oldhousehugger
Well-Known Member
On working on the pump body, I would lap the end plates if you can to try and get out any gear swirls if possible and also the pump body barrel which is what gives the gears their clearance. I believe I rubbed mine down to about .002 clearance thicker that the width of the gears and crossed my fingers because the bushings were worn in my pump as well. When you are lapping keep rotating the part every few strokes so it doesn’t wear down on one side more than the others. Remember the gears are designed to butt at exactly 90 degrees into the ends so if you rub one side of the body down more than the other you could theoretically have the ends catawampus to the gear bore so be careful. Measure twice cut once.
You can’t do anything about wear on the gears themselves unless you have some very fancy rotary grinding setup to get both gears exactly the same width.
When you think about it though the input shaft drives the idler gear so there shouldn't be any weird torques going on. When it makes pressure the driving gear teeth push on the driven gear teeth to seal between high and low side. The pressurized oil is trying to squeeze back around the outside of the pump bore and past the ends of the gears. Anyhow the closer you can get the gears to fit to the end plates and the less clearance there is between the outside diameters of the gears and the pump body the better it will pump until something rubs. I'll bet if you were real careful you could lap the pump body down to where the gears were just barely missing the end plates.
As far as the input shaft having the seals wearing groves in it, my bearing dealer miked the old one and sold me the next size undersize from the original ID. That gave the lips on the seals (I remember there being 2 back to back) something to seal against.
There is oil lubrication on both sides of the seal so it would theoretically never run dry.
Finally replace all your o-rings. I found a distributor here in Dallas called H&D (http://www.hddistributors.com) which sells all the local hydraulic repair shops their o-rings and seals. I took all my old o-rings down there and they measured everything and were able to supply me everything I needed to rebuild the pump. They have a minimum charge for any order but sometimes having the correct 82 cent o-ring is well worth the 20 bucks of a minimum if that’s all you need to get going again.
I think I mentioned before that Messicks up in Pa. (http://www.messicks.com/NHC/85073.aspx) has a great website for getting parts drawings of the 4500. Some of the parts are off the AG version and some unique to the backhoe/utility version. They show to have several of the front and rear o-rings as well as the OEM seal. If it were me I’d explore alternative sources before going with the dealer. Ford / New Holland has had to store those parts for 30 or 40 years and they are proud of their space and parts museums. Ha Ha. Who can blame them. Try getting OEM Dealer parts for a 40-year-old Ford car. Not going to happen.