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Discussion Starter · #1 ·
Hi all,

Today while driving home, my car was acting unhappy. The steering wheel was shaking proportional to speed. Annoyed by this, I went under the car when I got home. What I found was that the left front wheel was considerably hotter than the right. Moreover, when I put the front in the air, the left side was dragging more than it should and damn near locked after I stood on the brake pedal for a moment. So, the left caliper is seizing.

Last year I replaced both front calipers with rebuilt units (both were in bad shape plus I got an amazing deal - $15 a side - on new calipers), the front pads as well as the rotors. This year I had the system apart to paint the calipers (black) since they were surface rusting. At the same time I re-cleaned and re-lubed the slide pins. So, I'm leaning toward the flexible lines as a possible culprit. However, how do I test the flexible lines to know whether they are at fault? Short of replacing it (and the rest as well), I can't think of any way to know whether or not the left front line has swelled into a check valve.

Any advice would be appreciated!

Thanks,

Luke
 

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The flexible lines really only flex much one way. They're brake lines on a bmw...not the sort of thing that fails.

On the other hand, one possible cause is that you spent $30 an axle for calipers and pads. I can't imagine how that could be, but, of course, I suspect less than bmw quality in some aspects...like maybe functionality! :lmao:

Best you can do now is clean things up. Rotor can get hot from having the pads slip and they'd then grind on the lip of rotor...if you have one. They often are loose in the piston. Maybe your piston seals ripped and dirt got in causing the piston to seize. maybe you didn't use brake grease on the caliper bushings...or maybe the bushings are just crappy material.

I don't know how to test the lines other than to confirm they're not leaking. Only other possible is that you have air in your lines. Try a good 2-man bleeding. When you're done...before you start the car...pump up the brakes until you feel they're really firm. Then start the car.
 

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Discussion Starter · #3 ·
Thanks for the response. First, to set the record straight, I didn't spend $30 an axle for calipers and pads, just for rebuilt front calipers (which is still cheap). I got them on clearance from BavAuto and they were rebuilt from original Ate castings. I don't have reason to believe that these would fail in less than 10,000 miles (even being on clearance). As for pads and rotors, these are genuine BMW parts. The system was bled using proper tools and methods and has worked fine until now.

As for why the rotor is hot, there is no question that the caliper is seizing. The wheel is acting exactly as in this video - http://www.youtube.com/watch?v=pnh_vydPoK8 (see 2:30 - 3:00). Also, this video (as well as http://www.pelicanparts.com/BMW/tec...6-Brake-Lines/101-Projects-56-Brake-Lines.htm) suggest the lines as a possible cause.

The question remains, other than to replace them and see, is there any way to test the line?

Thanks again!

Luke
 

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Ate OEM brake lines are $17 each from autohausaz. Since your original lines are >10 years old, just replace them (my replacement rule for brake lines). Opinion ... because you bought rebuilt calipers on the cheap doesn't mean they are any good. I've rebuilt many calipers myself, and while there's not much to it, a rebuild really should last for years. If I were going to keep the BMW for a long while and the caliper needed rebuilding, I'd do it myself or buy new (yes, ouch at $221 each new at autohausaz). Or you can keep buying rebuilts for <$50.
 

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Discussion Starter · #5 ·
I tend to agree - pelican has them for $16.75 a piece as well. In any event, it would still be nice to know if the caliper is shot. I agree that a proper rebuild should last for years - and have rebuilt many myself that have done just that. However, I don't believe that a rebuilt caliper is, a priori, bad.

Luke
 

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It has always puzzled me why bmw uses single piston calipers on these cars. Granted, they seem to work just fine when they are working. But even my lowly toyota pickup has 4 piston calipers. hmm wonder if they would fit on bmw.
I'd suspect your on sale rebuilt calipers. See if they are working smoothly - if not - you know what to fix.
If they are working smoothly it could be brake lines - but I'd consider that unlikely unless they look like they might fall apart.
You could swap brake lines right to left. but if you do that you might as well replace them both.
It could be master cylinder.
My guess is sticky caliper. On a cheap rebuild probably due to bad rubber boot. I assume bmw calipers use rubber
boots on the one piston they have - I could be WRONG
 

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I'd like to jump in here because I am having a similar problem. I had a hot rotor and shaking at around 30 mph. Dealer said stuck calliper so I order a new BMW replacement calliper from Bavauto for $320.00. It solved my problem but only for about 2,000 miles and now the exact problem is back. Is there anything other than a stuck calliper piston or bad calliper guide pins that can stop the calliper from moving back after you apply the brakes?
 

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I'd like to jump in here because I am having a similar problem. I had a hot rotor and shaking at around 30 mph. Dealer said stuck calliper so I order a new BMW replacement calliper from Bavauto for $320.00. It solved my problem but only for about 2,000 miles and now the exact problem is back. Is there anything other than a stuck calliper piston or bad calliper guide pins that can stop the calliper from moving back after you apply the brakes?
If it is the rear brakes it could be a stuck parking brake shoe. Are you certain the problem is from the caliper that you replaced, or could it be from the other side?
 

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Discussion Starter · #9 ·
tvardigan - assuming the corner is still binding, it could be the line. In my case, it wasn't. It was a bad caliper (dmax - I fully admit that being cheap bit me in the ass ;) ). That said, my flexible lines were in bad shape so I was glad to change them out as well as the bad caliper.

As a test (and to answer my original question in the thread), I propose that you put the corner in the air, step on the brake to see if you are getting binding on that corner; then, if you are, back off the bleed screw slightly to relieve any pressure that the line is holding in. If the rotor stops binding, then your flexible line is to blame. If nothing dramatic happens, then you have issue with the caliper (either piston or guide pins). Either way, you will want to bleed the corner after opening the bleed screw.

Good luck,

Luke
 
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