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Four Speeds, up to '80 (all models)
From the beginning BMW transmissions have acquired the reputation for
having 'weak' synchronizers and premature bearing failures. By concentrating
our rebuilding efforts on theses two problems, we have discovered the
machining techniques and design changes needed to produce transmissions
that are as strong and dependable as they can possibly be. Each synchronizer
is machined to each individual gear cone for the most precise fit. This
insures that each synchro works at its highest level of efficiency,
allowing the driver to shift as often and as quickly as he/she desires,
with confidence that the gearbox will shift gracefully for years.
The fitting of tapered roller bearings to the layshaft of the 4 speeds
is necessary to prevent the normal load that the engine applies to the
gearbox from destroying the stock ball bearings. With their superior
load rating capacity, tapered roller bearings are the absolute best
bearing to compliment the Ultimate Transmission philosophy
Early 5 speeds, '80 - '82 (all models)
With the introduction of the 5 speed overdrive transmission, also came
the latest "innovation" in shifting - the 'Moly' synchronizer
instead of using a tapered brass machined saw tooth clutching surface.
These new synchros rely solely on the high friction property of the
abrasive, molybdenum coating rubbing against a smooth tapered cone.
Although they perform acceptably at first, after a few thousand miles,
the high points of the coating wear down as well as gather material
from the tapered gear cone itself, and very quickly this once, rough
surface becomes glazed over and slippery. This can happen with aggressive
driving (especially in the M cars) as quickly as 12,000 miles. If pampered
and coaxed into gear, moly synchros can last 40,000 to 60,000 miles.
Because of their inferiority, we do not use 'Moly' synchros. Instead,
we use the all-brass, machine tapered tooth synchro, each of which is
individually fit to each gear cone for as close to an exact match as
possible. The reasoning behind spending this extra time is simple. The
inherent weaknesses of a transmission should not 'cramp your style',
rather, you the driver should be able to shift in the manner that best
suits you, whether it is aggressively, gingerly or a combination of
both.
Models (83 & Later)
The continued use of the "moly" synchros and the introduction
of the aluminum shift forks, found in all '83 and later model BMW's,
easily sum up the worst transmission "improvements" to date.
With increasing frequency we are repairing gearboxes with as few as
18,000 miles because of "grinding" between shifts (usually
involving 3rd gear). We find shift forks already worn to the point of
popping out of gear.
The necessity to replace the aluminum shift forks is obvious. We do
this with a bronze fork cast especially for us. This restores the durability
of the forks as well as the solid feel of gear engagement during quick
shifting that was characteristic of the earlier transmissions. Although
we could still do the same machining that we do to all the pre '83 gearboxes
to increase the working ability and longevity of the all brass synchronizers,
we were stuck with these "moly" synchros because of their
dimension changes. Re-tooling for all brass ones was inevitable.
The changes mentioned below represent an important breakthrough for
all '83 and later BMW (Getrag) transmissions. Contrary to what one would
expect, the newest ones are not the best. Until now, these gearboxes
have been decidedly inferior to their forerunners, at least with respect
to performance and longevity. Now, however, we can confidently assert
that these transmissions can be transformed into the strongest and most
dependable to date.
MM Machine Synchronizers
The "Moly" synchronizers fail to clutch properly because of
glazing problems, mismatched inside tapers, low wear clearance and excessive
movement between shift hub and cone. Using brass synchronizer blanks,
Metric Mechanic custom fits each synchronizer to its gear cone to eliminate
synchronizer rock. These new tooth type synchronizers with cone matched
tapers, greater wear clearance and minimal shift hub-to-cone freeplay
offer a more smooth, positive shift, and long life.
MM Silicon Bronze Shift Forks
The superior wear characteristics of silicon bronze make this substance
an excellent choice for our recast replacement shift forks. Unlike the
short-lived, soft, flexible factory aluminum shift forks, ours restore
the sureness of precise, brisk movements from gear to gear. This is
accomplished not only by virtue of the material alone, but also by the
fact that our shift forks are machined to closer tolerances than the
factory to eliminate one of several areas within the transmission involving
excessive clearances. |
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