Rebuilt vs. Remanufactured

The light duty GM 4-speed automatic with overdrive has been one of the most popular transmissions of all time. What started out as the infamous 700-R4 and has now evolved into the 4L75-E transmission. These transmissions offer great performance in a small package that fits really well in many hot rod applications. The other advantage is that they were available during the engine changes that GM has made going from the original small block design to the LS platform, 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 engines, but with many of the older 700-R4s and early 4L60E versions, the lack of big power capability offers some room for upgrades.

Getting more to the point of the article: 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 rebuilders 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 built re-manufactured unit that is purpose built for the way you drive and the type of engine you will be using. Also keep in mind that even with the popular connect and cruise packages out there, those are not new transmissions, they are re-manufactured units as well, built by an outside contractor, and then sold through GM. We see a lot of misunderstanding with those since they are promoted by GM and Chevrolet. There are no new 4 speed automatics coming out of GM any longer. This is why re-manufacturing should be one of your top criteria when searching for a new transmission and the next biggest concern should be who is building that transmission. Always, always, always, check for background history, reviews, references, etc. on any transmission builder you’re looking to buy from. Price shouldn’t always be the leading reason to buy from a company. I can’t tell you how many times we’ve been the second choice based on price alone, but now that person is spending double because the first guy couldn’t deliver as promised.

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 stock built 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 to run 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 500 or more foot pounds of torque you really need to consider going with the 4L80E series of transmission instead. Those units are much better suited for big torque and what we will recommend. Below we’ve outlined some of the upgrades and changes we make for the different levels of the 4L60E we build here. Starting with the parts below, these are upgrades that all our 4L60E units receive.

Intermediate Band – This is the band that applies to the reverse 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.

Blue Printing the Valve Body

We spend a lot of time on the valve body to ensure that they are outfitted with all of the latest critical updates. The list below details what each of these updates mean for the transmission. Once the updates are applied we then vacuum test each valve for wear to provide zero leaks between the valve and bore. We also pack in Brand New Accumulator Pistons to replace those plastic ones that are prone to cracking and loosing pressure.

New Solenoids – The valve body solenoids can and do fail over time. They can develop a short in the wiring, the plunger can get stuck, or the return spring can fail. We always replace the solenoids with brand new OE units rather than take our chances that a used solenoid will hold up for as long as we would like it to. This is another area that many budget built transmissions neglect due to the extra expense.

Performance Spring and Shim kit – The spring and shim kit is a carefully selected group of components that work together to carefully tune line pressure, accumulator pressure and shift calibration. It’s the best way to get an impressive transmission that responds to throttle and increased load with quick, firm shifts.

Actuator Feed Limit (AFL)Valve – The AFL valve is a solenoid feed regulator valve that feeds the EPC solenoid and shift solenoids. The OE AFL valve design has a large reaction area and is highly affected by side loading, which wears the valve body bore. The EPC solenoid oscillates the torque signal and AFL oil, which increases valve action. As the bore wear increases, oil pressure is reduced to the shift solenoids, which causes solenoid and ratio codes. The same AFL oil loss results in lower line pressure. This is a commonly overlooked upgrade since it requires special machining to be done to the valve body.

TCC Regulator & Isolator Valve – Severe wear of the Torque converter clutch (TCC) regulator valve bore, caused by oscillation of the OE valve, allows regulated converter apply pressure to exhaust. This is a primary cause for TCC-related slip code P1870 and overheated converters. Exhausting apply pressure also diminishes line pressure, which can result in burnt clutches. Excess wear at the isolator valve bore reduces TCC apply pressure. We recondition the bore and install the new TCC regulator and isolator valve kit which then restores normal TCC operation by shoring up the hydraulic integrity of this circuit. This new TCC valve also gives us a 10% higher apply pressure, and the hard coat anodize finish prevents premature wear.

Forward & Reverse Abuse Bore Plug – The bore plug is held loosely in place with a coiled spring pin, allowing the opposing spring and oil pressure forces to stroke it within the bore. This constant oscillation causes the plug to wear and allows PR oil at the low overrun valve and 3-4 clutch oil at the 3-2 downshift valve to exhaust at the abuse valves. This excessive oil loss can result in delayed apply of the low/reverse clutch and a tie-up of the 3-4 clutch and 2-4 band. This upgraded forward and reverse abuse bore plug resolves these problems by use of an increased plug diameter to restore proper valve body clearance and by using a smaller retaining pin hole to reduce plug movement which results in excessive wear. This plug is used in two locations in the valve body: to separate the forward abuse and low overrun valves, and to separate the reverse abuse and 3-2 downshift valves.

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.

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.

The parts below are added to our builds that support 450 ft/lbs of toruqe and up.

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 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.

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.

If you’re going big torque on a 4L60E there’s a few more items that will further help the holding power. The items below here are all added into our 550 ft/lb packages in addition to everything above.

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.

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.

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.

Additional upgrades for heavy duty race use

2.84 Ratio Input Carrier Kit – The steepest first gear ratio of any four-speed automatic (3.06) belongs to the GM 4L60 (700-R4)/4L60-E family of transmissions. The shift from 3.06 ratio (1st gear) to 1.63 ratio (2nd gear) is a dramatic RPM drop that causes performance engines to fall out of their power band. The 2.84 input carrier kit transforms the popular 4L60 series from an OE “wide ratio” 3.06/1.63 to a “close ratio” 2.84/1.55 for game-changing acceleration on the track. This keeps performance engines in the optimal power band while allowing a longer pull in first and second gears, improving consistency and performance. Manufactured and engineered for outstanding durability, the 6-pinon carrier’s gears are precision-ground to OE standards, thrust washers feature highly wear-resistant PTFE-coated material and the captured bearing is thicker late design. Lube channels direct oil to the pinion pins, and the carrier can be disassembled for inspection and service. No special modifications to the transmission have to be made for this upgrade.

Heavy Duty 2-3 Shift Valve – When the GM 4L60-E family of transmissions evolved from the 700-R4, the overrun clutch apply no longer applied in 1st and 2nd when accelerating from a stop in D3 shifter position. This change was made to improve coast down drivability in D3, but had the side effect of reducing the torque capacity of the input section. In order for us to improve input sprag and forward clutch durability we install this heavy duty 2-3 shift valve that applies the overrun clutch in D3 1st, 2nd, & 3rd gears. We feel it is a critical upgrade for all heavy-duty and performance vehicles.


We would like to extend a huge Thank You to our friends at Sonnax for all their help with the information and images used in this article. They continue to be innovators in the support and development of the highest quality automatic transmission replacement parts and education.

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