The Ultimate Transmission - In Depth Explanation

Transmissions
A. The Metric Mechanic "Ultimate Transmission" with it's Exclusive 5 Year Warranty
1. Introduction - Stating the Problem
Obviously, the only way we could give a 5-year warranty certificate would be if rather than just "rebuilding", we were actually "re-engineering" the BMW manual transmission. This is exactly the case! BMW transmissions are quite strong for the most part but they do have two weak areas:

1. Layshaft bearing failures
2. Short synchronizer life

We have re-engineered the synchronizer assembly for improved clutching action (a synchronizer is a form of a clutch) and we have greatly extended the wear limit of the synchronizer. This allows our transmission to be shifted more aggressively without the fear of premature synchronizer failure. To cure layshaft bearing failures, we've substituted tapered roller bearings for the ball and/or flat roller bearings used in new and rebuilt gear boxes. Tapered roller bearings are the absolute best bearing to compliment the Ultimate Transmission philosophy. When a layshaft bearing fails it can become quite serious. The bearing can come apart and quickly destroy the transmission. Synchronizer failures make the transmission miserable to shift. In solving these two problems we have produced a very strong long lasting transmission.

History
The Ultimate Transmission was born in 1979 out of our autocrossing experience. We were a three to four man racing team involved in approximately 25 races per season over a 5 year period. In the beginning, our transmissions lasted an average of 2 to 3 races before the synchronizes would crunch. Yes, we were shifting extremely hard. We decided NOT to give up on our shifting style but instead to FIX THE SYNCHRONIZERS so that they could take the abuse. Enter an improved BMW transmission! At the end of our autocrossing career, after 465 races, the new gearbox still wouldn't miss a gear - no matter how hard we shifted it. In 1980, we began selling the gearbox locally to other autocrossers and street drivers who also began shifting them much harder. Thanks to this "testing" we found that the new demands now imposed on the gearbox eventually led to premature layshaft bearing failure. So, two years later, we found a FIX FOR THE BEARINGS as well. Enter the "Ultimate Transmission" with redesigned synchronizers for improved shifting and tapered roller bearings to support the layshaft!

Layshaft Bearings
Layshaft load occurs in both the radial (across the shaft) and axial (along the shaft) planes. The OEM ball bearing has a moderate load rating but most of its load capacity is in the radial plane. The roller bearing used in later model transmissions is stronger, but also only in the radial plane; it is not designed to accept axial loads. The tapered roller bearing, as used in the Metric Mechanic Ultimate Transmission, can accept virtually equal radial and axial loads. The critical benefit of the tapered roller bearing is its high load rating. The BMW transmission case imposes a tight limit on the size of bearings and tapered roller bearings are much stronger than a comparably sized roller or ball bearing. The only drawback to tapered roller bearings is that they are slightly noisier than ball bearings. However, it would seem to be a small consolation to its obvious superiority.
The reason for the tremendous durability of the Ultimate Transmission is the 3000 lb. margin for safety provided by the use of tapered roller layshaft bearings.

Synchronizer Life Span
The illustration shows a BMW synchronizer and figure B shows small teeth on the inside of the synchronizer ring. These small teeth form the clutching surface between the synchronizer and the gear cone. As the small teeth wear, the gear takes longer to match the synchronizer speed, resulting in progressively slower shifts. Normally the BMW synchronizer is considered worn out when the teeth are worn down more than nine ten thousandths of an inch (0.0009"). With the Ultimate Transmission, this wear limit has been extended to 45 ten thousandths of an inch (0.0045") as illustrated in figure C. These measurements correspond to .031" & .001" respectively, measured from the base of the synchro to the top of the gear. Since the tooth form becomes wider as it wears, the rate of wear decreased geometrically. In other words, by allowing five times the amount of wear, we allow twenty-five times the amount of wear area. This increases the clutching action of the synchronizer to enable very quick up and down shifts, even under racing conditions, without the need to pause between gears.

Synchronizer warpage and rocking
The factory method for determining whether a synchronizer is still usable or not is if the air gap between the bottom of the ring and the base of the gear cone is greater than .031" (usable) or less (not usable). This method will tell you if a synchro is worn out but it will not tell you if it is a good one. Eighty-five to ninety percent of the synchros we see would pass the factory test, and yet none of them work. They fail because they warp to such a degree that they no longer match the tapered cone on the gear and therefore no longer grip the gear cone well enough to stop the gear. Often, new synchros rock on the gear cone even though they obviously conform to factory specs.
The synchros we use are matched individually to each gear cone to alleviate warpage and a series of machining procedures are used to increase their effectiveness and longevity.

Blueprinting the Ultimate Transmission
There is considerably more to what makes an "Ultimate Transmission" than the simple substitution of superior Metric Mechanic parts for factory synchronizers and bearings. So much so that a transmission rebuilt in this fashion would not last. Even two gearboxes of the same model and same year can be quite different, not only with respect to how they shift but also as to the actual dimensions of their parts. Therefore, each gearbox should be "set up" to its own particular specifications to insure that it performs at its individual best.

Bearings and their Shimming
JUST AS NO TWO TRANSMISSIONS PERFORM OR "FEEL" THE SAME, NEITHER SHOULD THEY ALL BE SHIMMED ALIKE.
Bearings and Their Shimming
Given the above, it would stand to reason that each transmission must necessarily be assembled and shimmed according to the exact dimensions of the parts involved. In theory this is what is prescribed in the factory procedures, but in actuality, this is not what is done. As different as they are, these gearboxes are assembled with a "standard" set of shims, each varying only slightly from set to set and certainly not according to the variations of the individual groups of transmission components. Excessive end play (.020" to 025") is always found in the shimming of the layshaft as well as .005" to .010" at the input shaft plus an unnecessary amount of distance between the input and output shafts. Even the output shaft bearing is, in most instances, not precisely captured.

The set-up method we use is as follows:
To insure the ideal positional relationship among the input, output and layshafts, all shaft bearings are totally captured, allowing for no end play.
Specifically - the output shaft bearing shim is chosen so that all clearances are removed guaranteeing that...

1. the output shaft cannot change position relative to the housing and...
2. The bearing itself cannot "free-spin" in its saddle

- the tapered-roller layshaft bearings are machined to fit the individual housing to capture the layshaft and preload (.0015" to .002") it to insure stability at operating temperature.
- the input shaft is positioned closer (usually .040" to .060") to the output shaft for a clearance of .008" to .010", and then the input bearing is precisely captured in its saddle to maintain this clearance.

Gearboxes

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.

The "Ultimate" 5-speed Transmission Conversion
One of the most popular 'updates' for all BMW models with 4-speeds, as well as any model with an automatic, is the conversion to an overdrive 5-speed or a close-ratio 5-speed transmission. The BMW overdrive 5-speed will slow the engine speed down about 20%, giving you better engine life and fuel mileage. It also gives the driver a more relaxed feeling when driving at highway speeds because of the reduced engine noise of a slower turning engine. A 5-speed conversion has the effect of updating and modernizing a BMW. Since such a transmission was not an option until 1980, most of the parts in each model's respective conversion kit are fabricated or otherwise modified by us to fit the application. This means that not only are the kits comprehensive (including related hardware), but we have taken special care to "work the bugs out” to insure a hassle-free, "bolt-in" operation.

We have 5 speed conversion kits available for all BMW models with 4 speed transmissions. The following is a description of the parts necessary to convert a 2002 with a 4-speed to a 5-speed overdrive transmission.

1. The 5-Speed Transmission Conversion Kit for 2002
2. The 5-speed overdrive "Ultimate Transmission"
   is the only gearbox warrantied for 5 years, with no mileage restrictions. It includes tapered roller bearings on the layshaft as well as "solid brass" synchronizers for trouble free performance. NOTE: The price of the transmission is outright, i.e., with no core exchange. See CREDITS for core exchange options.
3. A special four bolt flange
   is necessary for the 5-speed to properly mate with your four-bolt driveshaft flange.
4. A Reverse Gear Synchronizer
   is optional on all '83 and later models. Although not a necessity, it is still a very convenient accessory for avoiding the "grinding" that sometimes occurs when shifting into reverse gear. Although no gear tooth damage can occur, your 5-speed could get ever more difficult to shift into reverse if grinding is severe and frequent enough.
5. The Shift Linkage Assembly
   has been re-engineered to a shorter, simpler and more efficient design. (This was necessary due to the additional length of the 5-speed transmission.) Most importantly, by using the late style shifter, extension rod and coupling we can incorporate our Short Shift Kit which results in a more distinct and tighter shift pattern.
6. Changing the Clutch Slave Cylinder
   is necessary because BMW 5-speeds use a late model clutch slave cylinder with a 2-bolt mounting system. You will have to change the remaining hardware and parts of the hydraulics to accommodate the 5 speed. This allows you to use your same pressure plate and disc. The advantage to this modification is that these later style parts are more easily serviced, readily available (some are used in the newest BMW's) and are still compatible with the remaining hydraulic system.
7. A Shortened Driveshaft
   is necessary because of the increased length of the 5-speed transmission. Most of our conversion kits include a good used driveshaft that has been (1) carefully inspected for sound universal joints and undamaged front flanges, (2) shortened and balanced and (3) fitted with a new center support bearing, front coupling and front alignment bushing. You do have the option of ordering a factory new driveshaft (versus "used") that we will gladly shorten and balance.
8. A Transmission Crossmember
   must be fabricated to provide some sort of rear support for the transmission. Of all the procedures needed to perform the 4 to 5 speed conversion, none is a greater headache than this fabrication. Inevitably this involves traumatizing the underbody either by drilling holes, cutting, welding or some other kind of reshaping. However, Metric Mechanic has devised an innovative type of mount bracket that BMW themselves would envy. With this crossmember you not only get to make use of the stock mounting points, but in addition this cylindrical style mount is structurally superior to any BMW mounts.
9. There are Options to offset some of the cost of this conversion:

• 5-speed core - our core charge is high for two reasons. First, because so many 2002 owners want to convert, 5 speed cores are increasingly hard to find. Second, the prospect of reducing costs by so much will hopefully encourage those purchasing this conversion kit to locate a 5-speed core in their area. Any BMW 5-speed core from any model, '80 and later (USA) and '77 and later (EURO), will qualify.
• 4-speed core - If the 4-speed transmission you are replacing is “rebuildable" (see Question and Answer Section), it is worth additional reductions in the overall price.
• 4-speed driveshaft - as long as your driveshaft is still in one piece it has value to us and would therefore be worth returning.
  

Background
Prime Directive - getting from point A to point B as quickly as possible. The basic variables in the "quickest - time" equation are:

• engine size (horsepower)
• vehicle weight
• gearing
• driver's ability.

Gearing
as a variable, has always had the narrowest of ranges for two reasons. First, with respect to differential options, the number of readily available ratios is four; 3.45, 3.64, 3.90 and 4.11. Although 3.64 is most common, most racers prefer at least the 3.90 (also the most common limited-slip ratio) and often even the 4.11. Even though tire diameters vary somewhat, most drivers are limited to basically two choices.
Furthermore, as far as transmissions are concerned, gearing really is a constant in the "quickest - time" equation. With the exception of a minor ratio change from 3.8 to 3.7 for first gear and an insignificant one of 2.05 to 2.02 for second gear in late '78 and '79 320i's, all four speed gear ratios are the same. The only gearing alternative from the factory was the 5-speed close ratio transmission. This was a European option that offered five gear selections between the normal range of the stock four. This is totally different from the "overdrive" 5-speed that has become standard equipment on all '80 and later models.

The distinct advantage of a close ratio gearbox is that there is less rpm drop between gears, which keeps the engine in closer proximity of its peak horsepower range. Theoretically, if you can avoid dropping out of the engine's power band you're maximizing horsepower to the rear wheels, which translates into quicker track times.

The disadvantage to the close ratio 5 speed is that you still have another gear to shift through which does cost some time, besides being an inconvenience. The rationale is that there is still a net gain. There is more time lost when the engine rpm falls further from peak horsepower as with the stock 4-speed, than the time lost by making an extra shift. In addition, even though 1st gear is somewhat taller (3.4), by using the preferable 3.90 or 4.11 differentials, you have effectively returned 1st gear to "stump - puller" status which renders it nearly useless. And finally, if you are lucky enough (or wealthy enough?) to acquire a close ratio 5 speed in good working order, you are still faced with the cost of the additional parts and labor needed to make the conversion (usually over $3000.00). Some classes prohibit the use of anything but a 4-speed anyway, which eliminates any 5-speed transmission as an option.

At the Present Time
Given the above situation, what the vast majority of racers ultimately do is resign themselves to a stock 4-speed gearbox but have two or more differentials to choose from. This strategy takes the most advantage of their engine's power range, depending upon whether they are road racing or autocrossing and according to whether the particular course is basically “slow" or "fast". Even though a "slow" course calls for a "shorter" (higher ratio) differential and a "fast" course needs a "taller" (lower ratio) one, all courses have characteristics of both types in them, therefore the challenge.

An Alternative
In answer to this dilemma, a new racing transmission has been developed that incorporates the advantages of the 5-speed close ratio (the closeness of the gearing) and the convenience of the 4-speed (no complicated conversion necessary).

The Logic Behind The 44LCR and 64CR Competition Gearboxes
Let's face it, a 3.8 ratio first gear is all but worthless for a road racer and has debatable value for an autocross driver. We all know that even a stock 2002 or 320i can barely get through an intersection before you feel the need to shift into 2nd. The lower (higher ratio) first gear is the wider the proportional distance between the remaining gears, since fourth gear is, by design, necessarily 1 to 1.

The greater the distance between 1st/2nd, 2nd/3rd and 3rd/4th, the further away from its horsepower peak the engine is and the longer it takes to work its way back into its power band after each shift. However, by raising first gear to a ratio (3.0) approximately halfway between first and second in a 5-speed close ratio (3.4/2.2) you have a much more useful gear. It can take you up over 40 miles per hour (see shift charts). Even as tall as 3.0 it is still a shorter first gear than any BMW automatic transmission (2.83). At this point, we have narrowed the total shift range by nearly a whole number (1.0-3.8=2.8 compared to 1.0-3.0=2.0). As it turns out, third gear ratio is best left in the stock position due to what we want to accomplish with second gear.

In competitive situations that occur in both road racing and autocrossing, the two shifts that will be of greatest benefit will be the ones from second to third and third to second. A ratio of 1.6 was chosen because it allows second to be as close to third as possible and yet no further away from the new first position than it is in the stock 4-speed. What the 44LCR/64CR evolve into is second, third and fourth gears closely resembling third, fourth and fifth, respectively and first gear being a compromise (but actually more useful) between first and second in the close ratio 5-speed (see above chart).

Applications
Because of their unique combination of gear ratios, the 44LCR and 64CR Gearboxes offer distinct advantages for competitive drivers.

Let's say, hypothetically, that you're on the track approaching a turn that you want to take at 55 mph. Let's also assume the following; your engine's power band is between 4,000 and 7200 rpm, your rear end ratio is 3.90 and you're still using a stock 4-speed. First, you know that you are going to have to slow all the way down to nearly 55 to downshift into second because setting up at even 60 will rev the engine to nearly 7000. And even at 60, your rpms in third are below 4500, so there's little time to be made by staying in third, at the bottom of your power band. So, you decide to downshift into second after you have entered the turn. Just before you're coming out, with the revs already at 6300, you have to shift again on reaching 7200, only 7 or 8 mph away!

If by chance you are using the new 44LCR Racebox, you could downshift into second well before the turn, let's say at 70 mph, (8,000 rpm with the stock gearbox but only 6350 now), and by the time you have slowed to 60 for the turn, your rpm is well placed into the lower-middle of your power band instead of nearly at the top end. Furthermore, you need not shift until you are well out of the turn at 80 mph (7200 rpm), instead of 63 mph (7200 mph, stock ratio 2nd).

The same reasoning applies in road racing and autocrossing for an advantageous upshift from second to third. With the same car as above, for instance, you might have a straight-away that you would like to be doing 70 mph on, but you're in second (stock 2.0) and are already at 7200 rpm. Upshifting now into third would drop the rpm all the way to 4600, just barely into the bottom of your range. However, if you are in the 44LCR's second (1.6), you are already in the middle of your peak horsepower and you can run all the way to 80 mph if you so desire.

Another special advantage for the autocrosser is the ability to run some of the "tighter" courses entirely in first gear! Because of its unique ratio (3.0), you have the advantage of taking the tightest turns in a gear that's tall enough to still reach 45 mph (see charts), which thereby eliminates the need to waste time shifting.

Testing
Prototype 44LCR and 64CR Gearboxes have already been in the field in road racing, autocrossing and even street applications for more than three years. As a matter of record, at the Tulsa BMW Oktoberfest (1987) autocross event, Lee Terry and Margo Potheau won first place trophies in 2002’s fitted with this transmission. Also, a road racer in Ohio informs us he has been consistently placing either first or second with the help of the 44LCR.

Conclusion
In the true spirit of the Metric Mechanic's philosophy of promoting creative ideas and mechanical innovations, comes the first gearing alternative for competitive driving. Beyond being simply an alternative, the 44LCR and 64CR Competition Gearboxes offer solutions to racing situations by providing a competitive "edge" in a particular area previously not addressed.

Metric Mechanic's Bronze Bushing Short Shift Kits
Our "BRONZE BUSHING SHIFT KITS" consist of couplings and lower shift levers with silicone and bronze bushings machined to a precise fit to the shift rod extension. Made of the same material as BMW valve guides, our bushings have several times the life expectancy of the nylon replacements. Also, in these kits we include the two rubber bushings that will remove any "play" between the upper and lower shift levers.

Bonus! The Bronze Bushing Kit As A Short Shift Kit
All six cylinder model BMW's (and 318's) have a very long "throw" - the distance the shift knob travels from one gear to another - that is cumbersome and quite unnecessary. Because of the particular lower shift lever we use in our kits, the throw is shortened 40%, without changing the stock height of the upper shift lever and knob. This change further clarifies the "H" pattern which enhances the fun and responsiveness of shifting.

Even the throw of a 2002 shifter is shortened by 15% by using our kit, which leaves only the 320i's unchanged.

Option
If in addition to a shorter "throw", you would also like a shorter upper lever (i.e. the shift knob height reduced by 25 - 30 mm), then order the "short shift" kit with short lever. This kit will also include the "push on" style shift knob.

More Transmission Info

• Getrag Identification Chart
• 4 Cylinder Transmissions (Getrag) & Gear Charts
• 6 Cylinder Transmissions (Getrag) & Gear Charts
• Ultimate Transmission Series - Individual Descriptions (part 1)
• Ultimate Transmission Series - Individual Descriptions (part 2)
• Ultimate Transmission Series - Individual Descriptions (part 3)
• Metric Mechanic Specialty Transmissions