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Old 06-21-2005, 07:54 PM   #1 (permalink)
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Default VTM-4 does not work

The VTM-4 does not work on my 2003 Pilot. Yes, I am doing it right. I had a situation this weekend where I pulled off the highway in some very soft sand. Fortunately the AWD kicked in, and I barely made it out. My rear differential did not lock (only one rear tire would spin). My Pilot has 32,000 miles on it, and I am planning on taking it in before the warrantly expires. Does anybody know how to check the VTM fluid and how to do it your self every 15,000 miles?
Thanks
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Old 06-21-2005, 08:00 PM   #2 (permalink)
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long thread on this subject

Rear Differential Fluid Change

easy to do i understand.
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Old 06-21-2005, 09:23 PM   #3 (permalink)
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are you sure? did you put it in "1 or "2" and hit the VTM-4 lock button on the dash?

you said "....AWD kicked in....", so it leads me to believe you didnt manually engage the VTM-4 lock and just let it do its thing automatically.
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Old 06-21-2005, 09:27 PM   #4 (permalink)
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Default Re: VTM-4 does not work

Quote:
Originally posted by jonaz
The VTM-4 does not work on my 2003 Pilot. Yes, I am doing it right. I had a situation this weekend where I pulled off the highway in some very soft sand. Fortunately the AWD kicked in, and I barely made it out. My rear differential did not lock (only one rear tire would spin). My Pilot has 32,000 miles on it, and I am planning on taking it in before the warrantly expires. Does anybody know how to check the VTM fluid and how to do it your self every 15,000 miles?
Thanks
Have you had the fluid changed before now?

Was it done by a Honda dealer?
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Old 06-22-2005, 02:06 AM   #5 (permalink)
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Yes, I came to a complete stop, put it in 1st gear,and pushed the VTM button. Only one front and one rear tire spun. I have tested the VTM feature on a couple of other occasions, and it did not work. I am quite familliar with rear differentials, transmissions, and gearing, and I am quite sure this thing does not work.
I bought my Pilot used, so I have no idea if the VTM has been serviced before. I read over the maintenance schedule, and I know its supposed to be changed at 15,000 mile intervals. Ive changed out the differential oil in my Ranger and Exploder before, so I am confident I can do whatever needs to be done, but Im not sure what.
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Old 06-22-2005, 07:58 AM   #6 (permalink)
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Quote:
Originally posted by jonaz
Yes, I came to a complete stop, put it in 1st gear,and pushed the VTM button. Only one front and one rear tire spun. I have tested the VTM feature on a couple of other occasions, and it did not work. I am quite familliar with rear differentials, transmissions, and gearing, and I am quite sure this thing does not work.
I bought my Pilot used, so I have no idea if the VTM has been serviced before. I read over the maintenance schedule, and I know its supposed to be changed at 15,000 mile intervals. Ive changed out the differential oil in my Ranger and Exploder before, so I am confident I can do whatever needs to be done, but Im not sure what.
I would be concerned that the rear fluid has either not been changed (usually results in noise) or has been changed with the wrong fluid.

The procedure is the same as any standard differential.

THE FLUID IS NOT!!!

It must use Honda VTM-4 Fluid. This is a specific hydraulic fluid similar (but NOT the same as) ATF. It is so picky about fluid types that some people have had problems caused by even a few drops of other fluid in the pump used to fill the differential.

Get a NEW pump!
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Old 06-22-2005, 08:05 AM   #7 (permalink)
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Quote:
Originally posted by jonaz
Yes, I came to a complete stop, put it in 1st gear,and pushed the VTM button. Only one front and one rear tire spun. I have tested the VTM feature on a couple of other occasions, and it did not work. I am quite familliar with rear differentials, transmissions, and gearing, and I am quite sure this thing does not work.
I bought my Pilot used, so I have no idea if the VTM has been serviced before. I read over the maintenance schedule, and I know its supposed to be changed at 15,000 mile intervals. Ive changed out the differential oil in my Ranger and Exploder before, so I am confident I can do whatever needs to be done, but Im not sure what.
The front differential is open, so one side will spin in loose conditions.

The rear locks through a set of computer controlled clutches. (It is not a true differential)

If you give it enough power with one (or both) wheels stuck you could get the clutches to slip and have one wheel slip. If you did this much you would wear out the clutches.

How hard did you push to get it out?
How long did you try?
How do you know only one side spun? (If you got the speedo up to 18 MPH the lock will disengage)
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Old 06-22-2005, 01:24 PM   #8 (permalink)
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Unless there is alot of noise from the diff indicative of imminent failure, I'd guess there is an electrical/electronic problem thats stopping the diff from doing its stuff rather than mechanical
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Old 06-22-2005, 01:30 PM   #9 (permalink)
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Quote:
Originally posted by rocky
Unless there is alot of noise from the diff indicative of imminent failure, I'd guess there is an electrical/electronic problem thats stopping the diff from doing its stuff rather than mechanical
Good guess, but what is someone filled it with good old 90 weight?

Bet that would lube up those clutchs and quiet the thing down real good.
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Old 06-23-2005, 08:10 AM   #10 (permalink)
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Quote:
Originally posted by N_Jay
Good guess, but what is someone filled it with good old 90 weight?
...
Yeah, everyone knows you don't put 90W oil in you Pilot's rear diff. You put it in YOUR ENGINE!!

http://www.piloteers.org/forums/show...833#post183833
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Old 06-23-2005, 08:56 AM   #11 (permalink)
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Quote:
Originally posted by krygny

Yeah, everyone knows you don't put 90W oil in you Pilot's rear diff. You put it in YOUR ENGINE!!

http://www.piloteers.org/forums/show...833#post183833
Now you have done it. Think how many are running out now to get the oil upgraded to your specs
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Old 06-23-2005, 08:58 AM   #12 (permalink)
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Quote:
Originally posted by Sunday Rider


Now you have done it. Think how many are running out now to get the oil upgraded to your specs
Does Mobile make a synthetic 90W?
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Old 06-23-2005, 07:11 PM   #13 (permalink)
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Quote:
Originally posted by jl_ss


Does Mobile (sic) make a synthetic 90W?
As a matter of fact they do!
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Old 06-29-2005, 12:09 AM   #14 (permalink)
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Took my Pilot into the dealer to have the VTM looked at. The dealer told me that there was nothing wrong with it. I explained to him very slowly, that the rear differential was not locking. He said that he didnt know what that meant, and according to his documentation, there is nothing describing the VTM system as being a locking differential. Does anybody have any documentation describing the VTM and what it is meant to do?
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Old 06-29-2005, 12:57 AM   #15 (permalink)
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Quote:
Originally posted by jonaz
Took my Pilot into the dealer to have the VTM looked at. The dealer told me that there was nothing wrong with it. I explained to him very slowly, that the rear differential was not locking. He said that he didnt know what that meant, and according to his documentation, there is nothing describing the VTM system as being a locking differential. Does anybody have any documentation describing the VTM and what it is meant to do?
Variable Torque Management 4-wheel-drive (VTM-4)

"Ensuring a high level of all-weather stability, traction and control is the Pilot's VTM-4 (Variable Torque Management 4-Wheel Drive) system. Unlike conventional on-demand systems that work only when the wheels are slipping, VTM-4 proactively delivers torque to all four wheels during acceleration for excellent dry-road vehicle dynamics as well as outstanding control in wet, icy and snow conditions. A unique "lock" feature is provided to maximize traction for extremely slippery or "stuck" conditions. A compact transfer case is bolted directly to Pilot's front-mounted transaxle. A two-piece propeller shaft delivers torque from the transfer case to a rear axle drive unit. Two computer-controlled, electromagnetically-powered clutches engage as needed to provide torque to the rear wheels."

"The Pilot's innovative VTM-4 four-wheel drive system was designed to deliver outstanding traction, stability and control in all weather conditions as well as good medium-duty off-road performance. It was also designed to minimize the weight and packaging penalties associated with conventional four-wheel drive systems.

The VTM-4 system is unique in its operation. Unlike many competitive systems that use an engagement strategy triggered by wheel slippage, VTM-4 anticipates the need for all-wheel drive and engages the rear wheels whenever the vehicle is accelerating. Additional torque is applied to the rear wheels when wheel slip is detected, up to an approximate maximum of 50-percent in low gear. Another unique feature of the system is the VTM-4 Lock function.

Activated by a button on the instrument panel, the VTM-4 Lock mode delivers maximum torque transfer to the rear wheels to aid extraction from extremely slippery or "stuck" conditions. The feature works only when the vehicle is in first, second or reverse gears, and automatically disengages at speeds above 18 miles per hour.

When cruising under normal conditions, the Pilot provides front-wheel drive power for improved efficiency. Torque is proactively distributed to the rear wheels when the vehicle is accelerating or wheel slip is detected. The level of torque delivery, front to rear, is determined by the amount of acceleration (rate of change in velocity) and wheel slip (difference in rotational speed) and is controlled by a dedicated CPU with sensors in the braking, engine and transmission systems.

To avoid the weight and bulk of a conventional transfer case, VTM-4's torque transfer unit is a compact cast-aluminum housing bolted directly to transaxle. The transfer case is a single-speed, permanently engaged device without a low-range, reducing weight and space penalties while maintaining excellent on- and off-road capabilities. Attached to the front wheel differential's ring gear is a helical gear that provides input torque to the transfer unit. A short horizontal shaft and a hypoid gear set within the case turn the drive ninety degrees, move it to the vehicle center line and lower its axis by approximately 3.75-inches.

VTM-4 Engagement Modes:

There are three distinct modes of VTM-4 engagement:

(1) The first mode, called Acceleration Torque Control (ATC), works whenever the vehicle's throttle is depressed, even on dry pavement - a feature unique to the VTM-4 system. Sensors in the engine and transmission monitor vehicle speed and acceleration. The amount of torque applied, as directed by the system's ECU, is determined according to vehicle speed, the amount of acceleration and transmission status (gear setting). This benefits not only the Pilot's ability to gain traction from a standing start, before wheel slip occurs, but also its overall dynamic stability on both dry and slippery roads. Reducing the propulsive force carried by the front tires under acceleration reduced torque steer and cornering adhesion. Rear wheel torque rises smoothly from zero to a preset maximum in proportion to vehicle acceleration (both forward and reverse). During constant-speed driving, all power is driven to the front wheels for improved fuel efficiency.

(2) The second engagement mode occurs when wheel slip is detected. Differences in rotational speed between front and rear wheels are measured by sensors in the ABS system and monitored by the ECU. In response, the ECU commands an increase in torque delivery to the rear wheels. Torque application is adjusted according to the amount and the rate of change in wheel slip. As slip increase, more power is delivered to the rear wheels for improved traction.

(3) The third mode of engagement is VTM-4 Lock. Lock mode occurs when the driver shifts into first, second or reverse gears and depresses the VTM-Lock button on the instrument panel. When lock mode is selected at vehicle speeds below 18-mph, the system ECU commands a preset maximum amount of rear-drive torque to be delivered to the rear wheels for improved traction in very low-speed, low-traction, conditions. As control is regained and vehicle speed increases, the system gradually reduces rear axle torque until it is completely disengaged.

The maximum torque delivered to the rear wheels is sufficient to climb the steepest grade observed on any public road in America - 31-degrees (60 percent slope) - with a two-passenger load on board. The Pilot will also move from rest up a 28-degree (53 percent slope) dirt grade. On a split-friction grade (different amounts of traction at each wheel), VTM-4 automatically provides sufficient rear-wheel torque to help the vehicle climb a steep, slippery driveway to enter a garage.

Propeller Shaft:

The two-piece propeller shaft that carries torque from the transfer case to the rear-drive unit is made of high-strength steel tubing to permit a smaller diameter. Minimizing driveline dimensions improves both ground clearance and interior room. The cross yokes attached at each end by friction welding are forged steel for high strength and low weight. The center support bearing is rubber isolated to block the transmission of driveline noise from the interior of the vehicle. A low-friction plunger joint located near the center of the propeller shaft accommodates relative motion between front- and rear-mounted driveline components.

A tuned-mass damper inside the front portion of the propeller shaft cancels any bending tendency in response to powertrain vibrations. Equal-length, front-wheel half-shafts have a plunger joint at their inboard end and a ball-type universal joint at the wheel end. Rear half shafts are similar in design but use a double-offset joint at the inboard end and a ball joint at the outboard end. All universal joints are constant-velocity type.

Rear Axle Drive Unit:

The Pilot's rear axle drive unit consists of a hypoid ring-and-pinion gear set supported by a cast-aluminum housing which switches torque from the propeller shaft's longitudinal orientation to the lateral orientation necessary to drive the rear wheels.

A connection from the ring gear to each wheel's half-shaft is made by left- and right-side clutches. Each drive clutch consists of three elements: an electromagnetic coil, ball-cam device and set of 19 wet clutch plates which are similar in design to clutches used in an automatic transmission. Ten of the plates are splined (mechanically connected) to the ring gear while nine of the plates are splined to a half shaft.

When the VTM-4 system's electronic control unit (ECU) determines that torque should be distributed to the rear wheels, an electric current is sent to the two electromagnetic coils. The resulting magnetic field moves a rotating steel plate toward each fixed coil. Friction between that steel plate and an adjoining cam plate causes the cam plate to begin turning. As it does, three balls per clutch roll up curved ramps, creating an axial thrust against a clutch-engagement plate. This thrust force compresses the wet clutch plates, engaging the corresponding rear wheel.

Unlike mechanically actuated four-wheel drive systems, the VTM-4 system is infinitely variable. The amount of torque provided to the rear wheels is directly proportional to the electric current sent from the ECU and can be adjusted from zero to a preset maximum. This current constantly changes to deliver the optimum rear torque calculated by the ECU. An internal gear pump circulates VTM-4 fluid to cool and lubricate the clutches, bearings and gears within the rear drive unit. Use of high-strength, low-weight materials - such as die-cast aluminum for the housing - minimizes the bulk and weight of the hardware."
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