Coast Valve removed from RTV today and OEM one adjusted and put back in

[Wayne_H]

OK, I bought the coast valve like many others and installed it in my RTV-900. No longer was I smashing my dogs nose on the hood of the RTV if I took my foot off the gas quickly.

Today, after hearing we could adjust the stock valve, I looked at my stock valve and decided to adjust it and re-install it. To do this, all you need to do is loosed the set scew which locks a flat head screw. That flat head screw adjusts the spring tension on the valve. I opened mine up two turns, cranked the set screw back down, and back in she went.

Now it still has breaking, but it is way smoother than before where it would send you flying if your foot came off the gas peddle. It apparently still has holding power, but just not the same agressive breaking it had before.

I guess I'll run it like this for a while and then see if I can sell my coast valve.

Does anyone know if adjusting the stock valve is a bad idea? Why isn't anyone talking about doing it on the forum? I can't see that it would do any harm.

Wayne

 

[groundcover]

I just learned to ease up on the gas foot,no big deal. The first stop after getting off the Polaris can be sudden though!

 

[DelfinoTX]

Wayne, can you post a pic of the stock valve location please.

Oh, and where did you hear we could adjust the stock valve? was it in this forum or another?

Thanks,

DelfinoTX

 

[Wayne_H]

Nobody on the other forums really talked about adjusting the OEM valve, but I have "heard" that some dealers would do it. After looking at it for a few minutes, it was clear that the allen screw locks in the spring tension, so all you have to do is loosen that, and then unscrew the flat head screw, which in turn relieves tension on the spring.

The plug which covers this is removed with a 10 mm allen wrench. The pictures I took are looking down. If you have a 10 mm allen that works with a 3/8" socket, life will be easier. But after you take the plug out, use a magnetic pick up too to remove a spring, and then use the magnetic pick up tool to take the valve out. I can do it now in less than five minutes, for me the hardest part was locating the 10 mm plug. But, there is only one 10 mm plug on the back half of the transmission, and it is very close to the hydraulic oil tank on my 900. I hope these pictures work!

Wayne

 

[Slatecreek]

I have also read where the stock valve could be adjusted and that dealers were doing so, but have been reluctant to try this myself. Very interested in how this works out for you. Is there any loss in power or any other side effects of doing this? Keep us posted.

 

[Wayne_H]

I'll let you know if there are any adverse affects. So far I can't tell any difference, but it still brakes with the trans, just not as agressively as before.

Wayne

 

[DelfinoTX]

Guys, this adjustment is what my RTV has needed all along... I reduced the spring tension on the valve three and a half turns and it works great.. There is very little engine braking now. Just enough to slow the machine down gracefully. This also makes backing up a breeze. No more whiplash! Awesome!.. I can see that this valve set to the factory setting provides for engine braking downhill, but I live in an area that is very flat.. No need for it.. This valve adjustment is a no brainer. Tip: Use a piece of 3/4 inch PVC to slip the valve in and clamp with a vice. this will prevent dents or scratches to the smooth areas of the valve and hold it tight when making adjustment to the spring tension. This valve has to slide up and down for the check valve function and is held in place by a very light spring.. any scratches or indents in the valve body will cause it to fail. Be careful and don't drop it..

Oh, another Tip on edit: I also removed the throttle return dampener.. The small one way piston that slows the return of the throttle linkage to idle.. Man what a difference in drivability!

Thanks again for the great info Wayne!

DelfinoTX

 

[workhorse]

This is really bizarre, trying to figure out why Kubota engineers designed what they did. They put in a coast valve at a specific setting, but it appears the deceleration was too jerky when you drop the accelerator pedal, so they add a damper to decrease the rate of deceleration? The damper is a waste if the coast valve was set for smoother operation. There must be a reason the coast valve was installed at that setting. Controlled downhill speed? Other reason? It's beyond my pay grade.

 

[Wayne_H]

I can't figure it out either... but I do have a non OEM coast valve for sale if anyone wants it. I did complain to my dealer about the stopping being too agressive, and he did not have a fix... Being a John Deere person, I'd have to say the engineers in Japan don't speak the same language the folks in the US do....

Wayne

 

[Dargo]

This is really bizarre, trying to figure out why Kubota engineers designed what they did. They put in a coast valve at a specific setting, but it appears the deceleration was too jerky when you drop the accelerator pedal, so they add a damper to decrease the rate of deceleration? The damper is a waste if the coast valve was set for smoother operation. There must be a reason the coast valve was installed at that setting. Controlled downhill speed? Other reason? It's beyond my pay grade.

My dealer told me that he wouldn't adjust the factory valve like discussed because it caused cavitation and accelerated transmission wear and heat with tiny air bubbles all throughout the transmission. He told me that is why the purchased "coast valve" does not have a spring, and is just a solid valve. There is no spring to give allowing cavitation, thus a market for that design over just making adjustments to the factory valve. To me, not being any expert by any means in hydro transmissions, this made sense. Why would the factory make dampening rigs etc. if they could just adjust the spring rate of the valve without causing damage?

Again, I am not a hydro transmission expert. I'm just going by what I was told along with the fact that Kubota made other changes to try to alleviate the abrupt stopping rather than change the spring settings on the existing valve. So I obviously have no definitive proof that adjusting your own valve will do damage, how fast it will do damage, or exactly what damage it will do. I'm just going by what my dealer told me and applying that information to the fact that Kubota made other changes to help the sudden stop rather than just turning a screw on the existing valve.