BMW E36 X-Brace Buffer Stop

Addendum:  Before you run out and buy this inexpensive rubber stop, be sure that your x-brace has the welded bracket to take the buffer stop.  Early production x-braces do NOT have the bracket welded on. 

This "Buffer Stop" is a rectangular shaped piece of thick rubber that actually attaches to the front of the X-Brace toward the front of the car. When installed it is only a small fraction of an inch away from the engine's oil pan cooling fins. This small distance between the buffer and the cooling fins is by design to limit engine lifting and twisting.

I will "attempt" to explain it's purpose and those of you who Auto-X, Track or Drag their M3s should be most interested. This was explained to me by my BMW Technician/Mechanic that also races "Nascar Modifieds" and tests drives (for set-up purposes) some of the "Winston Cup" cars.

As he explained to me, the drive-line has a built-in BMW design of -3 degrees of "pitch" from the rear-end's pinion gear through the driveshaft to the transmission/engine under normal and common driving. When hard acceleration (high engine torque) takes place BMW wants a 0 degree MAXIMUM pitch (or perfect line-up) on this drive-line for efficient transfer of power to the pinion gear thereby producing good traction and proper "Front Bite" (for track handling).

What happens in reality is that the drive-line goes "positive" by some unknown degree during a portion of this high peak engine torque delivery period. It limits the efficiency when anything other than 0 degrees (straight-line) of pitch is produced.

It can cause the entire rear-end housing to twist, turn and jump (wheel hop). The incorrectly pitched driveshaft will attempt to "search" wildly like an object that has lost it's centrifugal force or orbit. It wants to find the perfect straight-line setup but can't due to the engine's torque throwing the pitch "positive" thus causing the rear-end's geometry to become upset. This causes the shocks and springs to react poorly which cannot adjust.

"Front Bite" is also adversely affected due to the incorrect drive-line pitch and the car's handling behavior suffers.

Keep in mind that the time period for the poor pitch condition and it's reactions to it are dependent upon various factors. Standing still starts, lower gear vs. higher gear upshifts, cornering on track, the rear-end's gearing ratio, etc. are all factors that influence it's behavior (until the engine's torque no longer causes a positive pitch but becomes a 0 degree pitch).

Whew! With all that being said, the purpose of the Buffer Stop is to eliminate this positive pitch condition. How, you ask? The Buffer Stop limits the drive-line's mis-alignment by stopping or buffering the engine from twisting and lifting (due to its torque) beyond a certain point as referenced by where the Buffer Stop is mounted on the X-Brace. It compresses against the engine's oil pan cooling fins when the torque lifts and twists the engine beyond a 0 degree pitch line-up. It can only be mounted in one spot on the X-Brace so there is no adjustment for it's placement.

There you have it. For $16.80 that little simple piece of rubber on your X-Brace will make your M3 handle better at the track or strip! I hope this has enlightened those interested. It might be the best rubber you ever bought!!!???... (Had to say it.)

Contributed by Bob ///M3.  .