@JonF I've just gone thru a long process of replacing pins and rebuilding cylinders on my L35/BT900.
The plumbing of the swing cyl is simple to see, but confusing to explain.
The cylinders are plumbed such that when one cyl is extending, the other is retracting - but you probably already know that. I'm including info for others here that may have issues with BT900 or just curious.
Just because they have been rebuilt, doesn't mean that the cylinders or other parts aren't damaged. Some thoughts for you:
1) The nuts holding the piston to the rod could be loose.
2) The plumbing could be incorrect somewhere (or damaged)
4) Piston seals could be improperly installed causing internal leaking
5) the swing boom itself could be damaged. (Or the pins/bushings)
5a) the boom should move rather easily side to side when the cylinders are not pinned to the boom.
6) Your actual controls may be worn out/mal-adjusted such that they do not depress the valves correctly
7) Make sure that the control for the Backhoe is pushed all the way in. The one in picture 5
8) Swing CYL bushings rusted not allowing free movement.
9) Low/dirty hydro fluid / dirty filter
10) Pump has low volume (is loader working ok?)
11) Connections to/from backhoe are worn/leaking/clogged/misaligned.
It appears you have new pins on the swing cylinders where they meet the boom. Do the cylinders move side to side easily when disconnected?
The swing cyl have large shafts that are mounted into bushings on the bottom of the swing frame and held in place in the top by the large, thick bar (again there are bushings in that top bar that mate with the shafts on the top of the cyl). These could be horribly rusted not allowing free movement.
The seals for the cyl may be NLA, but are plain old seals any hydro shop can match. The hoses between the cylinders are NLA, but I think I found the last in existence via Messicks - but I wanted OEM because I really didn't know how long to make them. I can give you those measurements if you need them.
What's critical are the 90 deg fittings because there is not much room in the swing body;
On MY tractor however the bottom of the CYL double nipples are already 90 deg so the hose fittings are straight.
Plumbing is as follows:
1) Easy to get confused on LEFT and RIGHT.
2) TOP Hose from valve goes to LEFT CYL top double nipple (EXTEND LEFT - RETRACT RIGHT)
3) BOTTOM Hose from Valve goes to RIGHT CYL top double nipple TOP (EXTEND RIGHT - RETRACT LEFT)
4) BOTTOM LEFT CYL Double nipple goes to RIGHT CYL TOP single nipple
5) BOTTOM RIGHT CYL Double nipple goes to LEFT CYL TOP single nipple
NOTE THE DIFFERENCES BETWEEN CYLINDERS - RIGHT is upside down.
On BOTH CYL Double nipple EXTENDS the Rods.
THIS IS THE TOP BAR WITH BUSHINGS
BOTTOM OF MY TRACTOR's double nipples are already 90 deg.
