8HP SWAP conversion

Conversion to 8HP Transmission

1. ZF 8HP transmission
2. Adapter plate (engine to transmission)
3. Custom converter
4. 8HP adapter kit
5. ECU / TCU control unit & software
6. Custom driveshaft / axles
7. Electronic gear selector / shifter & indicator
8. Transmission cooler and hose / fittings
9. Modified mounts / crossmember
10. 8HP ventilation

ZF 8HP Transmission

The ZF 8HP is an eight-speed automatic transmission manufactured by ZF Friedrichshafen AG. It has become a popular swap option due to its fast shifting and ability to handle a lot of power.

Quick facts:

• 8 speeds
• Various designations: ZF 8HP 45, 50, 70, 75, 90, 95
• Used in several vehicles as it is a modular transmission
  BMW: Including the 5 Series, 7 Series, X5, and X6, as well as sports cars like the M series.
  Audi: In models such as the Audi A4, A6, A8, as well as their SUV, the Q7.
  Jaguar Land Rover: Used in the Range Rover and Land Rover Discovery, as well as in Jaguar’s luxury cars.
  Maserati: The transmission is also used in some performance and luxury cars from Maserati.
• Capable of handling high torque, OEM specifications can be greatly exceeded
  8HP45: Designed for engines with up to 450 Nm of torque
  8HP70: Designed for engines with up to 700 Nm of torque.
  8HP90: Used in vehicles with even higher torque, up to 900 Nm.
• The 8HP transmission can be found as a spare part from a scrapyard or donor vehicle.

ZF 8HP Adapter Plate (Engine to Transmission)

To mount a ZF 8HP transmission to an engine that is not originally designed for this transmission, an adapter plate is required. This 8HP adapter plate is used to connect the engine and transmission.

The adapter plate is used to mount a transmission to an engine where the engine has one type of bolt pattern and the transmission has another. Once this is done, you have an engine and transmission joined together with the help of the adapter plate.

ZF 8HP Custom Converter

In addition to fitting the engine and transmission together, the crankshaft and the input shaft of the transmission must be connected for the power transfer between them to function.

This is done with a converter adapter.

Further down, you can read about the driveshaft/axles.

ZF 8HP Adapter Kit

Once you know which adapter plate and converter adapter you need and their functions, you can purchase a complete adapter kit that includes both the adapter plate, converter adapter, and bolts.

ZF 8HP Control Unit ECU / TCU

For an 8HP transmission to function, it needs to be electronically controlled by a TCU (Traction Control Unit) or an ECU (Electronic Control Unit). This applies to all automatic transmissions.

Note: TCU can also be referred to as GCU (Gearbox Control Unit).

TCU (Controller)
A TCU is often used to control just the transmission, while the ECU manages the engine. The ECU sends information to the TCU, and the TCU sends information back to the ECU. This setup is used when the ECU does not support automatic transmissions/8HP. However, if the ECU can control the 8HP automatic transmission, then only an ECU is preferably used.

Note: The ECU may have limited functionality compared to using a TCU.

ECU
When an ECU can control the 8HP transmission, no TCU is needed, which often simplifies installation and future adjustments.

Software
Optimized communication between the engine and the 8HP transmission results in an extremely responsive and functional vehicle. Just as you can tune the engine for more power to make the car faster, upgrading to an 8HP transmission can also significantly improve the car’s speed.

Should I use an ECU or a TCU?

• Adjustments are easier with just an ECU that can control the 8HP transmission.
• An ECU + TCU combination can provide better control when they are connected and working together.

ZF 8HP Custom Driveshaft / Axles

To connect the 8HP transmission to the differential, you can either fabricate a completely new driveshaft or modify an 8HP driveshaft and one from the differential into a single unit.

Things to consider:

1. Length adjustment
   You will most likely need a shorter or longer driveshaft compared to the original. Here, the length is measured between the transmission’s output flange and the differential’s input flange.
2. Output shaft flange
   Compatibility with the transmission's output shaft flange is easiest achieved by using the original. Upgraded versions are often available on the aftermarket.
3. Support bearing (for 2-piece shafts)
   If using a 2-piece driveshaft with a support bearing, it’s important that the bearing is suited for the engine's power output to avoid vibrations.
4. Balancing
   Once a driveshaft is fabricated or modified, it must be balanced to avoid vibrations.
5. Upgrading (for higher power output)
   An original driveshaft is designed for the stock power output. If the engine produces more power than stock, a reinforced/upgraded driveshaft may be necessary.
6. Flange to differential
   Compatibility with the differential's output shaft flange is easiest achieved by using the original. Upgraded versions are often available on the aftermarket.
7. Universal joints
   Ensure that the universal joints are tight and free of play to avoid issues.
8. Driveshaft Slip vs Fixed Yoke
   Some older transmissions use a "slip-yoke" (where the driveshaft slides into splines to compensate for movement). This can stick and cause vibrations.
   Modern transmissions like the ZF 8HP use a "Fixed yoke" / Hardy disc, which is preferable.

In summary, your new driveshaft should be able to handle the power it will be subjected to and be free from interference with other components.

Note: A driveshaft that is not straight or has faulty joints will vibrate. A vibrating driveshaft robs power and can damage the vehicle.

Electronic Gear Selector / Shifter & Indicator

Gear Selector / Shifter
The ZF 8HP uses an electronic gear mechanism that can either be transferred from the donor vehicle or purchased as an original part. However, there are many alternative upgrades available on the aftermarket.

Gear Indicator
An electronic gear indicator/display is recommended to show which gear the 8-speed transmission is currently in.

ZF 8HP Transmission Cooler and Hoses / Fittings

The ZF 8HP transmission requires its own cooling system. It is recommended to use new parts as dirt in this system can cause unforeseen issues, and it is impossible to fully clean or flush it. The parts used to connect the cooling system to the 8HP transmission are as follows:

1. Adapter to the transmission
2. Oil cooler
3. Lines

ZF 8HP Transmission Mount / Crossmember

To fit the engine and transmission into the car's chassis, modified transmission mounts or a different crossmember are needed. This is often custom-made for each case, but there are some ready-made parts available on the aftermarket.

ZF 8HP Ventilation

All transmissions have some form of ventilation to release the pressure that builds up when air and oil heat up and expand. Without proper ventilation, the oil would be forced out through the weakest seal.

When the 8HP is transferred to another chassis, paired with a different engine, or placed in a different position, the ventilation system may need to be replaced.