Update on all 7520s

[Dougster]

By the way, the loader is as slow as it ever was. It really disappoints me. My BIL has a Kubota M6800 with loader and his loader will work circles around mine! That's Sad!

As a retired mechanical engineer with considerable positive displacement fluid systems design experience and performance testing experience (not to mention interest in this particular tractor), this 7520 hydraulic flow / loader speed issue continues to intrigue me. This should not be a particularly difficult problem to investigate and (hopefully) resolve. But can I just ask one question: Did you folks notice this slow loader issue at the time you were shopping and buying? Or did it show up later?

Not trying to be cute or difficult... just trying to understand whether this is a machine design issue or a maintenance/wear problem.

Dougster

 

[SPYDERLK]

Dougster, to be cute but hopefully not difficult, pls read #64 down near the bottom. Some dont get the chance to even get that close and rely on spec alone.
larry

 

[Dougster]

Dougster, to be cute but hopefully not difficult, pls read #64 down near the bottom. Some dont get the chance to even get that close and rely on spec alone.
larry

Hi Larry - I think I've read every post on this issue (Yes, I do need a real life!!!) until I was blue in the face as this was my former occupation... i.e., testing & troubleshoooting fuild systems albeit on a much larger scale. Believe me when I say that I'd like to help. Even more, I'd like to know the answer to this mystery as the 7520 is my post-lottery winning dream machine! But first, I'd like to know if the problem was there from day one... i.e., a design issue that everyone experienced... or something that only some experience... or something that generally got worse after a time.

Forgive me if I've forgotten some of the particulars over time. I am old.

Dougster

 

[SPYDERLK]

Dougster. It was slow on my tractor from day one. I was not able to find a 7520 to test drive despite inquiring with a Mahindra sales rep I met at a dealer and getting no help at all. In deciding, I went by extrapolating specs from the 6520 I was able to locate on my own. The loader speed has neither improved nor worsened. I suspect mine has the wrong pump.
larry

 

[Dougster]

Dougster. It was slow on my tractor from day one. I was not able to find a 7520 to test drive despite inquiring with a Mahindra sales rep I met at a dealer and getting no help at all. In deciding, I went by extrapolating specs from the 6520 I was able to locate on my own. The loader speed has neither improved nor worsened. I suspect mine has the wrong pump.
larry

Two more questions please: 1) If you can see the hydraulic pump you can photograph it and post it here. Unless the 6520 and 7520 have pumps that are visually and dimensionally identical, wouldn't that solve the mystery of the potential wrong part right away? and 2) This is not rocket science... so why can't a simple flow test be conducted to measure hydraulic flow?

Dougster

 

[bindian]

Dougster. It was slow on my tractor from day one. I was not able to find a 7520 to test drive despite inquiring with a Mahindra sales rep I met at a dealer and getting no help at all. In deciding, I went by extrapolating specs from the 6520 I was able to locate on my own. The loader speed has neither improved nor worsened. I suspect mine has the wrong pump.
larry

Larry,
Take the part number off of your pump, then ask a Mahindra parts guy the part number on the 17 gph pump that is suppose to be on the 7520. Two different capacity pumps can look alike on the outside. Other than that, you could have some obstruction or trash blocking a line or oriface in the cylinder. Airliners use 3000 psi in their hydraulics and every now and then, something gets caught in a check valve or restricted check valve or even an actuator. A by-passing cylinder can also give slow response time. Raise the loader all the way up and leave it for a day or so. If on start up, you can raise the loader, it is fluid (and pressure) by-passing the cylinder piston causing all or some of the problem. With out having a schematic of the hydraulic system it is hard to pin point what is doing on where and when. All I have is the Ops manual on the ML275, which is on the 6520 and 7520. Basically, any port or fitting that has small inner diameters could cause an obstruction. A bad line that is coming apart internally is another thought that can cause a slow response.
hugs, Brandi

 

[SPYDERLK]

Dougster. I was told by a tech rep when I 1st brought this up that they are putting the 17GPM pumps in both the 6520&7520. A picture would merely confirm the same pump - not its volume. The pump in mine is a two section pump showing identical cross section front to back. The main hyd section is about twice the length of the steering section. These two things suggest to me that they are a 2to1 volume ratio - not a 3to1. When you combine that with my measurement of fluid delivery of 11to12 GPM based on timed lift rate of the loader, you are led to the conclusion that the steering and main outputs have been combined for the 17GPM figure. Mahindra reps make statements to the contrary. We need the pump specs and geared/crankshaft ratio. Thats all we need in order to know if we should look for a malfunction or an inflated claim.
larry

 

[SPYDERLK]

Brandi. You have good suggestions. Pls see #62. I believe its all been covered except for a leak on the suction side, or inadequate pump displacement or incorrect crank to pump gearing. I want the pump specs. The p/n would just tell us it is the one they mean to be on the tractor.
Oh - just thot about what you said re a check valve being off its seat. On further thinking I think thats ruled out too tho. When my engine broke I used the starter to turn the engine and raise the loader so I could tow it. Anything but the smallest leak anywhere would have used all of the meager pumped fluid.
larry

 

[Dougster]

When you combine that with my measurement of fluid delivery of 11 to 12 GPM based on timed lift rate of the loader, you are led to the conclusion that the steering and main outputs have been combined for the 17 GPM figure. Mahindra reps make statements to the contrary. We need the pump specs and geared/crankshaft ratio. Thats all we need in order to know if we should look for a malfunction or an inflated claim.

I do sympathize... and I can certainly understand your suspicion. But... mechanical engineer to mechanical engineer... even the pump specs are not nearly as good as one accurate, instrumented pump flow test... including accurate measurement of engine RPMs. You have already conceded that there is no way to tell the difference between a 6520 pump and a 7520 pump... or that there may be any difference at all if you, in fact, have a 6520 pump. Indeed, they may be the same pump with different drive RPMs at spec engine RPM (as you have implied).

Forget about the loader for a bit. Spend the cash and do the pump flow test.

That's my last word on this. Now I'll shut up and fade back into the wallpaper.

Dougster

 

[bindian]

Hey guys,
Something doesn't add up between the 6520/7520 4WD sales broucure and the Model ML275 FEL Operator's Manual. The broucure shows a 9.3 second time to raise the boom on the 6520 and 6.2 seconds on the 7520.
My KMW ML275 Operators Manual specifications shows that both the 6520 and 7520 at full rpm will raise the boom at 6.2 seconds. So some advertised spec is wrong somewhere. Has anyone timed the 6520 4WD FEL yet? 11.4 and 17 gpm should show a good difference in time. I played with the 6520 4WD and raised the loader. It seemed fine for me. But I have only ran a FEL on a Kubota L3400 before. I will time it this week while at the dealer. So let me get this striaght. Time it from level on the ground to full height? Is this right? The broucure says RPM is 2500. The ML275 Ops manual says at full rpm. Which have y'all been using? My 6520 Ops Manual shows a photo of the tack and it redlines about 2750. Which is fast as I will rev it. So I will time at 2500 and redline.
Also, the broucure shows the 6520 4WD weighs 7300 pounds. My Ops Manual says it weighs 6141 pounds. Is the broucure weight with the FEL? I haven't found a seperate listed weight for the ML275 FEL. One of the first trailer trips I will make with my 6520 4WD,FEL, and BH will be to the local salvage yard's scale.
hugs, Brandi