BMW E60 / E61 Rotor Repair - COVID Lockdown Parking Rust and Brake Vibration

 When the COVID lockdown hit back in March, daily commuting stopped, kids were pulled from school, shopping essentially stopped except for weekly trips to the grocery store, and the BMW wagon went from use 4 to 6 times a day to a couple times a week. The drop in use was dramatic, and one result of this was a couple of instances of the brake pads bonding to the rotors with corrosion. You would go to use the car, all the brakes would be stuck, and after a few seconds of throttle, eventually the corrosion bond would break and the car would start rolling normally. 

BMW E61 535xi Front Rotor

Use of the car has gradually returned, and we did a local road trip in August. The brakes in the car were completed replaced when I did the turbo project 2 years ago, since then the car has only travelled about 20,000km. During the road trip I noticed minor brake pedal vibration - more apparent during light braking, less apparent with a bit more force on the pedal. 

When I brought the car into my garage in September to look at the low boost pressure issue, this was on my list of issues to repair. 

Rust ridges on front rotor left from pads freezing to rotor

I thought about purchasing new pads and rotors to sort out the issue, but 20,000km is next to no use, and I wanted to avoid the cost and the waste. I got onto google and looked for brake rotor turning services. At one time this was common, now, almost impossible to find. There was one machine shop in east Montreal that gave me a reasonable quote for turning the rotors, but when I went to drop them off, the machinist had sufferred an accident and would be off work for a month. No go. 

Frozen brake pad prints on the front rotor

So - if a part is broken, you can't really break it any more trying to fix it. I decided to try sanding the rotor surfaces with a Dewalt 5" orbital sander with 200 grit paper, to try to remove the ridges. 

Frozen brake pad prints on the front rotor

I sanded the complete surfaces, front and back, of both disks. I did two passes, not wanting to remove too much material and creating a bigger problem than I already had. I was careful to spend the same amount of time and pressure as equally as possible around the surface of the disk, just spending slightly more time on the ridges left by the various brake pad prints on the rotor surface. I didn't try to completely remove the brake pad prints, but smooth them out and hopefully reduce the pedal vibration. 

Front disc following sanding - pad outlines are still visible.

The sanding removed some of the ridges left during the pad bedding into the rotors. I knew that the pads would have to bed in again, so I was patient for the last month and tried to modulate my brake pressure to allow that to happen gradually. 

I would say that this has largely solved the problem, although, with very light application of the brakes there is still a slight vibration. With normal stopping pressure, the vibration is not apparent. It seems to have improved the braking feel, but it's not perfect. It seems to be improving with time however, so I'll let it go for another month or two and report back whether the problem resolves itself. For now - I've saved the cost of a pair of rotors and pads. So far, so good. 

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BMW Underbody, Suspension and Rear Bumper Rust Repair with POR-15 System

While I had the BMW wagon in the garage replacing the rear axles and sorting out the turbo control vacuum issues, I noticed the start of some corrosion in critical areas - on the steel body near the rear subframe and brace mounts in particular. 

Rust bubbling the paint near the spare tire well - frame stiffener mount

I had some time so I decided to take action now to avoid larger problems further down the line. Two years ago, when I did the turbo replacement project, I also dropped the differential to give it a thorough cleaning, replace all the seals, and paint the steel body. At the time, I used Tremclad spray paint. After 2 years, 2 winters on the road, the rust was coming back and I was almost back to where I started. From some research on the internet, I found the POR-15 system - a polyurethane based prep and paint system that seemed to be much more durable, so I decided to give that a try. 

Rust returning to the differential case - 2 years after Tremclad application

The first component I cleaned up and painted was the right front bearing carrier. I had the drive axle out of the car to repair the oil leak, and some of the suspension components disconnected, so this was a good time to access the part and get it done. 

Bearing carrier - loose rust removed, degreased, and treated with the rust conversion primer.

The POR-15 system is comprised of a few basic steps:

• Remove loose rust
• Degrease using the POR-15 degreaser
• Prime using the rust conversion primer
• Paint - at least two coats - using the polyurethane paint.

Bearing carrier painted with POR-15 Black Paint

What's interesting with the system is that the degreaser and primer are both water based - and the paint required humidity to cure. This allows you to perform the steps fairly quickly one after the other. You don't need the part to be perfectly dry before painting (although you don't want any standing water on the part which may affect curing by causing bubbling under the paint). 

Surface rust on the rear bumper

More surface rust on the rear bumper

Rust on right side rear bumper mount

I had pretty substantial rust on the rear bumper, trailer hitch and bumper mounts. Large areas of paint were flaking off the trailer hitch, and large areas of the rear bumper were rusting badly. 

Loose paint and rust removal with 3" carbon steel wire cup brush on grinder

I pulled the rear bumper and mounts from the car, and the trailer hitch. I used a 3" cup brush on my Dewalt 20V grinder to remove loose paint and rust from the parts. It took about an hour to do all the parts - there was substantial rust and the cup brush worked fantastically. What a tool, highly recommended. 

3" Wire Cup Brush - great tool for cutting through paint and rust

With the parts cleaned, I washed them with soap and water to remove all the loose scale and grinding dust, prior to degreasing. 

After loose paint and rust removal, rinsed and ready for degreasing.

To degrease the parts, you use the POR-15 degreasing solution, diluted 4:1 with hot water. I use a plastic brush to scrub the parts and get into hard to reach areas. When complete, rinse the parts with hot water. 

Immediately after rinsing, you can do the rust conversion primer since it is water based. Apply the rust conversion primer to all bare and exposed rust and metal. I use a 1" paint brush to scrub it in as good as possible. The instructions suggest you leave the surfaces wet for at least 20 minutes, I went back and reapplied the primer about 5 times over the course of an hour to ensure a good application. 

POR-15 Metal Prep and Degreaser

POR-15 Rust Conversion Primer applied - it's slightly foamy - keep it wet for the entire treatment time

Once the rust conversion treatment is complete, rinse the parts off with hot water and allow to dry before the paint application. 

Bumper surface following rust conversion primer treatment. 

The POR-15 coating comes in a limited number of colours for various applications. There is Gloss Black, Semi-Gloss Black,  Silver,  Gray  and Clear. In addition, there is a high heat caliper paint available in Black,  Blue,  Red,  Silver and Yellow. I have the Silver, Gloss Black and Silver caliper paints. For touchups on the underbody steel, I used my silver paint, just so that it wouldn't contrast too badly with the seafoam green factory color. For the suspension parts, rear bumper and hitch, gloss black obviously from the photos. 

POR-15 Gloss Black applied to the trailer hitch

POR-15 Gloss Black applied to the rear bumper and mounts, and trailer hitch

The paint application is pretty straightforward - I use disposable brushes so I'm not bothered with cleaning them. You need a minimum of two thin applications, applied before the coating cures completely. You can recoat once the initial application is dry to the touch with a slight finger drag (stickiness). If you allow the first coat to cure completely, you need to sand before the second coat - it's important to time your work. 

POR-15 Silver applied to rust touchups on the underbody (battery box next to suspension compressor)

I wasn't able to get up around the rear suspension mounts with a tool to remove loose paint, there is not a lot of access in those areas. I've ordered a dremel flex extension - will see if that allows me to get at the flaking paint in those areas and I'll post an update when I get that done. I really wanted to get all the corrosion protection done before this winter. 

Gloss Black POR-15 on the rear differential case. 

I painted the rear differential in the car. The Tremclad provided some protection, so I didn't have massive pitting and flakes of rust, so prep was pretty quick and easy. The differential is exposed to road salt and grit, so I'm looking forward to how well the POR-15 holds up over time. 

Reinstalling the bumper and hitch components - spacer washers for bumper held on by masking tape

It was totally worth removing the hitch to treat the rust on the hitch - there is no way I could have done a proper job of it on the car. It's common to see rusty hitches - but I hate seeing the rust on my car. If I'm going to keep it, I want it to look good. 

Ready to lift the trailer hitch back onto the car

Reinstalling the hitch was fairly straightforward. I treated all the hardware by soaking it in the POR-15 primer overnight. Once everything was reassembled, I coated all the fasteners with the black POR-15 coating. 

I didn't completely disassemble the hitch, so I needed to pull the crossbar into position with a load strap

Rear bumper and hitch installed. Looks great in gloss black - will mostly be covered by the bumper cover.

So - another job done. Looking forward to seeing how well the POR-15 holds up over time. The final step was to apply fluid film in critical areas - around fasteners, where there is metal to metal connections, and inside the rear bumper cavity that was inaccessible for painting. One other comment - removing the rear bumper cover on the E61 is really quick and straightforward, much simpler than removing the front bumper cover. It only takes about 10 minutes, and it's probably worthwhile removing it periodically just to clean out the road salt and grime that collects within the rear bumper that caused a lot of the corrosion in the first place.

Sources

Some POR-15 products are available at Canadian Tire at a reasonable price. For everything that Canadian Tire didn't carry - I simply ordered from the POR-15 online store - quick delivery in a couple of days. Real simple.

Let me know if you have any comments or questions below. 

 

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BMW Exhaust Heat Shield Repair

Some repairs will require removal of the complete exhaust system, in my case, removing the engine for turbo replacement, and replacing the left rear drive axles. With the exhaust removed, you have access to all the heat shields, and the driveshaft tunnel heat shield needs to be removed in order to inspect the driveshaft and the front driveshaft flex disc. 

In my case, I had some pretty serious galvanic corrosion of certain heat shield connections, particularly at the driveshaft tunnel brace, and a couple mounting holes for other various heat shields. This is a Canadian car, and it's used summer and winter, exposed to a lot of road salt and spray. I checked into replacement OEM parts from the dealer, but they are pretty expensive (probably due to the shipping cost of large, lightweight parts). 

I did a quick repair, which consisted of cutting a square of architectural aluminum, 23 gauge (0.57mm / 0.023") thick, larger than the hole to be repaired.

E60/E61 Muffler Heat Shield. 

I would contour the patch to the shape of the heat shield. It doesn't need to be exact, because the aluminum is pliable, and it will take the final shape required when replaced in the car. 

Patch riveted onto Muffler heat shield.

Inside view, note the gray spray paint which is cold galvanizing compound.

Once the patches are complete, I'll spray all the general area of all the fasteners, front and back sides, with a thick coating of cold galvanizing compound. The galvanizing compound contains zinc, which is sacrificial to aluminum on the galvanic scale, meaning that theoretically the zinc should oxidize before the aluminum when put back in service, protecting the aluminum from corrosion. 

Heat shield replaced on the car with a new body nut.

In one case, I installed the body nut reversed because the weld screw had broken off and was shorter than usual. 

Galvanic corrosion around the driveshaft tunnel brace

What's interesting about the galvanic scale and the corrosion of the aluminum heat shields, is that the heat shield corrosion is probably protecting the steel chassis and body of the car from some corrosion. 

Patch on the driveshaft heat shield, in the area of the driveshaft tunnel brace. 

Driveshaft tunnel brace was so badly corroded I simply replaced it with a new OEM part

Driveshaft tunnel brace - bottom side

The heat shield repairs that I did 2 years ago and just recently inspected have been holding up will, with no further issues. 

One maintenance habit I'll make now that I'm committed to keeping the car until it runs into the ground will be to try to remove the underbody protection (not necessarily all the heat shields) and get underneath the car to spray off all the salt following the winter driving season. The amount of salt and road sand that the underbody protection can capture is impressive. 

I'll do a separate post on the corrosion repairs I've done on the body, and the rear bumper. More to follow. 

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BMW E61 Hydraulic Liftgate Pump Rebuild

The liftgate hydraulic pump in my 2010 BMW 535xi Touring lost hydraulic fluid level about 2 years following a quick fluid level top off. This time, there were two issues: i) bad seals on the liftgate cylinder; and ii) failure of the seal in the hydraulic pump accumulator piston, leading to leakage below the pump. 

I'll do a writeup on replacement of the lift cylinder separately. This post describes the replacement of seals and o-rings in the pump assembly.

BMW Hydraulic Liftgate Accumulator bore, piston and spring following dissasembly

When your liftgate starts struggling to reach the full open position, troubleshooting is fairly straightforward. The pump is located in the rear compartment, directly below the liftgate cylinder on the left hand side of the car, attached the left rear fender. To access, remove the left hand rear storage compartment door, then remove any audio components hindering access. Be very careful disconnecting the fibre optic connections on the audio components.

BMW Hydraulic Pump - low fluid level, fluid weeping from the accumulator (left side of pump)

Once you can see the pump, you'll note the "+" sign on the side of the plastic fluid reservoir. The oil level should be in the center of the "+" sign. In my case, the fluid reservoir was nearly empty, with traces of hydraulic fluid dripping from the accumulator housing (to the left of the fluid reservoir). 

Unfix the pump, lift to show bottom of accumulator and fluid weeping from vent hole

There are some gymnastics required to unfix the pump. Some can remove the pump without removing the left rear cargo area trim panel. If you're removing the pump for a rebuild, it may be easier to take the time to remove the trim panel. 

Once you have the pump removed from the car, and the hydraulic lines to the cylinder disconnected, you're ready to work on the replacement of seals. In the photo below, working clockwise from 12 o-clock, you have the motor top right. You have the mechanical pump mid right - between the motor and reservoir. The reservoir is bottom right. To the left of the reservoir is a hydraulic accumulator (a piston and spring designed to maintain hydraulic pressure, which holds the liftgate in the open position without the motor / pump running.) Just above the accumulator is a valve body, where the hydraulic lines connect and where the pressure sensor (top left) connects. 

Right side: Motor, pump and reservoir. Left side: Accumulator, valve body, and pressure sensor.

Removing the pressure sensor is straightforward. Remove the two hex head cap screws, and pull the pressure sensor straight up. The pressure sensor is sealed with a single o-ring - 9mm x 2mm. (All o-rings mentioned in this post are described by inside diameter (ID) then thickness. For outside diameter (OD) - double thickness and add to the ID.)

Pressure sensor with cap screws, and o-ring seal at base

I removed the motor, it is sealed to the pump with a single o-ring (41.6 x 2.4mm). I made no attempts to remove any pump components, I removed the pump, tried not to change the indexing of the drive spring, replaced the o-ring and replaced the motor. 

Motor removed. The o-ring stayed in the pump recess, it removed with a pick. 

In order to remove the accumulator piston, you need to split the two halves of the pump assembly. There are two long hex head countersunk screws which hold the two halves together. When you split the two halves, you'll note 5 oil passages which are sealed with small o-rings (4 x 1.5mm). Replacing these o-rings is very simple, just pop out of their recesses and clean any debris with a clean, lint free rag. 

Left and right halves separated - note 5 sealing o-rings.

Once you have the two halves separated, you can disassemble the accumulator. There are four hex head countersunk screws which hold the bottom plate to the accumulator body. Remove them slowly, and remove them equally (a few turns on each screw in rotation) because the bottom plate of the accumulator is under spring pressure. By separating the two halves of the pump, you ensure that the piston is at the top of the bore by removing any hydrostatic pressure remaining under spring tension. 

Accumulator piston removed from bore, note bits of piston seal disintegrating, dirty fluid

The piston will only come out of the bore with the two halves separated. Try to remove the piston square to the bore - to avoid the metal edges of the piston from scoring the aluminum bore. Same when replacing the piston, avoid rocking the piston in the bore, and insert squarely. The piston is a urethane U-cup seal, 35mm ID, 45mm OD, 7mm tall. 

Accumulator disassembled - piston, seal, spring, base and screws

Old accumulator piston seal on the left, new urethane U-cup seal on the right

New seal on the piston, old seal on the right

The final seals which are replaceable are the reservoir to pump seal which is a 39.4 x 3.1mm o-ring, and the reservoir drain/fill port, which is a 6.1 x 1.6mm o-ring. Reassemble in the reverse order of disassembly. Ensure that the accumulator is reassembled before assembling the two pump halves. 

After having rebuilt the pump, and disconnected / reconnected the cylinder hoses, you will need to bleed air out of the system. Reinstall the pump in it's normal location behind the left rear wheel well, but keep the reservoir off the pump. I used some 1/4" vinyl tubing to draw oil from my replacement oil can, and to reject oil and froth from the return line to an empty aluminum can. 

Bleeding the pump using vinyl hose. Note froth returning to the aluminum can. 

I used AeroShell 41 Hydraulic Fluid for this repair

Once the froth turns to a consistent air free oil flow, you can stop bleeding, remove the vinyl hoses, and partially replace the reservoir cup. I then refilled the reservoir using a syringe and vinyl hose to get the fluid level back to the "+" sign on the side of the reservoir. I used a regular stainless steel band clamp to hold the reservoir on the pump. 

Refilling the reservoir with the pump mounted in the car

Reservoir replaced, topped up to the correct level. 

I purchased extra seals when I completed this project, I'll put some seal kits up for sale on eBay for anyone interested in doing this repair.

I've made some repair kits available at this link. 

I've made some hydraulic fluid and refill kits available at this link.

Let me know if you have any questions in the comment section below. 

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