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Transmission Rebuild & Upgrade - Gearing Up

A properly built transmission is just as important as a built engine.

Big Mike
Mar 27, 2014

When it comes to motor vehicles, the term "powertrain" refers to the group of components that generates power and delivers it to the road. Oftentimes, the portion of the powertrain that is most focused on is the part that generates the power—the engine. Consequently, the most important aspect of the part that delivers the power to the road—the transmission—goes untouched.

The task of rebuilding a transmission can come across as daunting, as even the most experienced techs who have countless motor builds under their belts may find the innards of a transmission intimidating. Cracking open the housing of a transmission, you expose the numerous intricacies comprised of gears, synchros, bearings, shafts, etc. that work harmoniously to transfer the power generated in the engine to the ground where we need it.

When rebuilding a transmission, it’s always great to upgrade or use new parts. For bearings, OEM Honda parts can’t be beat, and a Gear-X final driveline set and a Wavetrac LSD are must-haves for better performance.

Knowledge through experience is an invaluable asset to have, and when it comes to the inner workings of a Honda transmission, only a few can claim to be experts. H&A Transmissions, Inc. was started in 1992 as a remanufacturer focused specifically on Honda and Acura transmissions, providing services not just for dealerships throughout the country but for smaller, independent repair specialists and DIYers, as well. In 2003, a sister company by the name of GearSpeed was established to handle the aftermarket side, and that's why we chose to work with them to build our Honda transmission.

Transmission upgrade and rebuild GearSpeed technician 05 Photo 5/12   |  
Rebuilding a transmission is no easy task. That’s why it’s best to leave it to the professionals such as GearSpeed.

The specific transmission we used is a Honda Prelude M2A4 transmission. For enthusiasts utilizing or looking in to utilizing the H-series powerplant for their project, most Prelude transmissions are commonly shunned due to the long gearing and lack of a limited-slip differential, two things that are definitely not ideal when it comes to getting from one point to the other in the least amount of time as possible, a goal that any enthusiast—from drag racers to road course racers and anyone in between—are looking to achieve. Although there are some OEM JDM transmission options that provide more optimal specs, they can be hard to come by and pricey. These aspects of OE Prelude transmissions have contributed greatly to the emergence of the popular H2B kits that adapt an H-series motor to a B-series transmission, and even H2D kits that allow for the usage of D-series transmissions. These options have their varying pros and cons but are only viable for those putting the H-series powerplant in a Civic or Integra chassis, not for those with a Prelude or Accord chassis.

Transmission upgrade and rebuild OEM honda open differntial 06 Photo 6/12   |   Transmission Rebuild & Upgrade - Gearing Up
Transmission upgrade and rebuild wavetrac LSD 07 Photo 7/12   |  
Here’s a good look at the OEM Honda open differential versus the Wavetrac LSD that will help reduce wheelhop and improve traction by putting power down evenly to both wheels.

This transmission was built specifically to address the "cons" of the OE-spec transmission, namely the relatively long gearing and the stock differential. For the former, we turned to Gear-X, the driveline-specific company under Special Projects Motorsports. Gear-X provides final drives as well as custom and close-gear ratio sets for numerous Honda/Acura transmissions. By having a longer final drive, you effectively make the gears shorter, and shorter gears make the car go faster, so we utilized the Gear-X 4.64 final drive for the Prelude transmission versus the stock Honda 4.266. For the differential, we turned to Autotech Driveline, which produces the well-known Wavetrac Differentials. By having a differential of this type, you get quicker acceleration and faster cornering because you have power being sent to both drive wheels rather than just one. Additionally, the patented Wavetrac design differs from other helical gear differentials on the market as it increases grip in low-traction situations and does not lose drive when one axle is unloaded—an invaluable characteristic for track enthusiasts.

Transmission upgrade and rebuild bearing tool 08 Photo 8/12   |  
Most DIY mechanics won’t have a lot of the special tools that are needed to remove and reinstall bearings. Using other methods is a risky endeavor we recommend against.
Transmission upgrade and rebuild steam cleaning 09 Photo 9/12   |  
The guys over at GearSpeed put time and effort into the little things like steam cleaning the casing and parts to ensure everything is free of debris and crud that can mess up the rebuild very quickly.

We won't go into the nitty-gritty of the install since it's best left to the experts, but the before and after results are definitely worth mentioning. The new final drive and presence of an LSD have changed the way the car performs so much that it feels like a completely different animal. The shortened gearset keeps the engine in a much more ideal rpm, with First and Second gear disappearing in a way that could only make us smile. The Wavetrac LSD sends the power to both wheels, eliminating the infamous "peglegging" we experienced before. Now the Prelude surges forward with much more apparent traction. Another advantage of the LSD is the reduced wheelspin during launches, and the nasty wheelhop is all but gone.

We're just getting used to the Gear-X final drive and Wavetrac LSD, but we already know it's a killer combination any Honda racing enthusiast will find beneficial in more ways than one. It's greatly enhanced the driving experience, both in normal road and freeway conditions as well as in a track setting. So as tempting as it may be to just keep adding power to your engine, maybe it's time to allocate some of those resources for a properly built transmission. You won't regret it.

Transmission upgrade and rebuild final assembly 10 Photo 10/12   |  
Taking apart a transmission is the easy part; putting it back together properly is hard. Experience pays off here.
Transmission upgrade and rebuild final check 11 Photo 11/12   |   Transmission Rebuild & Upgrade - Gearing Up
Transmission upgrade and rebuild reinstall 12 Photo 12/12   |  
After final assembly, everything is checked over before it’s installed back into the car.
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