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Wednesday, July 26, 2017

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Doug Vetter, ATP/CFI

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Saturday, September 24, 2016

Rear Brakes Overhaul Complete

When I put the car away last week following the failed test drive I figured the problem was either a damaged brake line that was acting as a check valve or -- however unlikely -- a defective new caliper. My dealer called yesterday to indicate the second new caliper had arrived so I scheduled some time today to put the car up on jackstands once again and attempt to diagnose the problem.

As my car is equipped with an open rear, even with the car in Park I am normally able to rotate the rear wheels. When I attempted to move the wheels now it was painfully clear that the left rear caliper was applying considerable pressure to the pads. Pushing the wheels with considerable force caused them to move only a few inches. Had I performed this simple test prior to going out on the test drive I would have likely avoided the overheating incident.

(Image: Closeup of the left rear brake caliper with inner pad fully retracted)

I pumped the brake pedal five or six times until it firmed up, and then opened the bleeder screw. Convinced that the problem was upstream of the caliper I was expecting to see a fountain of brake fluid come out of the bleeder but amazingly it did nothing but drip slowly, much as I have known the lines to do when swapping out other brake components. This proved that there was no significant hydraulic pressure in the lines and the likely cause was, in fact, the caliper.

I started to remove the caliper and after pulling the guide pins found the caliper and pads firmly gripping the rotor. So tightly, in fact, that I had to use a screwdriver to pry the caliper away from the bracket -- something I've never had to do to any caliper in the history of owning the car. The caliper eventually succumbed to my persuasion, however, so I pulled the pads and set them aside before using a 14mm open end wrench to loosen and detach the flexible line.

With the old part in hand I headed to the dealer where they processed a work order that allowed me to take advantage of the part warranty. Looking at the replacement caliper I sighed with relief when I noticed that the piston appeared a bit further recessed into the caliper bore.

Back at the garage I screwed the line to the caliper, mated the inner pad with the piston and attempted to fit the new caliper over the outer pad and rotor. The difference in fit was like night and day. The caliper just slid over the pads with room to spare. After I installed the guide pins I pushed and pulled the caliper along them and found just the right about of play. I then bled the brakes, pumped the pedal a few times and eagerly returned to the left rear tire to apply that sanity test I forgot earlier. Thankfully, I was able to spin the wheel with minimal effort. So, as it turned out, not only was my original caliper frozen, so was the new one! What are the odds?

I took the car out on my mile-long test loop and once again stopped half way through to get out and inspect the brakes. I smelled nothing and touching the wheel revealed no significant heat. Returning to the garage I once again sprayed the car down to clean off the dust that had settled in my absence, but this time I noticed no obvious effects when the water hit the left rear brake components. That gave me sufficient confidence to declare the problem fixed and prepare to head home. This turned out to be great news, particularly considering that the next thing I planned to replace was the ABS pump assembly. The quote for that little gem came in at $1275, including an extra "we feel sorry for you" discount.

After putting the E46 to bed I hopped in the E36 and headed home, again pulling over a couple times to verify the condition of the brakes. As I turned a corner my attention was directed to an annunciation in the gauge cluster: CHECK ENGINE. Obviously unrelated to the brakes but frustrating nonetheless, I just shook my head and resolved to accept the reality that taking care of an old car is a neverending process. So it appears as one problem is resolved I'll be facing a new one in the coming week. Till then...

Video: Troubleshooting stuck rear brake caliper

Mileage: 264200