I have a 64 Oliver 550. It's a working tractor, but someone restored it in the past 10 years. It has an aftermarket (though about as old as the tractor) front end loader.

I recently blew an O-ring on the main hydraulic pump (manufactured by Vickers) and hydraulic fluid was leaking into the transmission. I was able to get things apart and fix the pump, but it doesn't seem to be adding pressure to the system. It is circulating hydraulic fluid, but not with the pressure needed to raise and lower implements etc. I saw no visible signs of distress on the pump. I've bled air from the system. Any thoughts?

From reading another post (<!-- w --><a class="postlink" href="http://www.reocities.com/dieseltempo/Oliver/pumprebuild.html">www.reocities.com/dieseltempo/Oliver/pumprebuild.html</a><!-- w -->), I noticed the appearance of a small spring b/t the back pump cover and main cover. In this post, they say that without this spring, &quot;the pump will not build pressure when starting.&quot;

I may be second guessing (the pump's not right here), but I don't recall this spring when I reassembled the pump. Meaning I lost it during the disassembly. A classic move.

IF this is indeed true, does anyone have any tips for sizing and sourcing a replacement spring, and could this small spring be the source of all my current troubles?

Thanks for any feedback! I need to get this machine back moving again!