Hi, Name is Tim. I have a 2004 bobcat T300 with 3452 hrs. which I am experiencing some problems with the brake release on drive motors (one side only). Oddly enough, the right releases fine and the track wil spin with no problem yet the other side (Left) will not or justs barely moves but squeels like a pig. I have a test guage on the left side hydrualic line to measure the pressure received at the drive motor brakes and i measure approx 100 psi. I cannot test the other side unless I tears off the trackes etc and I would prefer NOT to go thru that again. I suspect the brake is not releasing due to not enough pressure? (local bobcat techs initially stated I should have 390-430 psi but then changed his mind after and stated he didnt know afterall and didnt want to assist any further) Can anyone tell me what I should have for BRAKE RELEASE pressure at the drive motor? I do not see this spec listed in the manual. (bobcats service manual sux btw, poorly written / drawn) Furthermore, I am now having some trouble with the arms lifting and bucket tilt, not enough pressure there as well. I have recently installed a new charge pump and tested pressure at the charge pump after doing so (approx 960 psi at high idle) so I dont beleive this is the problem. Any suggestions would be helpfull and appreciated.
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The brakes have charge pressure going to them, spec is 390 to 430 psi. If one side is releasing, you know that is all good. My guess is the brake seal blew out. The brakes are spring applied, hydraulic release. Also, if the brake is leaking bad enough, it will cause a system drop and can affect other functions. Charge pressure is the base pressure for everything. I don't know where you tested 960 psi, that is insano high. I'm think with that kind of pressure, you are wrecking stuff. The charge pressure releif vavle needs to be adgusted. Did you ever have any low charge preasure codes before replacing the pump, those really don't go bad. The easy way to test the brake is hook a porta power with a gauge to the brake. This can be done under the cab by the brake vavle, pump it up and see if holds pressure.
THank U for your response. I am testing the hydraulic line that feeds the brake. The line is disconnected from the drive motor and the pressure guage is installed at the end of this hydrualic line. the drive motor brake port is blocked off. Since I am testing before the drive motor I am testing real pressure that serves the brake (Left side) therefore I beleive the drive motor assembly should at this point be irrellivent. The 960 psi was measures at the charge pump output while at full throttle. The measurement at idle was muchless (approx 400psi). According to bobcats manual and the manufacture of the charge pump, this is correct pressure output. I did have low pressure codes popping up and the tracks locking up repeatedly before I had the charge pump replaced (pump was hammered inside) but since then I no longer have the low pressure warnings and the tracks worked fine . I also had both drive motors rebuilt to elliminate any future problems with them. Its been several months of use and now I have this problem occurring. It seems odd (Baffling) that one brake would release fine and yet the other is not due to low pressure since both brakes are served in parrallel after the the brake valve. Bobcats manual hydrualic schematic shows two brakes yet the same manual in discussion(s) state the machine only has one brake..which is clearly inaccurate since I already had both drive motors rebuilt and visually inspected the motor interior components to confirm brakes on both motors. No idea where to find this charge pressure releif valve..or how to addjust it =(
o.k I just tested the parking brake switch to see if the right side brake works..it does NOT. the right track does NOT lock when U apply the parking brake so this adds a new perspective to the equazion. any suggestions would be helpfull. Thanks
At rest the brake is on. Mechanical failure of the brake is the only way it wouldn't lock.
390 to 430 psi is spec at max throttle.
Does anyone know how the brake control block (internally) is constructed? I know there is one primary feed port and two output ports but are they seperated internally or just one output (internally). I seem to have a condition where i have approx 340 psi (at full throttle, approx 220 psi at idle) input pressure but no pressure output onj onee side of the output which leads to the drive motor.
Any suggestions on any easier method to remove the brake valve without having to remove the track and sideplate?
Can anyone tell me what the psi pressure should be that fdeeds into the brake valve? I have approx 230 psi at idle and 330 at full throttle. IS this correct? Seems abit low to me?
Can anyone tell me what the psi pressure should be that feeds into the brake valve? I have approx 230 psi at idle and 330 at full throttle. IS this correct? Seems abit low to me?
O.K it seems I have an electrical issue to deal with as well. I am reading 5.28 volts at the brake switch solenoid when it should be 12 volts. This tells sme the brake solen oid is not functioning properly whichc is perhaps the reason I dont get any hydraulic pressure out of the brake vale itself. The voltage (5.28v) remains the same even with the relay removed or instaled. I do however get 12 volts to the relay. Anyone have suggestions on where to look next with this type of problem?
You did try a different relay?
Even check the contacts in the fuse box that the relay plugs into, they can get corroded and not make good contact.
HI, Thanks for taking time to respond. Today I pulled the acuator valve out of the interior of brake valve block and found that one of the load side port screens that feed thru the block and to the drive motor(s) was glogged with metal shavings. I cleaned it out..and reinstalled it but this didnt improved the end of line pressure at the drive motor much..(stiil only 240 psi at full throttle)..IM guess I still have blockage in the line feeding the drive motor from the brake valve. IM goinna pull the line out next and inspect for blockage. I still have an electrical voltage problem (only 5.28 volts) to the brake valvbe block which im stumped on. I checked the grounds but that doesnt seem to be the issue. Anyone have any idea as to why I would see a reduction in voltage from 12 volts to 5.8? (Note: even if I apply 12 volts directly to the brake valve coil I still dont see any improvement on the pressure feeding the brakes.)
THanks for the suggestion. I will do that tommorrow. Funny however even if I apply 12 volts directly to the brake valve coil itself from the battery I still dont see much improvement in end line pressure to the drive motor. hhhmmmm
today I checked the contacts for the FUSE in the fuse box and cleaned them up. put the fuse back in and now I have the proper (12v) voltage at the solenoid. Thanks for the input on that.
O.K this issue is solved. I removed the brake spool from the brake block and cleaned out some blockage. Further I cleaned out the canister filter again..and further I cleaned the fuse terminals in the fuse box which brought my voltage at the solenoid back up to from 5.8v to 12v..Now all seems to be working properly again. (what a pain in the ass) now on to the next issue i.e arm lift function stopped working
Excellent work. You may want to put dielectric grease on the connectors to try and stop them corroding any more too.
If the problem comes back, you can always cut the connectors off and install inline fuse holders. Far less than a new harness....
THanks for that insight. DO u have any ideas on what / why the arm lifts stopped working? Before I go much further on that issue I need to find out the operating pressure PSI for arm lifts. ANy idea where I can find that info?
mrdeere1959
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- Nov 1, 2011
- Messages
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look in your service manual
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