B1750HST hydrostat problems

[chipdip268]

Hi all... new to the forum here....wonderful site..
I have a B1750hst that has been giving me fits and I can't seem to figure out what the deal is. It will work like a hoss and run perfectly fine for about 20 minutes and then it loses drive. I have checked with the local dealers here and they are baffled too . I have replaced the hydro oil twice, cleaned the suction screen twice and still having problems. As far as describing what it is doing, it will stall out after about 20 minutes... the hydro pedal shutters in F and R and the tractor will not move... the engine does not stall, the FEL and backhoe work perfectly fine but no drive.. if you slow the rpm's down, and barely move the pedal it will try to move.. kinda like rocking a vehicle in snow. If I can get it to start moving, it will travel fine unless I get on an incline or sink in any ground then it stalls out again... I bought a new cartridge filter for the hst but haven't put it on yet. I am thinking, correct me if my presumption is wrong, that as I continue to use it maybe there is some grit or dirt in the oil and it is getting stirred up and eventually clogging the cartridge filter and starving it for oil. I plan on getting it to the point of where it stalls and then immediately remove the filter and hopefully capture any dirt that is trapped in it... then crank it over and see if oil purges out to make sure the charge pump is working, and then put the new filter on. Anybody got any input on this idea?? Any help or ideas are appreciated... Thanks

 

[traildust]

It works fine for about 20 minutes than nothing? Hmmm...

Would it matter if it was driving during that time or if you started, let it run and never drove it for 20 minutes and then tried driving? Does it matter?


You mentioned fluid levels good, JUST by chance how about the vent? Is it free and clear of any lady bugs?


Scott

 

[chipdip268]

I don't know... I haven't actually done that..Last weekend I did some digging around a stump using the backhoe and then when I went to move it, it just sat there in the dirt. I had to use the hoe to get it out of the hole that it was in because of the ground being soft, and when I would try to move it it would just lurch the pedal and then make a low sounding "waaaah" I would venture to say that it will do the same thing, but I will give it a shot when I get home from work.

 

[traildust]

I don't know... I haven't actually done that..Last weekend I did some digging around a stump using the backhoe and then when I went to move it, it just sat there in the dirt. I had to use the hoe to get it out of the hole that it was in because of the ground being soft, and when I would try to move it it would just lurch the pedal and then make a low sounding "waaaah" I would venture to say that it will do the same thing, but I will give it a shot when I get home from work.

Have you thought about the clutch?

When the tactor will behave on first start-up, get the tractor safely against a tree or wall set the brake nice an tight and push the pedal. See if this exposes any clutch issues. As you know, the engine should seriously bog down and maybe even die. If it is a good clutch the tractor will fight to stay alive and the wheels will spin. Bad clutch and it will explode ripping your legs off.......Just kidding

Also just for fun don't forget to check the hydro vent.


Scott

 

[Butch]

I have never tried it but.... if you were to push the clutch is and then try to go forward or backward.... is the HSD supposed be disengauged and the tractor not move?

I will try that tomorrow... I believe the clutch should disengauge the HSD from the transmission.

If that is the case sounds like you may have a clutch issue. Can you smell any thing getting hot?

Butch

 

[traildust]

I have never tried it but.... if you were to push the clutch is and then try to go forward or backward.... is the HSD supposed be disengauged and the tractor not move?

I will try that tomorrow... I believe the clutch should disengauge the HSD from the transmission.

If that is the case sounds like you may have a clutch issue. Can you smell any thing getting hot?

Butch

Hey Butch,
For grins I did just that today to see if I could replicate his issues and that's when I started thinking clutch.

Tractor running and clutch all the way in, pushing the FWD / Revers pedal has no effect, no sounds no nothing.
Leaving the FWD pedal pressed I slowly began releasing the clutch and I could simulate the pullsating pedal.

I also put the High Low in neutral to see if maybe this could cause something. Absolutely nothing happens trying the the pedal and clutch combinations.

This is what makes me think he has a clutch issue as well.


Scott

 

[chipdip268]

Well, I got the tractor out and went stright for the dirt pile... once i started into it I tried to spin the tires and it just stalled.... but I did notice that when it stalled, the rpm went back to normal with the pedal down like it was bypassing or like i didnt even have the pedal pushed down at all.... could it be a relief valve in the hst?? It does it in forward and also in reverse like when i try to backdrag. You can start to hear the whine of the hydrostat as it tries to push and push the pedal a little bit farther and all of a sudden the drive kicks out... kinda like a relief valve or something.... If it is the relief valve(s) is it very hard to get to them to check or clean them or how much work is involved in it? If anyone has a picture of what i would be looking at it would be appreciated.... or if anyone has any ideas??

 

[Butch]

I have to leave that question on the relief valve to Brother Vic... too far above my pay grade...

 

[chipdip268]

I have to leave that question on the relief valve to Brother Vic... too far above my pay grade...

I hear ya on that. Last night I went and did some more testing on the tractor and I found that when the tractor loses drive, the FEL still works even with the hst pedal all the way down. So that would pretty much eliminate the clutch possibility wouldn't it? It just sure feels like it is a relief valve but from what I understand there is 2 of them one for R and one for F, but it does it on both of them

 

[kuboman]

I hear ya on that. Last night I went and did some more testing on the tractor and I found that when the tractor loses drive, the FEL still works even with the hst pedal all the way down. So that would pretty much eliminate the clutch possibility wouldn't it? It just sure feels like it is a relief valve but from what I understand there is 2 of them one for R and one for F, but it does it on both of them

Front end loader is a separate system run from the engine. You have a hydrostat issue. Maybe a relief valve or bad charge pump or a dozen other problems but it sound like your clutch is fine. The clutch disengages everything behind it such as the tranny and pto.

 

[Butch]

I have to agree with Kubotaman.... the hydraulic pump is independent of the hydrastatic drive... so the FEL and 3 pt hitch will work irregardless of whether the clutc is in or out.

My only advice is grab a shovel and dig a little deeper into the problem.

For what it is worth it could be one or more of MANY things that have to be logically rulled out or as I like to say "troubleshot down" one at a time

Keep us posted

 

[chipdip268]

Well,I have changed the filter, same ole problem.... it is definetly not the clutch because I can see the shaft spinning freely ..... I think it might be the charge pump... I tried a few different things though.... when traveling and I release the pedal, it jumps as it is trying to slow down.... also, can i put a pressure guage on the top of the charge pump where there is a 1/4 hex plug? Thanks

 

[chipdip268]

Just wondering if anyone could tell me... if I take the hst oil filter off, bypass the clutch switch and crank the engine over, how much oil should pump out of the oil filter plate? I tried it but I am not sure if it should actually flow, squirt, or what...

 

[Butch]

Oivey.... that is Jewish for "oh shi*"! Got no clue but am certainly interested in the responses on this one....

Butch

 

[chipdip268]

Well, got good news and bad news.... the HST is pooched. Forward pressure is about 1500 psi, and reverse is about 1200 psi. Time for servicing. A friend that owns a hydraulic shop and machine shop said he can rebuild it for about $400.00 Hopefully that will solve the problems, if not the next step is a new hst for $2,200.00. I will keep ya'll updated. In the mean time, I just bought a new z-turn to take it's place so the grass doesn't turn into a jungle

 

[eserv]

Hi
It probably just needs a new charge pump. have you checked the charge pressure? ( should be 60 to 90 psi warm). Low or no charge will cause low high pressure and all the other thinks you describe. by the way, high side pressure should be 3400 to 3600 psi.
Ed

 

[chipdip268]

Hi
It probably just needs a new charge pump. have you checked the charge pressure? ( should be 60 to 90 psi warm). Low or no charge will cause low high pressure and all the other thinks you describe. by the way, high side pressure should be 3400 to 3600 psi.
Ed

How do I check the charge pump pressure? I paid the shop to check the the rest. Can I check the charge pressure myself? All I could find on the charge pump were some allen head plugs.

 

[chipdip268]

Well, I picked up the tractor from the shop. According to them the forward pressure is 1350, and the reverse pressure is 1550 psi. The charge pump is putting out 80psi. So, it is tractor splitting time. I already ordered a WSM from Messick's and it is supposed to be delivered today. I will take pics as much as I can as I go along and completely tear down the HST and rebuild it, and take what needs new parts to a machine shop. It is going to be a pretty neat project as I enjoy a challenge. As soon as I get the manual I will try to recheck everything they did and compare numbers and we will go from there.

 

[chipdip268]

Here's an update... Got the tractor split, hst pulled and opened up. The valve plates are scored, with one score on the pump side pretty deep, and the cylinders are scored too. I weighed some options and found a good used one that I am going to put on rather than order a new one and take a chance on getting dirt in it. But here is another problem.... before it was put out of service, the 3 point stopped working, then it started working at the dealership, except that if someone stood on the lift arms, it would raise up and then lower and back up about 2 inches kinda like it was cycling over and over and the lever was stationary. Any thoughts??