Hydraulic Pump and Brakes

Those familiar with the operation of the piston hydraulic pump will understand, but for those who have never dug this deep into a tractor, let me give you my layman’s explanation of how this little machine works.  The pump is driven by a gear arrangement at the rear of the camshaft.  The gear in the pump is attached to a shaft which has an eccentric plate at its business end.  As the shaft and plate rotate, the eccentric plate, in sequence, depresses six steel “pistons” which fit into “shafts” with a very close tolerance within the pump.  As each piston is depressed, it forces hydraulic fluid into the pressure line.  At the back of the piston “shaft” is a ball bearing which serves as a check valve to prevent hydraulic fluid from returning into the shaft once pressure on the piston is released.  The ball bearing is spring loaded to keep slight pressure on the ball and, when pump pressure is released, its normal position would be against the bottom of the shaft.  The spring is attached to a roll pin, which also serves to act as a limiter on the distance the ball bearing can travel as it backs off the shaft under pressure.


One of these roll pins had broken and it and its spring had traveled through the pressure line and lodged in the sump where the line makes a right angle to travel up to the hydraulic ram that ultimately lifts the three-point hitch arms. 


Now I had another unanticipated problem.  There appeared to be no way to pull out the broken section of roll pin that remained in the pump head and drive in a new one.  A new pump head could be purchased, but the price of approx. $250 for the head alone persuaded me to consider other options.  I could probably leave the broken pin and operate the pump with only five of the six pistons fully working, but this would very likely compromise the pressure I could expect to generate from the pump and affect the lift rate of the three-point hitch, if it worked at all.


Again, Gap Tractor came to the rescue.  On my next trip down there, specifically in search of the correct step plate under the brake pedals plus a tool box and headlights, I inquired about a used pump.  They did not have one on the shelf, but thought they could find one for about $400.  In walking through their used parts inventory storage area, I noticed what appeared to be the head from one of these pumps.  It had two relief ports instead of the normal one and was rusty and dirty, but all six pins were intact and in every other respect appeared to be just what I was looking for.  For $25 it was mine.  I dropped it into a bucket of parts solvent upon returning home and allowed it to soak for several days while I focused on other aspects of the rear section of the tractor.


At this point, the rear wheels were still attached as they had come at purchase.  Using the hydraulic lift to manage the front of this section, I wheeled it out of the garage to clean off the big chunks of fossilized grease.  Once the big chunks were gone, it came back inside and was set on blocks and jack stands before the rear wheels were removed.


With the wheels removed, I focused my attention to the brakes, first vacuuming and flushing many years’ accumulation of brake grime and field dust accumulated therein.  The brake shoes would need to be replaced.  They were thin to the point of almost wearing down to bare metal.  They are held in place with springs and a pivot point consisting of a pin within a bushing.  From experience with another tractor, I knew it might be a challenge to remove these pins.  I was not disappointed.  I was able to punch out the pins on the left wheel brake, but the pins on the right-hand side were rust welded in place.  No amount of hammering was going to move them.  I tried soaking each end of the bushing with penetrating oil over several days.  Even using the limited heat I was able to produce from a propane torch was of no avail.  I realized I was going to need more serious heat, but I didn’t have it at hand.  What I did learn was that most every problem does have a solution.


Subpages (1): More Problems