Kubota RTV 900 transmission problem - hardley moves in gear!
- Thread starter PACKASAURAS
- Start date
aurthuritis
Well-known member
sent you another PM. should help i hope
aurthuritis
Well-known member
ok i think i may have misunderstood the relationship between the feedback lever and the control lever. it should work like this>>> when you move the control lever it acts like a fulcrum against the feedback lever and moves the spool and that lets pressurized oil into a passage that pushes against the servo piston which in turn moves the swash plate. when the servo piston moves it also moves the feedback lever and that moves the spool that either opens or closes the ports balancing the pressure on both ends of the servo. does that make sense?? so it would be possible to move the lever as in your photo. SORRY
i still think the servo piston is sticking or has leaky orings.
i still think the servo piston is sticking or has leaky orings.
aurthuritis
Well-known member
sent another PM with helpful information
Thanks for your help and additional information/links. The sectional drawings are very helpful and clarify things a little. I'm hopeful we have narrowed this down and it links us back to when I was changing valve plates and the guide above input shaft too the swashplate appeared jammed. Hoping to get onto this again today 
aurthuritis
Well-known member
yes the guide will have to be disengaged from the servo piston. can the servo assy be lifted from the transmission? you might be able to clean and lube the servo piston from there and reassemble to try it,sorry. there is another piston in the system that actually controls the swash plates also. if that piston is stuck or sticking it could be the cause. that could be the binding linkage you mention or it could all trace back to the servo. i think you are getting real close. i hope this is all working out for you.
I've opened tranny up and pulled out guid to allow piston to be pulled out. Guide pin was loose and has elongated hole on swash plate - is this all pointing to the piston? I can push it in and out but takes great effort. In order to get swash plate out do i need to disengage drive? I cans seem to get it over the splines and suspect it will need replaced.
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aurthuritis
Well-known member
well i commend you! i think it is time to evaluate the wear pattern discovered. it seems to be just about everywhere. could be time to consider a rebuild of the current transmission or just purchasing another used or rebuilt / new hydrostat. sorry
aurthuritis
Well-known member
sent you a PM
Ouch...by rebuild does that just mean renewing all swash plates, revolver pistons, bearings, piston etc? Feel a bit uneasy opening engine....i need to remember how to put this thing back together!! Tried opening up piston but only got as far as removing two nuts...threaded bolt moving in and out very loosely and no signs of any other way to open up further. Thanks very much for your help/advice, please keep it coming!! Many thanks
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aurthuritis
Well-known member
i see wear on that piston. what does the bore of the housing look like. inside of that piston is a captive spring and the threaded part is the stem. the piston is supposed to move back and forth on that spring with spring resistance of course. if you decide to go further you need to examine the swash plate and bearing surfaces for scratches and wear. it is beginning to appear the wear is everywhere.
The chamber looks and feels rough but suspect this is how it was cast? Bores cleaned up well and have ridges but suspect this is from manufacture? I cant feel any resistance in piston or feel any signs of a spring. I've seen exploded diagrams of this which made me think i could open up, but it appears sealed so will need to replace. Have you ever opened up casing? Is it much harder than i have already done? I trust we think it's work the money and effort reviving this machine?! So it looks like the piston has caused this issue? Swash plates, bearings etc all look ok with no major visible damage.
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The piston cleaned up quite well. Whilst it is showing marks you cannot feel and undulations or scores with fingers or finger nails. When nuts are screwed in i can push threaded rod and feel resistance from a spring - feels very strong. Even with wear in lever and guide they still have a snug fit in piston (don't worry not thinking of keeping them in!!). Thought I'd share a few more photos.
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aurthuritis
Well-known member
it is a hard call. not knowing what the high side pressure is makes it difficult and can only guess if the positive displacement pumps and motors are ok. looking at your photo of the piston and the bores of the housing looks like a lot of wear to me and if that isn't just dirt in the photo then i would say that bore is trashed too. i don't like the idea spending money on a new servo unit that would just have to be re spent on a new or rebuilt transmission. if your engine is running good you shouldn't need to worry about that part because you can separate engine from tranny and just replace the transmission.
just my opinion <<<"if it were mine i would choose one of two options 1.put it back together and get all of the adjustments done and have the dealer check the pressures to see if the high pressure system is ok and consider living with the shortfalls until i could source a new or good used transmission>>> 2. just go ahead and get a new transmission now and bite the bullet.
just my opinion <<<"if it were mine i would choose one of two options 1.put it back together and get all of the adjustments done and have the dealer check the pressures to see if the high pressure system is ok and consider living with the shortfalls until i could source a new or good used transmission>>> 2. just go ahead and get a new transmission now and bite the bullet.
I will price up tomorrow. The marks in the bores in the photos is just dirt and they have cleaned up well. There are ridges in the bores but I think they were introduced at point of manufature? - very profile and clean. The inside of the piston chamber appears and feels rough but again think this has occured during manfufacture?
Its very frustrating that I need to split the unit just to get the swash plate with guide out/in! I am very tempted to clean all down, split unit, put in new swash plate and guide, new piston and lever assembly and put all back together, however with all that time I would regret should it not be successful!! I trust high and low pressure pumps are the "revolvers" with pistons? The piston ends do have very light marks on the ends as would be expected with rotating parts under pressure. Do we think a faulty piston has caused this damage?
Its very frustrating that I need to split the unit just to get the swash plate with guide out/in! I am very tempted to clean all down, split unit, put in new swash plate and guide, new piston and lever assembly and put all back together, however with all that time I would regret should it not be successful!! I trust high and low pressure pumps are the "revolvers" with pistons? The piston ends do have very light marks on the ends as would be expected with rotating parts under pressure. Do we think a faulty piston has caused this damage?
aurthuritis
Well-known member
in the machined surfaces there shouldn't be any ridges,this indicates abnormal wear patterns. the scratches on the surface of the pistons plungers on the pumps is abnormal also. normal wear for a high hour machine would be a finely mirror polish,and even that is still wear. as the wear increases the tolerances increase and leaves less and less useful hours in the machine. it is just me but what i see is abnormal wear on multiple operating surfaces likely caused by a corrosive or abrasive environment. now if you could fix this with just a few orings and get satisfactory service that would be different but every new part you purchase and put in an already worn system is just another part you get when you replace the whole thing. like i said earlier though> if you reassemble and with cleaned up old parts and everything is free to operate it might just give satisfactory service for a few hundred or more hours before you need a major overhaul.
I thought id post this photo again on it's own, to make it larger. These fine ridges look machined? Re the condition of the inside of the chamber, this is a sealed system so why would environment impact it and why is there not similar issues further in tranny at pump casing? Will price full transmission kit (K7561-91122) and refurb kit (K7561-91154) tomorrow. I'd best sit down to make the call!!
