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727 TorqueFlite rebuild Tips and Tricks

727 TorqueFlite rebuild Tips and Tricks 727 TorqueFlite rebuild Tips and Tricks

The good ol’slush box. Late model transmissions, particularly automatics, have advanced way beyond the years of the two-speed Powerglide, in fact there are now 8-speed automatic transmissions that provide a deep first gear with close-ratios and dual overdrives, all of which help the makers achieve the ever-increasing MPG requirements. While these modern equivalents are impressive, many of these transmissions are based on decades-old designs. Take the 727 Torqueflite, considered by many to be one of the most dependable automatics ever built. While it has not been built for 30 years, the overdrive used in most new MOPAR offerings is based on the same design, and even share many internal components.

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We recently went through an early ‘70s 727 transmission. Building a transmission is not for the faint of heart. Transmissions require specialty tools and are unlike anything else in a car. You should not attempt to rebuild an automatic transmission using a 4-page magazine article; you need a real tech book that is dedicated to that particular transmission. There are 4 major designs on 727, most of the internals are the same, but there were changes along the way that require specific parts and setting for that year range of transmission. We set out to show you a few of the tips and tricks for building a high-horsepower 727 transmission. Some of these you don’t even have to get inside the case to perform, you can upgrade your trans from under the car.

There are several areas that are critical to survival for a street\strip transmission- convertor, clutches, steels, bands, servos and valve body. There are other components, but this is where the power gets transferred from the engine to the driveline.

Convertor- The torque convertor is spec’d by the engine and not the transmission. The convertor needs to match the camshaft and gearing of the car. For our 727 (which will sit behind a 600-hp 383 Mopar), we picked up a Street Fighter convertor from TCI. This should provide a 3000-stall, which will put the engine right in the middle of its power band.

Clutches- There are several levels of clutches, determined by their color. Blondes are light-duty clutches. This is what you would find in a stock transmission and stock rebuild kits. Don’t use these, they do not have the holding power you need. Moving up the chain are high-energy clutches, Red Eagles, and Raybestos Blue Line. These clutches provide increasing levels of holding power and are made of Kevlar\metallic blends. Most of the time, Red Eagle clutches are good for just about anything, but monster power needs the Blue Line clutch, which has the most hold of them all. Our rebuild kit came with blondes, but we swapped those out with some Alto hi-energy clutches.

Steels- between each clutch (there are several clutches in each pack), rests a steel plate. This is essentially the flywheel to each clutch. With use, these see a lot of heat and eventually they warp and glaze over. There are two main types of steels- stock and Kolene. A Kolene steel is an otherwise stock steel plate that has been treated with a salt bath nitriding process. This increases the nitrogen content in the metal, giving it better wear and fatigue resistance to the tune of 200-500% over standard steel. If you have the option, pick up a set of these, they are better.

Bands- Just like the clutches, the bands are made from different materials. Kevlar\metal blends offer the best holding power of all. For our 727, we went with an overseas Kevlar band because they are just as good as the Raybestos brand, but less costly. For Ford and GM trannys, stick with the Raybestos, the overseas versions just don’t hold up as well for some reason.

Servos- The forward and reverse servos in the 727 are particular weak points. This is what applies the forward and rear bands inside the transmission. If these break, you lose the ability to drive, which happens a lot on these transmissions. It is the single biggest weak spot on this transmission. We upgraded our servos with a set of billet servos from our local Transtar transmission component supplier. The forward servo increases holding power by 11% and comes with a heavy duty strut band. The reverse servo simplifies the application and eliminates the breakage issue.

Valve body- The stock valve body is more than capable of handling its job in a performance transmission, but it needs some tweaks. The brains of the transmission, this is the part that controls the shift points. Part of our TCI master rebuild kit is a shift kit, which allows us the modify the shift patterns, firming up the shifts and tightening the shift timing. Unlike GM and Ford shift kits, this one requires you modify the valve body itself, so be careful.

We spent an entire day rebuilding the 727 in a transmission shop. We took our 727 to a professional transmission builder; this is the best way to go. You need to research your shops though, as most tranny shops only build stock units, you need to get references for local builders of high-performance transmissions, a stock tranny just won’t hold up to 500+ horsepower.

The 727 is considered to be the best automatic of the era, these things are near-bullet proof, but they can always be better.

The 727 is considered to be the best automatic of the era, these things are near-bullet proof, but they can always be better.

Before you start building, make sure it will fit your motor. There are two bellhousings- big block and small block. The big block pattern measures 6.5” apart at the top two holes, the small-block pattern is actually wider than that. Make sure you check this.

Before you start building, make sure it will fit your motor. There are two bellhousings- big block and small block. The big block pattern measures 6.5” apart at the top two holes, the small-block pattern is actually wider than that. Make sure you check this.

When building a transmission, clean, clean, clean.  If it is even a little dirty, it can wreck the whole build. Most tranny shops will use a high-heat washer like this to clean all the parts.

When building a transmission, clean, clean, clean. If it is even a little dirty, it can wreck the whole build. Most tranny shops will use a high-heat washer like this to clean all the parts.

The clutch on the left is a blonde, it is good for stock builds only. The clutch on the right is an Alto Hi-Energy clutch, which has significantly more holding power. You can see the metallic content in the hi-energy clutch.

The clutch on the left is a blonde, it is good for stock builds only. The clutch on the right is an Alto Hi-Energy clutch, which has significantly more holding power. You can see the metallic content in the hi-energy clutch.

Soaking the clutches is critical when rebuilding. If you install them dry, the clutches will burn up as soon as you crank it over. The bands need to be soaked as well. This is just basic tranny fluid, nothing special.

Soaking the clutches is critical when rebuilding. If you install them dry, the clutches will burn up as soon as you crank it over. The bands need to be soaked as well. This is just basic tranny fluid, nothing special.

The old reverse band is glazed and cracked, which is no good. This is part of the consumables for the transmission. We used a new band, this is for reverse, so it is not as critical as the forward band.

The old reverse band is glazed and cracked, which is no good. This is part of the consumables for the transmission. We used a new band, this is for reverse, so it is not as critical as the forward band.

The forward band is important, all the forward motion is applied by this band. The inner band is a stock unit, the outer band is the overseas Kevlar unit that we used. This is the most popular currently being used by high-performance Mopar tranny builders.

The forward band is important, all the forward motion is applied by this band. The inner band is a stock unit, the outer band is the overseas Kevlar unit that we used. This is the most popular currently being used by high-performance Mopar tranny builders.

Once trick to get better holding power from the band is to buff the drum. This removes any glazing and gives the band a better surface to grip. Micro scratches are a good thing here, a polished drum will be too slippery.

Once trick to get better holding power from the band is to buff the drum. This removes any glazing and gives the band a better surface to grip. Micro scratches are a good thing here, a polished drum will be too slippery.

This is typical glazing on a functioning transmission. This is not bad, steels that look like this can be reused.

This is typical glazing on a functioning transmission. This is not bad, steels that look like this can be reused.

This is burned steel. The discoloration is heat tempering, and it has warped this steel, which is bad news. Don’t reuse something like this.

This is burned steel. The discoloration is heat tempering, and it has warped this steel, which is bad news. Don’t reuse something like this.

If you do reuse the stock steels, they need to be buffed off, just like the drum, to remove glazing. If the steel was heat damaged, the steel would not come back to the proper color.

If you do reuse the stock steels, they need to be buffed off, just like the drum, to remove glazing. If the steel was heat damaged, the steel would not come back to the proper color.

Another sore spot for the 727 is the planetary assembly gear. This is made of aluminum, which can strip out under high-horsepower applications. Only the diesel versions use a steel planetary, so if you can find one, grab it.

Another sore spot for the 727 is the planetary assembly gear. This is made of aluminum, which can strip out under high-horsepower applications. Only the diesel versions use a steel planetary, so if you can find one, grab it.

Rebuilding a transmission requires specialty tools that can be rather expensive for the casual builder. This compressor was built by the tranny shop, and is actually more versatile than the factory-built tools.

Rebuilding a transmission requires specialty tools that can be rather expensive for the casual builder. This compressor was built by the tranny shop, and is actually more versatile than the factory-built tools.

The billet forward servo simplifies the factory design. The factory unit has a spring-loaded plunger to actuate the band, the billet unit is a solid piece that slides in a sleeve. This eliminates binding and breakage, along with increasing the holding power.

The billet forward servo simplifies the factory design. The factory unit has a spring-loaded plunger to actuate the band, the billet unit is a solid piece that slides in a sleeve. This eliminates binding and breakage, along with increasing the holding power.

The sleeve installs on the servo and then the assembly in installed into the bore in the transmission. This is one of the best upgrades you can make on a 727. Special Thanks to Wes Bene and Raymond Cabat at Transtar in Oklahoma City for getting these to us in a rush.

The sleeve installs on the servo and then the assembly in installed into the bore in the transmission. This is one of the best upgrades you can make on a 727. Special Thanks to Wes Bene and Raymond Cabat at Transtar in Oklahoma City for getting these to us in a rush.

The reverse servo does not do anything for performance, but it does eliminate the breakage often found in reverse gear. Instead of a flimsy piston, the billet servo is much larger, supporting the piston in the bore. If you lose reverse all of a sudden in a 727, the stock servo is likely the culprit.

The reverse servo does not do anything for performance, but it does eliminate the breakage often found in reverse gear. Instead of a flimsy piston, the billet servo is much larger, supporting the piston in the bore. If you lose reverse all of a sudden in a 727, the stock servo is likely the culprit.

Assembly lube is a must. NEVER install transmission components dry, the tranny fluid does not get circulated through the transmission at first start up, a dry install is a dead tranny.

Assembly lube is a must. NEVER install transmission components dry, the tranny fluid does not get circulated through the transmission at first start up, a dry install is a dead tranny.

We had to use three feeler gauges to compress the reverse servo support ring. It kept getting caught in the snap-ring groove.

We had to use three feeler gauges to compress the reverse servo support ring. It kept getting caught in the snap-ring groove.

You need to test the movement of the servos by applying a little compressed air in this port. The piston should move smoothly in the bore. Both forward and reverse servos can be installed under the car, you don’t have to rebuild the tranny to make these improvements

You need to test the movement of the servos by applying a little compressed air in this port. The piston should move smoothly in the bore. Both forward and reverse servos can be installed under the car, you don’t have to rebuild the tranny to make these improvements

The heavy duty band strut for the forward servo is on top, the stocker is below. This is the bar that applies the band to the drum. Any flex here will mean more slippage and less power to the wheels and more heat in the band.

The heavy duty band strut for the forward servo is on top, the stocker is below. This is the bar that applies the band to the drum. Any flex here will mean more slippage and less power to the wheels and more heat in the band.

The strut installs between the servo actuator arm and band. You can see how the stock strut can flex under pressure.

The strut installs between the servo actuator arm and band. You can see how the stock strut can flex under pressure.

The shift kit requires removing the wall of a passage in the valve body with a drill bit. The bit needs to be marked at 3\8” from the tip.

The shift kit requires removing the wall of a passage in the valve body with a drill bit. The bit needs to be marked at 3\8” from the tip.

The  using the supplied guide, the valve body is drilled. You have to be really careful here, as going too far will result in a ruined valve body.

The using the supplied guide, the valve body is drilled. You have to be really careful here, as going too far will result in a ruined valve body.

You need to remove as much of the wall as possible. Make sure you clean out all of the shavings.

You need to remove as much of the wall as possible. Make sure you clean out all of the shavings.

Next, the separator plate is drilled in several locations with supplied drill bits. You have to pay attention, the pictures in the instructions were a little blurred. These mods will improve shift timing and firmness. You can make these mods without tearing down the tranny as well.

Next, the separator plate is drilled in several locations with supplied drill bits. You have to pay attention, the pictures in the instructions were a little blurred. These mods will improve shift timing and firmness. You can make these mods without tearing down the tranny as well.

About Jefferson Bryant (201 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).

14 Comments on 727 TorqueFlite rebuild Tips and Tricks

  1. William gaddy // October 5, 2015 at 7:11 pm // Reply

    I growed up around cars, my grandfather’s shop , two uncle’s were racer’s I rebuilt lawn mower engine when I was 8, I’ve been a gear head all my 46 yrs .rebuilt ,ford,chevy,mopar engines,, i never tried a automatic transmission, but I think is time ,,,

    • Jefferson Bryant // October 6, 2015 at 11:56 am // Reply

      We enjoy shifting gears on our own also, but there are some advantages with having an automatic. Autos aren’t all bad.

  2. William gaddy // October 6, 2015 at 5:45 pm // Reply

    I’ve always heard automatic transmission was hard to rebuild and also mystical can’t be that hard ,,die hard mopar fan

  3. Mike Gieser // May 21, 2016 at 12:18 pm // Reply

    Just turn the reverse servo at a slight angle to get below the snap ring groove, push the seal against the wall with the piston; it will slide right in without a feeler gauge.

  4. I’m glad you mentioned using only the type of clutch that will meet your needs. Like you mentioned, blondes are simply stock so they will not be good for an upgrade clutch. Evaluating your project and determining how much holding power you need will help you decide which clutch is the best for your transmission.

  5. Johnny maples // September 30, 2016 at 9:02 am // Reply

    Can you use 1978 servos in a 1964 torqueflite
    727

  6. Hi jfferson did you have video for rebuild transmission can we buy it

  7. Did you have video for transmission rebuild can we buy

  8. Johnny maples // October 14, 2016 at 12:41 pm // Reply

    Looking for the kit and tools needed drill bits
    Templates .
    To convert a 1964 torqueflite valve body to
    a full manual valve body

  9. Johnny maples // November 5, 2016 at 6:26 pm // Reply

    Looking for a kit for a 1964 torqueflite
    To change valve body to a full manual
    Shift .
    Transmission is out of a 1964 New Yorker
    413 big block.

  10. Johnny maples // November 5, 2016 at 6:29 pm // Reply

    Need manual valve body kit 1964 torqueflite
    727 big block

  11. Johnny maples // November 5, 2016 at 6:33 pm // Reply

    Also need diagram and instructions on valve
    Body change over to manual

  12. I’m 61been a mopar nut since 70 when I brought my Challenger that I still have, been though many 4speeds about to attempt a 727 with a gear vendors od I need all the help I can get. Thanks

  13. The picture caption on the reverse servo piston not doing anything for preformace. If your are running reverse manual valve body or you sift the transmission to 1 the rear band is applied this is where the weak rear cast servo piston is prone to breaking.

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