BMW ZF 6HP26/28 - fault code 4F95, Strip Down and Inspection Description, More in the Description!!

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Details:-
BMW 535d E61 2008
131,000 miles/211,000 km's
Stage 1 Tune to 340bhp/680nm November 2017

ZF 6HP28
Transmission Stage 3 Tune November 2017
Gearbox first Serviced March 2018 at 95,000 miles/153,000 km's
(35,000 miles/56,000 km's Overdue, Two Years Overdue)
First instance for transmission slip at 112,000 miles/180,000 km's March 2019

Fault Code 4F95 - Gear Monitoring Coupling B-E, Implausible
This means a clutch slip has been picked up by the Transmission Control Unit (EGS) during 5th gear, the EGS was unable to determine which clutch produced the slip hence logging a fault code which involves both clutches, the EGS is also unable to ascertain the cause of the slip whether it be due to a work clutch or fluid pressure loss within a clutch drum.

Customer Complaint:-
On the A180 cruising at 70mph I put my foot down in my 535d to complete an overtake, the gearbox dropped from 6th to 5th and kept going back to 6th straight away, I did it again and I heard a big bang and the gearbox went to 2nd, the engine revved to red line so I quickly pushed it up to neutral and pulled over, when I was stationery I attempted drive and it was in 2nd straight away, I turned car off and on again and it drove fine.

So what happened to the customer?:-
As the transmission changes from 6th to 5th the C clutch is disengaged and the B clutch engaged, the E clutch remains Engages through the gear change, as the B clutch is engages the transmission picks up that either the B clutch or the E clutch is slipping or even a combination of the two so automatically switches back to 6th gear, so disengages the B clutch and re-engages the C clutch, repeated attempts to complete the down shift causes the clutch slip to become excessive and the logs a fault code and goes into Transmission Fail Safe mode, during this mode the Transmission will select the highest gear that doesn't use either of the two offending clutches and disengage the Torque Converter, in this instance 2nd gear is selected which engages the A clutch and the C clutch and when the speed range is within what the selected gear can achieve the Torque Converter is then re-engaged causing the engine to rev high until the speed is reduced. As the customer found, Transmission Fail Safe isn't cleared until the Ignition is cycled off and back on again, this allows the car to then be driven normally to get you home but the fault code remains logged until cleared, if a clutch slip is detected again then it is possible for Transmission Fail Safe to return, further more logging of the same fault to many time will force Transmission Fail Safe to become permanent until cleared via diagnostic equipment.

Why has this happened?:-
There are many contributing factors to be considered with issues such as this, for a more in depth look at this please go to our Facebook page.

So what is the Opinion With the Gearbox in this Video:-
The main cause would appear to be late servicing with the Power/Torque increase and Transmission Tune not helping things much. Some of the bushings do have excessive play which would allow the clutch drum assemblies to flex excessively causing unequal pressure on the clutch pack, particularly on the E clutch which resulted in the excessive shoulder wear of the top clutch plate. One thing missing from the video is the excessive play on the E clutch Input shaft with the Stator bushing which doubles as a seal for the E clutch which when worn will leak E clutch fluid pressure leading to poor clutch engagement, the adaption readings via diagnostic confirm small discrepancies with the E clutch fill pressures and fill times indicating an issue on that clutch.

What to do from here?:-
From here it's time to overhaul this Gearbox, all Clutch drums will be stripped down, all bushings and clutch drum seals replaced to ensure there is no excessive clutch drum assembly play and no possibility of future pressure issues after reassembly, the effected E and A clutch frictions discs and steel discs will also be replaced too ensure respective clutch condition is 100% and new mechatronic seals and a new sump with filter will be fitted, after the gearbox is refitted it will be filled with new ZF Lifeguard6 Oil and test driven.

Thanks for watching and if you managed to read all of this I salute you ;-)

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Видео BMW ZF 6HP26/28 - fault code 4F95, Strip Down and Inspection Description, More in the Description!! канала RGA BMW Services