Dozer hydraulic question

EddieWalker · Oct 10, 2005

I have a 1988 Case 1550 Dozer. It has three hydraulic pumps. One for each drive motor and one for the blade.

They drive pumps are on the same tank withe the blade being on it's own system.

The drive side started getting air into the system. At first it was just a bit and it would clear up, but it got worse to the point the fluid is all whitish in color. I'm looking for the leak, but since it's sucking air in, not leaking fluid out, it's eluded me so far.

I kept running it since everything else was working great.

Then everything started slowing down. After running it for awhile, the drive motors will both have less power, and the longer you operate it, the less power you have. The blade is also affected to the point that raising it will completely stop the tracks.

When I let it sit for a bit while turned off, it will have all it's power back, but will slowly loose power again.

My guess is there's something wrong in the drive gear in the bell housing, but Case says it's a solid gear and not the problem.

Case came out and picked it up last week and called me today to tell me that all three pumps went out at the same time. This seems very unlikely. The didn't do a preasure test, just drove it around some and came to that conclusion.

Cost to replace the drive pumps are $20,000 per side. I didn't ask about the blade pump.

For over $40,000, I'll buy another dozer and sell this one cheap. That's just rediculous, but I also think they don't want to work on it and are trying to drive me away.

I told them to do the preasure test on the hydraulics to see what the readings are. When I get those numbers I'll post tha info along with what the readings should be.

Until then, any thoughts would be greatly appreciated.

Thanks,
Eddie

Highbeam · Oct 10, 2005

Ouch! 40,000$ to get back a dozer no better than when this little problem appeared. It won't be worth anymore than you paid for it. Wise to unload it if that happens.

Cool that the dozer was hydraulic driven. I expected finals and clutches.

The best thing you have going is that everything works right when the fluid has rested. Still hot and thin but rested. This tells you that the pumps must be pretty good I would think.

Maybe a second opinion?

Taylortractornut · Oct 10, 2005

Eddie Just because they work for Case dont make them mechanics. THey may be just parts changers. Id find it hard to beleiceve all three pumps went out at once. I also belive that they are Sunstrand pumps and can be ordered off the shelf. I think the 750 or 850 Deeres used the same pumps. One thing I ran into on hydraulics mostly on scrapers with a hdrosttc transmission on the elevators was that the rubber linings in the hoses would suck together and they would stop up after gettin warm. Ive had days of changing hose after hose to find it.
The only thing I can think of that killed 3 pumps at once was that the air coming in caused it to cavitate the pupmps all at once and that may have killed them. I have some friends that do all of our work on our machines they have alot of experience in Case hydrostats.

MMM · Oct 10, 2005

My guess- If drives work when air is dissipated and oil is still hot, your drive pumps are probably ok since the foaming in tank being common to both and causes performance loss due to compressive qualities of air. The blade problem is odd, being on different tank and probably coincidence, (not neccesarily a pump, could be relief, cyl,, etc.).
The time to look for suction side leak is when machine is shut down. Good luck Eddie.

Dirthog · Oct 10, 2005

yes all three pumps very well could be out at same time with air in system you have starved them for oil and no pump will last long that way. also pressure test will tell you very little unless the pumps are junk you need to do a flow test and with the system warm you will find the flow droping off as the system builds pressure and warms up that is why if you let it set and cool down it will work again for a little while.

TiminMN · Oct 10, 2005

Is there a "charge pump" ? Charge pump is a high volume low pressure gear pump that supplies oil to the main pump. It's rare for these pumps to go bad but is can happen. Should have a screen intake that might be plugged a little.

EddieWalker · Oct 10, 2005

The results of the test are disouraging. They hooked up the some guages to the charge pumps. If the readings are bad there, than the pumps are bad.

The right drive pump reads 300 pounds, which is fine. 350 is brand new with 280 being the minimum.

The ;eft hand pump, which I had rebuild last year for $3,000 starts out at 300 pounds, but dromps down to 150 pounds after it gets warm.

Only the two drive pumps are on the line with the air in the system. The blade is it's own system with it's own tank. The fluid in that line is good.

When the left pump went out last year, I lost control of it and nothing worked. The other side worked fine along with the blade.

The mechanics at Case said this one pump being bad could cause all the problems, but this makes no sense to me. I'm not very knowledgable, so maybe this is the problem, but I think I'll be chasing ghosts on this.

Thanks,
Eddie

MadReferee · Oct 11, 2005

Eddie,

Have you tried posting your problem on one of the dozer specific boards? If not, then you should give it a try. The dozer experts might be able to help. Here are a couple you might try:

ibdozing.com

ytmag.com (see crawler/dozer board)