll likely have to do it yourself though as few dealerships or repair shops will go inside one! You'll be surprised just how simple it is when you take it apart , just be as clean as you possibly can, these things hate dirt!!
Go for it!

[dusty-t]

Yup sounds like a plan. I will start tomorrow. I am really slow. 20 yrs worth of rheumatoid arthritis. But I do have a fair bit of sticktoitiveness. I have a wsm and a real good machine shop nearby. Thanks for the advice and if I bugger this up I won't blame anyone but me. And Yeah your brother is only about 30 min from me.:cool:

[dusty-t]

Hey Guys. Well it seems the project is on. Did some rippin and tearin tonight. Tomorrow I'll start pulling it apart.So far I have only stripped the the back.One question, in the fourth picture is a little black plastic thingy, is this a vent.

[dusty-t]

Well so much for that project. I was going to lie and say that other stuff broke and I didn't have time. And stuff did break down, but that wouldn't stop me from doing the Kubota. When I did the clutch, I had to do the clutch, it was busted and wouldn't move. And doing a clutch is something I am familiar with. T Since I cleaned the cooler it seems to have more power every time I drive it. So I put the wheels back on it and took it for a toot. That hill that it had trouble with. I can now stop half way down and back up it again. It is making the engine work quite a bit more than it did before. It has more power than it has ever had since I have owned it. The hydrostat is new territory for me. I guess I am wimping out. I don't want to tear a tractor that I really really like apart when it is working better than it ever has. Having said that am I going to do more damage by using it. I mean it has been like this for 4 years. And it is better now than it has ever been. I know it is not as powerfull as it could be. I guess what I am saying is that I am happy with it the way it is. AM I MAKING A MISTAKE ??. :confused: I don't worry this much about my kids.:eek:

[eserv]

Hi Dusty-t
Was the cooler plugged up or restricted? I guess if you are happy alls good, right? I don't think you'll cause any more damage running it like it is provided it doesn't overheat. If you can hold onto the cooler lines it is cool enough.
Ed

[dusty-t]

Hey eserv.Yeah the cooler was restricted. Quite a bit. I soaked it in gas for three days,then flushed it with tranny fluid umpteen times. But that was before I had the hydro tested.I only ran it for maybe 10 min before I took it to kubota to have it tested. And so far there does not seem to be much for heat. But the motor seems to be working harder now which means the hydro is working harder. I'll run it for a while tomorrow and keep an Eye on the hydro for heat. And thanks for helping, I appreciate it.:cool:

[dusty-t]

Ok Guys are you ready for this. I really didn't want tear that b7200 apart again.So I put wynns tranny flush through it. I figured if the hydro was pooched anyway so what did I have to lose. Well it will now dam near climb a wall in high range. Three point hitch don't work but I can climb a wall. Well actually the three point hitch does work when I'm climbing the wall. OK it was a small hill of about 45 degrees it wasn't a wall. And when I get back on the level the hitch won't go down. Any ideas anyone. If I wrecked the hydraulic pump I can deal with that. As long as my hydrostat is alright. And if I wrecked both then I will really feal like a goof. OK I started the tractor, both ports on the hydraulic block have plugs in them. If I turn the lever out the engine lugs down in a hurry. To me that means that the hydraulic pump is working. That leaves the 3ph valve which I tightened the bolts on yesterday. If I rev it up to about 2500 rpm the hitch will come up slowly.

[dusty-t]

Hey Vic And Mr K. maybe you can make a video about what not to do to your B7200.:D

[dusty-t]

Ok so it seems that using wynns tranny flush at least in the short term was a good idea. The hydrostat has a lot more power. The 3ph lever was just worn and sloppy and slipped off the fork, but the fork or the internal thingy that looks like an H was turned a bit so that didn't help. Anyway fixed it up stuck it back together and the 3ph works fine. Would someone please let me know of any information on the long term effects of using tranny flush. Thanks.:cool:

[eserv]

Hi Dusty-T
I don't think the tranny flush will do any harm........ Don't really understand why it did any good either!! Unless it made the oil a little heavier. I meant to ask you what oil you had in there? A hydrostat is about the only mechanical thing I've ever seen heal itself! Sometimes with a good oil change and new filters they will sort of wear themselves in over time. I wouldn't count on it but I have seen it happen.
Ed

[dusty-t]

Hey Ed thanks for the reply. I had dextron in it, flushed it and changed to hydraulic oil. It really surprised me when the power jumped like that.

[eserv]

I wouldn't recommend Dextron, I think it is too light for the kubota. That being said many are using it with good results. I recommend Kubota UDT ( of course I would, I work for the damn company!!) But It is a really good Universal Differential Transmission oil and many many times I've had customers call with problems and I ask them to change to UDT and the problem goes away!! especially true with powershift and hyd. shuttle tractors.
Ed

[dusty-t]

The engine actually gets warm now. In the last 4 years it hasn't had to work. But just warm not hot, hydrostat too. I figured I was in for a lot of time and a fair bit of cash to fix this. So far I am really really pleased. But I'm not counting my chickens yet!:D

[Service Dept Vic]

Ya, we already had a meeting on that earlier this weekend!

[Service Dept Vic]

Dusty-t, you've got a simple issue on that 3 point, something that you over looked. Remember, the 3 point works just like a bottle jack or floor jack. Think of it that way when you are diagnosing the problem. It's real simple hydraulic/mechanics!

[dusty-t]

Ya thanks Vic, I had it apart a couple years ago to put a new relief valve in. I had an awfull time getting the control arm and regulator arm into that fork thingy. Turned out when I put it together the fork thingy was twisted a bit and the control arm fell out. I'm either going to start using pictures to explain what I mean . Either that or start learning the names of thingys. Anyway I figured out the trick to make it go together easier and right.Please for the love of God do not ask me how I did it now!

[sdcassel]

What was the end result; were you able to rebuild your HST? I have the same problem; the transmission works fine except on a grade or really loaded.

The dealer tested and the charge pressure is zero. The screens are clean, so they say the only option is a new HST unit for $1600 (parts alone). I can't find a machine shop willing to look at it, since Kubota doesn't show any serviceable parts.

I've got too much time and $$ invested to give up now!

[sdcassel]

Is there any way to test a used HST that was pulled from another B7200?

[Service Dept Vic]

Not really.

[sdcassel]

Can an HST from a B7200 be rebuilt?

[sdcassel]

We pulled the charge pump off the front of the HST. The rotor was shattered and the key sheared. Now I'm looking for used parts to avoid the $1600 price tag for the entire HST.

[sdcassel]

I found a used B7200 HST to pull the charge pump rotor from. I know of one other person that the only thing wrong with their HST was a shattered charge pump rotor (and probably sheared key). I'm thinking that when I get the intact rotor I'll see if a machinist can duplicate it. How common is it for that rotor to fail, and what might cause it? My mechanic thinks someone may have serviced it before and reassembled it incorrectly; the key may have sheared and scrambled the rotor.

[dusty-t]

The end result was that the hydro was much improved. I don't think it is as good as when it was new but it was a lot better than it had been. You must understand, this tractor had very poor service before I got it. I think it was just 25 or so years of junk build up in the system. I flushed the system again, changed filter, checked screens and put kubota fluid in it. I sold to it to a guy local to me about a month ago, and no bad reports so far. And yes I explained the history to him. Good luck with yours. I have been so busy lately I haven't been on here much. I have a B8200 that I need to get at too. Keep us posted.:D

[sdcassel]

The charge pump inner impeller (gerotor) was not reproducible, according to the machinist. I'm waiting to hear back from an outfit in Tupelo, Mississippi that rebuilds HSTs to see if they can get the part for the charge pump, which is manufactured by Kayaba. In the meantime, I used the impeller out of the used HST, and my transmission works good as new! I split the salvage HST and transmission, and will re-sell them on Craigslist to try to recoup some of the $450 I had to pay for the salvaged unit, just for that one little part! But that beat the $1600 for a new HST. I will make sure the buyer of the HST(E) knows the inner impeller is missing.

[eserv]

Hi
On the f series tractors you can direct the return oil from the hydraulic lift into the charge curcuit to get a machine running with a failed charge pump ( not all that uncommon a failure either! I think it might be moisture in the oil freezing and locking the pump which breaks when you then try to start the tractor) I have never tryed using return oil on a b series, it would be a lot harder to do because of the design of the hyd. system. Using a little enginuity almost any pump could be put into service to act as a charge pump even a power steering pump driven off the fan belt! Now we ARE getting a little redneck! It would get an otherwise useless tractor functional again considering Kubota only supplies expensive new Hydro assemblies for them
Ed Service

[dusty-t]

Hey Guys, This thread just keeps coming up with more info. Someone has to get into fixing these old hydrostat units. $1500 for the hydrostat unit is a lot less than I was quoted.They don't seem to be that complicated a unit, yet most of the service techs I talk to have either a blank look or fear in their eyes when discussing repairing them. And this isn't just kubota, it is any make of hydrostat. Sdcassel and eserve you guys seem to be ahead of the game on this. Sdcassel you are the first guy on here that I have seen who actually had the moxy to even rip the thing apart let alone fixing it. And Eserve you sound like you have done the same more than once. Thanks for the replies guys, it really gets a guy to thinking.:cool:

[Service Dept Vic]

Awesome information guys! I'm like Dusty-t, a little reserved about opening up Pandora's box!

[sdcassel]

I have half a mind to find a machinist that will reproduce the impellers for the HST charge pumps! No telling how many discarded HSTs are out there that only need those charge pump parts replaced! Seems like a guy could make a living off saving others like me some serious $$$!

[brokersdad]

Funny I came across this post because I posted here a couple weeks ago how i thought my L3010 was lame for power. I was talking to the service rep at the local dealership and he told me that in the L3130 I believe they found some to have low pressure in the hydostatic, but the one in particular he told me about, he claimed they made an adjustment and it made a huge improvment . He said it was about an hour and a half job to check it over but he highly doubted I had an issue there. As that post i made then stated, I think it was me anyway not used to running it. :) Anyway, what he said to me, anyone know if adjustments are possible , just so i know in the future.

[dusty-t]

Hi Brokersdad, There are several different relief valves to set the pressures in different parts of the hydrostatic transmission but unless you have the proper equipment and know how its not some thing you want to try at home. There is a setting for the hydro pedal so that it centres properly and doesn't creep, and there is a dampener so that you don't smack your face off of the steering wheel when you take your foot off the pedal.:D Dusty

[brokersdad]

yea Dusty, not something i would ever attempt, just was curious if it was something that could be checked if a problem ever arises :)

[Greg]

Hi Brokersdad, There are several different relief valves to set the pressures in different parts of the hydrostatic transmission but unless you have the proper equipment and know how its not some thing you want to try at home. There is a setting for the hydro pedal so that it centres properly and doesn't creep, and there is a dampener so that you don't smack your face off of the steering wheel when you take your foot off the pedal.:D Dusty

Ahh, good info. I nearly slammed my face into the steering wheel this week when testing my my loader hook up. Makes sense that there is an adjustment for this.