Taking a deeper look at what goes into a Bowler Performance Transmission.
Welcome to Part 2 of our series on building the ultimate autocross automatic. Follow along as we further explain the parts and procedures incorporated into the 48 Hour Camaro's 4L75E.
The light duty GM 4-speed automatic with overdrive has been one of the most popular transmissions of all time. It started out as the infamous 700-R4 and has evolved into the now 4L75-E transmission. These transmissions offer great performance in a small package that fits really well in many hot rod applications. The other huge advantage is that they were available during all the engine changes that GM has made over the last 30 years, so it is easy to adapt one onto any generation of GM V8 engine. They have also gained enough popularity for being such a great performing transmission that there are plenty options for adapters to mount this series of transmission behind many other non-GM brand engines. Although these transmissions have proven themselves to be extremely reliable they are not without their faults and weaknesses. The later model versions have been upgraded to handle the increased power of the LS series of engines, but with many of the older 700-R4s and early 4L60E versions, the lack of big power capability offers some room for upgrades.
During our time building these transmissions we’ve found that the stock 700-R4 and 4L60E tops out at about 375 ft./lbs. of engine torque capacity. This is perfect for a 190hp V8 engine, but as soon as you start adding on performance parts, especially on a Big Block engine, you can quickly exceed that and start running into problems with clutch slippage and broken internals. We’ve worked through enough of these transmissions to know where the weaknesses are and have put together a couple different performance upgrade packages to allow these transmissions to hold all the way up to 550 ft./lbs. of engine torque reliably and consistently. We are well aware that there are other transmission companies out there claiming that their 700-R4 or 4L60E will hold up to 1000 ft./lbs. of torque, and yes it may hold up for a little while, but it won’t be long before you find the weak spot. If you're building a project that is going to be putting out 550 or more foot pounds of torque you really need to consider going with the 4L80E series of transmissions instead. Those units are much better suited for big torque and what we will recommend.
Another point we would like to address is the difference between a rebuilt transmission and a re-manufactured unit. Typically a rebuilt unit is just the basics, new clutches, seals, and bearings. Rebuilt transmissions almost always re-use as many of the original parts as possible to keep the costs down so that they are an appealing option. A rebuilt transmission likely hasn’t been tested on a dyno, and probably doesn’t carry much of a warranty if it has one at all. A re-manufactured transmission is what we build here at Bowler Performance. A re-manufactured transmission more than likely only re-uses the original case and a few of the major internal components only if they meet a certain criteria. The end goal with a re-manufactured transmission is to build a unit that is just as strong as it was brand new, or better, depending on how it will be used. Many of the items we have listed below are over looked and ignored by the budget re-builders due to the extra time and cost associated with the parts and procedures. Those $800 rebuilds may get you going again for a little while, but if you want a transmission that is going to hold up to years of high horsepower abuse it is worth your time and money to invest in a quality re-manufactured unit that is purpose built for the way you drive and the type of engine you will be using.
Out with the old! The parts above are all removed to make room for the new components we install for our re-manufactured units.
In with the new! Only the highest quality components are selected for all our transmissions.
Below we will go through the different parts we upgrade and why we feel these upgrades are key to creating a stronger transmission.
Throughout the entire assembly process all clearances are checked and double checked for precise fitment.
Input Drum Reinforcement - The input drum assembly is known to crack where the input shaft is pressed into it (where the overrun piston rides). We install a hardened steel sleeve that reinforces the input drum to prevent this failure. Our input drum reinforcement upgrade includes a custom manufactured overrun piston designed for use only with a stamped steel forward piston, eliminating the need to use aluminum forward pistons.
Heavy Duty Input Shaft and Housing - Limitations of the GM 4L60 series OE input housing are the root cause of 3-4 burnup in performance applications. The weak OE backing plate flexes during clutch apply, allowing heat to build up unevenly within the clutch pack’s limited space. Stop the flex and you stop 3-4 clutch failure. The heavy duty housing design makes room for a taller clutch pack anchored in place by a stronger backing plate, making it the only way to increase clutch capacity and protect against destructive heat. Numerous other improvements to the housing ensure maximum durability and protection against failure in higher horsepower, higher pressure applications.
Heavy Duty Reaction shell - A chronic problem with both OE and thicker aftermarket shells is failure of the rear planetary bearing. The replacement reaction shell we use avoids the weight found in traditional, heavy-duty aftermarket shells due to a unique combination of improved design and manufacturing for a super strength shell that's only slightly bulkier than OE. To prevent thrust loads from overwhelming the captured planetary bearing, the heavy duty reaction shell features a larger bearing and custom roller clutch race. These parts re-route thrust loads through the carrier, completely bypassing the delicate bearing. This change stops spline stripping, prevents hub breakage, and eliminates planetary bearing failure.
4th Gear Super Hold Servo - The 4th gear super hold servo gives us 40% more apply surface area for greater holding power. Vehicles with these transmissions often exhibit poor 3-4 shift quality and experience band failure in performance applications. We combine this servo kit with an improved 2nd gear servo kit for unmatched holding power and shift performance.
2nd Gear “Corvette” Ratio Servo - The 2nd gear "Corvette" ratio servo provides increased apply area resulting in improved holding power for firmer 1-2 and 3-4 shifts. The servo piston features D-rings in place of the OE seal rings for improved sealing during apply and release.
Wide Reaction Sun Gear Bushing - The wide reaction sun gear bushing is one-and-a-half times the width of the OE version and fills the entire sun gear bushing groove. This wider bushing maximizes support, provides better control of lube oil, offers more support for the sun gear and reaction shell, and has a longer life span than the OE bushing. The bushing is steel-backed bronze that is precision machined to provide minimal clearance with the mating shaft.
Heavy Duty Output shaft - Output shaft failure is common as power levels are increased. The heavy duty output shaft is precision engineered and manufactured for unbeatable performance in high-horsepower street and strip builds. Built from a high-strength, specially heat-treated 300M steel alloy with rolled splines for maximum performance. The shaft features many unique refinements including a torsional design that allows energy to be absorbed, reducing peak loads to critical areas.
Oversized Pressure Regulator Valve - A worn OE pressure regulator valve can be detected in two ways. The first is a dynamometer test that reveals low line pressure during boost conditions. The second is vehicle symptoms such as clutch slippage, reverse chatter and 3-4 clutch failure. Any of the above problems indicate bore wear that should be addressed. The oversized pressure regulator valve permits pump covers to be restored to OE specifications by correcting for wear and leakage at the pressure regulator valve.
Intermediate Band – This is the band that applies to the input drum when 2nd gear engages. We replace the stock intermediate band with an extra wide version that gives us 15% more holding capacity than the stock width and allows for a much firmer shift. This wider band also has a much stronger case anchor to reduce the chance for a failure under heavy load. Along with this band comes an all new input drum. Used drums can be “dished” in the center from years of use and this will prevent the new band from applying evenly and fully against the drum resulting in slippage or premature failure.
Frictions and Steels - Also known as the clutch packs. We replace all the existing frictions and steels with brand new components. The frictions we use are a proprietary blend of materials that give us exceptional holding power and a long life span.
Stay tuned for Part 3! Next week the third and final installment will focus on the valve body blueprinting and dyno testing.
For those attending the Barrett-Jackson Collector Car Auction in January, the DIY Pavilion, where the build will be taking place, is located near the staging lanes outside the auction arena. For those not able to attend in person, updates and live feeds of the 48 Hour Build will be available via Facebook and Instagram.
The 48 Hour Corvette is equipped with a Bowler Performance Prepped Tremec T56 Magnum 6 speed. It is going up for auction on Saturday January 20th. Click the picture for more details.