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621B Lost All Hydraulic Function

631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
621B Wheel Tractor
Machine Serial Number - 8HC00010
Machine Build Date - 1985/07/04

We have a low hour 621B that has been running great up until this week. The operator was running across the fill dragging up and says that he suddenly lost all hydraulic function. According to the operator the machine had been running great all day and that there were no obvious strange noises, thumps, bumps, etc. to accompany the sudden loss of hydraulic function. The bowl, apron and ejector would not move but he could steer the machine. However the response on the steering was slower than typical to the machine. To get the machine out of the fill we backed it up over a small hump to push up the bowl and then let the cylinders hold it there. So I guess that says the valves are not stuck open/closed being we can lower and hold the bowl up/down?... Transmission still takes gear fine and pulls normally. (not sure if the two are related but there it is)

We got the machine up to "pit row" (same job where we've had the D8H go down) for a look at by the mechanic. We pulled the in tank hydraulic filters and found that one of them, the lowest one, was crushed and both seemed awfully heavy even after draining out. Good news is there was no metal to be seen anywhere in the filters after cutting them open, but they were dirty with filtered out dirt. Oil was clean and has no water or other obvious contaminates.

Thinking that maybe this was the issue we replaced with new filters and started the machine back up. No change. We could still steer the machine but no implement function.

Has anyone dealt with this before where you have no implements but do have steering? I am looking at service manuals but with our machine being ex-military, I am trying to sort out what is the closest standard serial number prefix to match our machine. Best I can see is that 45P seems to cover the year our machine was built. My goal is to find a pressure testing procedure for the hydraulic system. It would seem to me that if the pump let go that we'd have nothing anywhere. I would imagine that the steering circuit would require the same pressures as the other implement circuits would given the amount of push needed to move the tractor unit side to side.
 

Welder Dave

Senior Member
Joined
Oct 11, 2014
Messages
12,260
Location
Canada
I would guess steering has it's own priority pump. Is the implement hyd. pump turning? Wondering if a pump coupler or spline broke or wore out. Maybe a collapsed suction line?
 

631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
Thank you Nige. I’ll print these off for the mechanic’s use in the field. He’ll be grateful for them while we’re waiting for the manual to come in.

If you don’t mind me asking where do you pull this info down from? I poked around SIS but wasn’t able to find these document. Am I missing something like a tab to look under or are these documents not available to general users like myself that are just utilizing the SIS system for parts lookup and purchasing? I have managed to find that I can see service info for basic oil changes etc. but not these detailed documents.
 

Welder Dave

Senior Member
Joined
Oct 11, 2014
Messages
12,260
Location
Canada
It was interesting reading the supplementary steering pump is only supposed to work with the wheels turning but wondering if maybe it's what's allowing it to steer but more difficult. It might help diagnose a problem with the implement pump that also has the steering pump attached.
 

Mark250

Senior Member
Joined
Aug 30, 2015
Messages
1,243
Location
victoria,Australia
Occupation
heavy equipment technician
my 2 cents, if you have lost implement functions i would suggest that the implement vane pump section has stripped the spline in the vane cartridge or on the shaft i have seen both for these symptoms also common to crack the vane pump cam ring especially if some cowboy decides to up the relief valve settings
also check that the relief valve orfices are not blocked.check the relisef valve first as it is easier to do

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631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
We have pulled the hydraulic pump off to be inspected at a local shop. Found some loose screws that had worn. No metal shavings nor anything obviously broken. The screws clamped the pump section together if I’ve got that right. They’re only about 3/16” diameter.
 

631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
So we have had the pump rebuilt and now that the rain seems to have given us a 48hr break tomorrow we’re shooting to get the pump back in.

The hydraulic shop said we had some bad seals and the screws holding everything together that were worn have been replaced. We’ll stick it all back together and see what happens. I’ll look at getting some photos up.
 

steve wherley

Active Member
Joined
Jan 19, 2014
Messages
44
Location
minnasota
we had seen the the filter on hyd relief valve would brake off and valve would stick open, ez to pull and check later filter does not stick out on relief and is flat on front of it
 

Dave Neubert

Senior Member
Joined
Jul 18, 2018
Messages
1,651
Location
Monroe NC
So did they replace the cartridge or just the seals in the pump were the vanes rounded off or still sharp and was the outer part where the vanes ride smooth or wash boarded
 

631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
So did they replace the cartridge or just the seals in the pump were the vanes rounded off or still sharp and was the outer part where the vanes ride smooth or wash boarded
I’ll have to find out. When we picked up the pump the shop owner has gone out of town for a month and didn’t come back into town until recently. We checked pressure on the pump and it was only making 300psi. Should he at 1000psi. He said to pull it off and bring back for him to look into it further. I don’t think he bench tested the pump honestly. It’ll be warranty work.
 

631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
we had seen the the filter on hyd relief valve would brake off and valve would stick open, ez to pull and check later filter does not stick out on relief and is flat on front of it
I’ll look this up in the manual and show to our mechanic. Could be the culprit and sounds like an easy check
 

631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
we had seen the the filter on hyd relief valve would brake off and valve would stick open, ez to pull and check later filter does not stick out on relief and is flat on front of it
Steve,
So we got caught up enough to get back to this issue with our 621 and it was the relief valve hanging open with trash in it that was causing the low pressure reading. We got the pump back off the machine had it retested and it was fine. (That was an unpleasant conversation to have with the shop owner after I was assured the pump was not making pressure.) Anyway, that’s what lead us into the valve body to check it out. That and what everyone’s posted here and me taking some more time to sit down with the shop manual to read through trouble shooting. Pulled the relief and found small amounts of trash there from the filter and also a plugged hole in the relief valve body. Cleaned it all up and back on the road she went.
 

631G

Senior Member
Joined
Apr 27, 2008
Messages
336
Location
Georgia
Occupation
Civil Superintendent
So did they replace the cartridge or just the seals in the pump were the vanes rounded off or still sharp and was the outer part where the vanes ride smooth or wash boarded
Dave I never did get an answer on this from the shop. They did however have the pump back fine the first time. Issue was on my end which was embarrassing when going to the shop to get the pump. The shop owner was gracious about the ordeal and didn’t bear up on us too bad…
 
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