977L oil problems

ecat · 11-02-2009, 07:07 PM

I purchased a late 70s 977L last May (1408x) worked on it all summer cleaning it up and painted it. I thought someone really screwed up by putting too much oil in the transmission because I drained 90 gallons of oil out of it. The book says it holds about 25, so I was wondering how someone could be so stupid as to overfill it by 70 gallons. But the little I have operated it, it seems the hyd. tank keeps getting lower and the trans keeps getting fuller. How are these two separate systems mixing and how can I fix it. is it a seal between a couple pumps or what, any advise appreciated.

ATCOEQUIP · 11-02-2009, 08:30 PM

You hydraulic pump is probably driven by either the torque convetor housing gears or tansmission gears. You either have a bad hyd pump shaft seal, or a failing pump that's putting pressure on the seal.

ecat · 11-02-2009, 08:42 PM

Is this pump an external pump, ie. something I can fix myself or is it something that requires taking apart major components. I know there is what I believe is a pump on the converter housing, would that be it????

surfer-joe · 11-02-2009, 09:16 PM

It's an external pump, but when the seals or the drive shaft get worn, the pump is designed to leak fluid forward past the outer seal into the transmission oil system. There is a small drilled hole that felicitates this from in between the two shaft seals. Best bet is to exchange the pump, replace all connecting hose o-rings. Not a terribly difficult job, but on a 977L, not the easiest either.

After draining the trans to get the mixed oil out, change the filter, clean out the screen and magnets and refill with correct viscosity oil, for your area probably a 30wt TDTO. I can't remember if the torque divider in that model has an outlet screen or not, but if it does, remove and clean it too while you are in the area.

The hydraulic tank will be fine so long as it's filled to the full mark. You might want to sample the hydraulic oil however to see if the pump was worn bad enough to throw some debris into the system. Run the trans a few days and do the same.

Good Luck!

ecat · 11-02-2009, 09:42 PM

when I was cleaning it, countless hours, or maybe more like days with the pressure washer, I had been over every square inch of that machine. I think I know what pump it may be, i will trace the hose from the hyd. tank. One good thing, its clean enough to eat off of so working on it will be a bit more desirable. I would guess you would get to it from underneith with the belly pan removed. I had a local guy who is in the dirt moving business tell me that he always ran the same 30w oil in both the trans and the hyd. tank so all the oil is mixed in it I know, and the oil is very clean. Dont know if he was full of crap or thats ok. Before I painted it I changed all the filters and the screens in all locations, clean the magnets and so forth

Knucklehead · 11-07-2009, 09:49 AM

Right or wrong, at the mine I work at, we are running sae30w in everything but the fuel tank!!!

AmerIndependent · 11-07-2009, 02:08 PM

Here is an illustration of the hydraulic pump that is causing the transferring problem.

It is mounted to the back of the torque converter and the shaft seals are apparently faulty allowing the higher pressure hydraulic system to push oil into the power train system.

The bad news however is that the seal failure could be the result of a worn hydraulic pump that is allowing the shaft to drop and side load the seal, if the pump is removed I would disassemble and inspect it as I know its no picnic getting it out of there and wouldn't want to have to do it twice!

As far as oil viscosity is concerned, many of our local fleets also run 30wt in both systems but we are in a warm climate, I would be concerned about the time it would take for the pump to get its prime in subzero temperatures.

ecat · 11-07-2009, 11:52 PM

I absolutely love Forums, you can usually get enough good information to make a wise decision on what to do. Thanks for the comments and diagram, at least I am almost positive of what to do and will proceed with the pump removal and fix or replace. From what I have heard and what was posted right or wrong this machine has 30w in everything also, we do not hardly ever get sub zero weather here and I wouldnt be operating it in that weather anyway, so I guess 30w is fine in all systems. plus I have about 50 extra gallons of the stuff anyway from the original overfill.

ATCOEQUIP · 11-07-2009, 11:59 PM

When you break it down to repair pump, be sure and replace o-rings of connections in the piping. By now, the o-rings in the connections of the pressure piping will be hard as a rock and flat. You've got the oil drained to facilitate the pump repair, now's the best time to replace o-rings and any aged suction pipe connection hose.

wagspe208 · 03-02-2010, 09:33 PM

Is this common on 977s? Or 955's or just an age thing?
Wags