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Wednesday, August 5, 2020

Doug's Domain

Doug Vetter, ATP/CFI

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Sunday, June 10, 2012

Front Suspension Overhaul - Day 6

Today I didn't get much more than a couple hours in before temperature and humidity became annoying once more but I did manage to (finally) disconnect the calipers and inspect them.

This was the first time I'd ever opened the brake line in this manner so I was naturally a bit cautious about doing so. To begin I made a point to use my 11mm flare nut wrench to avoid rounding over the fitting. As I loosened the fitting I found fluid began to leak out of the connection almost immediately but even with the hose fully disconnected I saw nothing more than a drop every few seconds. To make life easier come bleed time I decided to seal the end of the hard lines using a cap from an assortment I bought online. The best cap turned out to have an ID of roughly 3/16” or about 3mm but several were flexible enough to work.

With both lines capped my attention turned to the brake calipers. I removed the brake lines, pulled the bleeder screws and drained the fluid from the calipers into one of my new waste oil containers. The first thing I noticed is that the fluid in one of the calipers was a bit darker and cloudy than the other, which proves that flushing fluid doesn't necessarily push all the fluid out of the system. With the calipers drained I reinstalled the bleed screws, fired up the compressor, inserted a block of wood between each caliper piston and caliper frame and then proceeded to apply just enough pressure to the brake line port to push the piston out of the bore. The piston started to move slowly at first and then slammed hard against the wood. Sound advice: keep your fingers clear of the piston when you do this!

I went into this process thinking I'd refurbish the calipers and install the seal repair kit along with new caliber guide bushings. Unfortunately, an inspection of the pistons showed pitting in a couple areas. One piston was in decidedly better shape than the other, but still scored. While I have always known that rust on the polished outer surface of the piston is undesirable I lacked the experience to know how much rust (if any) represented a go/no-go condition so I posted a question over at bimmerforums and attached the picture shown above. Amazingly, in less than an hour, two well-respected pros on that forum responded “it's a paperweight”. Since the pistons are unavailable separately I have decided to add a new set of calipers to the list of parts I have to order this week. I can get ATE OEM units from Turner for $225/each and new BMW calipers for a bit more ($285 each). I'm not yet sure which I'll buy.

While I'm back at the salt mine this week I expect to deliver my parts to the powdercoater. My hope is to get those parts back by next weekend so I can begin assembly. However, as I have yet to pull the steering column, and doing that job should be a bit easier without the subframe installed due to clearance issues I won't shed any tears if the powdercoater drags his heels and delivers next week. In any case, I expect the car to be down for at least another couple of weeks and probably longer given that I'll have to get the car aligned before I can return it to service.

Mileage: 222600