Cat 303.5 needs an Aux Return line for a Thumb?

Hi All,

I'm new to the forums. New to heavy equipment too. Bought a Cat 303.5e in May 2019. It's been a learning experience! The machine had no work tool. I found a bucket at a scrap yard and had ears cut to match the EFI coupler on it. I welded the ears on the bucket and now I can dig! Almost all the routine maintenance is at least 50 hours over due. I have the fluids and filters to do that. I've been surprised by the learning curve. There is so much to these machines and I feel so powerful with it.

I want to add a thumb, so I can more easily move logs and things. I can see on the boom, the flexible hydraulic line is missing. Maybe it blew before I got it? Do I need that line to get a thumb on the machine? I see from the manual that port 7 on the valve is for the Aux Return, but it is plugged off.

Can I buy and run a new aux line myself? Is that hard? I tried cat's parts website, but not sure which exact hose assembly I need. I attached some photos so you can see what I see.

If you need more details, I'm happy to provide. I tried contacting Finning and NC machinery, but I'm such a tiny fish, seems they don't have time for me, but I get that. HE Forums though, you are amazing and I've learned so much here already!

On another post here, someone asked a similar question and he utilized the quarter turn valve to add a thumb with only one coupler. I'm not sure how to do that, but it seems like my machine has a quarter turn valve on the aux hydraulic line too. What do I use that for? How does it work? Can I use it for a thumb without getting a new aux return line? Should I do that? Which direction should I turn the valve so it'll work?

It appears that your machine is set up for one way flow with a hammer. The hose that is missing I speculate would have went to a return oil manifold. I believe you would need additional solenoids and a proportioning Valve to do what you are trying to do. A much simpler method would be to use a Stiff arm thumb and use your bucket to clamp against the thumb.

Something like what is shown in the image

Thank you funwithfuel! I'd had that thought too, just get a fixed thumb. What confuses me is that there are 2 couplers on the stick. The one on the right hand side has a hardline attached. Would the machine be made with that coupler, but without a line going back to the valve? Why have the hardline and coupler on the machine at all?

Someone either had a hose failure, swapped a stick, stole the hose for another machine or something. Either way, with one side of the valve blocked off, odds are it was born with one way flow. You could switch to 2 way, but you may have to invest in other items.
Stiff arm thumb, no hydro failure, it just works

put a hydraulic thumb on our 304e (2012) a couple of years ago just pinned it up and hooked up to hydraulic couplers already there. a very handy attachment. did check that valve pressure not over do the cylinder.

I don’t deal with the smaller than 308s normally but for the medium and larger normally you see them come with aux lines on both sides of the stick and boom for use with attachments and you set it up for one or two way flow from there. Hammers are one way flow but still have a return line. Thumbs obviously use two way flow. Stuff like mulcher heads you even have to add a case drain line for the hydraulic motor.

Sometimes we have to add aux kits to machines that did not have them from the factory. You should contact a compact equipment branch of the dealer for that kind of info if you still want a hydraulic thumb.

A serial # would greatly help. It would tell if it came with 2 way flow or not.

RKY00587. What does everyone know that I don't?

The cat folks pull it up on the computer and seem to know everything about the machine and I'm in the dark...

Any reason the hammer supply line cant be run to an electrically operated solenoid valve and then said valve can use the return line.
Guess the missing item is some form of crossover relief and there can be a displacement concern thus that item can be 5 ported and internally tied to the return line.
~
This is a summary of the theory of what I figured must be done for those machines (like mine) that have 'flow hydraulics only' with no control other than for a hammer.

I think you're right. Someone removed and capped the line. If you install that, you're pretty much there. From what I can tell, your machine shipped with 1 way or 2 way flow, changeable with the valve.
Do you have an OMM? It tells you about it in there.
This is the line you need. Item 8. Part number 3828815.

In fact the Cat thumb is available to buy as a complete arrangement. Part number 4522740. I would cautiously say that if you purchased that plus the missing hose, it would just be a nuts-and-bolts job to convert it. Can you confirm your stick already has the anchor for the cylinder fitted?

OK we are getting close! I hope! Here's a side view of the stick. Is the anchor the hole? There is also a plate to weld onto just above the coupler but it's hard to see in the photo.

No, I don't have the OMM yet, but will get one soon. I know I need one. I do have a service manual. I didn't realize there was a difference until recently. I got the service manual thinking it would show me how to do all the routine fluid changes, but I think now the OMM is for that.

Cat parts says it can't verify it'll fit my machine when I enter the serial and check. Is this normal?


Under compatible models it lists model 303.5E2. Is mine an E2? Or just E? Would the thumb fit both the E and E2?

Edit: I checked and mine is a 2012. From what I can tell the E2 came out in 2014.

I also checked the aux line fitment and it said it was a fit!

Will I need the cat brand bucket and coupler too? Or might it work with the EFI coupler and bucket I scrounged and welded to the fabricated ears?

PJM said:

No, I don't have the OMM yet, but will get one soon. I know I need one. I do have a service manual. I didn't realize there was a difference until recently. I got the service manual thinking it would show me how to do all the routine fluid changes, but I think now the OMM is for that.

Click to expand...

A paper Service Manual should include an OMM provided that it is complete. The OMM has a habit of disappearing from most Service Manuals.
You can download an OMM in pdf format direct from Cat as follows: -

Got to https://catpublications.com/
Click on "Continue as Guest"
Type SEBU8746 in the box and click Search. The illustration below should appear. $66 for a downloadable pdf. The CD & paper options that are listed will attract S&H charges on top of the price.
If you want a Parts Manual, type SEBP5957 in the Search Box. (that's where Cmark's illustrations in post #11 above came from - although they were from the online version)

Yes, 4522740 is compatible with your machine.
Whether it will work with a non-Cat coupler, who knows? But here's the instruction for fitting it. It may help you out.

* Actually, scratch that. Start a conversation with me and let me know your email address and I'll send you a copy.

Regarding the OMM and bearing in mind you're new to HE, have you looked in the pocket behind the seat?

No, there was no OMM behind the seat. I'll order the aux line and test the hydraulic pressures. If all is a go, I'll get a thumb and report back! Thank you all so much!

a two way cylinder has two hydraulic hookups, no need for extra return or case drain if you will. the thumb i bought pinned thru the bottom of the stick and cylinder top pinned to stick with padeyes already installed. when i added quick attachment coupler i added some extentions to the thumb fingers. mine had hydraulic plumbing and couplers to stick already there. Mark and Nige are really up on cat stuff.

Iron@Dirt said:

a two way cylinder has two hydraulic hookups, no need for extra return or case drain if you will. the thumb i bought pinned thru the bottom of the stick and cylinder top pinned to stick with padeyes already installed. when i added quick attachment coupler i added some extentions to the thumb fingers. mine had hydraulic plumbing and couplers to stick already there. Mark and Nige are really up on cat stuff.

Click to expand...

I think I'm using the wrong language. When I say, "aux return line" what I think I am referring to is the "secondary auxiliary line." In my head, it was that way because I want to add an auger too and thought that line was to return the hydraulic fluid to the tank. Really though, it's just another hydraulic line that can push or pull fluid from the work tool. I don't need an extra line, I just need to connect the line that is already on the stick to the valve.

Also, I think this thread should be in the Excavators forum, rather than general. Can I or a mod move it?