Service of the Hydraulic Standpipe 883788M91 on MF 135 Models w/ Pressure Control

[klancf51]

Repair/Replacement of Hydraulic Standpipe 883788M91 on MF 135 Models with Pressure Control
Tractor models with pressure control use standpipe 883788M91 which has a diverter block to supply hydraulic fluid to the pressure control valve. This standpipe cannot be removed by pulling it straight out through top of the lift cover. Pulling or rotating this standpipe is generally detrimental to the gland seal in the diverter block. A key point is this: in all cases of O-ring installation for static seals, excessive twisting, turning, rotating, or oscillating of glandular components relative to the O-ring should be minimized. Unlike standpipe 828299M1 (used on models without pressure control), standpipe 883788M91 contains 3 static hydraulic seals which use O-rings:

• two radial type seals (one on each end of the standpipe)
• one gland type seal (in the standpipe diverter block)

Leakage at any of these seals will negatively impact the performance of the lift. Since this standpipe has a 3rd seal in the diverter block, the service procedure is different from tractors which do not have pressure control. The service manuals I use do not provide a procedure for removing or installing this standpipe. The following is the procedure that successfully worked for me. Refer to the MF 135 Parts Manual for identification of the parts.

Removal of Hydraulic Standpipe 883788M91

1. Remove the seat and lower lift links.
2. Drain about 4 gallons of hydraulic fluid from the center housing. Remove the response control assembly from the right side of the center housing.
3. Remove the roller from the control valve lever through the opening in the right side of the center housing.
4. Remove the cap screws from the transfer plate. Leave the transfer plate connected.
5. Remove the cap screws securing the lift cover and raise the lift cover with a suitable hoist.
6. With the lift cover raised, grasp the standpipe from below the lift cover to keep the standpipe diverter block attached to the pressure control tube while the transfer plate is being pulled from the standpipe. If upward force is applied to the transfer plate without holding the standpipe in place, the standpipe diverter block will be moved upward along the pressure control tube. For standpipe 883788M91: always try to limit the movement of the standpipe relative to the pressure control tube in order to avoid wear to the gland seal in the diverter block.
7. Fully loosen (but don't remove) the two cap screws (1/4" x 5/8") which secure the pressure control valve to the control lever support bracket (898322M91).
8. Disconnect the fitting holding the control valve tube (898248M91) at the pump control valve.
9. At this point the pressure control valve can be moved away from the control lever support bracket enough to get a 3/4" flare wrench (or better still, a flare crowfoot) on the connector (898301M91) that secures the pressure control tube to the pressure control valve. Fully loosen the connector so that it is disconnected from the pressure control valve. Apply upward force on the standpipe to provide the clearance needed to separate the connector and pressure control tube from pressure control valve - be careful with the seal on the connector. At this point the pressure control tube can be withdrawn from the standpipe diverter block. The standpipe may now be removed.

Installation of Hydraulic Standpipe 883788M91

1. Inside the diverter block (where the pressure control tube connects to the diverter block) there is recess with an O-ring (359291X1) and perhaps a backup washer (361160X1). These create a gland seal for the pressure control tube to the standpipe diverter block. Replace the O-ring and backup washer as necessary. It is helpful to apply a small amount of seating lubricant (e.g. pure silicone grease) to the O-ring before installation.
2. Make sure the pressure control tube end is correctly chamfered (10-20 degrees) and does not have a sharp edge, nicks or burrs. Also pressure control tube should have an appropriate surface finish of 32 micro-inches RMS (I used 150 grit production paper). This is so that the pressure control tube will "bite" into the O-ring and provide a good static seal.
3. Apply a thin film of seating lubricant (e.g. pure silicone grease) to the chamfer of the pressure control tube. With the offset bend of the pressure control tube correctly oriented with the diverted block, insert the pressure control tube straight into the diverter block. Be careful to avoid damage to the O-ring or excessive twisting of the tube. It should require some insertion force and fit snugly. To check the pressure control tube connection, apply air pressure to one end of the standpipe use fingers to simultaneously plug the pressure control tube and the other end of the standpipe. The pressure control tube connection to the diverter block should pressurize and feel air-tight.
4. Replace the O-rings: two (195561M1) on the standpipe and make sure the backup washers (195874M1) are installed. The backup washers are important: they prevent extrusion of the O-ring into the extrusion gap in the gland (in plain language: with a backup washer the O-ring will perform better and last longer). Also replace O-ring (195561M1) which seals the transfer plate to the lift cover.
5. Insert the standpipe through the hole in lift cover from below and secure it so it doesn't drop down.
6. With the pressure control valve loosened from the control lever support bracket, the connector for the pressure control tube can be threaded into the pressure control valve. A 3/4" flare wrench can then be used to tighten the connector to the pressure control valve. Tighten the pressure control tube connector to the pressure control valve, being careful not to pull the pressure control tube out of the diverter block.
7. Reconnect the fitting for the tube at the pump control valve.
8. Tighten the two cap screws securing the pressure control valve to the control lever bracket. At this point the standpipe assembly should feel stable and tight, but it should also have some maneuverability because the pressure control tube has an offset bend and the O-ring seals allow for some movement of the standpipe assembly and pressure control tube during the alignment of the standpipe to the pump.
9. Place a new lift cover gasket on the center housing.
10. The lift cover should now be slowly lowered until the bottom of the standpipe is about 1/4" to 5/16" from the pump recess. Be careful that the standpipe is not disturbed or damaged. Align the standpipe with the pump recess (I inserted a 1/4" x 30" metal rod through the standpipe and used it a locating dowel to "find" the recess in the pump). When the standpipe is in alignment with the pump recess, slowly lower the lift cover and place the standpipe in the recess: remove the rod and insert a 6" Phillips screwdriver (with a plastic handle) into the top of the standpipe. Using the screwdriver as a lever and your finger (through the side port), align the standpipe into the recess in the pump. When the standpipe is in the recess, use a hammer to tap the top of the screwdriver (the plastic handle will protect the standpipe) and start the standpipe into the recess in the pump. At this point the standpipe should be started in the pump recess. The objective here is to maintain the seal of the pressure control tube to the diverter block by minimizing any upward force on the standpipe: avoid landing the bottom of the standpipe on the top of the pump which will force the standpipe diverter block upward from the pressure control tube.
11. Fully lower the lift cover and tap the screwdriver to fully seat the standpipe into the pump recess. Remove the screwdriver.
12. Install and tighten the lift cover cap screws (55 ft-lbs).
13. Install the transfer plate and tighten the cap screws (55 ft-lbs).
14. Install the roller on the control valve lever.
15. Verify that the standpipe and pressure control tube have no leakage.

Thanks to those who provided me (and others) with tips on the standpipe.