Go BottomHydraulics quot leaking down quot
 | JParker
Join Date: Oct 2003 Posts: 152 Richmond, VA 
 Pics
|
2004-07-12 90704
My B7800 is in for its 50 hour service, but just before it went in I found two things that may explain a few of the unusual problems I have been having, but that concern me.
While washing it down, I heard sounds coming from the brush hog frame, then noticed in about 15 minutes it had lowered itself from 3" height to resting on the ground. I started the engine and repeated the test with the same result.
Earlier the same day, I accidentially crushed the tire of a walk behind trimmer I was carrying in the bucket. The bucket was level with the 4-in-1 jaw slightly open to keep the trimmer from falling out. Wheels straddling the jaw. I set the joystick lock to prevent accidentially bumping it. About 45 minutes later I went to unload the trimmer and found its tire firmly crushed in the bucket jaw. It appeared to have closed under pressure, not just from its own weight.
The dealer found a scored valve in the 3 point control that they are replacing under warranty, but are still looking into the jaw closing issue.
I store the tractor with 3 point down, loader down and loader pressures released.
Are these type of leakages common in new machines or does it sound like trash in the systems?
Reply to |
Quote Reply |
Add PhotoHydraulics quot leaking down quot
 | oneace
Join Date: Mar 2004 Posts: 1490 south central pa 
Pics
|
2004-07-12 90709
unfortunately ALL tractors have some sort of hyd. imperfection no matter what color. Some times it is repairable warranty item other times it is considered acceptable by factory standards. ....
Reply to |
Quote Reply |
Add PhotoHydraulics quot leaking down quot
 | beagle
Join Date: Jan 2004 Posts: 1333 Michigan
Pics
|
2004-07-12 90714
There is plenty of history of excessive machining shavings in the filters and screens of new machines. The scored 3-point valve could easily be explained by shavings left behind from the manufacturing and assembly process. The 50hr change should take care of this problem in the future. All hydraulic systems have some drift. Seals and especially spool valves have a certain amount of leak by. You are doing the right thing by keeping the pressure off the system during storage. This will drastically extend the life of your seals.
I haven't had any problems with the hydraulics in my 7800. I'm sure you will not have any problems once the 50hr is completed. The system and components are tried and tested. ....
Reply to |
Quote Reply |
Add PhotoHydraulics quot leaking down quot
| JParker
Join Date: Oct 2003 Posts: 152 Richmond, VA
Pics
|
2004-07-26 91988
Thanks,
My machine came back last week and I got in some seat time this weekend. They re-piped the jaw to "run off the bucket circuit".
Now it is controlled by side to side stick action.
Maybe my immagination, but I seem to have lost a good bit of jaw closing force. I'm going back out there one night this week to be sure and see if I can crush some 2x4's or something.
I'm still interested in a good practical hydraulics book (or web site) if anyone knows of one I can buy. Trade school text book...
I know theory basics, but need practical. Pump makes pressurized fluid, valves routes it where needed, bigger cylinder = more power but slower, prv keeps things from breaking...
But what is the typical flow diagram of a tractor, what is a power beyond unit, what is inside that diverter valve for the jaw, how does the oil get back, how can I add rear hydraulics to a B7800 for that top link... ....
Reply to |
Quote Reply |
Add PhotoHydraulics quot leaking down quot
 | TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
|
2004-07-27 92007
Some years back I did a web search hydraulics texts etc. The search turned up several course outlines form community college classes that mentioned texts, but I didn't try to find any of the texts. I have the JD FOS-hydraulics book. It's pretty good and would answer many of your questions.
I'm curious about the 4in1 crushing the wheel if you're interested in pursuing it. Sounds like it may have gotten some pressure from somewhere, but it'd probably take a lot of blab to figure out the possibilities. A far-fetched possibility is that if it were sitting in the hot sun, then some closing pressure might develop. ....
Reply to |
Quote Reply |
Add PhotoHydraulics quot leaking down quot
| kubotaguy
Join Date: Nov 2003 Posts: 360 Shepherdstown, WV
|
2004-07-27 92016
I've notice on my 7800 when the tractor sets overnight the MMM mower will bleed down to the ground but the bucket may only drop down an inch or so (can't store the loader on the ground due to room). Is that normal for the mower deck to bleed down or should I have the dealer check it out? ....
Reply to |
Quote Reply |
Add PhotoHydraulics quot leaking down quot
| beagle
Join Date: Jan 2004 Posts: 1333 Michigan
Pics
|
2004-07-27 92047
It isn't a good idea to store you machine with load on the hydraulics. This will lead to pre-mature wear on the cylinder seals, and also leaving the cylinders extended means the shaft is exposed to the atmosphere. It is best to have the shaft stored in the cylinder body so it is in the fluid. Some leak down is normal. The mower is lifted by the three point, so it is the three point circuit that is leaking down. I have never left mine up with any implements attached, so I couldn't compare to mine. I do know that it doesn't take long to leak down even during operation. Dropping 4 or 5 inches over night is probably nothing to be concerned with. ....
Reply to |
Quote Reply |
Add PhotoHydraulics quot leaking down quot
| JParker
Join Date: Oct 2003 Posts: 152 Richmond, VA
Pics
|
2004-07-30 92351
Update...
The jaw was only able to put a few 1/8" deep x 1" long dents in the 2x4. I dropped off the 2x4, the keys and a note to the dealer. I haven't heard the result yet, but the dealer offered to come check pressures and haul it back to the shop if needed. I had to ask them to hold off till after the weekend so I could hog the pasture first.
TomG - Thanks for the line on the book, I'll check a local dealer and Amazon.
I've heard and do the same as Beagle. After shutting down, I lower all hydraulics and then cycle the loader valve through all positions to be sure all pressure is off. The dealer and people here say a little leakage is normal. My 3pth was leaking down 3" in 15 minutes before the repair. I should know after tomorrow if that has been corrected.
Like I told the dealer, the bucket thing was a suprise. I can live with it if needed to get back the bite strength, but they want to check some pressure readings first. Apparently there is a relief valve in the bucket circuit that may need adjustment. ....
Reply to |
Quote Reply |
Add Photo
Go Top
Share This