cant figure out photos. this site doesn't like me. to post a reply I have to preview and then go back to edit to get a cursor.
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SkidRoe
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Check out this link for photos: http://www.skidsteerforum.com/DesktopDefault.aspx?tabid=54&frmView=ShowPost&PostID=2445
Ok. Motor and pump are out. 2 check valves on top and 2 relief valves on bottom. Hoping I found the problem. The valves have a plunger like end that fits in a recess in the threaded cap. It has a small spring behind it. To pull mine out takes two hands and some wiggling. There a little looser towards the bottom but still stick half the time when you push them down. Be about a week before I put it back together. Waiting on some parts. Lots of missing bolts also. Whoever worked on this before was terrible. The flywheel had 3 different styles of bolts in it. Also waiting on a puller I ordered. The pump pulley takes a big puller. Then I can find the water leak behind the bell housing.
TriHonu
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- Apr 15, 2007
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Is the hydrostatic pump a Sauer-Danfoss? If so, you can download the Parts and Service manuals from their website: Danfoss Literature
I have a 763 circa 1995 that has the Series 40, M35 pump.
TriHonu
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I just opened your Photobucket images. You have the same pump as my 763.
Click HERE to view the available manuals.
The Model Numbers have changed over time. I had to call Sauer Technical Support for help to download the correct manual for the M91 model number. The tech told me the M91 indicated a tandem pump and the 35 was for 35cc per revolution.
I had a few questions about the correct hydraulic fluid for these pumps and they provided a phone number to one of their engineers and he answered my questions and provided further links to a couple of Sauer Technical Documents on oils. Good company that readily provided support.
Thanks for the info.
getting older sucks. never saw the snap rings that retain the plunger. bobcat manual says to remove them. pump manufacture says replace. Parts Manual Axial Piston Pumps, Series 40 MMF035D and MMV035D 520L0601 • Rev BA • Nov 2013 71 Series 40: M25, M35, M44 pumps, and tandem pumps Redesign the retention method in check valve assemblies As a product improvement, Danfoss changed the retention method in the check valve assembly, and SCR valve assembly. The old design allowed the check valve and SCR valve assembly to be disassembled. That retention method had the potential to hang up the valves on the retaining ring. The new design uses a different style. The retaining ring will not hang up on the valve; however, it does not allow the assembly to be taken apart. All new repairs, conversions, or purchases of a check valve or SCR valve require the entire assembly be exchanged. The new and old assemblies are totally interchangeable. The special plug part number 4350182, and the internal retaining ring part number 4350183, are obsolete. They are no longer available as service parts. All Series 40: M25, M35, and M44 single and tandem pumps This change became effective at serial number 96-40-xxxxx.
7LBSSMALLIE
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well done. clear concise and to the point. might keep me from chasining my tail. THANK YOU.
Its back together. Still feels funny left side reverse. cant test because the bics keeps locking it up. flashing green lights for the controls and drive.
Finally using it some. looks like the drive system is weak with left side reverse being the worse one. Going to limp it along like this for a while. tear it apart this winter.
Weakness in one direftion could be a bad drive motor seal.
Got the drive pump apart. Simple except for a snap ring. You need some really good pliers for it. Only thing looks bad is the valve plates. Going to flip the wear plate on the swash plate.
A sheet of glass and wet and dry sand paper flatten these plates nicely. I have done a few with great results.
Start out pretty course, i think i started with 400 and worked up to about 1,000. It doesn't need a mirror finish, it just needs to be smooth and flat. I used WD40 as a lubricant, keep turning the plate while rubbing it over the sand paper so you won't work one side more than the other.
Don't know how much you can sand off but I will find out soon. loader parts source only shows a 6669400 and 6669401 part that's a $177 dollars each. Its the only part they show for a 753. Bobcat says I need a 6666290 and6666291 part that's $335 each. They don't know if the parts interchange. Anybody know the difference in the numbers. Bobcat shows both numbers but doesn't know the difference. Bobcat breaks the parts down by serial number. L P S has 1 part for all 753.
Hopefully we are talking about the same parts. We are talking about the wear plates in the drive pumps right?
They do have two plates, they are mirror images of each other. If you look close, you will see the ports for the fluid to flow into the valve ports, on the trailing edge, you will notice a shallow slot going into the port. Hard to explain but sort of like -----( opening here ) you will note that the slot is on one side only on these ports. The other plate will be the exact opposite.
I wonder if the different numbers are due to updates. The same part can have multiple numbers.
I'd give the sanding a go, if they are too deep, then you will need new plates and ensure the face of the rotating group is not worn too.
If you get stuck, look up my profile and email me.
I know this is an old post but I am hoping to glean some information from it as I have a 753 with only 1500hrs showing the same issue in reverse on the left side! I am convinced it is a sticking relief valve also. What is the best way to work out the pump model in order to find out if the check and releif valves are serviceable. It would be handy to know if I can service them or need to swap out the assembly prior to removing the engine. Could you please point me in the right direction.........Do I contact Bobcat and get them to run the serial number and give the information on the pump types used?? Thanks in advance
The pump should be a sunstrand, pretty well all the same with the 753 series.
I'd swap motors from side to side see of the issue moves, if it does, the motor seals may be bad and need replacing. Start with the simple things first.
The relief valves are fairly accessable on the top of the pump. You just need to remove the centering parts to gain access from memory.
I have the exact same symtons as "digsalot" and ScottMC" - left hand motor plays up in reverse. Has eithier of the two bobcats been fixed 100% ? If so what was the root cause? I have checked the two valves on the top of the hydraulic pump (Under the centreing plate) and now I'm at the pont where i need to swap the drive motors and test, or remove the engine/pump to check the relief valves on the bottom. Hoping someone can confirm what the actual fix was. Thanks for your help.
Do the easier test first, swap motors.
I had a 753 that had no power on one side, forward and reverse. I cracked open the drive motor and the Orings had turned to powder. Replaced the Orings, and it was like new.
Just an update on this so far, keep in mind the my LH motor was the one playing up especially in reverse. I removed both the drive motors with the intention of swapping LH to RH and RH to LH and therefore isolating the issue to the LH Drive motor, or a pump issue further up the circuit. On the advise of a You-tube video, I disassembled LH drive motor to find 1 missing Inner O-ring, and 1 Centre O-ring perished and broken. Both of the plastic seal cover things had chips and nicks missing too, but the LH drive motor had no signs of being opened before indicating they were original seals. Then out of curiosity I thought I would inspect the RH drive motor as well and found all o-rings intact (Not original seals, have been replaced at some stage). The reason i disassembled the RH was to see if the RH seals were in the same condition as the LH seals, and therefore I could ignore the missing broken LH seals as the casue of the problem. Given that the good motor (RH) has intact seals, and bad motor (LH) has missing/broken seals im feeling confident new seals could fix it. However, my hydraulics guy has suggested that the missing and perished O-rings in the LH drive motor is not the root cause of my problems and wants me to remove the engie/pump to inspect the relief valve on the underside of the pump. I can understand his theory on this, but ill be replacing both Drive Motor seal kits and re-testing before the engine and pump comes out. Ill keep the forum updated on my progress but in the mean time has anybody else got a thought on this?
