Troubleshooting Power Bob-Tach not working

A common problem with Bobcat skid machines is Power Bob-Tach not working. There's a couple of things that can cause this problem, this is a thread that will discuss a few things one should look at when troubleshooting the problem. I must warn you that if you have to actually work on the control valve that operates the power bob-tach, it's located deep in the bowels of the machine, an absolute PITA to get to. If you're a person that typically exibits restrained demeanor and refrains from using swear words, well, you will use them once you start working on this thing.

The first thing one should do is make sure that the bob-tach cylinder is actually not working and problem is not caused by stuck locking pins on bucket coupler, make sure the attachment locking pins work freely. If you've determined the bob-tach cylinder is not working, remove the center console in cab that has the bob-tach control switch. Turn the ignition on, engine not running, test the center terminal on switch with a test light to make sure the circuit has power. If terminal tests good, place the tip of test light in the two out board teminals on switch, operate switch to make sure it's working proper.







Once you've confirmed power is good and switch is working proper, it's time to start using the aforementioned swear words. Start machine, raise the loader arms fully and fit the loader arm safety prop on right side of machine, shut down machine. Raise the cab and lock into raised position. If you have an access cover on right side of machine behind arm lift cylinder, remove that cover. Not all Bobcat machines have this access cover, if it's not on your machine, you're going to have to do repairs by diving in under cab, this case requires swear words followed by exclamation points.

Now locate the valve that operates the Power Bob-Tach. With the cab raised, looking from front of machine toward rear, you'll see the hydraulic pumps in the center of the machine. The pumps in the center with large hoses going to them are the drive pumps. Mouted to the rear of drive pumps, to the left side, is the work equipment pump that operates loader functions.







If you look at the work pump, on the backside of pump, yes, so deep in the machine that you can nearly feel the fires of Hell burning back there, you'll find the solenoid valve that operates the power bob-tatch.







This view is looking down the backside of the work pump, there's the two coils that operate the solenoid valve.







This view is looking from right side, there's so much stuff in the way it's very difficult to get good pics of the control valve.

At this point, one could disconnect the harness connectors and test the harness for power from switch in cab, but this is a difficult process in itself, hard to get to connectors with test equipment and still operate the switch in the cab. I have put a jumper wire at switch to power the harness, then climb under cab and test at connectors for power and ground. Be sure and check the condition of the pins/sockets inside the harness connectors, I have seen a case where it was simply pin socket had spread open a bit and not allow good connection with pin.

If things have thus far checked proper, and securing nut is still on solenoid valve holding coils in place, it's probably time to pull the solenoid valve out of the control valve body. Remove the securing nut that holds the coils on the solenoid valve stem, this one required a 5/8" wrench to remove nut. Use caution, do not drop the securing nut as you may not find it to recover it in the abyss of the machine.







The coils will now simply slip off leaving the stem in place. Take note which coil came from outward end of stem and which one is inboard. If you switch these coils upon reassembly the bob-tach will work backwards of switch position.







Here's where the real fun begins. It takes a 7/8" wrench to remove the stem and there's not much room for a long wrench in here. Additionally, [the genius] that designed this valve has it fitted in a "recess" in valve body so you can only grab a hold of a little more than half of the width of the hex of the stem. This won't allow using a box end wrench unless you grind the wrench to remove the taper on the outer edges of a typical box end wrench. You can't use a deep well socket as the stem is longer than a typical 1/2" drive deep socket. If you can't get the stem broke loose with an open end wrench, you'll have no choice but sacrifice a box end wrench and grind it so it will grab the hex. This is a spot where Snap On angle wrenches come in handy.







Once you get the stem loose, it will simply slip off the actuator pin for valve spool.







Once the stem is removed, grip the actuator pin with a dry rag and try to pull it from the valve bore. There could be a fragment that is preventing the spool from being removed, try pushing spool in and out and pray it comes loose, otherwise, we're looking at valve body removal.

This is a view of removed components.







Take care when handling the acuator pin and spool assembly. The actuator pin is connected to the spool and can be accidently disconnected at this notch in the spool.







Clean all components well with starting fluid or brake cleaner, then re-install the removed components. Check the seal o-ring on stem seat before installing, replace if it's either hardened or damaged. I'm not sure what the proper size o-ring is, I used a 568-908 but I don't know that's the proper size, I'd like to know what the proper o-ring size is.







Keep in mind that a common cause of power bob-tach spool sticking is metal fragments in the hydraulic oil from either a previous component failure or a component that's beginning to fail, possibly one of the pumps or a drive motor. This would be a good time to check the hydraulic filter for debris as well as check the drive motor case drain filters.

Thanks Willie59 for the excellent detail on that project. That will be very helpful when doing that repair.

Hopefully, you'll never have to go there JBGASH. :yup

That does look real awkward willie, sure hope i don't have to do one soon!!

i'll add this to willie's excellent thread.

i've extended a couple of deepwell sockets to fit over the stem to extend the length. an impact socket WILL NOT fit into the counterbore, i used a chrome 12 pt.

the nut holding the coils on is 5/8" hex, some very early valves had a spacer between the coils

i also have a couple of old connectors from the coil side of the harness, (they are different, male and female) extended the leads on them to be able to watch a meter or test light while operating the switch in the cab.
i actually use an old cab warning buzzer instead of a meter, that way i'm not trying to see the meter, or worry about a test light that suddenly decides to not work.

the older valves have 3/8" allen head bolts holding them to the pump
if you have a large frame machine with A/C you'll need a short piece of 5/16" allen wrench, and a combo wrench to get the bolts broke loose. they had thread locker on them from the factory, and were waaaayyy over torqued. with A/C you have to leave a couple of the bolts in the block when you remove the block.
install new bolts as they have a habit of breaking when you reinstall them
mid frame machines, the A/C compressor is mounted on the rear of the engine, you can usually reach the bolts working from the (rear) rh side of the engine, if you remove the belt guard and alt belt.

new M series machines have a different valve and use hex head bolts, but has been moved farther back out of reach, but so far the valves have not been sticking from debris..... leaking valves are another story



99% of the time , if the valve is sticking, (especially the early valve design, parts are NLA) cleaning, and freeing up the spool only buys you a short time of power bobtach operation, the valve usually needs to be replaced

Possible advice from willie

Hi willie, excellent post. I'm new to the forum and I'm not sure how to navigate it yet, but is it possible that this is my problem? I have a 753 and the right controller will not operate the bucket but when I click the trigger switch it will open the bucket, if I reverse the solenoid the trigger will close the bucket. But to no avail, will the thumb slide switch work. I tried to meter the handle but could not come up with positive results so I got lucky and scored a brand new one for $100 on eBay so I said what the heck. well it didn't fix the problem, I did however get to grind down the controller arm where it swells and fixed that problem.. Any advice would be helpful. I'm was hoping that cleaning the valve would solve my problem but no luck. Or maybe I didnt do it correctly but the trigger still opens or closes the bucket, depending on which solenoid its on.
Thank you

Welcome to HEF Smoky03.

Are you talking about operating an attachment with the hydraulic connections on the left loader arms that's controlled by the thumb switch on the right drive lever?

The right

The right hand thumb switch that is suppose to control the opening and closing of the bucket

Well, forgive me for my ignorance, but I've worked on Bobcat machines for years and I've never seen one that uses the thumb switch on the right handle to open/close the bucket, unless you're talking about something like a 4 in 1 bucket that operates by the auxiliary lines from the left side loader arm connections. :beatsme

Willie, it's a s185 turbo bobcat, oops, forgive me I put the wrong machine and I was told that the right hand thumb switch was to operate the bucket, it is a 4 in one bucket, please forgive me, I misread your reply and I feel like an idiot here..
Yes, I'm trying to control the auxiliary lines that are on the left. Which has the 4 in 1 bucket attached

The right hand controllers not opening and closing the bucket, I was able to do some testing today, it appears that I don't have proper voltage, I'm not sure. I don't have wiring diagram but the ground is good, have power on what appears to be pin one, than at the white wire w red strip has about 4 volts, than when I move the thumb switch to the left, it goes to 6, to the right, it goes down to about 2. I could not get any voltage reading at the solenoid, I'm not exactly sure if I'm reading it correctly, I have never had to measure pulse voltage, which is what I understand it to be.
When I pull the right index finger trigger it will open the bucket very quickly, than starts to draw the motor down, like it has a load. If I reverse the plugs at the solenoids, it closes the bucket very quickly.
Also, while measuring the voltage, I get no reading at the solenoids using the trigger so I'm a little confused. I did check all the fuses. And both solenoids are reading the same ohms, I think they were around 4 so I'm assuming that's correct, I've read it around here somewhere but being they both read very close to each other, I'm assuming they are both good.
Thank you for your time and help... It's greatly appreciated!

In post #8 you stated it was a 753? But nevermind, an S185, I still don't know if we're on the same page here, again, I've never seen a Bobcat open and close a bucket using the thumb switch on the right stick, unless we're talking about an attachment. That thumb switch on the right stick only controls the auxiliary hydraulic lines on the left side loader arms. And if you are, in fact, talking about that thumb switch on the right stick, not the rocker switches on the right stick, testing voltage won't tell you anything because that thumb switch works using Pulse Width Modulation.

Since we're talking about an S185, do you ever hear three shorts beeps from the alarm?

I'm very sorry, I got mixed up on the model, my wife was showing me a 753 last night.. You are correct, the right thumb, in the middle, not the rockers. i do not get 3 beeps. It has a solid beep when I turn the key on, about a second, than stops. Glo shows in the display and than counts down, unless it's warm, it just goes to the hours
Also I edited my previous post, #12, I am using 4 in 1 bucket

Ok, now we're making sense. You have to remember, when you're troubleshooting via the internet the information has to be accurate in order to achieve the desired result, otherwise we'll never get there.

As I stated, that thumb switch operates the auxiliary pipes on the left loader arm for attachments, and the thumb switch is used to control two way proportional flow to the pipes, for attachments like you mentioned, a 4 way bucket. The trigger on the right stick is for one way full flow for attachments like a motor on a brush cutter, doesn't need proportional flow and only needs to flow in one direction.

On a G series or K series machine a single long beep from the alarm is normal when you power up the ignition, this beep is part of the self test of the ECM and it also lets you know the alarm is actually working. If you ever hear three short beeps from the alarm during operation, that's an active fault the ECM is seeing. Since you're not hearing three beeps then most likely the system is working proper. However, a common problem is with the thumb switch itself going bad. Again, there is no way to test it, and you can't replace just the switch, you have to replace the entire knob unit on the right stick.

You could also have a problem with one of the cylinders on the 4 way bucket. Do you possibly have a different attachment you could use to test the machine? If not, what happens when you disconnect the aux lines going to the 4 way bucket, then operate the thumb switch. Does it load the engine when you sweep the switch left and right?

My apologies for not have the proper terminology!! I will try to be more specific, thanks!

I have already replaced the right hand controller. I ran the new controller wires and changed each pin with what was there one by one. Unfortunately i do not have any other attachments but I will try and disconnect it tomorrow and see if it strains. Does the high flow/ normal flow ( not sure if that's exactly what the button says) ( it's about the third button over from the right, by the hour display) need to be on for the bucket to work or should the bucket be working without either selected? I did notice today that the right side hydrolic was leaking but I didn't think it was leaking that much that it would prevent it from opening and closing at all, maybe that's the problem. I was assuming that since the trigger would open or close the bucket, depending on which solenoid I manually plugged in, that the bucket should be opening or closing via the thumb switch

On a G series or K series machine, starting from the left, the first button is the work lights, the second button is bucket positioning (if equipped), third button is activate high flow aux hydraulics (if equipped), forth button is to activate low (normal) flow aux hydraulics, fifth button is aux hydraulics pressure release.

To activate the thumb switch control for auxiliary hydraulic you press the forth button one time, you should see the lamp for variable flow light up on that button.

Ok, I have high flow and normal button is the fourth, it's a 2 function button like the lights, if you push one time, I believe the bottom light lights up for normal flow, push a second time and it goes to high flow, I have the second button the that says bucket position, and I think it has 2 settings as well but I dont think I have that option because nothing happens, I think my third button says something like leveling mode or something to that effect, it doesn't do anything either as far as I can tell. And the last button is pressure release, if I push and hold it shuts off the motor. And yes, 1st button is work lights also, one push front light, push twice and front and back lights.

I did try to find all the operation for these buttons but I dont think I have those option because nothing happens. However, I do know that the normal/high flow button is there and when I put it in normal, pull the trigger on right controller, it opens the bucket real quick, but you said that's for one way operation I believe, like maybe an auger or something.
Well id like to thank you for now and I will confirm my buttons, the actions, and disconnect the bucket tomorrow and get back to you!! Thank you so much!!

Bobcat G series left control panel.

That is correct, my apologies once again!! I will do my checking tomorrow and get back to you. Thank you