For the 1986 and a half model Fiero GM made a change to the automatic transmission mounts of the 4 cylinder cars

Broken crutches stink

For the 1986 and a half model Fiero GM made a change to the automatic transmission mounts of the 4 cylinder cars. GM also changed the design of the Torque Reaction Strut, or "Dog Bone." These changes have resulted in several problems.

The single transmission mount places ALL torque loads on the strut. The old dual mounts provided considerable torque damping even before adding the strut.
The engine is held vertical only by the strut in the new mounting layout. Without the strut the engine will simply flop against either the trunk wall or the exhaust.
The new design strut is softer than the old design. The new type strut will likely fail within 15-20,000 miles. The older type will last longer but still isn't strong enough for this application.
Neither strut design was intended to take the amount of load that the new transmission mount placement places on it. The new type strut will easily allow 2" of engine motion. The old type allows less but still more than is tolerable. This amount of motion can result in damage to both the intake and exhaust systems.

WARNING: When working on the torque reaction strut the car MUST have the wheels blocked and the parking brake on. Put the transmission in neutral to unload the strut. Make sure the engine is supported before removing the strut to prevent loading of the intake or exhaust systems. DO NOT EVER operate or move the car without the strut. Attention to this warning is critical in 86.5 and up Fiero with automatic transmission. You can be seriously injured if you get pinched between the engine and body. You can damage intake and/or exhaust parts by allowing the motor to load against them.

As we can see in the drawing above, the old mounting setup can easily support the motor even without the strut. (The mounts are red. The mount under the motor is not shown.) In the new setup the motor has nothing but the strut to hold it vertical even when not running.

The old mounts provide torque damping because the mass of the motor and transmission must try to climb out of the valley created between the mounts. So when the car is moving forward the engine is trying to climb onto of the rear mount, and stretch the front one. The strut is loading as well but only receives full loads under hard acceleration or braking. The strut is also a backup device should the one of the mounts fail.

The new single mount places both the transmission mount and the engine mount near centered with the crank. (The transmission mount is slightly aft of the crank.) If you take out the strut there is nothing at all to hold the motor up. Even at rest the motor will want to flop over in whatever direction gravity is pulling it. The strut receives nearly the entire torque load of acceleration and braking.

To make matters worse, most of the cars with the new mount got the new, softer, torque reaction strut. At first look these struts appear to use a solid cylindrical bushing in each end but they don't. The bushing is shaped like 2 cones facing each other, and the strut loops are actually oval shaped. When heavily loaded the cones spread away from the center and try to leave the loop of the strut. This heavy loading wears the cones rapidly making the strut even weaker. This strut simply was not made for the amount of load the single transmission mount places upon it.

When you put the new mount with the new strut it is common for top of the engine to have between 1 and 3 inches of travel depending on the condition of the strut bushings. This is a really bad thing. This large motion will focus very large loads on the exhaust resulting in broken exhaust manifolds and cracked pipes. Such large motions will likely allow the air cleaner to contact the trunk wall with considerable force. This can literally tear the TBI unit off the intake manifold, as the air cleaner bolts are also the TBI mounting bolts. At the very least you will likely loosen the TBI unit enough to cause leakage at the base.

Another problem with this setup is the potential for the engine to oscillate at certain speeds and loads. This results in the feeling that someone is tapping the brakes or bumping the back of the car. If the oscillation is bad enough you may also hear or feel the engine banging the trunk wall and/or the exhaust as it rocks for and aft on it's lower mounts.

These problems need to be corrected quickly when detected. Continued operation under these conditions can wreck anything and everything connected to the engine. You can break the exhaust, coolant lines, AC system, intake, and other things. Anything that is connected between the engine and frame is easy to damage when the motor moves more than it should. (This part is true of all failed torque reaction struts. NEVER drive any car with the strut or it’s hardware disconnected or damaged.)

There are 2 ways to fix this situation. The first is to replace the strut or at least its bushings with polyurethane bushings. This will limit engine movement and eliminate oscillation. The other is to retrofit the older dual transmission mounts. This is more time consuming than difficult. Of the 2 solutions, the first is easiest, and likely least expensive. The retrofit however is the stronger of the two and also allows access to the side cover on the transmission.

Note: Polyurethane bushings are only available for the old style strut. The new style strut will have to be replaced with either an old style strut with poly bushings or an after market strut such as “the Ultimate Dog Bone”. After market struts cost a few dollars more than OE ones. Using an old style strut with black polyurethane bushings retains a stock look yet gives improved stiffness to the strut. Polly bushings in the strut will increase vibration transmitted to the body of the car.

(Note: pictures below will be added when I get time. That could be awhile.)

Pic 1. Old style strut with one original bushing and disassembled polyurethane bushing.

Pic 2. New style strut shown with original bushings, one installed and one removed viewed from top. This strut is not polyurethane compatible.

Pic 3. Installed view of old style strut with new polyurethane bushings. (87 4 cyl.)