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Cat 307D hydraulics

M

mjsnodgrass

Member
i have a cat 307D excavator. i'm having issues with the front blade bleeding off. when the machine is off with the blade up it does not leak
off. when traveling the blade bleeds off and drops. when working with the blade down, it bleeds off and my stability suffers. the blade
cylinder does not leak internally. does this machine have 24v coils that control some of the hydraulic circuits? thanks for any help.
 
That sounds like the rotary coupling seals are shot, that's the unit that carries the fluid from the car body plumbing to the undercarriage plumbing, if the seals have failed in the coupling oil can leak internally from one function to the other, have a look to see if when say you lift the blade up fully and hold it against the stop see if anything else is trying to move, if something moves then the coupling needs resealing.
AJ
 
Hmmm Im skeptical that it is an issue with the rotary union. Id think an issue there would also show up when the engine is off, and would also be noticed by poor track drive performance. Excuse my ignorance, but by what method is the blade controlled? Is it electric over hydraulic? A peek at the valve or switch that the control lever is connected to will tell you.

You can find the rotary union in the very center of the car body (the frame that the excavator track frames are mounted to) swing bearing (the bearing the allows the top half of the machine to rotate). Should be several hoses, and perhaps wires attached to the top half (rotating) and a similar set attached to the bottom half (stationary).
 
Dead centre of the machine with all the pipework attached to it top and bottom, some can be sealed in situ but I can't remember about the 307.
AJ
 
i figured it would be in center of machine. just didn't know if it was under the the frame or on top of under carriage. right under the boom. not alot of room. will clean the area up tomorrow and have a better look. there is a manual valve with float detent in the cab that operates the blade. i believe it controls the 3 rd valve from left on main gang valve. there is a relief valve on both sides of that valve. i'm going to take them off and look for a piece of dirt or something in them as soon as i can get a gauge on them to see what the relief is set at. thanks for the help
 
That unit consists of two main pieces, the outer housing and an inner shaft like piston, that shaft has lots of drilled ports to transport the oil down from the top oil lines and comes out of the side of it in a stepped pattern which lines up with grooves in the outer housing transporting the oil to the pipework, between each oil groove there is a groove to carry a seal, there are several of those seals to keep the oil separated and in it's respective groove, if any of the groove seals fail it can allow oil to pass into the next groove and depending on what the function is for, it could be the return for the function you are using, you would need to make sure what's wrong before you start as it is one messy job and no point in doing it unless it needs it, have an equipment mechanic look at it for you.
AJ
 
you're right aj. pretty messy dirty job. found out since i turned 70 it's a lot harder to work tight places on those machines haha. thanks.
 
Yep and the smaller the machine the harder it is to undo and reconnect the plumbing, I had to do a tiny JCB recently and it would make one cry to undo and connect the plumping, the pipework was like matches in a box they were that close together, was the seals shot in yours?.
AJ
 
i have it out but haven't taken it apart yet. i've cut and bent 4 proto wrenchs in half to do this job. after you take the hoses off, you
need to remove the orb fitting to get to the next hose. a friend has access to the 307 shop manual. it says to remove the swing motor to
get the swivel out. i didn't have to do remove the motor to get the swivel out. knowing that, i probably won't be able to get it back in
haha. i have no doubt the swivel is the first part they installed when they built the machine. thanks aj.
 
no broken seal rings, but when i took the retaining plate off and picked unit up it came apart. rings were pretty well worn. really hope
new seals fix my issues. thanks aj.
 
no broken seal rings, but when i took the retaining plate off and picked unit up it came apart. rings were pretty well worn. really hope
new seals fix my issues. thanks aj.
 
good call on the rotary swivel aj. seems to have fixed my blades issues and the machine seems to have more power at the
tracks. when i got it started i pushed the drive pedals forward. the machine moved in reverse. thought i hooked hoses up
wrong. then i realized i put it in the shop blade first and had cab turned around so i wouldn't have to climb over the blade
when going under machine. all good. thanks again aj. this is about the 5th time you bailed me out. i appreciate it.
 
Glad you got sorted as it is a messy job you would not want to reseal it for no reason, the seals are wearing parts and do ware, you will have noticed how much tighter it was to assemble it than taking it apart, I have done hundreds of those joints in all brands of equipment, at the shop we have a pit on site we'd dig a hole but nothing will stop the oil dripping on you, nice machine the 307.
Happy digging
AJ
 
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