The I6 driveshaft procedures

The I6 driveshaft procedures

"These build journal entries are part of a special series on the development of the E46 M3 V2 Carbon Driveshaft by YFCM Composites. 

This specific journal entry covers the preliminary checks, while-you're-in-theres, recommended hardware and installation notes along with final validation checks to fit the the carbon driveshaft to your SMG3 and 6spd E46 M3. 

These entries are written in collaboration with M Lee: lead engineer and patent holder to YFCM's innovations."
- Matt

Preliminary checks.

Inspect & Replace worn bushings and mounts!

The E46 M3 is prone to various chassis woes: this is a chassis mod and drivetrain mod. 

If your bushings and mounts are worn - I highly recommend you change them, it's a smart while you're in there. You can also refit your diff if it's been clunking as the driveshaft will make this more noticeable. 

We replaced my diff bushings with a new differential cover [...]

[...] and upgraded to solid subframe bushings.

Recommended Hardware

  • 1x Flexdisc "guibo" (SKU: 26112226527)
  • 6x Standard CV flange / Diff bolt (SKU: 33217571990)
  • 6x Self Locking Nut for Guibo / Transmission flange (SKU: 07129900047)
  • 6x Hex Bolt for Guibo / Transmission flange: there are 2x SKUs and lengths. I recommend the longer version.
    • M12x58mm (SKU: 26117635643)
    • M12x62mm (SKU:  26117523709) 
    • You can optionally spec an even longer Genuine BMW M12x71mm (SKU: 26117527475)


Installation Steps.

Get to the driveshaft. 

You need to remove the center exhaust bracket, disconnect 02 sensors off the exhaust and remove the entire exhaust systems.

This install was part of the complete mechanical restoration and upgrade. 

You don't have to go that far deep. 

Fitting the driveshaft.

In my initial 2021 installation, we needed to lift the transmission all the way up with the engine supported. We also loosened the differential bushings and pried off them to get the YFCM to fit.

Update 2023.

There's a faster, easier way to do it by unbolted the front differential bolts and letting it hang to fit the driveshaft into the flange, and raising it up as an assembly.

You can see the technique here that we used on the V10 M5. 

We first fitted the guibo to the transmission flange instead of the driveshaft for the S54, the slight angle made it easier than fitting the carbon driveshaft on the S85 and S65. 

To gain access and torque the bolts at the differential, and the transmission flanges, put the car in Neutral. You can then rotate driveshaft by hand. 

Make sure the Guibo points in the correct direction, we had it wrong the first time. It will have arrows on the side: they should point towards the engine.

Mandatory Validation Steps.

The 1 piece carbon driveshaft design eliminates the center support bearing and as such removes a dampening zone of the driveline. 

You need to meet these clearances before completing the installation as it may otherwise lead to vibrations and catastrophic failure of the driveshaft if left unresolved. 

1. Telescopic Flange Measurements

The CV flange is telescopic and allows for some play for the rubber bushing in the powertrain such as the engine mounts, transmission mounts, diff and subframe bushings.

As the 1 piece carbon tube design is engineered to flex and move with the drivetrain, YFCM carefully engineered the tube length to match with the CV flange.

It must have a 64mm / 2.52 inches distance between both points pictured. 

If you installation does not come within the specifications listed below, you may have worn bushings and/or mounts across the powertrain. 

It's ideal to have had the car under the load if you changed any bushings. 

Here's how we took the measurement on the M3 V8. The car was still on the lift. 

2. Carbon Tube Clearances

Carbon tubes are larger than steel driveshafts and more susceptible to being damaged by screws and bolts that are at the top of the tunnel.

Careful attention to clearances and free range of movement of the tube must be validated. 

The driveshaft tunnel is a tight fit, but it works.

There should be at least 20mm / 0.8 inches separating the tube from any physical element across the driveshaft valley.  

3. Refit OEM heat shields. 

The OEM heat shields are fully compatible with the driveshaft's increased diameter. They are a mandatory component to your installation as they will protect the carbon tubing, and its adhesives from heat related problems. 

They do not need to be bent to fit. If they don't appear to fit, they are deformed from their original design. The heat shields are flexible metal, they can be easily put back to their original shape. 


Up next: my S54's drivetrain feels like a bolt action rifle for all the right seasons.

If you liked it raw, this is rare. 

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