Hi guys, I have a 741 that has given me issues since day 1. Hydraulics function great but I lose almost all drive function when the machine warms up. I'm assuming the hydrostatic pumps need to be rebuilt but would appreciate any help or suggestions you have before I pull the pump apart. I plan on testing the charge pressure first then testing each hydrstatic pump output. I have already replaced the bronze filter numerous times and even ran without one for a short period and it still has the same symptoms. When I first start it, it runs and drives strong but after working for a little bit, it wont turn without me making a million k turns. I have experience rebuilding pumps on zero turns and I am pretty mechanically inclined so I'm not afraid of the job, just looking for any other tricks or tips before I pull this thing apart. thank you
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I ti spossible the pumps are worn, but the older machines had a hidden filter that caused this exact issue, see if yours is the same.
Lif the cab, is there a square block on the hydraulic pump with three hoses on the left side? or is there a big fat hose that runs to a block on the left side of the frame?
if it has the three hoses, remove the middle one and the fitting behind it. There is a suction line filter in here. Take it out and give it a good wash with solvent and compressed air.
If that works, you are good to go, if not report back, we can go from there if needed.
Lif the cab, is there a square block on the hydraulic pump with three hoses on the left side? or is there a big fat hose that runs to a block on the left side of the frame?
if it has the three hoses, remove the middle one and the fitting behind it. There is a suction line filter in here. Take it out and give it a good wash with solvent and compressed air.
If that works, you are good to go, if not report back, we can go from there if needed.
Hi Tazza! That bronze filter is the one that I have changed a bunch of times. I was surprised to find my hydraulic fluid looking like whole milk so I will be flushing the system multiple times today to try and clean everything out before I start pulling things apart. I'll give an update after I get things cleaned up and run it for an hour or so
Water contamination isn't great, if there is indeed pump damage from it, some can be repaired or replaced cheaply with after market parts.
Ok I just ran it for about a half hour and it seemed better but when I dig into a pile and try to spin the wheels I can barely get one side to turn and it whines and grinds. if I push both sticks forward the wheels do'nt move at all. It just makes a bunch of noise when both sticks are pushed forward. Are there any other small filters aside from the bronze one in the block? I lifted the cab and the pumps were pretty hot. The vane pump, port block, and metal line going from the port block to the drive pumps were all warmer than the rest of the system. however, driving it back into the shop it moves fine in a straight line. It only seems to have an issue when under a load (turning or going into a pile). Hopefully I've described the issue well enough for you.
quick update, looks like im going to be pulling the pump out. I capped all lines at the right wheel motor and pushed the stick forward and the engine didnt stall. My gauge only read about 2000 psi so looks like a rebuild is in order. Tazza, do you recommend pulling the pump out from the front or back of machine? I've pulled the engine a few times in this machine already so I'm familiar with the procedure. Looks like pulling it from the front would be very difficult to line the coupler back up on installation.
It really needs to come out the front. With the engine out, putting it back in is easier.
What i do is pull the engine, disconnect the drive motor lines at the motors, just the two big ones per side, the other hoses to the pumps where they attach at the top, the 4 mounting bolts but remember where the washers go, these are used to set the pump height.
A helper is good to get the pump up and out, but you can do it by hand.
When you get it out, give it a good clean before cracking it open. If you look up my profile, send me an email if you need a manual on the pump. I can hopefully give ou some more advise in an email too.
Thanks tazza, the pump is out. I capped all the ports and power washed the pump. its on a clean bench so I will be crackiing it open today. I'm send you an email now thank you
Can the barrel of the rotating group and the wafer plates be lapped? Or should I be buying new rotating groups and plates? I'm going to try and figure out how to post pictures of the wear
Well I've decided to have the pump rebuilt. I'm shipping it out to Michigan on monday. After pricing out the plates, rotating groups, and yokes/camplates, its much cheaper to have them rebuild it. AND it comes with a 1 year warranty! time to get some new lines made in the meantime
Good to hear you are getting it all done, not just bits and pieces. Best to do the job only once.
I'd ask them what they think caused the damage too, it looks like the oil thinned out too much, i'd ensure the oil cooler is lice and clear, just in case it got hot, you don't want to be doing the job again.
pcasey, Who are you using for pump rebuild? I have a 743 tandem pump that may need an overhaul
mike_belben
Member
- Joined
- Oct 5, 2016
- Messages
- 23
The old aluminum manifold block machines have a lot of springs and poppets to cause trouble with charge pressure. Operating at low charge will eat up a pump. They shoulda had OEM hyd gauges.
Hey everybody sorry for the wait I just finally got around to painting the machine. Everything finally works as it should and looks good. Rebuilt pump, new lines, and new filters and I finally have a happy machine. I used Pro-active fluid power for the rebuild they are located in michigan. Bonnie was great to deal with and price was reasonable. Heres a few pictures of the pump and machine, hopefully this thread can help somebody else out down the road!
So very blue, glad they got it all sorted out for you and it's all up and running again.
