Introduction: BMW E46 M3 Exhaust Muffler Back Box Flange Rusted Corroded Flanges Repair Kit Install Fitting Guide Instructions

The Problem

The OEM cast iron flanges rust / corrode and eventually split causing exhaust leaks.

A common fault on E46 M3 models is failure of the exhaust flanges caused by rust / corrosion of this part. Four flanges are used to clamp together and seal the intermediate pipe to the rear muffler / backbox. These are constructed of cast iron (despite being fitted to a stainless steel exhaust) and inevitably deteriorate and split. These parts are integral to the intermediate pipe and rear muffler and are not available separately from BMW. The only option until now has been to buy a new centre section from BMW at vast expense. Or to buy new flanges, cut them up, fit and re-weld them- a tricky job. None of these are an ideal solution to this common fault.

Symptoms of the fault

Upon inspection you will be able to see the flanges are rusted and corroded and often split or starting to.

It is common for this seal to fail causing the exhaust to blow which can cause MOT failure or advisory’s.

On occasions the exhaust may need removing for upgrade or perhaps for access to carry out sub frame repair, at which point the original flanges will need to be grinded to be removed and a suitable replacement will be required.

Vehicles affected and compatibility

BMW 3 Series E46 M3 07/1999 — 08/2006. All models: Convertible, Coupe, CSL.

Associated part numbers:








Our solution

Install our high quality stainless steel flange clamps which very simply attach in situ, curing vehicle faults and will last the life of the vehicle.

Our kit is the superior solution to this problem. Our high quality stainless steel flange kit splits around the exhaust pipes, allowing you to replace the flanges without having to remove the exhaust. Simply grind off the old flanges (often they will just fall apart) slot our new flanges in to place and fasten. Our clamps are designed to be very simple to fit with no grinding usually required, a straight fit unlike many others on the market. No welding required, our flanges are designed for the life of the vehicle and can be removed in future and reinstalled with no hassle. Our kit comes complete with all you require including both types of gasket seal ring and the correct spec stainless steel bolts, washers, lock rings and nuts.

You will receive

4x Stainless steel flange kits enough to repair both pipe flanges

4x Stainless steel bolts, nuts, washers and locking washers.

1x Gasket ring equivalent to 18111723379

1x Gasket ring equivalent to 18101405737

Step 1: Remove the Rusted Clamps

Grind off the rusted OEM clamps and remove.
Cut through the bolts retaining the clamps together and separate the intermediate pipe and rear muffler.
Remove the OEM gasket seal rings.
Cut across the clamps center sections and remove from the intermediate pipe and rear muffler.

Step 2: Clean Up the Pipes and Flanges

Using a wire brush or wire drill attachment clean away the surface rust from the flanges and pipe.

Step 3: Fit Our New Gasket Seal Rings

On the left flange fit our seal ring, this is chamfered on both faces and the flanges mate to these faces.
On the right flange fit our seal ring over the pipe with the chamfered face pointing towards the backbox.
Push the flanges together; the left 2 flanges will seal on the sealing ring and the sealing ring on the right flange / pipe will push in to the flange providing a seal.

Step 4: Clamp the Flanges Together

Using our stainless steel clamps, clamp the flanges together.

Start with the left hand side flange.

Fit a washer to a bolt and push through the clamps as shown, with the chamfered face of the clamp pointing towards the back box.

Fit clamps on the back box side of the flange with the chamfered face of the clamp pointing towards the intermediate pipe.

Push the bolt through this to form a clamp around the flanges.

Insert another bolt with washer through the lower hole to secure the two clamps together.

Fit a washer, locking washer then nut to both bolts and tighten.

This will draw the clamps together, ensure the seal ring stays in place and tighten the clamps so the flanges clamp to the seal ring.

These should not be over-tightened but just tight enough to keep the flanges clamped to the sealing ring.

Step 5: Repeat Process for the Second Flange

Repeat this process for the right hand side flange. Ensuring again that the chamfered faces point inwards towards the sealing ring / flange. Tighten up bolts to draw the sealing ring in to the flange to provide a seal.

Step 6: Test the Seal

Once the intermediate pipe is clamped to the back box successfully run the vehicle and check for any leaks. If a leak is detected tighten the clamps further.

This completes the repair. If you need any further guidance on this install or would like to purchase the parts shown please call us on +44 01843 446643 or email us at

Please also check out our instruction guide on YouTube.

Installation is carried out at installers risk, if unsure please contact us or a professional, X8R Ltd cannot be held responsible for any adverse result of installing this product or any injuries caused by install, if in doubt ask a professional. All images and texts are copyright X8R Ltd 2016