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> Ford Mustang Overdrive Manual Transmission, How To Choose An Overdrive Manual Transmission
post Dec 16 2010, 12:27 AM
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There Have Never Been More Choices For Classic And Late-Model Mustangs
From the December, 2010 issue of Mustang Monthly
By Jim Smart
Photography by Jim Smart

It used to be that transmission selection for classic Mustangs was simple. If you wanted a manual shift, it boiled down to the close- or wide-ratio 3.03 three-speed, Borg-Warner's easy-shifting T-10 four-speed, or the rugged and dependable Ford Top Loader four-speed box in either close- or wide-ratio. These days, it's easy to get cross-eyed with the available overdrive selections. You have a choice of at least three five-speeds and two six-speeds, plus Gear Vendors' overdrive unit, if you aren't content with a four-speed. We're going to show you how to make the best decision for your application.

Make Mine Classic
If you like the whine of first gear in your vintage four-speed, you can keep that vintage sound with a Gear Vendors overdrive for Top Loader transmissions. With a #3D6111C Gear Vendors overdrive kit, you can spline this unit into your Top Loader and get all the benefits of a good, old-fashioned four-speed along with the efficiency of overdrive. There's also a Gear Vendors overdrive kit for the 3.03 three-speed transmissions as well.

How you fill this void depends on what kind of shifting is desired for your Mustang. Remember, with transmission choice comes selecting all of the correct parts that go with it. This is Project Reclaim from Mustangs Plus and The Restomod Shop with its 331ci small-block. Our original game plan was a TKO five-speed transmission but Mustangs Plus has decided to go with a T-56 six-speed.

Gear Vendors overdrive is now available for Borg-Warner T-10 cast-iron and aluminum four-speed transmissions. Just ask for the #3D0T10R overdrive kit for 31-spline output shaft or #3D0T10P for 28-spline. The only difference is the number of output shaft splines.

You will have to have a custom driveshaft made for the Gear Vendor overdrive, which is available from Mustangs Plus. Outside of the shaft, the rest of the package is a no-brainer and easy to install. Gear Vendors overdrive is electronically engaged, either manually or automatically. Manually, engagement happens with the touch of a button. With Gear Vendors overdrive, you can make your four-speed an eight-speed and manually shift like drag racing great Ronnie Sox or cruise automatically into overdrive smoothly at around 40 mph.

T-5 Five-Speed
Ford Racing Performance Parts offers the World Class T-5, also known as the Upgraded Super-Duty T-5 five-speed (PN M-7003-Z), for classic and late-model Mustangs. Although not designed for the 4.6L or 5.4L Modular engines, the T-5 works with a huge range of Ford six-cylinder and V-8 engines. Believe it or not, you can bolt the T-5 to your 200ci six-cylinder if you have a '67-up engine with the larger bellhousing bolt pattern.

Ford's bulletproof Top Loader four-speed transmission has long been a favorite because it's indestructible. Mate it to a Gear Vendors overdrive and you have both durability and efficiency.

The T-5 is a rugged and dependable transmission that can take up to 350 horsepower and 310 ft-lbs of torque before you need to consider the heavier-duty Tremec TKO or 3550. In overdrive, you can expect 0.63:1, which drops engine rpm significantly. At 70 mph with 3.50:1 axle ratio, you can expect 2,000 rpm, depending upon tire size. Cruise all day and save a bunch of fuel with the World Class T-5.

Although it makes sense to buy a new World Class T-5, you have options out there if you're shopping for a used one. Introduced in the '83 Mustang at late mid-year, the T-5 has been available in a wide variety of applications since the early 1980s, including Camaro and Firebird. Those earlier T-5 transmissions had limited torque capacity, around 265 ft-lbs, which isn't saying much if you're running a healthy small-block. Yet this is what you can expect to find if you're canvassing the salvage yards because this transmission was available in the Mustang during '83-'90. When Tremec upgraded the T-5 to 310 ft-lbs of torque in 1990, it became known as the World Class T-5.

The Gear Vendors overdrive unit is lightweight and compact, ideal for a classic Mustang. Its roots are from heavy-duty recreational vehicles and off-road race cars. It is as rugged and dependable as a Ford four-speed. When you slip into overdrive, you're getting an overdrive ratio of 0.78, which means a significant improvement in cruise rpm. No special crossmember or transmission mount is required.

Tremec TKO
The Tremec TKO five-speed transmission from Ford Racing is a huge cut above the T-5 in terms of ruggedness and reliability because it is designed to take a lot of punishment. Two basic types are available - the TKO 500 can withstand 500 ft-lbs of torque where the TKO 600 will take up to 600 ft-lb. In either case, the TKO is a drop in replacement for the obsolete TR-3550. It is a bulletproof five-speed transmission designed for racing applications.

T-56 Six-Speed
Being able to say you have a six-speed is like finally sitting at the grownup's table. But do you really need a six-speed transmission in your Mustang? The Tremec T-56 family of six-speed transmissions was developed for rocket ship cars like the Chevrolet Corvette, Dodge Viper, Aston Martin DB7, and the SVT Mustang Cobra.

Here's the Gear Vendors microprocessor, which can be installed just about anywhere out of sight. This one has been installed in the glovebox for easy access, yet out of sight.

When we were planning Project Reclaim, we were thinking about a TKO five-speed, and that's what we ordered from Ford Racing. But when The Restomod Shop was doing sheetmetal work on Reclaim, they modified the transmission tunnel for a T-56 just in case there was a change of heart later on in the project. There was. When we examined the tunnel, it was concluded Reclaim might be better off with a six-speed.

The T-56 is an open-road manual transmission, meaning you have two overdrive ranges that enable you to cruise at Boeing 747 speeds. In most types of driving, you won't get past Fourth or Fifth gear. The T-56 six-speed and that six-speed shifter ball make great attention getters for cool restomods. And if you want low rpm at cruise, sixth gear is the place to be.

Here are three basic types of manual shift overdrive transmissions for classic and late-model Mustangs with sixes and small-block V-8s. From left to right: Tremec T-5 five-speed, TKO five-speed, and T-56 six-speed. No modifications are required for the T-5 and TKO transmissions aside from special aftermarket crossmembers, available from Mustangs Plus. Some minor transmission tunnel and support structure modifications are required to clear the T-56. Ron Morris Performance has a new bolt-on crossmember for the T-56, available from Mustangs Plus.

This is the Tremec World Classic T-5 from Ford Racing. It offers rugged and dependable performance and can withstand up to 310 ft-lb of torque. The T-5 has a 10-spline input and 28-spline output shaft. Aside from overall length, this makes the T-5 a perfect swap for the Top Loader. Overdrive ratio is 0.63.

The World Class T-5 calls for this M-6392-E bellhousing from Ford Racing. There's also a T-5 conversion kit with a bellhousing adaptor available from your favorite California Pony Cars dealer.

Here's the Ford Racing Tremec TKO five-speed. Expect an indestructible box that can take on 500 or 600 ft-lb of torque depending on which box you choose. You can also expect a transmission that will fit your Mustang without major modifications. It has 26-splines in and 31-splines out for rugged dependability.

Here's a TKO installed in a '65-'66 Mustang using a Ron Morris Performance kit from Mustangs Plus. The TKO clears everything just fine without major modifications.

The TKO shifter-to-tunnel indexing is perfect for classic Mustangs.

Tremec World Class T-5* Features
Short-throw shifter
310 ft-lb torque capacity
Double moly Second and Third gear countershaft cluster gears
Carbon-fiber 3-4 blocker rings
Improved synchronizers and bearings
1.0625-inch diameter 10-spline input shaft (just like classic Top Loader)
28-spline output shaft
7-tooth speedometer drive gear
Cobra-style heavy-duty pocket bearing
Steel input bearing retainer
Weight: 83 pounds
First Gear: 2.95:1
Second Gear: 1.94:1
Third Gear: 1.34:1
Fourth Gear: 1.00:1 Straight Drive
Fifth Gear: 0.63

The Tremec T-56 from Ford Racing was developed for high-end performance cars like the Corvette, Viper, and Mustang Cobra. With some transmission tunnel modification, it will fit a classic Mustang. It will also fit your Fox-body or S197 Mustang.

Why buy a new Tremec T-5 from Ford Racing? Because of what it will cost you in time and money to rebuild an existing one unless you're restoring a classic Fox-body Mustang. The beauty of a new World Class T-5 is convenience and reliability. Order one from Ford Racing or Summit Racing Equipment for under $1,400.

*For 289/302/351W/351C and '67-up 200/250ci sixes only

Boneyard T-5 Facts
1st 2nd 3rd 4th 5th**
'83-'84 Mustang: 2.95:1 1.94:1 1.34:1 1.00:1 0.72:1
'85-'89 Mustang: 3.35:1 1.93:1 1.29:1 1.00:1 0.68:1
'89-up: 3.35:1 1.99:1 1.33:1 1.00:1 0.68:1
If you're going to rebuild an older T-5 transmission, look to D&D Performance in Detroit for most of the parts you'll need for a complete rebuild. At press time, a complete T-5 rebuild kit is $189. Hard and soft parts are also available.

** Ford also offered a 0.63:1 overdrive ratio in 1983.

The T-56 has the same number of splines in and out as the classic Ford Top Loader - 10-spline in and 31-spline out.

It mandates the use of a cable clutch system, available from Modern Driveline. You can also use a hydraulic clutch system.

The Restomod Shop is going with a clutch pilot bearing for Project Reclaim T-56 six-speed. Although a pilot bushing is cheaper, the use of a bearing offers stability and longevity.

For Project Reclaim's T-56, we're using the same dust cover or separator plate you would use with the T-5 or TKO. Only minor modifications are required to adapt this plate to a T-56.

We've enjoyed great success using Centerforce Dual-Friction clutches in our project cars. The Dual Friction clutch holds tighter as engine rpm increases. This clutch disc is for a 10-spline input shaft, just like we would use with a Ford Top Loader.

It takes a couple of guys to muscle a T-56 into place. The T-56 clears a classic Mustang's transmission tunnel with slight room to spare. However, it's tight under there. The only modification required is to the tunnel reinforcement, which must be trimmed to make room for the T-56. Ron Morris Performance has a new bolt-on T-56 crossmember for classic Mustangs.

Tremec TKO Features
Higher center distance from main shaft to countershaft, which allows for larger gear sizes and greater torque capacity.
Rugged design with internal three-rail shift system that includes cast-iron shift forks.
Close ratio units available (2.87:1 and 3.27:1) for racing.
Tapered roller bearings at the input, output, and countershafts for reduced noise and operational smoothness.
All gears and shafts made of ASTM 4615 steel that can take a lot of abuse.
High-performance, short throw billet aluminum shifter that isolates road noise while giving you crisp shifts.
Neutral safety switch and backup light sensor.
Eight shifter locations available.
Electronic and mechanical speedometer locations.
Three input shafts available.
Three unique crossmember locations.
26-spline Input Shaft
31-spline Output Shaft (calls for M-4841-A driveshaft yoke)
Requires M-6392-R58 bellhousing for '79-'95 Mustang
Requires M-5059-A crossmember for '82-'93 Mustang
'79-'81 Crossmember requires modification
M-7550-T302 101/2-inch clutch disc required
One overdrive ratio available for TKO 500-0.68:1
Two overdrive ratios available for TKO 600-0.64:1 and 0.82:1
Weight: 130 lbs

Clutch cable mechanism is the same for a T-56 as it is for T-5 and TKO. You can also install a hydraulic clutch just like you would with the T-5 and TKO. Don't forget the bolt-on clutch fork dust cover.

Tremec T-56 Features
Double overdrive provides extended overdrive range.
10-Spline Input Shaft
31-Spline Output Shaft
Lightweight cast-aluminum case for reduced weight and increased strength.
Tapered roller bearings to support main and countershafts for reduced noise and smooth operation.
Needle bearings throughout for improved durability and reduced shift effort.
Advanced synchronizer technology.
Constant mesh synchronized reverse gear.
Integral clutch adaptor with front cover end-loading design for increased driveline bending strength and greater adaptability.
Multiple shifter locations.
Torque capacities ranging from 330 to 550 ft/lb.
Weight: 115-129 lbs

Shifter-to-tunnel indexing with the T-56 is perfect. The Ron Morris crossmember from Mustangs Plus doesn't straddle the factory crossmember location, but is instead set back using spacers.

Gear Ratios:
First: 2.97:1
Second: 2.07:1
Third: 1.43:1
Fourth: 1.00:1
Fifth: 0.80:1
Sixth: 0.62:1

Give It The Boot
Unless you're using a California Pony Cars' classic Mustang shifter handle on your T-5, TKO, TR-3550, or T-56, you're going to need a late-model leather shifter boot to conceal your transmission's shifter. If you're running the classic-style shifter handle, you will probably run a classic-style rubber shifter boot. In any case, we like this leather shifter boot (M-7277-A) from Ford Racing. Once installed, it makes your classic or late-model Mustang's interior look crisp and ready for action. About $81, plus shipping and handling, will put this piece on your doorstep. It can be punched or drilled to match your classic Mustang's bolt hole pattern.

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