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If it don't leak it's OK (verbose to epic proporti (archive)

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Posted by Ken F. on December 25, 1999 at 13:52:06:

In Reply to: Re: "bottom end stuff?" define? posted by john on December 24, 1999 at 21:11:35:

: : : : : : Was planning on driving home for Xmas, when Mon. a front caliper locked on. I suspect corrosion in caliper piston wall. Although it may not be the best repair, plan on cleaning & renewing seals in caliper, and bleed system. (cash flow not available for a new caliper) It'll be a street side repair. Question. Any suggestions for popping piston out if a supply of compressed air is not handy? Thanks in advance and best for the holidays

: : : : : i did it with the big screwdriver like the other reply to your post. be careful you don't drive the screw driver thru your hand (the one holding the caliper) A vise would be good, i don't have a big enough one. all 8 pistons sitting on my bench. i cracked off a small portion of one lip (by prying) not rendered inoperable. so look out and make sure you keep prying from different points around the piston as best you can (there's a couple really obvious GOOD spots) and they come out. biggest longest flat tipped you have. you need at least 12" of lever arm.
: : : : : BTW, where did you (will you) buy rebuild kits? i'm the quintessential cheapskate and i'm poised to go w/ BMP (i could share phone, address, pricing, part #'s) but i keep thinking there's got to be a cheaper solution, since it's just 4 square o-rings and the dust boots (which you don't REALLY need) so maybe we could converse on parts sourcing. Good luck!
: : : : : John

: : : : 02 calipers need to be resleeved to be properly rebuilt. Unless you like 2" of travel between the pedal and floorboard and terrifying suprises at stop signals.

: : Sure. After twenty + years of the pistons sliding back and forth the cylinder bore can become oversized. Just replacing the 0 ring is often not enough. You must remember the fluid is under considerable pressure when braking and,as in my case, finds its way around the seals. That is why when you buy a rebuilt set they have been resleeved to "true the bore."
: : If this sounds like "bottom end stuff" the same forces are at work.

: you lost me on this comment! obviously, newer is better, but if it don't leak, it's OK! I just want to make sure I get the best deal on a suitable repair. And my pistons and cylinders are fine. resleeving would likely amount to reduction in piston OD (centerless grind), plating back up to slight oversize condition and honing out piston bores to accept reworked pistons. all with net result of the OD/ID combination currently on my bench.
: Braking pressures and temperatures are severe, so i agree that attention to detail and proper repairs are important. there's just more than one way to look at anything. i'm not the type to throw money at something that doesn't need it.

: Merry Christmas! Thanks for the discussion.

John, Down here we have an old saying which states: You pays your money and you takes your chances!
First of all, If fluid leaks past the O ring it doesn't necessarily follow that it will escape past the dustcap. Thus a loss of pressure and no obvious indication of the problem. That said allow me to share my experience with you.
Upon noticing a leaky caliper on one of my 02s I decided it was time to rebuild the entire braking system. I rebuilt the calipers with the O ring and dustcap as you plan to do. I also rebuilt the master cylinder (a feat worthy of Houdini any of you who have attempted this will agree). I had my booster returned to me from the rebuild shop as it tested fine. I also rebuilt the rear wheel cylinders, replaced pads, shoes, and hoses. The brake linkage was fine.
Imagine my suprise when after installing all of these new parts the car wouldn't stop.
So it sat for 6 months while I tried to divine what I had done wrong. Until I discovered the BMWCCA publication of a compilation of 160 tech tips for 02 owners by Scott Chamberlain (Sept 93) and Michael Self (Oct 94).
#30 states "Rebuilding a brake caliper without sleeving is a waste of time. Buying a new unit is a better bet."
Immediatly after reading this I pulled a set of calipers from another car to test this theory. Sure enough, the car stopped fine.
One's personal knowledge of the outside diameter of the piston and inside diameter of the cylinder becomes a moot point when your grills, nose, hood, fenders and personal liability are at stake and the new ones work!
So suit yourself John, as for me, I consider my brakes one of the things worth throwing money at because who knows, I might wind up behind you at a red light someday.


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