Cat 740 transfer case oil in front diff

Hey Guys, hoping someone could point me in the right direction. Working on a Caterpillar 740 ADT S/N AXM00773 with approximately 13k hours on it. Oil is leaking from the breather for the front axle housing. I'm guessing the Oil is coming from the transfer case and getting in the front axle when the diff lock is activated. Does this make sense? I will not have access to SIS or a service Manual until sometime tomorrow and was just trying to get a head start.
I've never worked on this particular system on these trucks. Was told of the oil leaking from the breather and that the transfer case is using oil abnormally.
Thanks for any guidance ya'll may be able to provide.

Yes, that makes sense. The oil pressure for the diff locks is supplied by the output transfer gear pump. If it's transferring oil from the OTG case into an axle, you have something leaking in the diff lock mechanism.
Also be aware that the OTG has quite a small oil capacity and if it's allowed to run dry, it'll self destruct fairly quickly.

Thanks for the reply Cmark. We capped the line for now so the truck can be used while we have another 740 in the shop for brake repair.

I guess the front diff will need to come out in order make permanent repairs? I've never been into the differentials on these trucks, only the old D400D models.

Yes, you'll have to remove the front axle to get the diff out. It's easier to take out the axle and A-frame complete but you will need a special puller to get the A-frame free from the tapered pin.

That's what I was afraid of. If nothing else at least we'll get to restock our cribbing lumber supply.
This truck also needs a suspension cylinder resealed so we can get that taken care of while we're in there.

Thanks for taking the time to read my post and respond. Sounds as tho you've been into the diffs on these trucks before?
Reason I ask is because on a different truck (another 740) we changed the oil in the front diff and had a dowel pin come out with the drain plug magnet. Haven't had any other problems with that differential and no bad sample results. We may just have to get good at removing axle housings!

Hi cb75, that special puller is just a metal plate with threads and a studded bar that you can screw. can be done in a machine shop. it bolts on to where the cover is for the front axle a-frame pin, You could always use the cat tool.. but its a pretty penny, and those pins can be really stubborn sometimes...

Oh, and it is definitely easier working on those axles outside of the machine like mark says.

Btw, if you have internet access, Caterpillar's online parts website, parts.cat.com, is REALLY useful checking out what goes where.. especially when the SIS isn't handy.

I would be very worried about a dowel pin just "falling out".. how many hours has it done? and there was nothing else on the plug? its hard to imagine it just dropping out, may indicate something coming loose?..


BTW, would love to see what went wrong on that truck with the brake problems.. never seen the brakes actually fail apart from that inner duocone.. and the final drive bearings

Mrappels, the truck that lost the dowel pin has around 11,000 hours on it. Nothing else on the plug and no other issues with that diff since it was found. (The dowel pin)

I work on a lot of 740's and have had several of the A-frames out. I dont have a special puller to separate the tapered pin from the spherical bearing. I use a 25 ton cylinder, put some pressure on A-frame the a quick smack with a 15lb brass sledge it pops loose. The hardest part in my opinion is if you are taking the A-frame out is loosing the bolts that hold it to the axle. They thread into the A-frame and can get seized. Not to mention they are about 12 inches long. Last time I had to use a HY-torq to break them loose.

They're something else, aren't they..

ship660 said:

I work on a lot of 740's and have had several of the A-frames out. I dont have a special puller to separate the tapered pin from the spherical bearing. I use a 25 ton cylinder, put some pressure on A-frame the a quick smack with a 15lb brass sledge it pops loose. The hardest part in my opinion is if you are taking the A-frame out is loosing the bolts that hold it to the axle. They thread into the A-frame and can get seized. Not to mention they are about 12 inches long. Last time I had to use a HY-torq to break them loose.

Click to expand...