Worn Valve Plates Causing Slow Traveling Speed?

M

me37250

New member
Hi all. I recently bought a used RTV and have been trying to resolve an issue. Any advice would be appreciated.

Problem: 2007 RTV900 with 1137 hrs only achieves 10 mph top speed in high range on flat/level road. I measured this with a GPS. Medium range also yields 9 mph. It is also very sluggish in all gear ranges; I'm comparing this to another one that I've driven which performs very well.

Diagnostics: Engine RPM was measured at 1350rpm idle and 3100rpm wide open throttle. It fails the workshop manual "Traveling Speed Test". With the unit on jack stands, no-load, low range wheel speed is 124rpm (spec is 126-141 rpm). This verifies that the machine is slower than normal. As a next step, I checked the relief valve pressures. Charge pump relief pressure was measured at 103psi (spec is 75-104psi). Forward relief pressure was 3580psi (spec is 3271-3840psi). Reverse relief pressure was out of spec at 3100psi (spec is 3271-3840 psi).

Attempted solutions: I think I finally managed to get all linkages and cables adjusted; that's another story. Spark arrestor is gone. All fluids and filters changed at 1132 hrs using Kubota brand filters and UDT oil (I know, I'll go back with Super UDT). The reverse relief pressure valve is now set to 3400psi, but that did not resolve the traveling speed issue.

My next guess was that the swash valve plates or the pump cylinder assemblies were worn and were not building enough pressure when loaded. So... I decided to tear into the pumps.

QUESTION 1: How do you know if you need to replace the piston cylinder assemblies? I have included some pictures of my valve plates and cylinder assemblies. Based on the wear marks on the brass swash valve plates, I plan on replacing all three valve plates (charge, motor, assist motor). I figured you could place a straight edge across the cylinder face and measure groove depth, but the workshop manual does not mention an acceptable range.

QUESTION 2: What have I overlooked that would cause 10mph top speed?

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Adams Repair would be the one to tell you what is worn.

My machines were all too new to have any real wear.

Forward and reverse relief pressures have been set as high as 4,000 according to another Kubota mechanic I communicated with and he said no problems.
 
Here is what my book says about the plates.

Hopefully the scratches are just in the plates.
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Thanks. I found that page shortly after my first post... oops. I do not feel any defects with my fingernails, but that's a very subjective measurement. I zoomed in on the WSM image of the cylinder block in my electronic WSM. The surface appears to be very smooth, and it's described as "polished". Based on this, I think mine cylinder blocks are fine.

I decided to order the valve plate kit and keep my cylinder blocks. The valve plate kit is $150, the cylinder blocks are $300 each. I plan to carefully compare the old and new valve plates when they arrive.
 
i have a 2007 rtv 900 with 700 hours..top speed was 15 mph in high .. my dealer charged me $1100 for complete fluids and filters changes.... replaced a part in the hydrostat .. the transmission parts was $245 labor was 1 hour ...... now it will run 29-30 mph.. the fluid and filter change was for scheduled service....
 
Given that these develop 3,850 lbs max pressure in the system, it would take very small imperfections to create major pressure leakage.

Loss of any of that pressure would be critical.

Think of how little a cylinder hose fitting can be loose and how much pressure loss there is.

One small leak and the cylinder stops working and no the RTV it's only about 2,500 psi on the cylinder.
 
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Hello me37250
Nice pictures, If you plan on changing the brass plates Get the plate kit K7571-91374 comes with gaskets and instructions..
The finish on the face of the cylinder assy. Needs to be flat with new plates. I take mine to a hydraulics shop and have them put on the lapping table. Then clean them real good when you get them back, get all the diamond compound off them. then clean them again. Cleanliness is of utmost importance. When you go to put the neww brass on check your porting alignment. They are not all the same. Also before you install the brass blow dry the area use a lint free rag to wipe the surface where the brass will go. then put a dab of white lube (engine assembly lube) on between the brass and the valve body. You don't want even lint between there it will leave a high spot on the brasses other side. Now be just as clean with the cylinder assembly's.
I see in one pic corrosion on a spring, where did that corrosion come from and what else is it on or in?? every spring and plunger needs cleaned. Keep the plungers with the same cylinder, (same hole doesn't matter as much). As far as your speed... Sounds like you have checked all the linkages. Charge pressure sounds a little high (Charge pressure is the life blood of a hyrostat) If your charge pressure stays up when you stroke the pump, only fluctuates a little when you start to stroke the lever that is fine. While you have it apart check to make sure the pump swash plate is seated on the cradle bearings shoes it rides on (up and square) Square block on top engaged full in the servo piston.
Brakes dragging?? Has it been run in the mud alot?? Have found wheel cylinders get muck behind the seals and get sticky, you can free them up just to find them sticking again later. same with the brake levers them self's they get muck between the housing and shaft. Sticky P brake cable? Does the tranny get hot faster than the engine? Your brass really don't look that bad A little worn. If it is not a linkage problem or a brake issue. The wrong or dirty suction filter will cause a speed power problem but will show up on the charge pressure gauge.

I hope any thing I mentioned here helps.
Jim
 
me37250
Here is the real pisser.... You can pull the motor cylinder out wth the shaft. "BUT"" it comes real hard. 2 small heel bars and some tapping. The shaft is a lite press fit into a bearing in the case. ""BUT"" when you do this in the machine the spline coupling on the inside sometimes falls off into the tranny.. NOT GOOD Also when you go to put the shaft and cylinder assy. back in if the coupler did not fall off it is now hanging to low to line back up. I do this with the tranny standing on it's nose on the bench while mating the 2 tranny half's. I have not tried taking the breather cover off and putting a magnet in there to see if I could keep the coupler from falling off. Then lift it enough to get it to align back up with the splines.
 
AdamsRepair said:
Hello me37250
Nice pictures, If you plan on changing the brass plates Get the plate kit K7571-91374 comes with gaskets and instructions..
The finish on the face of the cylinder assy. Needs to be flat with new plates. I take mine to a hydraulics shop and have them put on the lapping table. Then clean them real good when you get them back, get all the diamond compound off them. then clean them again. Cleanliness is of utmost importance. When you go to put the neww brass on check your porting alignment. They are not all the same. Also before you install the brass blow dry the area use a lint free rag to wipe the surface where the brass will go. then put a dab of white lube (engine assembly lube) on between the brass and the valve body. You don't want even lint between there it will leave a high spot on the brasses other side. Now be just as clean with the cylinder assembly's.
I see in one pic corrosion on a spring, where did that corrosion come from and what else is it on or in?? every spring and plunger needs cleaned. Keep the plungers with the same cylinder, (same hole doesn't matter as much). As far as your speed... Sounds like you have checked all the linkages. Charge pressure sounds a little high (Charge pressure is the life blood of a hyrostat) If your charge pressure stays up when you stroke the pump, only fluctuates a little when you start to stroke the lever that is fine. While you have it apart check to make sure the pump swash plate is seated on the cradle bearings shoes it rides on (up and square) Square block on top engaged full in the servo piston.
Brakes dragging?? Has it been run in the mud alot?? Have found wheel cylinders get muck behind the seals and get sticky, you can free them up just to find them sticking again later. same with the brake levers them self's they get muck between the housing and shaft. Sticky P brake cable? Does the tranny get hot faster than the engine? Your brass really don't look that bad A little worn. If it is not a linkage problem or a brake issue. The wrong or dirty suction filter will cause a speed power problem but will show up on the charge pressure gauge.

I hope any thing I mentioned here helps.
Jim
Click to expand...

Thanks so much! No doubt, you are the right person to ask about these things. I was lucky and had ordered that kit. I will explore having the cylinders blocks lapped. You bring up a great point... although it has not been in the mud much, it does seem to have some corrosion issues. I wonder if the brakes are seized from corrosion? I will explore this possibility. Thanks so much for the hints.
 
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Sticking brakes

The Kubota engines and transmissions I work on, are run in a underground mine.
So they get run hard with very little care. They get run through mud and water all day, sometimes through cement water. They are always over loaded and run up and down steep ramp systems, at full throttle. I have found brakes hanging up so many times. From the wheel cylinders, P brake cables, to the brake lever shafts them self's. If you have played with these ramp type wet brakes at all you know it only takes just a slight pressure to apply the brakes. So when the brakes drag just a little, and you overload the RTV. The tranny temp goes up fast from brake friction and hydraulic load. The oil breaks down under high heat right at the brass plate and cylinder contact area. Scoring them. Now you have lost some of your flat sealing surface. The new HST (2 plus) units have a better cooler installed on them. To many people jump to the conclusion that it must be a tranny problem without looking at all aspects of the unit. I have had my transmissions installed by other people. I get this call your rebuild is no good. When i go investigate usually I find cables and linkages were put back on how they were set when they removed the old trans. Nothing adjusted properly, but mostly a brake problems. And that is why the first trans failed to begin with. Went to investigate a brand new $8000 trans out of the box problem. They said it won't do anything. Found when they installed it, they forgot to change the filters. Oh my! Don't want to know how much crap was in the old filter from the previous failed trans. (Low / erratic charge pressure) So Keep your eyes wide open, and your mind too.:wink:
 
I will definitely be investingating the brakes... after I get the trans put back together. Ha! I bought this unit used. It was leased to a chemical plant, so it drove around in some corrosive stuff. The pressure relief knob and posititive traction cables are seized, so I would not doubt that the brakes have an issue. I unhooked the pressure relief cable to eliminate the chance that it might be bleeding pressure from the trans, but I simply overlooked the brake situation. Guess I had my blinders on. At least I'll have shiny new internals. Thanks!
 
Sticking Brakes

So here's the update. I finally received and installed the valve plate kit. I refilled with Super UDT, and my first test drive max speed was exactly... 10mph. I didn't fix a dang thing.

Armed with a little more knowledge, thanks to AdamsRepair, I decided to investigate sticking brakes. Yep, he guessed it right. The passenger side rear brake lever was conspicuously stuck in the forward position. I completely missed this. Drove the lever back with a few slight hammer taps, and this sucker runs 25mph in high gear!!!!!!

It's fairly obvious now that I know what to look for. Depressing the brake pedal drives the brake lever forward. The driver side rear brake easily returned to the original position, but the passenger side would stick every time due to a problematic slave cylinder.

I disassembled and cleaned the slave cylinder, but this did not free up the cylinder movements. There must be some minor scoring that is causing the hard sliding. I have temporarily fix the issue by adding a bungee strap behind the brake lever. It aids in returning the brake lever to the vertical position. That should get me by until I replace the slave cylinder.

Lesson learned... ask a pro.
 
me37250 said:
I disassembled and cleaned the slave cylinder, but this did not free up the cylinder movements. There must be some minor scoring that is causing the hard sliding. I have temporarily fix the issue by adding a bungee strap behind the brake lever. It aids in returning the brake lever to the vertical position. That should get me by until I replace the slave cylinder.

Lesson learned... ask a pro.
Click to expand...
Check the shaft that goes into the brake housing, they get mudded in also.
You need to shoot some penatraiting oil in there and maybe some brake kleen
then try to blow the muck out with a blow gun, while working it back and forth.
The O Ring is only about 3/16" into the housing, groove is on the shaft. Muck an mud get in there.
 
AdamsRepair said:
Check the shaft that goes into the brake housing, they get mudded in also.
You need to shoot some penatraiting oil in there and maybe some brake kleen
then try to blow the muck out with a blow gun, while working it back and forth.
The O Ring is only about 3/16" into the housing, groove is on the shaft. Muck an mud get in there.
Click to expand...
any help would be appreciated,,,,i have a rtv 1100 which is a real dog,the tranny actually seems to slip,im told that is normal,but,id prefer the tranny to act more like the hydrostatic tranny on my JD 4115,,,,,my question is,to check the brake system not properly releasing,i assume it would also be ok to take a floor jack,and jack up the rear (both sides) and see if one wheel "locks up" or has more resistance than the other? please advise,thanks
 
just putit in neutral on a good level hard surface and see if it rolls easy. or jack it up and see if the brakes are dragging. why don't you put all of this in one thread so it isn't so spread out???
 
because every time someone contributes a though to me,i brings up a new question for me,,,,,,,,,
 
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