Hello everyone, I have a 2011 825i that the 4wd will not work in forward. It's very strange that 4wd works perfectly in reverse but as soon as you shift into forward, high or low, the front axle disengages. I jacked all four wheels off the ground and put a multimeter on the plug for the solenoid and got the same readings in forward and reverse so it doesn't seem to be an electrical problem. I took the plastic nut off the top of the solenoid and when 4wd is engaged it becomes magnitised and is hard to move so it seemes like it is working. I am baffled because it doesn't seem like it's an electrical problem and I would think if it's a mechanical problem 4wd wouldn't work in reverse. Anyone have any ideas?
Don't know what the root cause is, but here is some info from various sections of the repair manual. I realize pictures and other info is needed to make this complete, but I thought it might help you in some small way.
MFWD Service Kit Operation and Wiring Schematics Theory of Operation Pressing the brake pedal opens brake switch contacts B—D, interrupting the signal between the vehicle harness
and the MFWD solenoid. Flyback diode MFWDC-97 affords protection from inductive kickback.
Theory of Operation Pressing the throttle opens throttle switch contacts B—D and removes the voltage (high signal) from throttle delay module pin 5, triggering the delay timer. After 1 sec. of no voltage (low signal), the timer activates the delay module relay. This action completes the connection between the vehicle harness and the MFWD solenoid. Releasing the accelerator pedal immediately turns off the relay and resets the module timer. Flyback diode MFWDC-97 affords protection from inductive kickback. The ground circuit of harness AM147221 is isolated from the MFWD solenoid connections. This change allows the service kit to be compatible with early production vehicles that use a low-side connection to activate the MFWD solenoid.
4WD Drive Circuit Operation (EMFWD) (SN -060000) Function: To control the 4WD drive function as well as display a LCD symbol to alert the operator of the 4WD engagement status. Operating Conditions: •Key switch in run position •Transmission in gear •MFWD switch in the engaged position •4WD engagement sensing switch on •Machinemustbetravelingapproximately9mphorles s. Theory of Operation: The 4WD function is an electromechanical system that uses logic control to activate or deactivate the system.
When the 4WD switch is pressed, battery voltage is sent to the display panel (J2, pin E) which illuminates the 4WD indicator light. When the 4WD switch is pressed, battery voltage is also sent to the relay module (J3, pin 8 - “4WD switch input”). The relay module then provides a path to ground (J3, pin 14 - “4WD solenoid driver”) to the EMFWD lock solenoid. This engages the solenoid and 4WD. If machine ground speed exceeds approximately 9 mph, the relay module will not allow the 4WD driver signal and 4WD will not engage until ground speed is reduced. However, if 4WD is engaged under 9 mph, it will remain engaged after that speed is exceeded.
4WD Drive Circuit Operation (EMFWD) (SN 060001-080000) Function: To control the 4WD drive function as well as display an LCD symbol to alert the operator of the 4WD engagement status. Operating Conditions: •Key switch in run position •Transmission in gear •MFWD switch in on position •Machinemustbetravelingapproximately9mphorles s. Theory of Operation: The 4WD function is an electromechanical system that useslogiccontroltoactivateordeactivate4WDoperation . A magnetic pickup sensor mounted on the transaxle generates the pulses used by the relay module to calculate ground speed. Placing the 4WD switch in the on position sends a “High” (battery voltage) signal to the relay module (J1, pin 12 4WD switch input). Logic inside the module compares the “request” for 4WD operation to the measured ground speed. If the logic determines that conditions are met, the relay module then provides battery voltage (J1, pin 15 - “4WD solenoid driver”) to engage the EMFWD lock solenoid and activate the 4WD icon on the display panel. If machine ground speed exceeds approximately 9 mph, the relay module will not allow the 4WD driver signal and 4WD will not engage until ground speed is reduced. However, if 4WD is engaged under 9 mph, it will remain engaged after that speed is exceeded. Schematic Components A1 — Relay Module A2 — Display Panel A3 — ECU B30 — Speed Sensor G1 — Battery S3 — Key Switch S34 — 4WD Switch Y35 — EMFWD Lock Solenoid
Mechanical Four Wheel Drive (MFWD): The transaxle reduction shaft is coupled to a direct drive right angle gear case bolted to the side of the transaxle for MFWD output. A drive shaft connects the right angle gear case output shaft to the front axle MFWD gear case pinion shaft. The drive shaft turns any time forward or reverse gears are selected. The MFWD gear case pinion gear turns a ring gear connected through roller clutches to the left and right front axle shafts. MFWD power transfer through the front axle gear case is on-demand and is provided under specific operating conditions. When an operator controlled 4WD switch is in the ON position, the front axle will engage and provide drive to the front wheels if the rear wheels slip. A solenoid in the gear case engages an internal clutch to connect the ring gear to the axle shafts through roller clutches. There is no differential lock for the front axle.
Function: EMFWD can provide power to the front wheels when the rear wheels slip. With the operator controlled 4WD switch in the ON position, roller clutches in the front axle gear case will engage and provide drive to the front wheels if rear wheel speed is faster than front wheel speed. With no speed differential between the front and rear wheels, the front drive does not engage and the machine is driven by the rear wheels only. Operation: With the 4WD switch in the ON position and the transmission in either forward or reverse, voltage is supplied to a solenoid (A) in the differential case. The voltage is stopped when the machine is shifted into neutral. When the solenoid is energized, a plunger is extended into the path of the rotating tabs of the actuating washer (B). stopping the outer washer. Wave washers (C) between the inner and outer washers place a drag between the outer (stopped) washer and the inner washer (D).The inner washer is keyed to the roller brake assembly (E), which is connected to the roller cage (F) by tabs. The roller cage lies inside the ring gear hub (G).Each side of the roller cage contains cylindrical rollers (H) that roll around the output hub to each axle. The drag imposed on the roller cage through the wave washers and tabs forces the rollers slightly off center in the openings of the roller cage. When the rear tires slip and spin more than 15% faster than the front tires, the rollers move against ramps (I) in the rotating gear hub and are forced inward. The inward movement presses the rollers against the left and right output hubs. At this point, all components begin rotating together. When the machine stops and the transmission is shifted from forward to reverse, the voltage to the solenoid is momentarily stopped (neutral switch opened). This allows the springs on each roller to rotate the roll cage and rollers into a neutral position.
Last edited by 200mph; 07-25-2016 at 09:19 AM.
2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, Front and Rear 4" square 27 watt LED lights, Bad Lands 2500lb Winch installed in bed, Front and Rear CV Guards
Thanks for the info! It seems like all my electronics are doing what they are supposed to but I don't see anything in the diff that would work in reverse but not forward. Unless for some reason the rollers can't slide up the ramps.
I'm starting to get somewhere. I removed the solenoid from the front differential and I stuck a Phillips screwdriver in the hole and the front differintal would engage. It took a litter more pressure to get it to lock in forward than reverse so that makes me think the solenoid is too weak. With the gator jacked up and running in gear I had a friend flip the 4wd switch on and off while I had the solenoid in my hand. I could hold the plunger in with my thumb without much force. How strong should a good working solenoid be?
Did you measure the voltage at the solenoid with it engaged? Force would be proportional to supply voltage.
2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, Front and Rear 4" square 27 watt LED lights, Bad Lands 2500lb Winch installed in bed, Front and Rear CV Guards
I checked the voltage at the plug in my first test and it was 12v with the motor off. When I removed the solenoid I conected it to a battery to fiddle with it and it is still very easy to push the plunger in. After thinking how easily the Phillips screwdriver worked and the only difference between the two was the taper at the end of the screwdriver I decided to try something. I ground about a 45* angle around the plunger and put it back together. 4wd now works perfectly! I don't know if the solenoid is too weak and this is just a bandaide or if something in the differential is wore out but it works.
2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, Front and Rear 4" square 27 watt LED lights, Bad Lands 2500lb Winch installed in bed, Front and Rear CV Guards
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