8-Speed Automatic Transmission for Chrysler cars and trucks:
845RE / 870RE, ZF 8HP45 / 8HP70 / 8HP90
See the end of the page for the second generation.
Shortly after Cerberus took control of Chrysler, rumors of ZF eight-speed automatics in the company’s cars and trucks started to swirl. After Fiat took over, Chrysler CEO Sergio Marchionne confirmed the rumors; and in 2011, Chrysler said it would use the eight-speed in its large cars, behind the Pentastar V6 engine, in the 2012 model year (V8s adopted it in the 2015 model year). Ram pickups adopted the transmission in the 2013 model year, and Jeep Grand Cherokee and Dodge Durango shared it with the 2014 model year.
The transmission is a ZF design; when made by Chrysler, it has changes to match Chrysler equipment factory equipment and methods. The unit is also used by Porsche, BMW, and other high-end car makers. It is designated 8HP45 or 8HP90 when made by ZF; the Chrysler version of 8HP45 is called 845RE.
The 845RE name shows 8 speeds, “45 x 10” Nm of capacity, rear wheel drive intent, and fully electronic controls. It can be, and will be, used with 4x4 and AWD setups.
Differences between the 8HP45 and 845RE include, according to oh2o, the clutches (845RE has extra friction plates) and, for some vehicles, a higher capacity oil pan. Many internal parts do not interchange.
With the Pentastar V6 and HP8, the Chrysler 300 achieved 0-60 in 7.2 seconds, and cruised at 70 mph with the engine at a mere 1,400 rpm. Gas mileage was 31 mpg (RWD), up from 27, with city mileage unchanged. The torque rating of 331 lb-ft for this version of the transmission is far above the Pentastar’s 260 lb-ft. Dodge Charger, with the same setup, did 0-60 in 6.6 seconds and had the same gas mileage ratings.
Chrysler is making its transmissions (and most of the parts for them) in its various Indiana plants, and ZF is building them in Greenville, South Carolina. The Indiana plants and ZF also make the 9-speed automatic transmission for front wheel drive and all wheel drive cars.
ZF 8HP45 / Chrysler 845RE Technical information (and the HP70)
Variants of ZF eight-speed automatic include an AWD version and one with a built in 20-horsepower electric motor for a parallel hybrid setup.
Advantages of the transmission are not so much the eight speeds, which keep the engine in its optimal range, but:
- the wide range of gears, allowing for a low “performance” first gear and a high “economy” top gear;
- a claimed 98% efficiency in any gear, with an unusually fast locking torque converter; and
- shifts that take place faster than a person can sense them.
The transmission can be used in a mild or full hybrid setup, and allows input torque up to 900 Nm, or 664 lb-ft (8HP90) — high enough for any Chrysler gasoline engine, not quite enough for the Cummins diesel.
The efficient, low-mass triple-line torque converter’s lower inertia helps during shifting and starting, while its twin torsional damper system allows fast engagement with little “slip.” Other efficiency and shift-improvement features include a hydrodynamically cooled clutch, low-viscosity transmission fluid, and chain-driven axial parallel vane cell pump.
The transmission uses four planetary gearsets and five gear shift elements (two brakes, three clutches); there are two opened shift elements per gear, minimizing drag losses. Only two shift elements are open in each gear, cutting parasitic losses; and it can make extreme transmission shifts, such as eight-to-second kickdown, in one step.
The 8HP70 transmission in the Chrysler 300 and Dodge Dart weighs around 90 kg (198 lb), the same as the 6HP26 and less than the 5HP24 (the first numeral is the number of gears). The 8HP70 is larger than the 8HP45, but not much longer.
The tall first gear allows for early lockup of the torque converter clutch.
|Gear||1||2||3||4||5||6||7||8||R (RWD)||R (AWD)||Spread|
Chrysler will have 40 different “control maps” to change shift patterns based on operating conditions (covering both rear and all wheel drive systems).
The list price for this transmission, in December 2012, was $3,935 (this is what most dealers are likely to charge ordinary customers). Via a discount on-line dealer, the range was around $2,950 to $3,550 plus shipping.
[See the ZF 9-speed automatic]
The Chrysler-ZF partnership
According to Mike Kirk, Chrysler’s director of axle, driveline, and manual transmissions, there were two main reasons for Chrysler’s changes to the ZF automatics.
Kokomo was already set up with its own tooling and robotics, which are different from those used by ZF. Some changes to the transmission were made so they could use Chrysler’s equipment and methods.
Chrysler also needed to make many more transmissions than ZF; choices that make sense for 50,000 transmissions a year may not make sense for 200,000 per year.
Mr. Kirk said that the partnership with ZF had been mutually productive; while Chrysler owns the intellectual property of any changes they make to the transmissions, they keep ZF informed. Chrysler can patent any of their changes and methods, including the software and controls, and is motivated to improve the transmissions and production methods to stay balanced with ZF.
Standards for both manufacturers are high, and the two companies use the same end-of-line test centers, driven by the same software.
A first-hand look at Chrysler’s new 8-speed automatic transmission
Chrysler’s newest technology to improve performance and fuel economy is their segment-exclusive 8-speed automatic transmission, hitting the market in for model-year 2012. We had a chance to log a few miles in the 2012 Dodge Charger Blacktop equipped with the 292hp V6 and the new 8-speed transmission.
The transmission comes with the new touch-shifter on the console, with manual shift control using steering-wheel-mounted paddle shifters. This system debuted in the SRT lineup, but when these new 8-speed models begin reaching dealerships around the country, this will mark the first application of the Chrysler paddle shifters on a non-performance model…supposing that you don't consider the 292 horsepower Dodge Charger a performance model.
Chrysler has done it right, using metal for the shift paddles with a sleek, smooth finish. The SRT8 has the + and - signs filled in with black paint, while the V6 uses unpainted impressions.
Some paddle systems leave you hunting for the paddles when you get to crossing over your hands for shifting under hard cornering but that is not the case with the Chrysler paddle system with the ergonomically perfect levers making for quick, smooth shifts.
The other component of the new Chrysler 8-speed automatic transmission is the console mounted shifter that uses a “slapstick” motion rather than the traditional shifter movement. The low profile shifter bears a similar shape to the old school slapstick shifter and rather than the normal PRNDL pattern, the 8-speed automatic shifter has just Park, Reverse, Neutral and Drive/Sport mode (in cars without Sport mode and paddle shifters, it has Drive and Low). When you pull it back to move into gear, the shifter does not stay in place – instead returning back to the middle position. As you shift from Reverse into Neutral and then into Drive or Sport, the shifter clicks through the gears but always returns to the center position of the shift console. [Editor’s note: this behavior is incredibly annoying, which is one reason why Chrysler used a knob-based system on Rams and Cherokees, and a more conventional shifter on 2015 and newer cars.]
Chrysler’s 8-speed transmission combines aggressive gear ratios for the lower gears to bolster torque multiplication and low end acceleration, while also providing fuel economy friendly higher gears to improve mileage when cruising on the open road. Some may believe that they will complain about how often the transmission shifts, but I was blown away at the smoothness of the new ZF 8-speed automatic.
Under normal driving, such as accelerating away from a stop sign up to 55mph, the ZF-designed Chrysler 8-speed is seamless; you can barely tell when the transmission is shifting. Once you have gotten to a cruising speed of 55 to 70mph and the transmission has gotten through the gears, the low RPM range allows for minimal amounts of fuel consumption on the open road. The Chrysler 8-speed also has plenty of gearing to get the 2012 Charger with the 3.6L V6 from 0-60 in a hurry, and allows even the V6 to do a smokey burnout.
If you want manual control of the 8-speed Chrysler transmission for some spirited driving fun (or more smokey burnouts), you can use the steering wheel mounted paddle shifters (on cars that have them). From there on, the driver has full control of the upshifts and the transmission only downshifts when necessary to prevent the engine speed from dropping too low. Under most conditions, your hands don't need to leave the 10 and 2 positions; the paddles are in ideal areas for quick shifts, and when using the manual shift mode while exercising all 292 horsepower, the shifts are much more positive – like you would expect from a modern sports sedan.
Based on my time behind the wheel of the 2012 Dodge Charger Blacktop equipped with the 292hp Pentastar V6 and the new ZF 8-speed automatic transmission, it is clear that this new gearbox does a fine job of combining a sporty driving experience with high fuel economy. The sport shift mode allows the driver a more engaging driving experience and when left in Drive, the new transmission works through the gears with no notice of the high number of shifts.
Chrysler “broke the rules” again with the introduction of an 8-speed automatic transmission to mid-priced cars, but once consumers see and accept this system, we can expect others to use similar technology in mid-priced cars.
The second generation eight-speed automatic transmissions
The second generation ZF 8HP automatic was first used in the BMW 520d. “Comprehensive” changes have lower drag torque, a higher gear spread (distance between first and eighth), and lower vibration.
The changes, which increase efficiency “by up to 3%,” were partly made to deal with small, turbocharged engines, and to work better with engines that reach peak torque early on (such as diesels). The latter required a higher gear range, so that the eight-speed will move from 7.0 to 7.8 — incidentally beating the eight-speed currently used by General Motors.
- Internal losses were cut partly by adding sprints into the multidisk packages of the shift elements, to almost fully open friction shift elements and thereby cause less drag torque. Power losses were cut by over two thirds, according to ZF.
- Creep torque has been cut by fully opening a clutch during deceleration and when the vehicle is stopped, so that drivers don’t have to brake to keep the car from moving (which may feel odd to some drivers). The oil pump pressure has been cut in pressure by around 30%.
- New torsional vibration dampers eliminate vibrations from the engine, stopping them from moving along the driveline and into the driveline and the body.
- The new torque converter allows faster transmission of power and lets lock-up occur much earlier.
- Coasting with the transmission uncoupled can now occur at speeds up to around 100 mph, and stop-start systems can now work immediately instead of after 1.5 seconds.
- The transmission also improves downshifts, providing nested multiple downshifts for even quicker response times