Originally Posted by
Frank87
Hello BMW friends and sorry for bumping this old thread but perhaps I can shed some light on this.
I have rebuilt a 5HP18 box for my M60B30 and this has gotten me totally into autoboxes as I think they are amazing. I am currenty planning to fit a 5HP30 behind my 3.0 so I can flog it much more and to have the car prepared for a 4.0 or 4.4 swap.
First, let me tell you why adapting a 6HP is going to be a pain in the ass:
The 6HP has the gearbox computer inside the transmission itself. The wiring loom taps into the modern BMW CAN system. Older BMW do not have any CAN system and rely on analog signals. To get a 6HP to work correctly, you need to turn every analog signal into a digital signal and then feed it over an exact same CAN system. In theory this is all possible because all the required technology exists. In reality, this is extremely expensive and time consuming. Programming the 6HP26 for the M70 engine characteristics is not really a problem, the problem is feeding it the right signals in the right way.
Lets look into the 5HP30:
The 5HP series were fully electronic transmissions from the ground up. They need some signals to work properly like:
- Trans temp
- Throttle position
- ABS input
- RPM (measured on turbine or at engine)
And most importantly, they need to know the car its RPM / Torque curve. The transmission shifts based on certain parameters of temperature, throttle position, ABS and RPM input. But depending on the engine torque at that specific RPM and current Throttle position when shifting, the transmission can calculate the torque it will receive in the next gear. The transmission knows this because it compares the RPM / Torque curve to the RPM + Throttle position at the shift moment. This information is used to engage and disengage the required clutches at exactly the right time to minimize slip and prevent any jerking. Not having the right RPM / Torque curve programmed, leads to wrong shifts and increased wear. Words with numbers like "This box can handle 1.000Nm so it will easily handle a 200Nm engine" are therefore bogus. Not knowing RPM / Torque means shifts are bad. This is different for old hydraulic gearboxes that use vacuum modulation and governor shifting.
So: For an electronic box, it is an absolute must that the transmission software knows the engine RPM / Torque curve.
Luckily, we can easily find out what the M70 RPM / Torque curve is and there are plenty of professionals who can reprogram a 5HP30 computer into taking the M70 RPM / Torque curve as a reference. We also know a 5HP30 will fit an M70 just fine as these boxes are mated to the M73. A V8 bellhousing should also fit as they both use the same large double ear bellhousing.
So, knowing that:
- We can fit the box
- We can program the M70 RPM / Torque curve into a 5HP30 EGS
We need to feed the right signals to the 5HP30.
I think the solution lies in the E34/E32 M60B40 cars. These cars are equipped with the 5HP30 which means they have a complete OBD1/ADS compatible wiring loom running from the box to the EGS itself. These are EGS chips that do not use any modern CAN but more primitive CAN like protocols. They get many of their signals fed through one of the many slots they have. The old CAN does the rest The transmission needs:
- Turbine speed (it will deliver this signal itself) OR Engine speed
- Output shaft speed (it will deliver this signal itself)
- ATF Temp (It will deliver this signal itself)
- Input from the ABS system (So it will not shift when you are cornering)
- Kickdown signal (Knows you want to engage kickdown)
- Brake switch (Knows to disengage converter clutch)
- Winter / S / A button input
- Throttle position
Since the E34/E32 M60 vehicles are OBD1 / ADS, we would need to use as much as we can from a 540i or 740i regarding sensors, wiring and any other thing that can give us the nessecary signals.
The last signal challenge, is the ignition/injection retarder. Electronic transmissions send a signal to the DME to retard ignition/injection for a few miliseconds during shifting. This means the engine temporarily produces very little torque which makes it easier for the transmission to shift. This is noticeable in many BMW models as you very shortly notice the engine is "off" during shifting. Since the V12 uses 2 DME, we would have to find out of these DME are compatible with such a mechanism and then we need to feed them the signal.
Looking at hardware.. what box do you want to use? We have another minor challenge. The 5HP30 has 2 variants:
- V8 variant: 5 steels, 5 clutches in clutch B
- V12 variant: 6 steels, 6 clutches in clutch B
- Other clutch differences for the other clutches apply aswell. The clutch plates itself are also different.
The holding capacity of the V12 variant is PROBABLY better. The different valve bodies will also engage and disengage the clutches differently. It is safe to assume that all V12 5HP30 use somekind of refined CAN system as they were introduced on the more modern 5.4 litre engines.
Not only do we want to mate a V12 box to a V12, we also want to take the best holding capacity as we are doing custom engineering anyway. What you then need to do, is rebuild a V12 box and compare the actuation of the solenoid of a V12 computer to a V8 computer. If you see totally similar software but with different variables. You can copy the V12 shift program into the V8 computer and add the M70 RPM / Torque Curve. This means you are running a V12 box with a V12 shift program and correct torque curve on a V8 EGS. And this should work just fine. The V8 EGS will actuate the valve body based on the information of a box that uses max. clutch pack size.
All in all, I think:
- Getting a box to fit physically is no challenge. You can even choose the converter you want. V8 or V12 converter.
- Getting a wiringloom connected to an EGS which has the M70 RPM / torque curve programmed, is a minor challenge. The loom and EGS already exist and can be found in a 4.0. Programming it, is a matter of finding someone who knows how DME / AGS / EGS chips work.
- Feeding the standard signals is quite the challenge. You need to make sure you feed the signals exactly the way the 4.0 would feed them to the EGS. Biggest challenge may be the Throttle position as the M70 and M73 have electronic throttle bodies. If there is a way to get an exact same TPS signal out of these bodies, this very important signal is solved. Getting other signals digitally can also be done with custom sensors.
- Feeding the 2 DME the retarder signal is a moderate challenge. I am willing to bet M70 DME are compatible with this technology as the 4HP was a hydraulic box family converted to electronic controls.
- Building the hybrid V8 base software programmed to V12 standards with a different V12 RPM / Torque curve, is probably the biggest challenge. An alternative would be to use a 100% V8 box on a V8 computer with an M70 torque curve. However, I suggest you go ALLin on this one and try to get max. torque capacity behind that M70.
Collect box codes: 1055 000 017 / 032 / 040
A workaround for the CAN problem may be to fit an extra DME.. A 4.0 DME which you feed all the signals you have to feed it. The DME can then be connected to the EGS. Perhaps you can completely circumvent any custom CAN work like that :-). This DME will not control anything. A coder may also remove the any engine failsafe coding from that DME. Basically, that phoney DME is your translator and your EGS feeds the REAL DME's with the cutoff signal.
I have a much easier job fitting a 5HP30 behind a M60B30 as I will:
- Rebuild a V12 box and use a V8 input shaft (IF THESE ARE DIFFERENT)
- Copy V12 EGS software on V8 EGS so the Valve body is actuated properly
- Copy the M60B30 RPM / Torque curve on the V8 EGS and replace the M60B40 curve
- All signals already there
- All signals already fed to the EGS socket (EGS 5HP18 and 5HP30 E34/E32 V8 have same PIN layout)
I need some minor soldering but all in all, this should be possible.
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