743B troubleshooting

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richard

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I have a 743B that has stopped moving in one direction on one side. My repair manual says that it is in the replenishing valve or in the hydraulic motor. I was thinking I could do a pressure test at the motor to find out. What would be the best way to do this? Can I just remove the hose going to the motor and attach a pressure gauge? Or do I have to install some sort of relief/bypass mechanism? Also, how much pressure should I be getting at the motor? Thanks.
 

Tazza

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I'm not too sure how you test this, but the pump can suply 5,000 psi or more so be carefull. Check the usual things, like linkages etc if its not that it could be motor or 1 side of your pump. One thing other users have tried is to remove the motor and install the other motor from the other side to see if it works. If it did you know its your motor if not you know its somewhere in your pump be it the internals or the by-pass vavle.
I wish you luck!
 

goodtech

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I'm not too sure how you test this, but the pump can suply 5,000 psi or more so be carefull. Check the usual things, like linkages etc if its not that it could be motor or 1 side of your pump. One thing other users have tried is to remove the motor and install the other motor from the other side to see if it works. If it did you know its your motor if not you know its somewhere in your pump be it the internals or the by-pass vavle.
I wish you luck!
You need to put a flow tester on your hydrostat, You cannot dead head your hydrostat with a pressure gauge, otherwise it will be in pieces. The 743 hydrostats are pretty much bullet proof, the best thing for you to do it take to shop where they can flow test the hydrostat for you and that will tell you where you need to go from there. I not a fan of telling people to go to a shop, but for this you need some pretty expensive equipment to make sure that you can test it right without hurting anything. Good luck
 

Tazza

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You need to put a flow tester on your hydrostat, You cannot dead head your hydrostat with a pressure gauge, otherwise it will be in pieces. The 743 hydrostats are pretty much bullet proof, the best thing for you to do it take to shop where they can flow test the hydrostat for you and that will tell you where you need to go from there. I not a fan of telling people to go to a shop, but for this you need some pretty expensive equipment to make sure that you can test it right without hurting anything. Good luck
Oooh, sorry i just re-read your post, you said ONE direction on 1 side, this could be your shuttle valve in the hydro motor too.
 

richard

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Oooh, sorry i just re-read your post, you said ONE direction on 1 side, this could be your shuttle valve in the hydro motor too.
Thanks Guys! Goodtech, thanks for warning me about dead heading with gauge. I probably would have tried it and gotten hurt. Sounds like my cheapest test would be to swap the motors like Tazza said. BTW, if it is in the motor, does Bobcat sell rebuild kits for them?
 

Tazza

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Thanks Guys! Goodtech, thanks for warning me about dead heading with gauge. I probably would have tried it and gotten hurt. Sounds like my cheapest test would be to swap the motors like Tazza said. BTW, if it is in the motor, does Bobcat sell rebuild kits for them?
Yes they do, you just have to make sure you set the timing inside when you put it back together. You can get parts for almost any part of your machine.
 

richard

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Yes they do, you just have to make sure you set the timing inside when you put it back together. You can get parts for almost any part of your machine.
I have an idea.....since it will not move forward on the right side only, what if I just swap the two hoses going to the motor on that side only? Then, if I pull the right lever back and the machine still won't move forward, the problem would have to be in the hydraulic motor, right? You guys think this would work?
 

Tazza

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I have an idea.....since it will not move forward on the right side only, what if I just swap the two hoses going to the motor on that side only? Then, if I pull the right lever back and the machine still won't move forward, the problem would have to be in the hydraulic motor, right? You guys think this would work?
Its worth a go, it won't cause any damage as thats all the hydro pump does, changes the hose that the high pressure oil flows along.
 

richard

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Its worth a go, it won't cause any damage as thats all the hydro pump does, changes the hose that the high pressure oil flows along.
Well, I swapped the hoses on one side today and that side still wouldn't move in the forward direction so now I know the problem lies somewhere in the hydraulic motor. Occasionally, it will work, then it won't, it's intermittent. Maybe it's the shuttle valve like Tazza says. Are these prone to stick and can it be repaired/replaced without pulling the motor? My repair manual doesn't have a breakdown or any repair instructions for the hydraulic motor. Anyone have a breakdown or repair instructions?
 

Tazza

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Well, I swapped the hoses on one side today and that side still wouldn't move in the forward direction so now I know the problem lies somewhere in the hydraulic motor. Occasionally, it will work, then it won't, it's intermittent. Maybe it's the shuttle valve like Tazza says. Are these prone to stick and can it be repaired/replaced without pulling the motor? My repair manual doesn't have a breakdown or any repair instructions for the hydraulic motor. Anyone have a breakdown or repair instructions?
I saw it in my manual yesterday, have a look see on your hydro motor, on the outer part, can you see like an allan key screw? say 1/2” head. The shuttle valve is behind that.
From what i have seen, its actually quite simple. Do you want a diagram of it all? if so, just give me a yell and i will scan it in for ya.
See what Goodtech has to say, he will know this better than i do, i have never pulled apart a hydro motor.
 

Tazza

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I saw it in my manual yesterday, have a look see on your hydro motor, on the outer part, can you see like an allan key screw? say 1/2” head. The shuttle valve is behind that.
From what i have seen, its actually quite simple. Do you want a diagram of it all? if so, just give me a yell and i will scan it in for ya.
See what Goodtech has to say, he will know this better than i do, i have never pulled apart a hydro motor.
http://users.tpg.com.au/tazza_/hydromotor/
There are the details for pulling down and re-assembling a hydro motor for a 731, i think the 743's use the same motors.
Now i have looked, i'm not sure if that bit i was thiking of was the shuttle valve or not..... These pictures show a valve and valve plate.... This is the time we need Goodtech!
 

richard

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http://users.tpg.com.au/tazza_/hydromotor/
There are the details for pulling down and re-assembling a hydro motor for a 731, i think the 743's use the same motors.
Now i have looked, i'm not sure if that bit i was thiking of was the shuttle valve or not..... These pictures show a valve and valve plate.... This is the time we need Goodtech!
Yes, mine has the allen key screws you were talking about. That's what made me think I might be able to replace the shuttle valve without pulling the motor. I sure hope that's how you access it. I'll wait to hear from GoodTech before I do any more.
 

richard

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Yes, mine has the allen key screws you were talking about. That's what made me think I might be able to replace the shuttle valve without pulling the motor. I sure hope that's how you access it. I'll wait to hear from GoodTech before I do any more.
My service manual doesn't show anything about the hydrostatic motor, only how to remove/install it. In fact, in that section it says "SEE THE COMPONENT REPAIR MANUAL FOR HYDROSTATIC MOTOR DISASSEMBLY AND ASSEMBLY PROCEDURE". So I called my local Bobcat dealer today to order this "component repair manual" and they were not aware of one. The parts department did fax me a breakdown of the hydrostatic motor for my particular model out of their parts catalog, which was very helpful (btw, I can scan these in if anyone needs them). Looks like the shuttle valve IS behind those two allen key screws Tazza was talking about....and it looks like it could all be repaired/replaced without pulling the motor. Well, according to the manual, my problem is now down to A: shuttle valve not working properly, or B: damaged valve plate seals in the motor. I was thinking...since it sometimes works and sometimes doesn't, then it must be the shuttle valve not working properly because it seems to me, if the valve plate seals were damaged it would not work at anytime. Does this sound logical? Goodtech must be on vacation.....I sure hope he has some insight. Thanks again for all the help.
 

Tazza

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My service manual doesn't show anything about the hydrostatic motor, only how to remove/install it. In fact, in that section it says "SEE THE COMPONENT REPAIR MANUAL FOR HYDROSTATIC MOTOR DISASSEMBLY AND ASSEMBLY PROCEDURE". So I called my local Bobcat dealer today to order this "component repair manual" and they were not aware of one. The parts department did fax me a breakdown of the hydrostatic motor for my particular model out of their parts catalog, which was very helpful (btw, I can scan these in if anyone needs them). Looks like the shuttle valve IS behind those two allen key screws Tazza was talking about....and it looks like it could all be repaired/replaced without pulling the motor. Well, according to the manual, my problem is now down to A: shuttle valve not working properly, or B: damaged valve plate seals in the motor. I was thinking...since it sometimes works and sometimes doesn't, then it must be the shuttle valve not working properly because it seems to me, if the valve plate seals were damaged it would not work at anytime. Does this sound logical? Goodtech must be on vacation.....I sure hope he has some insight. Thanks again for all the help.
Neither does mine...
My 731 manual details ALL of the machine, including pumps and motors and how to re-time them. But my 743 manual doesn't, it details all the other parts just not pumps or motors. But it does detail repair of the engines these had including kubota, ford and deutz.
It looks like Goodtech has indeed left us.....
Good luck!
 

goodtech

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Neither does mine...
My 731 manual details ALL of the machine, including pumps and motors and how to re-time them. But my 743 manual doesn't, it details all the other parts just not pumps or motors. But it does detail repair of the engines these had including kubota, ford and deutz.
It looks like Goodtech has indeed left us.....
Good luck!
Boys I live a very busy life, I work for bobcat part time, and also have my own business, that is pretty big and starting to get into its busy season, so when I have a couple of minutes I love to get on here and help people that I can when I find the time. I would try your shuttle valve but I really doubt that is the problem, your motor is just probally just worn out. it is cheaper to buy a new one rather than trying to piece one back together, depending on what is worn out, but 95% of the time is is usually cheaper to by one. Also check your case drain filter and see how much brass it has caught.
 

Tazza

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Boys I live a very busy life, I work for bobcat part time, and also have my own business, that is pretty big and starting to get into its busy season, so when I have a couple of minutes I love to get on here and help people that I can when I find the time. I would try your shuttle valve but I really doubt that is the problem, your motor is just probally just worn out. it is cheaper to buy a new one rather than trying to piece one back together, depending on what is worn out, but 95% of the time is is usually cheaper to by one. Also check your case drain filter and see how much brass it has caught.
Good to soo you around Goodtech, i know the feeling, too much to do, too few hours in the day. The case drain filter, where is this located? im sure my 743 doesn't have one of these....
 

skidsteer.ca

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Good to soo you around Goodtech, i know the feeling, too much to do, too few hours in the day. The case drain filter, where is this located? im sure my 743 doesn't have one of these....
Don't believe a 743 has case drain filter. My 753 (@1993) didn't. My 773 g does, they are located on the small (1/4" or 3/8") hydraulic hose coming off of each wheel motor. (the other two main hyd hose are @ 3/4") It is an aluminum canister that threads aparts and has a bronze filter inside it. There will be one on each wheel motor. The G had nothing in them, so I just rinsed them in varsol and put them back in with a new oring for the canister Ken
 

goodtech

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Don't believe a 743 has case drain filter. My 753 (@1993) didn't. My 773 g does, they are located on the small (1/4" or 3/8") hydraulic hose coming off of each wheel motor. (the other two main hyd hose are @ 3/4") It is an aluminum canister that threads aparts and has a bronze filter inside it. There will be one on each wheel motor. The G had nothing in them, so I just rinsed them in varsol and put them back in with a new oring for the canister Ken
Your G series machine needs that filters, the pumps are alot closer tolerances and it will not take much to trash them. The filters are cheap. Now I'm going to have to look in the manual for where the case drain filter is located in the 743, I'm pretty sure that they have them.
 

Tazza

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Your G series machine needs that filters, the pumps are alot closer tolerances and it will not take much to trash them. The filters are cheap. Now I'm going to have to look in the manual for where the case drain filter is located in the 743, I'm pretty sure that they have them.
I know the “older” style 743's have them located in the port block on the hydro pump but i have basically striped one of my 743's and can't find one.
 
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