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Tremec Overdrive Transmission - Full-Size Gear-Jammin'

We Show You How To Hit The Highway With A Tremec Overdrive In A Classic Impala.

Mike Harrington Aug 8, 2007

Here's the Muncie M-22 "Rock Crusher," as it's known. Have you seen the prices these things are fetching on eBay? If you pull a Muncie out of your Impala, sell it on eBay to help fund the price of the new Tremec.

Have you ever had one of those strange dreams in which you find yourself running and getting nowhere? You struggle to make headway, but it seems no matter how much effort is spent, speed and progress are elusive. Now imagine what that must be like while driving your classic Chevy. A 427 sitting under the hood, a four-speed Muncie "Rock Crusher" under the floor, and 4.11 gears in the back. These are the most coveted parts any Bow Tie enthusiast could ever want. But on the highway, when the vehicle hits 60-70 mph, that recurring dream of running as hard as you can and getting nowhere is suddenly a reality. What would most of us do in that situation? We either mash the loud pedal a bit harder and wind out the rpm while the gear box howls like a Banshee, or we simply avoid long distance trips altogether. But why relegate your classic ride to a Saturday night malt shop cruiser?

The M-22, TH-350, and TH-400 were all great transmissions in their time, and even today are still being rebuilt and extensively used by hot rodders everywhere. However, their limitations are apparent when compared side-by-side to that of a Tremec five- or six-speed manual transmission. A Tremec transmission offers the user an overdrive gear or two that will break that high-revving rpm habit. These swaps into full-size machines are becoming more and more popular. For years, you never saw a gear-jammer in a full-size Bow Tie, but that's all changing. Now they're becoming almost as common as automatic ones.


Out with the old, in with the new. How could we resist a shot of the TKO-500 before the install?

Recently, Classic Chevy 5-Speed developed a Tremec kit that will fit 1958 through 1969 Impalas. For those who may not be familiar with Classic Chevy 5-Speed, they take a basic Tremec transmission and adapt it to fit a particular vehicle. This may sound simple enough, but when you consider shifter relocation, driveshaft length, bellhousing issues, adapters, etc., this can be a migraine for most installers.

Recently we made the trip to Classic Chevy 5-Speed to cover the install of a Tremec TKO-600 into a 1966 SS Impala equipped with a factory 427 big-block, 4.11 gears, and a Muncie 4-speed. We took the Impala on the highway before the swap and made note of a few numbers-especially the rpm. With the Muncie in fourth at 70 mph, the tachometer read 3,700 rpm. After the Tremec swap we once again traveled at 70 on the highway; this time we shifted into fifth gear overdrive on the new Tremec. Thanks to the 0.68:1 overdrive, the tachometer this time read an ear-pleasing 2,375 rpm.


Here's a side-by-side shot of the old bellhousing with the new Classic Chevy 5-Speed bellhousing that's made specifically for this kit. This Impala already had a manual transmission, but the Elite kit was used anyway. A new bellhousing, clutch, driveshaft, etc., were installed on this '66.

We also took along a decibel meter. While traveling at 65 mph, the decibels in the cab read around 88dB prior to the transmission swap. After the swap, the decibel meter read approximately 82dB while traveling the same speed, this time in 5th gear overdrive. A 6dB drop is a huge difference. A 1dB drop would be big.

What we noticed even more than the drop in decibels was the vibration factor. Traveling 65-70 mph down the highway with the engine turning around 3,700 rpm you can't help but get the residual vibration from the flywheel to the rear gears. When the Impala was shifted into overdrive it was as smooth as riding on a magic carpet. The vibration that resonated throughout the vehicle instantly dropped the moment the rpm dropped, boosting the comfort level of the occupants. Not only that, fuel economy will also improve when the engine works 32 percent less than it needs to.

Besides all this, we took the Impala out for a test run after the tranny swap. We put that big-block to work and were grabbing gears like hell wouldn't have them. The Tremec transmission is rated to handle approximately 900 hp and 500 to 600 lb-ft of torque (depending on the model), so we knew we couldn't break it during our fun runs. And yes, it passed our fun tests too.


Depending on the vehicle's original equipment, two different kits for the Impala are available: the Deluxe kit and the Elite kit. What's the difference? The Deluxe kit is an option for vehicles already equipped with a four-speed, and for those owners who want to step up to a five-speed and reuse the clutch, bellhousing, etc. The Elite kit is an option for vehicles that have an automatic and are swapping it out to the five-speed. There are also optional upgrades (clutch, third pedal, flywheel, etc.) available for either kit, so check the Classic Chevy 5-Speed website to view all the options. Pictured here is the Elite Kit. It includes:
>>New TKO-500 or TKO-600 transmission
>>New adjustable cross member (for '65-69 model years only)
>>New polyurethane transmission mount
>>Speedometer cable/adapter custom mechanical speedometer cable with integrated adapter and gear. Electric speedometer kits are also available.
>>New driveshaft. Steel driveshaft complete with premium Spicer u- joints and Spicer C6 slip yoke, custom built for your car. All driveshafts are balanced using state-of-the-art equipment. Aluminum driveshafts are also available for an additional charge.
>>Pilot bearing
>>Reproduction aluminum GM 621 bellhousing
>>Clutch kit
>>Clutch fork
>>Hurst shift knob (black or white)
>>Hurst shift stick
>>Reverse light switch connector
>>Complete hardware kit
>>Tunnel patch
>>Optional offset shifter-High performance offset shifter.
>>This direct bolt-on replacement shifter achieves perfect shift stick positioning within your stock console and requires no modifications to your console.
>>Customer Support
>> Extended warranty


This Impala had a center console, so it had to be removed. The carpet was peeled back and the shift boot was removed. Thankfully this '66 SS already had a manual transmission, so hanging the third pedal was already done


After the removal of the old Muncie, bellhousing, and clutch, the new equipment was installed next. Even though the Impala already had those pieces, we opted to install all new parts.


Once the bellhousing is installed, the Tremec transmission was lifted into place for just a minute to see exactly where the new shifter would be located. After the new shifter location was determined, we knew exactly where to cut into the floor.


Not much cutting is involved to relocate the hole for the new shifter, but it pays to check twice and cut once.


A cut-off wheel should do the job in a few minutes.


Just a few inches off the top and you can put the cutting tools away.


A few inches of the shift boot will also have to be trimmed.


This little piece of equipment is made only for The Classic Chevy SS Impala.


The transmission is temporarily installed again and the offset shifter is tightened into place.


Up top in the cab, the carpet is trimmed away in order to make room for the shifter's new position.


Here's why the new Tremec is temporarily installed. There are slight clearance issues with the top of the transmission and the tunnel in which it sits.


Fret not about the clearance issues in the trans tunnel. Grab a 5-pound hammer and create some new real estate. Draw a line where the tunnel needs to be peened out and have at it. It really is easier than it looks or sounds.


Now that the tunnel has been pounded into submission, the new TKO-500 is ready for its final install. Needless to say, all the hardware, including the new speedo cable, is provided from Classic Chevy 5-Speed. If new aftermarket gauges are being used, a VSS (Vehicle Speed Sensor) will need to be ordered at the time of purchase.


The new tubular transmission crossmember is also provided in this kit. Not shown in the photo is the transmission mount/bushing.



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