B7100 HST lost movement

[sardiscitydad]

Hi guys I’m not sure where to search for movement problems on a B7100 HST 4x4 . It started out with a jerky movement then there was almost no reverse but it still moved forward long enough to come out of the pasture. This was 5 months ago and it’s sat until today. I cranked her up and she moved forward and backwards for about 30 seconds then no movement. PTO and lift still operate just fine. The bush hog is still attached so there is no doubt about the pto working .
I have double checked all linkages and everything is as it is supposed to be there but I am curious if the clutch would cause this issue.
thanks for any advice as the tractor is from 91 and honestly she’s been a good one but if it’s an HST issue then she has served me well because I am not going to drop more than a few $$$ on her at this point

 

[85Hokie]

IF you try to shift from H to L ..... does the clutch allow you easily? Or engage the PTO? Both work as they should?

 

[sardiscitydad]

The PTO shifting works as designed. The high/low shift is a little tight at times coming to high but it has always been like that since bought in 91

 

[85Hokie]

When was the last time you checked your hydraulic screen?

 

[sardiscitydad]

Serviced everything 6 months ago so basically 1 month running time since the service as she sat for 5 months. Anything is possible so I will pull the screens tomorrow and double check

 

[North Idaho Wolfman]

Are you trying the PTO and the movement at the same time?
If you are and the PTO keeps on going without loosing RPM's it isn't the clutch.

 

[sardiscitydad]

Are you trying the PTO and the movement at the same time?
If you are and the PTO keeps on going without loosing RPM's it isn't the clutch.

I’ll check it out tomorrow after work. I do remember having the seal in the pump go out just as the rear movement was lost and it was low when I got back out of the pasture. I replaced the seal today, started her up and for 30 seconds everything was normal

 

[North Idaho Wolfman]

I’ll check it out tomorrow after work. I do remember having the seal in the pump go out just as the rear movement was lost and it was low when I got back out of the pasture. I replaced the seal today, started her up and for 30 seconds everything was normal

Oh well there is a bit more info.
If you're blowing the seal out of the Hydraulic pump the system is dead heading.
And yes on that model it will effect movement if it blows the main seal.
Check the engine oil level.

 

[sardiscitydad]

Oh well there is a bit more info.
If you're blowing the seal out of the Hydraulic pump the system is dead heading.
And yes on that model it will effect movement if it blows the main seal.
Check the engine oil level.

Ok an update that really confuses me.
i went back and drained the whole system to see if somehow something was in the screens, nothing as they were clean.
I put a new filter on, filled it back up with fluid and started the machine. I lifted the 3point and she started whining just like they all do as you begin movement. It lasted 3-5 minutes then nothing from the hst. I repeated the drain/fill/ start process again and just like before everything repeated as it did the 1st time.
Being a dumb old country boy from Bama I got to thinking
It was as if it is loosing its prime or sucking air from somewhere so I checked all the external lines then found another puzzle piece.
The return line behind the filter that goes to the cooler has very little fluid in it and nothing coming out of the cooler to the pump. I filled the lines up from the cooler cranked her back up, got movement for about 1 minute then nothing…….thoughts ???

 

[North Idaho Wolfman]

That all sounds like you have a suction side leak, or again a blown pump seal.
Suction leak sounds more likely.
Check the rubber hose section on the largest line just before the pump.

 

[sardiscitydad]

That all sounds like you have a suction side leak, or again a blown pump seal.
Suction leak sounds more likely.
Check the rubber hose section on the largest line just before the pump.

Thanks brother I will do that in a few days .
any idea how much suction is normal ?
redneck test..finger on the end of the line at the 1st junction under the tractor I can feel just a little.
I will order the seals for the pump and go ahead and rebuild it , change the rubber lines and clamps and go from there

 

[North Idaho Wolfman]

Thanks brother I will do that in a few days .
any idea how much suction is normal ?
redneck test..finger on the end of the line at the 1st junction under the tractor I can feel just a little.
I will order the seals for the pump and go ahead and rebuild it , change the rubber lines and clamps and go from there

These styles of pumps only have suction when they are full of fluid.
So the finger test is not any good.
Also it's not the power of the suction its if it sucking air in with the fluid is the issue.
It's not something that seals in the pump are going to fix, very unlikely they are bad.

 

[Vigo]

So let me stick my foot in my mouth here, since i dont know a damn thing about a b7100 HST specifically...

The 3pt and 'other lift' you mentioned are run by the pump on the side of the engine. It has nothing to do with propelling the vehicle (unless it pumps all your trans oil into your engine and runs the trans dry), and it has worked this entire time.

The having movement and then not having movement is probably related to losing 'prime' or 'charge' in the HST pump/motor circuit. This is likely to be related to the charge pump hydraulic circuit. The HST charge pump's strainer is on the clutch pedal side of the tractor while the 3pt pump's strainer is on the brake pedal side of the tractor.

If the two things are right next to each other and the 3pt works then it sure aint a fluid level issue, as has already been confirmed. But.. even if that strainer is clean, the potential issues could start as early as the sealing rings on the large banjo fitting for the HST strainer. Does it seep any fluid there?
If not, what about at the other end where that pipe has a hose clamped onto it?

It's most likely that that hose is the main source of the issues. Because it's location is below the standing fluid level, just turning the tractor off for a while would allow the air to eventually percolate past the charge pump and the fluid level to rise to the inlet of the charge pump, letting it work for the first several seconds upon restart. Once the charge pump is pumping, it sucks air from this hose section which gradually displaces the fluid which is normally leaked back into the case from the HST pump/motor circuit until that circuit is substantially air and it ceases to be able to move (probably gets louder as this is happening as well). The filter, and the fitting which leads out to the cooler are also fed by the charge pump, which is why when the charge pump starts simply cavitating in air, you have no fluid out of the line to the cooler.

So in all likelihood you just need to fix an air leak on that hose section.

 

[sardiscitydad]

So let me stick my foot in my mouth here, since i dont know a damn thing about a b7100 HST specifically...

The 3pt and 'other lift' you mentioned are run by the pump on the side of the engine. It has nothing to do with propelling the vehicle, and it has worked this entire time.

The having movement and then not having movement is probably related to losing 'prime' or 'charge' in the HST pump/motor circuit. This is likely to be related to the charge pump hydraulic circuit. The HST charge pump's strainer is on the clutch pedal side of the tractor while the 3pt pump's strainer is on the brake pedal side of the tractor.
View attachment 96449
If the two things are right next to each other and the 3pt works then it sure aint a fluid level issue, as has already been confirmed. But.. even if that strainer is clean, the potential issues could start as early as the sealing rings on the large banjo fitting for the HST strainer. Does it seep any fluid there?
If not, what about at the other end where that pipe has a hose clamped onto it?
View attachment 96451
It's most likely that that hose is the main source of the issues. Because it's location is below the standing fluid level, just turning the tractor off for a while would allow the air to eventually percolate past the charge pump and the fluid level to rise to the inlet of the charge pump, letting it work for the first several seconds upon restart. Once the charge pump is pumping, it sucks air from this hose section which gradually displaces the fluid which is normally leaked back into the case from the HST pump/motor circuit until that circuit is substantially air and it ceases to be able to move (probably gets louder as this is happening as well). The filter, and the fitting which leads out to the cooler are also fed by the charge pump, which is why when the charge pump starts simply cavitating in air, you have no fluid out of the line to the cooler.

So in all likelihood you just need to fix an air leak on that hose section.

Thanks Vigo for the input . You and wolf man are both suggesting to check the same things and I really appreciate the info

 

[Mountainman]

I sent you a msg sardiscitydad