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No More Slushbox- Auto to Manual Tranny Swap

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Modern muscle cars all seem to have one thing in common- automatic. Everything is either available at a push of a button, twist of a knob, or pull of a lever. It has all become so simple and lazy, which for some of us takes the fun out of driving. However, let’s face it; most of today’s drivers want the automatic features. Well count me out, that’s why we decided to swap out of lazy, boring, and power-consuming slush box for a Cobra T45 trans in our 1998 GT.

While swapping from an auto is not the most common swap, it certainly has its advantages. Better fuel economy for one, which is more important then ever with gas prices. Not only does your wallet feel the impact, so will seat of your pants, as a typical automatic transmission eats up 15% to 20% of the flywheel horsepower, not good if you want to go faster. Since Ford produces manual-shifted Mustangs, the swap is relatively easy, once you know what parts you need.

The trick here is research. We began our swap with a T45 out of a 98 Cobra. We found the car in a salvage yard, paid $500 bucks for the trans, driveshaft, pedals, and wiring harness. We looked on the internet to talk with people who had already performed the swap. Each one we found said the same thing- you have build a new crossmember for the tranny.

Armed with this information, we put the car on four jack stands and started pulling bolts. With the old slush box out, we replaced the flexplate with a new flywheel, clutch and pressure plate unit from Centerforce. Then the tranny slid right in and bolted up to the engine. With the trans supported by a jack, we examined the old crossmember and mounting points. Here is where things take turn. As it happens, the automatic and manual transmissions share a crossmember. The manual, however, mounts about 6 inches to the rear of the automatic. The automatic crossmember bolts to a set of welded brackets on the body. While everyone we spoke to about this swap told us you have to build a new crossmember, it is actually much simpler. The manual crossmember mounts are bolt in pieces, as most of the Mustangs produced were automatics. We made a quick run to the salvage yard where we purchased our tranny, and 4 bolts later, had our mounts. For those of you that don’t have access to the whole car, Ford still sells the mounts for a scant $35 each. Once the manual mounts were bolted in, the tranny was set down onto the crossmember and bolted up.

Another kink in our swap came when trying to bolt up the old GT X-pipe. The automatic tranny is 6 inches shorter then the T45. This extra 6 inches lands right in the middle of the X portion of the pipe. We could have taken the car to a muffler shop and had some modifications made to the original X-pipe, but by the time we paid for it, we could have just bought a new one, so we did. We used a BBK Cobra\GT Cat-less X-pipe to complete the swap. This is a direct replacement for the original piece and adds 17-23 hp alone.

The pedals and clutch cable installation were straightforward and easy, because this is a cable-operated clutch and not a hydraulic unit. The cable is self-adjusting to boot, so it’s super easy. The wiring was just as easy. The automatic harness unplugs and the manual harness plugs in. We used our Sniper Special Forces tuning software to tell the computer that it is now a manually-shifted car, although that part is not required to do the swap. In the event that you don’t have the manual harness, you can still start and drive the car by unbolting the shift-position box on the driver side of the transmission, plug it back in, and zip-tie it to the car, not the best solution, but it works.

Once everything was buttoned up, we took it for a spin. Talk about a night and day difference. Before, the car was sluggish, unresponsive, and just plain boring, but with the new stick, the car came alive. Of course, the 20 extra ponies from the new X-pipe helped, and off-the-line performance and high-speed passing capability increased several times over. With all the parts on hand, the swap can be completed in a day. The Mustang is much more fun to drive and certainly not automatic.

1.To begin the swap, the old X-pipe, driveshaft, and wiring connections were removed. Then, with the trans supported with a jack, the crossmember was un bolted and removed. Keep the crossmember it is needed later.

1. To begin the swap, the old X-pipe, driveshaft, and wiring connections were removed. Then, with the trans supported with a jack, the crossmember was un bolted and removed. Keep the crossmember it is needed later.

2.The bellhousing is unbolted from the engine. Most of the bolts are easy to get to, but the upper passenger side bolt is a nightmare. We used 5 long extensions and a universal joint to get it out.

2. The bellhousing is unbolted from the engine. Most of the bolts are easy to get to, but the upper passenger side bolt is a nightmare. We used 5 long extensions and a universal joint to get it out.

3.The trans slid right out. Note the black box on the side of the transmission- this is the gear position switch. If you don’t have a manual wiring harness, you will need to unbolt this piece and zip-tie it to the chassis in order to start the car.

3. The trans slid right out. Note the black box on the side of the transmission- this is the gear position switch. If you don’t have a manual wiring harness, you will need to unbolt this piece and zip-tie it to the chassis in order to start the car.

4.The Centerforce clutch pack and flywheel bolted right up. If you purchase the unit as a balanced kit (the pressure plate and flywheel would be shipped bolted together), a mark needs to be placed on the pressure plate and flywheel, notating the proper alignment.

4. The Centerforce clutch pack and flywheel bolted right up. If you purchase the unit as a balanced kit (the pressure plate and flywheel would be shipped bolted together), a mark needs to be placed on the pressure plate and flywheel, notating the proper alignment.

5.The auto shifter unbolts from the top, underneath the console. The hole left in the floor is the used by the manual trans shifter.

5. The auto shifter unbolts from the top, underneath the console. The hole left in the floor is the used by the manual trans shifter.

6.The T45 bolts right up without a hitch. Those upper bolts are easier to get to as well.

6. The T45 bolts right up without a hitch. Those upper bolts are easier to get to as well.

7.The shifter pops through the hole in the floor without any trimming. We swapped out the stock shifter with a Ripper from B&M. The console does not have to come out, we pulled it for easy access.

7. The shifter pops through the hole in the floor without any trimming. We swapped out the stock shifter with a Ripper from B&M. The console does not have to come out, we pulled it for easy access.

8.The manual trans crossmember mounts bolt to the chassis using a pair of pre-punched holes about 6 inches behind the auto mounts.

8. The manual trans crossmember mounts bolt to the chassis using a pair of pre-punched holes about 6 inches behind the auto mounts.

9.The old crossmember center section was then bolted to the new mounts using the old hardware.

9. The old crossmember center section was then bolted to the new mounts using the old hardware.

10.The T45 was set down on the crossmember and bolted in.

10. The T45 was set down on the crossmember and bolted in.

11.The transmission wiring harness is located at the rear of the passenger side of the engine compartment. The old harness simply unplugs and the manual harness plugs in and drops down to the tranny.

11. The transmission wiring harness is located at the rear of the passenger side of the engine compartment. The old harness simply unplugs and the manual harness plugs in and drops down to the tranny.

12.Everything plugs in, including the speedometer.

12. Everything plugs in, including the speedometer.

13.The old GT X-pipe doesn’t work with the Cobra stick, so a new BBK X-pipe was used. This piece is advertised to yield 17-23 horse alone, not bad for a 5 minute swap. We opted for the cat-less unit, which still has 2 O2 sensor bungs to keep the computer happy.

13. The old GT X-pipe doesn’t work with the Cobra stick, so a new BBK X-pipe was used. This piece is advertised to yield 17-23 horse alone, not bad for a 5 minute swap. We opted for the cat-less unit, which still has 2 O2 sensor bungs to keep the computer happy.

14.The pedals were held in with 5 bolts. There are 4 on the firewall and 1 at the top. The brake light switch just pops off.

14. The pedals were held in with 5 bolts. There are 4 on the firewall and 1 at the top. The brake light switch just pops off.

15.The clutch cable is fed through the firewall in the stock location.

15. The clutch cable is fed through the firewall in the stock location.

16.The new clutch\brake pedal assembly bolts right up. The clutch cable is self-adjusting, so just hook it up to the pedals and trans and press it down. All done.

16. The new clutch\brake pedal assembly bolts right up. The clutch cable is self-adjusting, so just hook it up to the pedals and trans and press it down. All done.

17.The console was reinstalled and the boot placed over the shifter handle. The B&M Ripper really makes a difference in the feel of each shift, you can really bang the hell out of it. Too much fun! That’s it, no more sloppy automatic shifts. Just don’t drop the clutch too much, cops seem to have a sixth sense about that sort of thing.

17. The console was reinstalled and the boot placed over the shifter handle. The B&M Ripper really makes a difference in the feel of each shift, you can really bang the hell out of it. Too much fun! That’s it, no more sloppy automatic shifts. Just don’t drop the clutch too much, cops seem to have a sixth sense about that sort of thing.

About Jefferson Bryant (205 Articles)
A life-long gearhead, Street Tech Magazine founder and editor Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 5 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced. You can follow Jefferson on Facebook (Jefferson Bryant), Twitter (71Buickfreak), and YouTube (RedDirtRodz).

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