| bart |
I recently picked up a 2001 MDX with 78K miles. When starting from a stand-still, or moving very slowly (< 5mph), if I accelerate hard I hear a "thunk" coming from the rear after about a half-second delay. This is accompanied by a slight jolt forward.
I believe this is the VTM-4 engaging the rear wheels to give better traction while accelerating. However, I thought the transfer of power to the rear wheels was supposed to happen more smoothly.
I had the VTM fluid replaced, and this didn't help.
Is this behavior normal? |
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| SuperTech |
Doubt this is the VTM-4. It only really kicks in when it detects slippage. And no offense, but the 2001 MDX just doesn't have enough power to really break traction unless it's wet.
Most likely causes of your noise, believe it or not...the front motor mount, a leaking rear shock, broken sway bar link, or the famous gas tank slosh noise. |
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| bart |
quote:
Doubt this is the VTM-4. It only really kicks in when it detects slippage.
"During stop-and-go driving, VTM-4 doesn't wait for front-wheel slippage to redirect engine power. Rather, it operates automatically and seamlessly, sending engine torque to computer-controlled wet clutches in the rear axle to power the rear wheels before the front tires have a chance to slip. Every time the MDX accelerates, a percentage of torque proportional to the degree of acceleration is transferred rearward."
http://tinyurl.com/y65g9f
So this is not correct? |
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| SuperTech |
There is always some torque sent to the rear wheels. But it doesn't send a lot of torque until slippage is detected. For the most part, the VTM-4 system functions pretty much like a FWD powertrain.
When I run these things through the gears when the wheels are in the air, I can produce the "thunk" from the rear differential because the front wheels began accelerating faster than the rears (slippage), so the electromagnetic clutches engaged to allow the maximum amount of torque to the rear wheels.
But you driving around your MDX on the ground...it'd be pretty hard to get the front wheels to overpower the amount of traction available and cause you to "peel out." So while there is some small amount of torque being transmitted to the rear wheels, the clutches will always be allowing some slip.
If you want to rule out the VTM-4 clutches as the cause of your noise, here's something to try. Go somewhere where you can reproduce the noise normally. Now, place the gear selector in 1. Push the VTM-4 LOCK button. Accelerate the same as you did before. Try not to make any turns since this is not good for the differential in high traction situations. If the noise is still there, the problem is not with the differential since the clutches were locked from the get go so there could be no harsh engagement. |
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