'75 980B Hydraulics

We're having a problem with the hydraulics on our 980B wheel loader losing prime. Usally within a couple of hours. No major leaks to speak of that would be introducting air into the system and it only does it when you park it with the bucket hydraulics relaxed. We left the bucket about 2' in the air with it curled a couple of nights ago to keep presure on the system and it held prime until the next morning. Our thinking is that something is bleeding through a back flow preventer or some type of check valve that we are unaware of. Any help would be great.

Troy

test

75 980B Hyd

I also have a 980 of that vintage and she is a good old girl always ready to work. Mine has a Balderson and 10 ft.Forks and the 5 yd. Bucket. I have not had that problem but will be watching to see if you find the answer. I will ask the Old time Cat Wrench that has a shop about 45 miles down the trail if he has an idea for you. I'll bet he does. I will stop by and see him next week and get back to you if I find out something. Later Cat 236 Alaska

Your pumps are losing their effeciency which is letting the oil drain back. If you also check the suction hoses from the hydraulic reservoir you will probably find them bleeding through the outside covers or leaking at the hose clamps. The other thing to check is whether or not you are getting air pressure build up in the tank as you operate. You should get a lot of pressure bleeding off when you open the cap some.

Generally if you have lots of oily dirt around the hoses, fittings and flange faces you got air getting into the system.

Do you have other symptoms. Noise in the pumps on startup, slow cycle times, low pressure and so on?

Sounds like low oil level maybe? Half the time the sight glass on these old machines are so cloudy you cant see the oil level. The tank should always have air pressure in it as John said also.

we have a 980c that had this same problem going on, it was the pumps going bad. he oil was bleeding back into the tranny trough the hyd. pumps.