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Our bobcat 751 will not go forward or backward. We put a new…

Our bobcat 751 will...

Our bobcat 751 will not go forward or backward. We put a new seleniod in it and check all fuses. New emergency brake also.

Mechanic's Assistant: What is the complete model and serial number of your machine?

Model is 751 f series serial number is###-##-####

Mechanic's Assistant: Are you fixing this yourself? What have you tried so far?

Yes we are. We have done everything I put in the first message.

Mechanic's Assistant: Anything else you want the equipment mechanic to know before I connect you?

No not that I can think of

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Customer reply replied 4 years ago
Do you have an estimated time on an answer?
Answered in 3 hours by:
7/30/2018
Mechanic: Fieldtech59, Shop manager replied 4 years ago
Fieldtech59
Fieldtech59, Shop manager
Category: Construction and Road Equipment
Satisfied Customers: 201
Experience: Construction equipment repair technician since 1986, JLG certified, Shop manager since 2006.
Verified

Greetings. I need more information about what the machine is or is not doing. You stated you put in a new solenoid, would that be the parking brake solenoid on top of the chain case?

With parking brake engaged, do the drive pumps make noise and load the engine if you move the drive sticks forward and backward?

Do the loader arm functions work properly?

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Customer reply replied 4 years ago
it is the brake solenoid on top of the drive chain. Yes it makes noise and loads the engine. And the arm functions work.When we try and make it go forward and backward it stops. All the lights are on in the cab that tells you what functions are working or not. We had this problem some months ago and changed a fuse that was no good and it was fixed. We have checked that and it is good.
Mechanic: Fieldtech59, Shop manager replied 4 years ago

Got it, thanks. So it stops abruptly like the parking brake engaged while you were driving, correct?

"All the lights are on in the cab...", I assume you're referring to the LED lights on the BICS controller, correct?

Does your F series have the BICS controller located on the wall behind the seat and mounted to the right of the seat?

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Customer reply replied 4 years ago
It was working just fine. We parked it and went to use it a couple days later and now this. Yes the BICS panel to the right of the seat is what I’m reffering to.
Mechanic: Fieldtech59, Shop manager replied 4 years ago

I understand, it was working fine, but we gotta figure out why its not working fine now. All the clues I'm asking are important for me to troubleshoot this with you.

Again, are you saying that you can actually start it up, disengage the parking brake and drive the machine momentarily, then suddenly it stops abruptly like the parking brake engaged with a thud, correct?

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Customer reply replied 4 years ago
that is what I’m saying.
Mechanic: Fieldtech59, Shop manager replied 4 years ago

Thanks. I know it seems I'm asking a lot of questions, but they're all important, and I'm trying to take this step by step and not overwhelm you with questions all at once. For example, I asked if the loader functions worked. One could ask "what's that got to do with this problem", well, on a Bobcat, everything to do with it. If the loader functions didn't work then I would advise to check the drive belt. That's the reason for all the questions, methodically working through it.

Alright, parking brake slams on, I hate it when that happens, especially if you're going full tilt, I've had it happen to me on a 773 G series. Whoa!

Now, when it happens, you're certain all the LED lights on the BICS controller are lit up? Are any of them blinking?

Does this happen rather quickly and often or do you have to run the machine for a while before it happens?

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Customer reply replied 4 years ago
we are certain all lights are on and have not seen any blinking. This happens after we use it and park it. It can be a light day or heavy day if that makes sense. And I understand why you are asking questions. If I want a call back do you charge our card or do we have to give it to you again?
Mechanic: Fieldtech59, Shop manager replied 4 years ago

That's all done by the website, I don't have any control of that or how you're charged. As for me, I don't receive any payment for my services unless the customer gives me a good rating, therefore I try my best to help someone fix their problem. It's not all about the money to me, just as important to get you fixed up.

Ok, you got a tricky problem, and one that's not going to be easy to pinpoint. That's the drawback of the C and F series Bobcat, the on board diagnostics, which is BICS in this case (Bobcat Integrated Control System), is very basic and elementary on the C and F, kind of like OBDI on cars in the mid 80's, gives you very vague info. On the later G series machines Bobcat greatly enhanced the BICS system.

If your not getting and blinking LED lights at the BICS controller then it's not giving us any info to work with so we're going to have to do this the old fashioned way. Aside from a bad electrical connection or a bad ground, neither which is easy to find, three likely causes of your problem are 1) faulty BICS controller, but let's not go there yet, or 2) faulty lap bar sensor, or 3) faulty seat switch (if your machine has it). If you have that seat switch that's the most common cause of this problem on the C and F series machine. There is no way to test it as it's a Hall Effect sensor, simply checking voltage won't tell you anything. Same with the lap bar sensor. The best way to check if the lap bar sensor or seat sensor is causing the problem is to leave the lap bar up and push the Traction Lock Override button. If that feature is working properly it allows you to drive the machine with the lap bar up, such as when you have a backhoe attachment on it and you're in the backhoe seat and need to move the machine. The traction lock override takes the seat sensor and lap bar sensor out of the BICS circuit, but the lap bar has to be up. Keep in mind if you try this, you no longer have a lap bar holding you back if that brake engages, might want to put the seat belt on.

Another thing, make certain you have good ground connections at your battery and anywhere you see ground cables/wires go to the frame, bad ground connections cause all kinds of problems on these machines. Let me know what you find out.

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Customer reply replied 4 years ago
Ok thank you. We will check this out and I will for sure tell you what we find. I don’t know where you are located but my husband is done for the day. So I will get back to you tomorrow.
Mechanic: Fieldtech59, Shop manager replied 4 years ago

No worries. I'm in Tennessee myself, and I'm covered up with work during the day so I just don't have an opportunity to log in here during work hours, but I'm here pretty much every evening up until near midnight.

Just to give your husband some info on that parking brake, he can read this at his leisure. That parking brake solenoid has three wires, red, white, and black, the black wire is ground. The solenoid consists of two separate coils inside, the hold coil and the pull coil. The way it works is when you drop the lap bar, make up that circuit, and sit in the seat to make that circuit (if you have seat switch), then the BICS controller knows you're good to go. With this, when you push the enable button to release the brake, the BICS controller does two things, 1) it powers up the brake relay at the fuse panel, this sends a battery voltage signal to the pull coil (white wire) on the brake solenoid, but it only stays powered up by the BICS controller for a few seconds, just long enough to "pull" the plunger inside the solenoid, and 2) it sends a voltage signal directly from the BICS controller to the"hold" coil (red wire), that's the circuit that's powered up whenever you are operating the machine and have the parking brake released. Therefore, if that brake is engaging while you're driving it would be from 3 choices, 1) loosing power on the red wire, 2) faulty ground, or 3) faulty brake solenoid, and yes, I'm aware that you've replaced it so that points to 1 and 2, but we can't discount the possibility either.

Fuse 7 (Brake) at fuse box protects the circuit that goes from battery through the relay that controls the white wire at solenoid, it has no connection to the red wire circuit, that comes straight from the BICS controller. The BICS controller is protected by Fuse 1 (BICS), but if it were bad or had a bad connection you would see the LED lights at the BICS controller go dark.

Again, and that's if your machine has it, the seat sensor is the most common problem. If it's not working properly you could simply run across a bump that makes you temporarily bounce in the seat (lift the seat slightly) and BAM, parking brake on. And as I stated previously there's no way to test it. Also, there's no way to by-pass it with jumper wires. Being a Hall Effect circuit it don't work that way. It's been many years since I've worked on C and F series, and I don't know if they still offer it, but Bobcat used to offer a kit the eliminates the seat sensor on the C and F. If it turns out that sensor is the problem, if it were me I'd be looking into that. Keep me updated.

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Customer reply replied 4 years ago
we tried what you said to do with the traction control button and it is still not working. We checked fuses and they are good and so is all the grounds we can find.Do you think it could be a relay of some kind?
Mechanic: Fieldtech59, Shop manager replied 4 years ago

Nope, it's not a relay. The only relay that controls the parking brake solenoid is for the pull coil that's activated when you first push the button to disengage the brake (power up the solenoid). The pull coil circuit is only powered up for a few seconds by the BICS controller. Once the brake solenoid is powered up the hold coil circuit takes over and power is dropped on the pull coil circuit. There is no relay for the hold coil circuit, that power comes directly from the BICS controller. So you power up the solenoid and begin driving, then it suddenly engages, then you're either loosing power on the red wire at the solenoid or you're losing the ground circuit to the solenoid. Again, to repeat, if you're losing power on the red wire, possibilities would be faulty BICS controller, faulty lap bar sensor, faulty seat sensor, or fault (bad connection) in the wiring. And again, there's no way for you to test the lap bar sensor, seat sensor, or BICS controller, only Bobcat has the equipment to do that. I was hoping we could get you fixed up, but we've pretty much exhausted all I can do with it, to go further than where we're at is going to require a Bobcat tech. I wish I could do more but we're in that area where Bobcat keeps stuff top secret, only they have access to it. I do hope you get it sorted out. Thanks for working with me, and feel free to not give me a rating since I wasn't able to get you going. Cheers

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Customer reply replied 4 years ago
Thank you for all your help we have someone here testing electrical stuff. I will pass on what you said. I will for sure give you a rating you did what you could.
Mechanic: Fieldtech59, Shop manager replied 4 years ago

I appreciate that very much, I always give it my best. Thank you and best wishes.

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Customer reply replied 4 years ago
Thank you!Ok so another question. They unplugged the selinoid and tested the other end and it made the travel light blink
Mechanic: Fieldtech59, Shop manager replied 4 years ago

Yes, the BICS controller would notice it (unplugged) as an "open circuit". That's the trick to these things in conventional ways, such as unplugging something, the BICS controller will notice it and react. About the only way you can test 12V circuits on a Bobcat, which that solenoid would be a 12V circuit, is to probe the wires to test them. As for the sensor circuits, seat sensor, lap bar sensor, they are a 5V "reference volt" circuit, but even then, it's a Hall Effect circuit, a simple test light or volt meter won't test those wires.

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Customer reply replied 4 years ago
Ok. They powered up the selinoid and it worked. They traced wires back and found a bar with plug ins on them. One said brake and they tested it and it was no good. I don’t know if I can send a picture.
Mechanic: Fieldtech59, Shop manager replied 4 years ago

Not sure myself without seeing it.

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Customer reply replied 4 years ago
I have tried to send a picture but it was unsuccessful
Mechanic: Fieldtech59, Shop manager replied 4 years ago

Drat!

Fieldtech59
Fieldtech59, Shop manager
Category: Construction and Road Equipment
Satisfied Customers: 201
Experience: Construction equipment repair technician since 1986, JLG certified, Shop manager since 2006.
Verified
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Customer reply replied 4 years ago
my thoughts exactly.
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