Transmission head to haed

4L80 vs 4L85 Transmission Comparison

As a pair, these two transmission systems represent a commitment to the electronically assisted shifting systems. Unlike models like the 4L60 that started out non-electronic and then were later modified, the 4L80 and 4L85 originally came out as computer-controlled units.

Transmission head to haed

These models are especially famous in hot rod circles as they can handle a lot of torque from enhanced engines. In addition, they give enthusiasts all the conveniences and perks of 21st-century transmission mechanics. The 4L85 was an improvement to the 4L80 with hardiness being the main separator.

4L80 Transmission

The 4L80 transmission was an improvement on the TH400 TurboHydramatic transmission. It is similar to the 400 in components and toughness but has an added lock-up torque converter, overdrive gear, and electronic controls. These transmissions are sometimes referred to as an E at the end, but the need became obsolete as most models in its class became electric.

The 4L80E was created for large trucks rather than smaller vehicles. It is even too large for some pickups. However, it has also found itself in opulent cars like the Bentley, Aston Martin, Jaguar, and Rolls Royce. It is also applied in some recreational vehicles and public transport like school buses.

An electric controller is required for the 4L80, which some owners have concerns about. There are, however, customers that appreciate the variety of controls that an electronic interface provides. Being electronically controlled also allows for precise and computerized diagnostics. Error codes are preprogrammed into the unit and when data from various components around the car is fed into the computer, it can tell you where the issues are as part of the onboard diagnostics.

4L85-E Transmission

The supermatic 4L85 e can handle almost 200 more lb-ft of torque at a rating of 690 lb-ft while the 4L80 is at 440 lb-ft. It has an extra-heavy-duty clutch plate that allows it to handle more than the 4L80. Another difference is that the 4L80 has four smaller gears on its planetary gear sets while the 4L85 has five.

The 4L85E transmission can also handle vehicles with up to 18,000 lbs in GVWR rating. As a result, this model can handle the torque requirements of off-road contests, and street and drag racing.

It is popular in vehicles like the Rally Fighter, Chevrolet Express (Duramax Diesel), GMC Yukon, Chevrolet Avalanche, and Suburban. It has been favored by big vehicles, customized communities, off-road enthusiasts, as well as people in the transport sector. The Supermatic 4L85E is also among the most vigorous transmissions offered by Chevrolet Performance. A 4L85 transmission for sale may cost you between $3,100 to $4,500 with 4L80s being in the same range.

Similarities

  • Both of these units have their origins in the TH400 TurboHydramatic.
  • They both have the same gear ratios. These are one 2.482, two 1.482, three 1.00, four  0.750, and the reverse 2.077.
  • Both have similar physical dimensions.
  • A lock-up pressure plate is present in both.
  • They use the same range of automatic transmission controllers with similar harness connections and features inclusive of but limited to:
    1. Transmission 20-pin connector
    2. Battery power rating
    3. Grounding cables
    4. TPS or throttle position sensor. This device is what is known as a potentiometer. It communicates with the TCM via voltage signals varying from 0.5 volts to roughly 4.5 volts. The range in volts represents the range in throttle shaft angle. When the throttle is closed the signal voltage is around 0.5 volts, and increases corresponding with the opening of the throttle. A wide-open throttle is synonymous with a signal voltage of about 4.5 volts. The TPS can be found on the injector pump housing.
    5. Transmission output speed sensor or TOSS. A magnet with a coil around it emits the magnetic induction that the rotor teeth on the output shaft synthesize. As this happens, AC power is generated in the circuit. This piece of machinery produces a shaft output signal to the administration module which uses it to compute vehicle speed, transmission yield rate, TCC slip momentum, and control shift caliber.
    6. TCU or transmission control unit. This is a computational device that can record, interpret, and analyze signals arriving from switches and sensors in the engine, transmission, and brake assembly. This is where the trouble codes are stored and retrieved from. Transmission control units are also constantly doing a self-diagnosis to record issues in real time.
    7. Transmission control module. The TCM is another computer that collects and synthesizes signals from sensors, but unlike the TCU, it conveys output prompts to solenoids on the control valve body. The solenoids in turn manage the shifting patterns, transmission operation pressures, and torque converter clutch behavior.
    8. Distributor cap tach lad for carburetor cars
    9. Ignition power rating

Differences Between the 4L80 and 4L85

The main difference between these two is the torque ratings and applications.

The 4L80 found favor in applications such as luxury vehicles, school buses, and motor homes. 4L85 was more adapted in vehicles such as the Yukon, Avalanche, and GMC Savana. These cars are liked for their off-road capabilities and weight-carrying capacity. 4L80s were also used in GMC trucks like the Sierra, Chevys like the Silverado, and the Hummer H1.

Torque rating differences are as follows:

  • 4L80 at 440 lb-ft
  • 4L85 at 690lb-ft

The GVWR rating also differs between the 4L80 at 16: 500 lbs, and the 4L85 at 18,000 lbs.

The planetary gear setup also differs. The 4L80 has four pinion gears on the assembly while the 4L85 has five.

4L85 Transmission Nuances

Although a huge leap forward in transmission performance, there are issues consistently found in this model. A common one is incorrect synchronizing when the drive is engaged. This can also be referred to as slipping. It presents itself as lag when moving from first to second gear, or from second to third gear.

The 4L85 can alarm you of a slip with increases in pump pressure. However, when the transmission is worn, pressure increases, meaning slipping may not occur until total failure. The pressure pump works to mask some of the well-known tell-tale signs of a slipping transmission.

Another pitfall of the 85 can be identified by the error code P0757, which translates to inadequate or bad transmission fluid. This will present itself as shift solenoids sticking. A change, filtration, or top-up will most likely solve this issue.

The early 12-pin tackle for the unit also leaked onto the harness, causing shorts, and subsequently, the transmission would go into limp mode. It is not complicated to solve this issue, as all you have to do is clean the plug.

4L80 Transmission Nuances

There are a couple of observed symptoms that are useful in diagnosing problems in 4L80. They are not 100% accurate all of the time as there are overlaps in signs, but they do help identify issues.

  • Smoldering smell. This is usually indicative of a burning clutch due to partial engagement when driving. Low transmission fluid or oxygenated fluid will also give off a burning smell. Depending on the state of the fluid, a change or top might be necessary.
  • Fluid leaks. A crimson fluid under your car after being parked for a while is the first indicator of a transmission fluid leak. Broken seals or gaskets are the culprits for this kind of leak. Friction between components and if left unattended may result in irreparable damage or installation of a new rebuild kit to get the vehicle back on track.

It is, however, easy to misdiagnose leaks if you are not experienced enough and a visit to the mechanic is the safest option. Having a robust preventative maintenance schedule is also a sure way to avoid such leaks. Consult your trusted mechanic to come up with a program appropriate for your vehicle’s needs.

  • Problems shifting gears. Many 4L80 owners have complained about losing either forward or reverse gears. It usually happens to one and not both, so you will either only have forward gears or just reverse. This is associated with a defect in the valve body, a very integral part of automatic transmission. In this instance, visiting your nearest qualified mechanic is your best option.

To avoid heavy bills, severe damage to the vehicle, and accidents, it is recommended to consult a trained professional whenever you notice something might be wrong with your transmission. It is very easy to ignore a small issue today that will cause a complete replacement or rebuild shortly down the road.

Steven Reilly is a qualified mechanic and his passion for cars goes beyond just the technical aspects. He is also an amateur racer and all round car enthusiast. When he is not driving them, he can often be found in his garage under the hood of a rare model. Steven Reilly has lost track of the number of hours he has spent setting up his fine collection of rebuilt models. He believes that cars can provide a constructive and fun opportunity to teach the youth important life skills. In line with this, he is developing a community outreach program, potentially dubbed ‘Cars for change'.