Lentech Automatics' AOD Transmissions
Lentech Automatics' Hot-Rodded Aod Is Perfect For Vintage Mustang Or Ford Restomods
From the December, 2000 issue of Modified Mustangs & Fords
Photography by Dale Amy
Like a high-tech Cupid armed with a laser-sighted crossbow, the restomod bug has taken precise aim and drilled you right between the eyeballs. The result? Your decades-old Blue Oval classic now enjoys many benefits of new-century technology. Maybe it sports a powerfully efficient, roller-cam EFI 5.0 or Windsor. Maybe it hunkers on a fully updated suspension glued to the terra firma via 16-inch Torq-Thrust IIs mounting the stickiest rubber modern technology can vulcanize.
But maybe something's missing. You watched as your manual-transmission buddies swapped out their Top Loaders in favor of highway-happy T5s, and were green with envy when this let them plug in a set of 3.91s and still get the same mileage as they used to with their 2.75:1 cogs--not to mention a huge boost in performance.
But you're an automatic kind of guy, with a C4 that's been as reliable as rocks, but admittedly could use some extra legs. Well then, how about an AOD? No way, you say? Not with that wacky 1-3-OD shift quadrant, its stumbly 2-3 shifts, and those stories of weak-kneed Third-gear actuation. OK then, how about if we told you someone had fixed all its factory shortcomings and, in the process, conjured up a high-performance AOD that can handle 700, or more, horsepower? Would that pique your interest?
Actually the company in question, Lentech Automatics, offers no less than four distinct AOD variants, the most serious of which is a three-speed-only (that's right, a non-OD AOD), manual-valvebody-and-transbrake-equipped strip specialist aimed at quarter-milers, capable of riding herd on more than 1,200 horses and handling single-digit e.t.'s. Lentech calls that one its Pro 5.0L AOD.
If that sounds a touch too much overkill for your '65 Mustang, any one of Lentech's trio of overdrive models--the Street Terminator, Street Terminator Lock Up, or Strip Terminator--might be just the ticket for the rides of most Mustang & Fords' readers, whether those rides take the form of restomod musclecars, street/strip cars, Ford-powered street rods, or even tricked-out pickups.
The one we'll look at in detail here is Lentech's $2,395 AOD Street Terminator Lock Up. This is a high-performance, strip-capable, yet street-friendly, AOD with a correct 1-2-3/OD shift pattern that allows the option of manual upshifting without resorting to the 1-Drive-1 foolishness necessary to trick a factory AOD into Second gear.
As its name suggests, it also offers a lockup power flow (in Overdrive) for maximum highway efficiency, and is wired for an electric Overdrive delete switch to toggle it out of OD when the occasion merits (as found on current computer-controlled AOD-E transmissions.) Perhaps most important of all, Lentech's Street Terminator Lock Up features a revised internal power flow that is much stronger than the factory's.
Seemingly intended to maximize fuel economy (remember, it was a design of the late '70s), that factory Third-gear power flow was responsible for most of the AOD's original weaknesses and quirks--like its tendency to bog the engine on a hard 2-3 upshift or, worse yet, burn out its 3/OD clutch pack. Both those ills can be traced back to the AOD's dual, concentric input-shaft architecture, designed to provide converter lockup not only in Overdrive but also immediately upon shifting up to Third. This was achieved not with the usual converter lockup clutch, but by splining the inner input shaft directly to the converter front cover (to the crankshaft, in effect) and using it to drive both Third and Fourth gears--through the 3/OD, or direct, clutch--at engine speed.
In contrast, the somewhat stronger outer shaft was driven hydraulically off the converter turbine, feeding First, Second, and Reverse (with converter torque multiplication) through the forward clutch. A shift from Second to Third, then, saw power suddenly transferred from the hydraulically damped outer shaft and forward clutch, to the direct-driven small-diameter inner shaft and 3/OD clutch. This tended to knock the wind out of the engine's sails, zing the direct clutch discs or, in extreme cases, even break the inner input shaft. Because of this odd power flow, Lentech's Len Bertrand tells us a stock AOD can handle 450 hp, at best, and will always be hard on 3/OD clutch packs.
Bertrand's crafty and patented solution in his Street Terminator Lock Up is to hand responsibility for Third gear over to the turbine-driven outer input shaft by making specific valvebody modifications which turn the AOD's Reverse clutch into a Reverse/Third clutch (much the same as it was on the strong old Borg-Warner FMX from which the AOD evolved). This revised power flow, together with internal modifications we'll detail in the accompanying photos, means that about 250 additional horsepower can be safely channeled through the Street Terminator Lock Up's Third gear. The icing on the cake is that Overdrive remains routed through the locked-up inner shaft, for the ultimate in highway efficiency.
Combining these features with Lentech's unprecedented one-year parts and labor warranty on all its transmissions (with two years on the converter and three on the valvebody)--whether in street or race use--provides some pretty compelling reasons for considering Ford's often-overlooked overdrive automatic. Lentech found great merit in the AOD; maybe you will too.
Lentech’s Street Terminator...
Lentech’s Street Terminator Lock Up AOD: four-speeds, crisp shifts, a 10-inch converter, a proper 1-2-3/OD shift pattern instead of the factory’s wonky 1-3-OD setup, lockup in Overdrive, and electric OD delete. Its 0.67:1 Fourth gear will drop highway rpm by 33 percent, giving your 4.30 gearset longer cruising legs than a 3.00:1 set.
A lot of Lentech’s magic is...
A lot of Lentech’s magic is worked in the valvebody, the brain of any automatic gearbox. Through a complex series of revisions, Len Bertrand and company brainwash the valvebody into directing Third-gear power flow down a much stronger route to and through the AOD’s planetary gearset. In here, they also correct the factory’s inexcusable 1-3-OD manual-shift pattern, and through the solenoid at the lower right, provide electric Overdrive delete.
Unless you opt otherwise,...
Unless you opt otherwise, your Street Terminator Lock Up will get a decisive-shifting, full-pressure (not modulated) valvebody, with operating PSI determined at time of build and tailored to your ride’s specific engine/weight/gearing combo and ultimate use. This explains why the 2-3 and 3-4 accumulators are missing from their respective bores in the corners of the case side of this valvebody. If you like, Lentech will fit a valvebody that will not automatically kick down from Overdrive under load—in other words, it will stay in Fourth even under full throttle, in case you want to run the Silver State Classic in the 170-mph class.
Like in the FMX, the AOD’s...
Like in the FMX, the AOD’s ratios come from a compound planetary gearset, having two sets of pinions mounted on a common carrier (instead of the twin carriers and common sun gear as found in the lighter-duty C4). If you have, for example, a very heavy vehicle, you may want to opt for the available wide-ratio planetary set, which bumps First gear from 2.40:1 to 2.84:1, and Second from 1.47:1 to 1.55:1. On the principle that direct drive is accomplished in a planetary gearset by locking any two members together, Lentech’s patented, Third-gear power rerouting uses the Reverse clutch to lock the reverse sun gear to the forward sun gear, all powered off the hydraulically damped outer input shaft and forward clutch (whereas the factory Third results mostly from the inner shaft and direct clutch locking the planet carrier to the forward sun gear).
Here’s the AOD’s concentric...
Here’s the AOD’s concentric input shaft setup (ignore the outermost splined shaft in the photo—it drives the tranny hydraulic pump). The inner shaft splines directly to the converter front face, and constantly drives the direct clutch at engine rpm. The outer input shaft takes power from the hydraulically driven converter turbine and sends it to the forward clutch. In the Street Terminator Lock Up’s power flow, the small shaft drives only Overdrive—generally used only for cruising—while the outer shaft has responsibility for First, Second, and Third (and Reverse).
We don’t have room to detail...
We don’t have room to detail all internal modifications, but Lentech lavishes plenty of attention on upgrading the various clutch assemblies, including the direct clutch shown here being checked for clearance after modification to fit six Raybestos high-performance friction discs (and plates) in place of the factory’s five. Likewise, the forward clutch is upgraded from five to six discs, and the four-disc reverse clutch is modified for optimal performance (the factory sometimes fitted three-disc reverse clutches).
Factory AODs have 12-inch...
Factory AODs have 12-inch converters with 1,500- to 1,600-rpm stall speed. The Street Terminator Lock Up gets a high-performance 10-inch unit from Torque Converter Specialties, featuring a forged front cover, fully furnace-brazed fins, and needle thrust bearings throughout. Lentech’s staff will confer with customers to select the appropr-iate stall speed between 2,400 and 4,000 rpm.
All Lentech AODs get a number...
All Lentech AODs get a number of internal lubrication improvements, including revisions to the pump stator and valvebody. But, because of internal oil passages in the output shaft, Len Bertrand advises one of the most important steps in assuring adequate oiling of the planetary assembly is to keep overall shaft endplay tighter than normal factory tolerance, at no more than 0.005-inch.
No Lentech AOD leaves the...
No Lentech AOD leaves the shop without being tested for mechanical and hydraulic function on the in-house tranny dyno. Even before this, the valvebody gets separately checked for line pressures and correct operation on a valvebody test bench of Lentech’s own design. If we were going to offer a 12-month transmission warranty regardless whether in street or race use, we’d put our products through this type of quality assurance too.