How to increase HST relief pressure on a CK30

[dfkrug]

This thread has resurrected an issue I have with my Kioti's HST and HSTs
in general:
http://www.tractorbynet.com/forums/bobcat-tractors/165728-attacking-power-problem-ct225.html

This issue was talked about in other threads over the years, including this
one:
http://www.tractorbynet.com/forums/...7703-what-going-hydrostatic-transmission.html

How does one increase the relief valve pressure? This applies to all the
M27 tractors (CK25/30/35, Bobcat CT225/230/235) as far as I can tell.
It has been reported that the CT235 uses a RV set at a higher pressure
than the other Bobcat M27s:

For the CT225/CT230, KRAZK reports that the HST RV is 280kg/cm2 (3980psi)
while the CT235 is 300 kgf/cm2, or 4260psi.

From page 4-37 of my CK25/30 service manual, it is:
280 kgf/cm2, which is 3980psi

I am still waiting for a report on the CK35 RV spec. Anyone have the
service manual?

So....I went out and removed my Forward RV, which is fairly easy, using
a 8mm Allen-head wrench. See pix.

The cap has a bizzare straight thread that measures 13/16-14tpi. The
RV itself is hand engraved to read "280". The valve has a screw-adjustment
that is welded at the end to keep it from loosening or being modified. It
can be reset after grinding off the weld, screwing the adjuster in and
rewelding. If the 300 kg/cm2 valve has the same dimensions, then it can be
used instead.

Now, we just need a guinea pig to make this mod. I have not, as I do not
yet have a guage over 4K psi, and it is not high priority.

 

[bbse]

Looks like a plan. Where do you check the pressures at? I would definitely consider playing with this down the road. I am going to try to do the dealer thing but it looks like if I don't call them, they don't call me.

 

[dfkrug]

There are 3 plugs right under the floor mat immediately below the 3-pt
speed knob. The one on the left is the FORWARD test port. When I get a
guage, I will test the pressure. Too bad my CT230 is gone, or I would
do that one, too.

I wish all tractors were this accessible.

I was also wondering who is the manufacturer of this HST. I know that
the 3-pt hydraulics are made by Mita OleoDynamica of Italy.

 

[tinman955]

How much of an increase will help?

 

[dfkrug]

Any increase is going to help some. I am not as concerned about this
issue as some of the new Bobcat owners who have run into it. I was
very surprised when I could not spin tires in a few rare situations, but
those do not occur often. I do believe that DaeDong has made some
incorrect design decisions with this tractor; no other HST CUT I have owned
has done this.

 

[tinman955]

I hear ya on that one, thats why I ordered a new SST tractor so I dont hv this issue anymore

Glad to see you are working out the details on this subject, keep up the good work.

 

[Sabretooth]

I hear ya on that one, thats why I ordered a new SST tractor so I dont hv this issue anymore

Glad to see you are working out the details on this subject, keep up the good work.

Tinman think you might need name change a new SST:drool: just does not fit with tin name maybe Platinumman or Diamondman. I'm just trying to get a Boxblade for my Bobcat forget getting another new tractor and I can only imagine what my better half would say or do

 

[tinman955]

Tinman think you might need name change a new SST:drool: just does not fit with tin name maybe Platinumman or Diamondman. I'm just trying to get a Boxblade for my Bobcat forget getting another new tractor and I can only imagine what my better half would say or do

Trust me I didnt want to buy a another tractor already but I absolutly am done with HST's!! I kept my last tractor about 1000 hrs and 15yrs, it was a john deere 955 awesome tractor!!

I love my bobcat, just need more tractor and dont mind using a clutch. Sorry to be off topic guys, this a very important subject that needs to be addressed. I believe HST's have their place just not in my garage anymore.

 

[SunnyJim]

Trust me I didnt want to buy a another tractor already but I absolutly am done with HST's!! I kept my last tractor about 1000 hrs and 15yrs, it was a john deere 955 awesome tractor!!

I love my bobcat, just need more tractor and dont mind using a clutch. Sorry to be off topic guys, this a very important subject that needs to be addressed. I believe HST's have their place just not in my garage anymore.

No worries. For me its the opposite. I have to clutch as little as possible so HST is for me.

Everyone has to meet their own need or preference.

 

[Highbeam]

SST as in skid steer tractor or SST as in shuttle shift transmission?