Horse Sense:
Though we normally think of all automatic transmissions as being of planetary-gear architecture, some manufacturers use a hydraulically controlled, manual-type countershaft arrangement.
The brain of the Street Terminator...
The brain of the Street Terminator Plus is its Lentech-reengineered valvebody with a proper 1-2-3/OD manual upshift progression instead of the factory's version that skips Second altogether. For this particular tranny's nonlocking, higher-stall converter, Lentech is installing the most aggressive of the three available Street Terminator valvebody calibrations. As do all ST 'bodies, it remains pressure modulated (as opposed to having fixed line pressure), it offers fully automatic or manual shifting, and it works with an electric OD lockout switch, similar to an AODE. The variable line pressure "window" has been narrowed by raising the minimum allowable pressure to make it less susceptible to failures caused by misadjusted throttle-valve cables. One other important feature is the elimina-tion of the factory's 2-3 upshift pressure cutback. Maintaining the same pressure scheme as in a 1-2 shift helps the tranny deal with elevated torque levels.
During the past few years, Lentech Automatics has become practically synonymous with high-performance AOD and AODE transmissions, and boss Len Bertrand is showing no signs of letting up on his goal of overdrive supremacy. Racers themselves, the crew at Lentech seemingly have an AOD or AODE for every power level-from subtle to psycho and for street and/or strip. One of Lentech's more recent AOD offerings is the Street Terminator Plus, a 700hp-capable, street-happy combination that struck Senior Tech Editor Mark Houlahan as the perfect downstream companion to the 347 stroker in his '90 hatchback.
New readers may be questioning why anyone would want an AOD, a transmission that in factory form suffered a bonehead 1-3-OD shift quadrant that inexcusably left Second gear out of the manual-shift scheme. This clearly nonperformance-oriented setup forced people wanting to manually upshift to whack the lever from First up to Third and then immediately back down again-a highly inefficient process that occasionally found Second but, as a side effect, caused all manner of grief within the gearbox.
As with all Lentech transmissions,...
As with all Lentech transmissions, Senior Tech Editor Mark Houlahan's Street Terminator Plus AOD is tested for shift characteristics and overall operation on the company's homebuilt tranny dyno before shipment. Now that this crisp-shifting, terrier-tough auto is bolted up behind the 347 in Mark's '90 hatchback, our resident Unhappy Buddha is a changed man, almost serene with contentment. Note we said almost.
More grief resulted from the factory's dual concentric input shaft configuration, whereby a hollow outer shaft was splined to the torque converter turbine and drove First, Second, and Reverse with converter torque multiplication, while a comparatively scrawny inner shaft was splined directly to the converter front cover (in effect, the crankshaft) and drove both Third (Drive) and Overdrive in perpetual lockup. A hard upshift into Third commonly bogged the engine when going from that torque-multiplied Second into locked-up Drive and-worse yet-tended to burn out the 3/OD (direct) clutch pack or band, or in extreme cases, even break the inner input shaft.
Well, forget all that stuff, because Mr. Bertrand has engineered changes either within the transmission itself or in the serpentine passages of its valvebody hydraulic brain. These changes morph the AOD from a factory weakling into a brawny and efficient automatic offering quick, precise shifts and the ability to shrug off outrageous power levels. We've documented a number of Lentech's improvements in previous articles, and racers have successfully proven their effectiveness in various drag classes.
In place of the 12-inch converter...
In place of the 12-inch converter used in the regular Street Terminator, the Plus gets a high-performance 9.5-inch unit with a billet steel front cover, needle thrust bearings throughout, and fully furnace-brazed fins. Lentech custom-tailors converter specs to the customer's application. For mostly street use with Mark's combo-347 stroker with heads, intake, cam, and 3.73 gears-a unit with 2,800-stall speed was chosen.
As with all Lentech AODs, the Street Terminator Plus benefits from valvebody revisions that provide a correct 1-2-3/OD manual shift pattern for those times when you want to shift for yourself, and that correct factory line-pressure deficiencies. Similar to its newer AODE brothers, it also has an electric Overdrive delete switch, so you can lock OD out when desired. Many of you may be familiar with the features of Lentech's original Street Terminator AOD. Two major changes differentiate the Street Terminator Plus. First is the substitution of a 9.5-inch converter in place of the regular Terminator's 12-inch unit, and second is the fitting of a hardened, one-piece input shaft instead of stock-style concentric shafts. Together, these changes raise the Plus' power-handling capacity from the Terminator's 400 flywheel horsepower to 700.
Len's staff will work with customers to determine the appropriate con-verter properties for their particular applications.
If there's anyone on the planet more committed to AOD and AODE performance and durability than Len-tech, we don't know who it is. Len never fails to impress us with his genuine enthusiasm for the street and strip potential of these underappreciated automatics, and his company stands behind its transmissions with a limited lifetime warranty. Bring on those power adders!
Though his naturally aspirated...
Though his naturally aspirated stroker's current 450hp output really doesn't merit it, Mark chose to upgrade the $2,795 Street Terminator Plus with a $349 Stage 2 input shaft and direct clutch drum option that replaces the Plus' already beefy, one-piece shaft with one of larger diameter-you know, just in case he accidentally engages that nitrous system.
With the Stage 2 option, the...
With the Stage 2 option, the input shaft's inboard (direct clutch drum) end is upsized to 26-spline diameter (right) from the factory's 23. By our measurements, this equates to a bump up from 19 mm to about 21 mm, and Engineering 101 says that a small increase in shaft diameter provides a large increase in torsional strength. More specifically, the strength of a shaft goes up as a square function of its radius.
The Stage 2 direct clutch...
The Stage 2 direct clutch drum is on the left and is responsible for driving both Third and Overdrive ratios. It features a new billet-steel hub welded in place and splined to receive the 26-spline input shaft. For comparison, the OEM drum on the right uses an investment-cast powdered metal hub in a 23-spline dimension.
One other option Mark went...
One other option Mark went with is the wide-OD-band upgrade. This includes a 2-inch wide Overdrive band (and matching Reverse clutch drum) in place of the usual 1.5-inch version, as well as the ratcheting diode sprag, with spiral lock ring kit (shown in the foreground), instead of the factory's spring-and-roller, one-way clutch. Len suggests this option may not be necessary in many applications, but it is essential if you're going to be running lots of power through Overdrive, as in sustained high-speed runs. The best bet is to discuss your application with Lentech to see if it's worthwhile in your particular case. Then again, at only $199, it's a fairly inexpensive upgrade.
As part of the high-performance-seal...
As part of the high-performance-seal kit used in every Lentech tranny, Teflon sealing rings are used in place of the factory's cast metal rings on the pump stator. The two pointed out with arrows are for the Reverse clutch, and two more are not yet installed at the top for the forward clutch. The Teflon rings prevent grooving or scoring of the clutch drums under higher line pressure. The large metallic ring on the back face of the pump is the intermediate band piston. An automatic lives or dies by its hydraulics, which are responsible for converter and shift operation, overall lubrication, and cooling. Lentech always changes the front bushing on the oil pump as well as various other bushings throughout the transmission whose clearances are essential in maintaining proper fluid pressures. A restrictor ball and spring are removed from the pump stator to increase fluid volume.
The AOD's three clutch drums-forward,...
The AOD's three clutch drums-forward, direct, and reverse (shown)-each contain alternating steel (externally splined) and friction (internally splined) plate clutch packs. When commanded by the valve body, hydraulic pressure pushes a piston within the drum against these clutches, locking together whatever they are internally and externally splined to.