Which way does the motor rotate on mounts in reverse? Moving forward, motor lifts the drivers mount and compresses passenger mount, just the opposite in reverse? Trying to diagnose a shake when starting out in reverse.
The pressure will mostly be on the passenger side motor mount (that's the one that will usualy brake). The motor spins counter-clockwise (sitting from the driver's seat) so the motor is going to naturally want to roll over onto the driver's side inner fender.
You've got it. In reverse you're "stretching the right motor mount. One of my trucks has a tendency to break the passenger side motor mount when I try to back up a steep hill while loaded. 5 times so far. Never a problem in forward gears and I believe the driver's side mount is original to the the truck. Weird.
GypsyR, I'm sure you didn't mean it this way, but it almost makes it sound that the engine spins in the opposite direction in reverse You're ALWAYS stretching the passenger side motor mount, wether the car's going forward or backwards (and the reason most people will only put a torque strap on the passenger side).
Driver's side. If you unbolt the mount or have a broken driver's side mount the engine will lift on the driver's side....been there done that many, many times. That is why you see the Torque straps used on the driver's side only.
Dunno, might have something to do with reverse being geared lower or something. All I really know for sure is the mount always breaks when I'm reversing, even lightly loaded.
Contrast this to stopping on a hill with a loaded car trailer behind it. Never a problem.
Though the engine always rotates in the same direction, the force transmitted to the driveshaft, rear end, and then the chassis is reversed when backing up.
This is how I see it. The reciprocating mass internal to the engine tends to press down on the passenger mount when the car is sitting still and engine reved. The motion is compounded by an order of magnitude in forward when the motor/trans is trying to spin the driveshaft and all behind it. Only when there is an oposing load does the motor build its 300, 400, 500 ft-lbs of torque really twisting the motor. However, when in reverse, spinning the driveshaft in the opposite direction easily overpowers the internal engine torque and tends to rotate the engine in the oposite direction, compressing the drivers mount. You don't see engine torque straps on the passenger side of race cars because the serious torque is there only in forward. Years ago my wifes Oldsmobile broke a mount. Never knew it when driving until one day when changing the oil, I backed the car up with the hood up and saw the motor raise about 3 inches on one side. Putting it in forward compressed the bad mount and the motor didn't move.
Equal and opposite....that's the easiest way to remember.
If you know the driver's side of the engine wants to lift going forward, then the opposite will be true when in reverse. It's how and in which direction the power is put to the ground which makes the difference.
Try observing your rear end housing when loading it in forward and reverse gear; it will be readily apparent what I am talking about.
Regarding your shaker, examine all engine mounts and the transmission mount carefully. Also, loosen and re-tighten to spec all pertinent fasteners. If any parts need to be replaced (bad mounts), replace all as a unit if none have been replaced very recently. A failing mount can precipitate cascade stress on the other parts, depending on how the vehicle is operated.
Johnpro likely was tired after a long day or had another sleepless night with his friends with badges and guns *G*