Bobcat 763 mysteriously using hydraulic oil

AdamjEdgar · Feb 12, 2021

Hi guys,
My Bobcat 763 is using hydraulic oil. I found a couple of leaks...1 was a seal and 2 was a cracked hose.
Both are now repaired and no more visible leaks under the cab.

I filled machine with oil and ran bobcat doing some grass slashing with my slasher for about half an hour this morning when all of a sudden I lost hydraulics...it was out of hydraulic oil again.
I checked under cab...no leaks, checked under belly plate of machine, no leaks, checked in engine bay area, no leaks.
The hoses and drive motor on slasher are not leaking either.

I am stumped...where could the hydraulic oil have gone?

Is it possible for the oil to leak from the track drive motors into the drive chain box under the cab?

willie59 · Feb 12, 2021

Yep, pull the plug at the front of the machine, that's the oil level for the chain case. If it dumps oil out of that oil level hole then that would be your hydraulic oil leak.

willie59 · Feb 12, 2021

Sorry, I should have said, remove the bucket/attachment from the loader, raise the loader arms and install the safety prop, then remove the plug at the front of the machine.

lantraxco · Feb 12, 2021

Yes, motor shaft seals can fail and dump oil into the chain case. The link below may help, there are manuals online available to a degree. Pull the check plug for the chain case, make sure you have a large drain pan under it.

https://www.slideshare.net/hjdkmsme...-manual-sn-512212001-thru-512249999-114037985

lantraxco · Feb 12, 2021

Bad Willie, bad, bad Willie! LOL. Safety third as Mike sez.

willie59 · Feb 12, 2021

Hey, I did quickly clarify myself.

To check that level plug you have to raise the loader arms to get good access. The practice I developed long ago on those machines, can't preach it enough, is to remove the attachment. It's a quick couple, get that weight off and toss it before you raise the arms and prop it.

lantraxco · Feb 12, 2021

willie59 said:
Hey, I did quickly clarify myself. To check that level plug you have to raise the loader arms to get good access. The practice I developed long ago on those machines, can't preach it enough, is to remove the attachment. It's a quick couple, get that weight off and toss it before you raise the arms and prop it.

Excellent advice, the newer machines all should have safety prop devices in place yes? Never hurts to remind folks those are NOT designed to hold a loaded bucket or grapple up in the air, lol.

willie59 · Feb 12, 2021

Bobcat machines have had incorporated safety props since I know at least the C series machine. And the prop is more than adequate to support the arms and bucket. But me, it's a quick attach, toss the dang bucket, no sense having that hanging over me when it's so easy to toss it.

Welder Dave · Feb 13, 2021

From what I've heard if the drive motor is leaking, it often has to be replaced. There's usually a problem in the motor that takes the seals out but maybe you'll get lucky. Not sure if your machine has case drain filters but would be good to check.

willie59 · Feb 13, 2021

Welder Dave said:
From what I've heard if the drive motor is leaking, it often has to be replaced. There's usually a problem in the motor that takes the seals out but maybe you'll get lucky. Not sure if your machine has case drain filters but would be good to check.

A 763 is an aged machine. Yes, they had case drain filters, would be something worth giving a look at, see if there's debris in there. Filling chain case with oil on a Bobcat is typically a failed drive motor putting excessive internal leakage pressure on the seals in the motor carrier, excessive debris in case drain filter would indicate that. But one could get lucky, being an aged machine, could simply be the seal in the motor carrier has simply gone south. Checking the case drain filter would be a good place to start.

AdamjEdgar · Feb 13, 2021

Thanks guys,
I thought that was the likely problem...I could see any other place where 30litres of hydraulic oil could "hide".
I assume now the case is overfull, when I remove drive motors, oil will leak out of the chain case sides?

Also, is there an alternative brand for the pair of inline return filters under the cab, i can source other than genuine...bobcat parts are a rip-off!(anyone know the filter specs?)

Welder Dave · Feb 13, 2021

You might have bigger problems than a couple filters. If you need a need a new wheel motor could be a $2000+ repair.

lantraxco · Feb 13, 2021

AdamjEdgar said:
Thanks guys,
I thought that was the likely problem...I could see any other place where 30litres of hydraulic oil could "hide".
I assume now the case is overfull, when I remove drive motors, oil will leak out of the chain case sides?

Also, is there an alternative brand for the pair of inline return filters under the cab, i can source other than genuine...bobcat parts are a rip-off!(anyone know the filter specs?)

Just pull the check plug and drain the oil level down to where it should be before you start tearing things apart.

Get the Bobcat part number run it through the Donaldson (my recommendation) or Fleetguard or WIX cross reference web pages, they'll have filters for it.

willie59 · Feb 13, 2021

The case drain filters for the drive motors are sintered bronze filters. They're typically washable with solvent unless they're wasted with debris from a failed motor, which then you would replace them along with replacing the motor. Removing the two filters and and disassembling them will indicate which motor is bad if it's filled one with debris

AdamjEdgar · Feb 14, 2021

Hi guys,
Too much back pressure on rhs inline return filters has caused the rhs drive motor inner shaft seal to blow inwards (see photos).
I am assuming my only option is to go in through access panel umder cab into chain drive area and remove the bolts that hold the drive motor mounting housing to pull this big seal and replace it?

Ps i tried sharing from Google drive...not sure if it worked from my phone so I attached images as well

lantraxco · Feb 14, 2021

Not seeing the pictures, but yep I think so. Only question is, is the motor bypassing excessively internally so that it will blow out the new seal in short order?

AdamjEdgar · Feb 14, 2021

Removing linkages etc to gain access to the panel

AdamjEdgar · Feb 15, 2021

Access panel is now ready to remove

AdamjEdgar · Feb 15, 2021

This is not going to be easy...that housing also holds bearings for the chain primary drive shaft.

lantraxco · Feb 15, 2021

That looks ugly, have you replaced the motor shaft seal? I'm not 100% sure that inner seal isn't supposed to keep gear oil from coming out?

Bobcat 763 mysteriously using hydraulic oil

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