This is in reference to a Cat D3G 2005 Dozer. My purpose is to know what dangers there are in working on hydraulic lines due to hydraulic oil pressure. If the tractor is off and the blade is resting in float mode, is there pressure on hydraulic lines? Specifically, I what to tighten some of the hose fittings in the area around the hydraulic pump where the hydraulic charge lines from the hydraulic tank and the drain lines back to the tank connrct to the pump, valves and blocks around the hydraulic pump. Thanks.
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Pressure on Hydraulic Lines
- Thread starter inyati13
- Start date
bobcatmechanic
Senior Member
usually you can ground all equipment turn the key on on most machines not start it cycle the controls through all the functiions and that should relieve all the pressure off the system
willie59
Administrator
I'm not certain about a D3G, but many Cat dozers now have pressurized hyd tanks similar to excavators, so you might want to loosen or remove the hyd tank cap to relieve tank pressure.
One thing I'm curious about, you mentioned that you need to "tighten some of the hose fittings". Do you have fittings leaking oil? It's very unusual for hose fittings to become "loose". Not saying it can't/doesn't happen, but just not the norm. Typically hose fittings are so tight they require some pop with wrench to get them loose. You much have suction line clamps that are loose, but if you have hose fittings leaking, I'm thinking you more than likely have failed flat face o-ring seals on fittings or failed o-ring boss fittings. Just a guess.
One thing I'm curious about, you mentioned that you need to "tighten some of the hose fittings". Do you have fittings leaking oil? It's very unusual for hose fittings to become "loose". Not saying it can't/doesn't happen, but just not the norm. Typically hose fittings are so tight they require some pop with wrench to get them loose. You much have suction line clamps that are loose, but if you have hose fittings leaking, I'm thinking you more than likely have failed flat face o-ring seals on fittings or failed o-ring boss fittings. Just a guess.
ATCO, I dropped the rear belly pan on my D3G. There was oil in the debris. The area above the oily debris has a number of hydraulic lines going to the hydraulic pump, and blocks in the vicinity of the pump. Some of the hoses have clamps. I want to tighten the clamps and check the other hydraulic hoses for leaks. First, I plan to claen the entire area so I can better detect where the oil is coming from. Your info was very helpful. To restate your point, if they are hydraulic hoses with O-ring seals, then they are probably tight already. I assume they can still leak if the O-ring is bad, etc. Provide any follow-up that might help, please.
willie59
Administrator
Hi inyati13, It's not unusual for gunk/dirt to build up in the belly of a dozer over time. It's a good idea for you to drop your pans and clean everything real good. Heck, I've spent hours washing on some. I haven't climbed in the innards of a D3G, but they're probably not unlike any other machine in what you are doing. I'm near certain a D3G is a hydrostat drive machine, so your not going to have a transmission in there. There will be 2 drive pumps, 1 work equipment pump, and 2 drive motors. All the hoses that have clamps on them would be oil supply (suction) lines that feed the pumps, low pressure lines. All hoses/lines that have work pressure on them will be typical hyd fitting connections.
Most likely, your machines components may have any number of 4 common hyd connections; 1) SAE 37 degree flare, commonly known as JIC fittings, 2) o-ring face seals, also known as flat face o-ring, 3) four bolt flange fittings, and 4) SAE straight thread o-ring, commonly know as o-ring Boss (ORB). The only one of these four fittings that don't use an o-ring is the JIC fitting connection. The other three fitting types all use an o-ring for a seal. And they all three require the proper o-ring. An o-ring that "looks close enough"...won't. It will fail if the wrong o-ring is used. And it's not unusual for an o-ring connection to develop a leak even though the fitting is tight. This is typically caused by heat over time. Heat will cause o-rings to get hard as a brick bat, causing the o-rings to lose their elastic properties for creating a seal. Get everything cleaned up good, then operate the machine for a while with belly pans and floor plate removed and start watching for anything going on in there.
Here's a link to a website that shows the fittings I mentioned above so you can get a look at them. At the top of the page are links to each of these fittings.
http://www.discounthydraulichose.co...t=21&Click=2&gclid=COm4i9enj6MCFYlY2god6EZbqw
Most likely, your machines components may have any number of 4 common hyd connections; 1) SAE 37 degree flare, commonly known as JIC fittings, 2) o-ring face seals, also known as flat face o-ring, 3) four bolt flange fittings, and 4) SAE straight thread o-ring, commonly know as o-ring Boss (ORB). The only one of these four fittings that don't use an o-ring is the JIC fitting connection. The other three fitting types all use an o-ring for a seal. And they all three require the proper o-ring. An o-ring that "looks close enough"...won't. It will fail if the wrong o-ring is used. And it's not unusual for an o-ring connection to develop a leak even though the fitting is tight. This is typically caused by heat over time. Heat will cause o-rings to get hard as a brick bat, causing the o-rings to lose their elastic properties for creating a seal. Get everything cleaned up good, then operate the machine for a while with belly pans and floor plate removed and start watching for anything going on in there.
Here's a link to a website that shows the fittings I mentioned above so you can get a look at them. At the top of the page are links to each of these fittings.
http://www.discounthydraulichose.co...t=21&Click=2&gclid=COm4i9enj6MCFYlY2god6EZbqw
John C.
Senior Member
I believe the D5G is a hydrostatic unit and while I haven't been into one yet I think they are running O ring face seals for the medium to high pressure stuff and flange fittings to the really high pressure lines that feed the track motors. As usual ATCO is providing the right info on opening the tank cap before cracking any lines. I don't recall ever hearing that there were any accumulators in these systems.
Your plan of cleaning out the area is great. I would suggest pressure washing and then run the machine looking for leaks. You can fix them as you find them that way. I would suggest getting a parts book if you don't have one now and seeing what kind of O rings you might need and then plan on stocking a couple extra of the common ones.
Good Luck!
Your plan of cleaning out the area is great. I would suggest pressure washing and then run the machine looking for leaks. You can fix them as you find them that way. I would suggest getting a parts book if you don't have one now and seeing what kind of O rings you might need and then plan on stocking a couple extra of the common ones.
Good Luck!
willie59
Administrator
I agree John C, and the only accumulator I could imagine it would use might be a small one for the pilot circuit for the joystick control valve, maybe.
dsichewski
Well-Known Member
the d3g is hydrostatic, and there shouldn't be any JIC fittings on it (cat tends to not use this style), for the most part it will be o-ring face seals, o-ring boss (usually used for fittings connecting into a valve block) and 4 bolt flange fittings (commonly used on pumps)
if you are replacing flange fitting o-rings make sure to check to see if they are an o-ring or a D ring...
good luck
if you are replacing flange fitting o-rings make sure to check to see if they are an o-ring or a D ring...
good luck
willie59
Administrator
Yeah, I had forgot about that one, Cat does use some flange fittings that use a D ring, have to get them from Cat I think.
Thanks dsichewski.
dsichewski
Well-Known Member
Yeah, I had forgot about that one, Cat does use some flange fittings that use a D ring, have to get them from Cat I think.
Thanks dsichewski.
No prob....I used to work for cat (Toromont Cat)....
but the d-ring/ o-ring can really throw one for a loop. lol
I found more so (not always) the hoses use o-rings and when there is a mounting block (like on steeling cylinders on a wheel loader) they use d-rings
one other thing, if you can before you start cracking lines see if you can hook up a vacuum to the hyd tank...this can help save you from getting a bath of oil...
willie59
Administrator
Yup, first learned about it years ago on the first 416B loader/hoe I worked on. Pump output flange fitting kept blowing seal. Tried various size o-rings, nothing worked. Finally got edjumacted that the flange fitting at pump didn't use o-ring, used D ring. Another lesson learned.
Since I got outstanding input on this issue, I will give some back. I got on the Whayne Supply (KY Cat Dealer) partstore and was able to view schematic diagrams of the power train area of my D3G. The diagrams of the hydraulic lines that go from the pump to the hydrostatic transmission that drives the two track motors use seals called "Seal-Rectangular". The other lines between the hydraulic tank and the pump and the lines that go into and out of the hydraulic filters (2) are all referred to as O-ring seals. I ordered a supply of these seals so will be ready when I isolate the leak. I am currently in Denver so will not be getting back on the D3G for about a month. Thanks again. As a post script, is it common for hydraulic leaks to be due to a bad hose? I could see where a hose that is exposed might become damaged due to abrasion or contact with a foreign object but in this area of the machine, they are protected. I got a piece of barbed wire caught between the track shoes and as it went around, it contacted the lift cylinder line and nicked the rubber. I would guess from what you all said above that the most common leak is due to bad seals. Is that correct?
willie59
Administrator
I'm not a Cat expert, and haven't worked on a D3G, so I'm limited in what I can say about your machine. Seal-rectangular? Can't say for sure, but that sounds like what we call a D ring seal. I'm curious as to what your referring to a hyd transmission? I would think you simply have drive pumps operating drive motors, just don't know your machine.
Hyd hoses can fail from a number of reasons, damage to hose is just one. Extreme heat causes hose failure as well, especially in drive systems as the high pressure loads on the drive motors causes oil to get very hot. This hot oil over time makes the rubber of the hose assembly become very hard. It can cause hose to develope pin holes, leak at compression ferrule of the fitting on end of hose, even sudden burst failure of hose. I've taken hoses off of drive components to replace them, and they are so hard from heat that the hose won't even bend, rigid as a pipe they are. Same thing happens to o-ring seals.
Hyd hoses can fail from a number of reasons, damage to hose is just one. Extreme heat causes hose failure as well, especially in drive systems as the high pressure loads on the drive motors causes oil to get very hot. This hot oil over time makes the rubber of the hose assembly become very hard. It can cause hose to develope pin holes, leak at compression ferrule of the fitting on end of hose, even sudden burst failure of hose. I've taken hoses off of drive components to replace them, and they are so hard from heat that the hose won't even bend, rigid as a pipe they are. Same thing happens to o-ring seals.
John C.
Senior Member
I don't work on Cat much but haven't seen a D ring in years. The same goes for the old metal backed seals.
As far as hose failures go heat and rubbing are the biggest culprits causing early hose failure. Heat causes the inner liners to go bad and then you will see oily dirt stuck to the outsides of the hose usually along the entire length. The rubbing thing is obvious but don't think that just because the outer cover is barked up that the hose is ruined. Generally the wires will be rubbed through before the hose looses enough strength to fail all at once. Also what generally isn't talked about is the fact that hydraulic hose has a working life and a shelf life. Working life in most hose that is not overheated or over loaded is somewhere around 5,000 to 6,000 hours. After that you are on borrowed time. That doesn't mean you have to change all the hoses at that time. It just means you have to plan for hose failures at a somewhat higher rate after that amount of operating time.
There are different flange fittings also on your hydrostatic system. The last I checked Cat is still using Code 62 flanges on all high pressure drive systems. Don't go to a will fit or assume that because the hose is a certain size that you will get the proper O ring. For those I only use the ones shown in the parts book.
As far as hose failures go heat and rubbing are the biggest culprits causing early hose failure. Heat causes the inner liners to go bad and then you will see oily dirt stuck to the outsides of the hose usually along the entire length. The rubbing thing is obvious but don't think that just because the outer cover is barked up that the hose is ruined. Generally the wires will be rubbed through before the hose looses enough strength to fail all at once. Also what generally isn't talked about is the fact that hydraulic hose has a working life and a shelf life. Working life in most hose that is not overheated or over loaded is somewhere around 5,000 to 6,000 hours. After that you are on borrowed time. That doesn't mean you have to change all the hoses at that time. It just means you have to plan for hose failures at a somewhat higher rate after that amount of operating time.
There are different flange fittings also on your hydrostatic system. The last I checked Cat is still using Code 62 flanges on all high pressure drive systems. Don't go to a will fit or assume that because the hose is a certain size that you will get the proper O ring. For those I only use the ones shown in the parts book.
ATCO, thanks again for the information. I am learning so much. I always like to know about something that I use and enjoy. Guys like you and sites like this are priceless. I don't know why I used the transmission term. It is hydrostatic drive as you say.