BMW E92 M3 - Underside Restoration

Описание: This 2011 BMW E92 M3 in Mineral White came into Redish Motorsport to address and treat some light surface corrosion that the owner noticed under the rear of the car.
This video documents how we went about treating and then protecting the chassis underside.

Initially, both us and the owner thought the corrosion was very minor in a few places like Subframe Mount Points, Chassis Studs, Battery Cable Brackets, but once the car was stripped and degreased we found corrosion setting in around the Boot Floor aperture near the Rear Panel, as well as some Spot Welds which have flexed in the Rear Wheel Arches, and the Underside Panels.
However, the most surprising was the micro bubble corrosion like blisters/pimples UNDER the factory electrostatic coating - seen in the video at 4:25    • BMW E92 M3 - Underside Restoration  
This was spread throughout the unprotected underside like above the Rear Axle area and some of the exposed sections of the Battery Tray, Boot Floor, Chassis Legs, and Inner Wheel Arches.

So we had to make sure all of these minor imperfections were tackled too.
That meant using wire-knotted wheels to removed and break off the start of the corrosion bubble and allow the white dusty corrosion like powder to be scraped off the metal.

We also had to do this to the heavier corroded area's (which were still fairly basic in terms of corrosion level) like around the Rear Exhaust Silencer Studs, Chassis Legs, Boot Floor, Subframe Mounting Points, Rear Shock Turrets, as well as the common Fuel Tank Breather Tube in the Right Rear Wheel Arch.

Once we had the corrosion removed and most of the area was back to bare metal we treated the metal with POR-15 Metal Prep to neutralise the corrosion and coat it with a zinc phosphate coating.

That was then washed off with a clean damp warm microfibre cloth, and then allowed to dry under the infra red drying lamps.

Then we protected the entire car with a disposable bodyshop car cover, and trimmed it accordingly to suit the rear working area including rear wheel arches, rear panel, side skirts etc.

Next we applied an Etch Primer to the bare metal areas and dried it using infra red lamps.

The second stage was to apply a High Build Primer over the metal underside as well as any BMW seam sealer remaining.

Then we moved onto first a thicker seam sealer which we brushed on over the overlapping panels where we had previously removed BMW seam sealer.

Once that was starting to cure, we applied the Sprayable Seam Sealer in a thin coat.
This was coated with our version of the BMW oem E-coat colour which we have blended from our work with the E46 M3's and have been using for a few years now.

We didn't want a heavy seam sealer as most of the rear underside of the E9x models don't have any sealer at all. At the same time we wanted to protect the metal chassis and give it a better chance of survival so opted for a very thin layer of sealer as shown in the video.

Once cured we then carried out a Cavity Wax process to all accessible and open cavities in the rear of the underside chassis before fitting all the genuine BMW grommets to seal the cavities from the atmosphere again.

Then we could start the rebuild process.

All plastics were first washes and then protected with Aerospace 303, except the Rear Wheel Arch Liners which we tried the rather expensive but excellent G-Technic C4 Trim Restorer which offered excellent results.

The Rear Subframe was already Powdercoated Gloss Black prior to it coming to us so we just cleaned this up again before installation and it was in great condition.

We also renewed the 2 Rear Silencer Heatshields, as well as HEL Braided Brake Hoses for the Centre Rear Flexi Joints.

Lots of BMW Fixings, Nuts, Bolts, Washers, Speed Clips, Plastic Nuts, Undertray Screws, Heatshield Washers were also replaced to not only make it look visually pleasing but to increase the longevity of the underside components.

Whilst we had the Nitron R3 Shocks removed we took that back to Nitron UK to have the Spherical Bearings changed (no better time whilst they were off the car). Nitron UK offered excellent customer service and were extremely helpful every step of the way. Well recommended company to deal with.

We refitted the Rear AP Racing Brake Kit, and carried out a Brake Fluid complete system flush and forced ABS electronic bleed (BMW ISTA) using the customer's requested fluid of PFC RH665 which has an amazing (dry) boiling point of 325'c!

Once the car was rebuilt we carried out a 18 mile road test on varying roads as well as another final lift-inspection and then confirmed we were happy with our work and the car was ready to collect so the customer could carry out their own wheel alignment to their own specifications.

It was a pleasure to work on such a 'young' car for this type of corrosion treatment and if it's something that's of interest to others then please feel free to contact us:

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