Date: 26 Sep 1999 18:30:20 GMT
From: johannes.hyvarinennopsamfi (Johannes Hyvärinen)
Subject: Re: welding frontbrakes 99 and 900


theomarnopsamknet.nl (TheoMar) wrote in <37ECAA1F.CF8E3DF8nopsamknet.nl>: >Still trying to repair my brakes. A while ago i discovered on >internet that it is possible to narrow the tolerence on 99(also 900) >frontbrakes by welding new material on it. >Can anyone explain where axactly i have to weld and how?? I've seen it done on my car, the results were good and it wasn't too much work. Let's see if I need a thousand words or more to explain this, one good picture would help a lot. First, let's get the terms straight: The front brakes are made of two main parts. The caliper is cast iron and contains the pistons. The other part, called "yoke" AFAIK, is made of a thick steel plate. It moves around the caliper guided by two grooves(?) in the caliper. The grooves are about 1 mm wider than the yoke is thick, and the yoke is pressed against one side of the grooves by a spring. Ideally, there is grease between the parts but it's kind of hard for routine maintenance. The problem is too much play between the _bottom_ of each groove and the corresponding edge of the yoke. The play should be less than 0.1 mm both sides combined, if you hear the noise there's more. You can roughly test the play after removing the wheel and brake pads by moving the outer edge of the yoke up and down. The wear is visible in the grooves after removing the yoke. Welding the cast iron caliper is probably a very bad idea, so the fix is to weld more metal to the edges of the yoke. I can't weld myself so my advice is not very detailed on this part. The metal from the welding machine (a MIG welder was used on my car) is enough, no need to use sheet metal or anything like that. After welding some stuff there you will need to grind most of it away to make the surface smooth. Try it on and reiterate until the play is below 0.1 mm (= until it feels right.) Don't make it too tight, the yoke needs to move freely even when dirty and in extreme temperatures. Standard disclaimers apply, don't do this on a racer as the welding might make the yoke lose some of its strength and fail under heavy pressure. It may be illegal in your country to even weld anything related to brakes, OTOH as long as it works nobody will look hard enough to find out :) If something is unclear, don't hesitate to ask here or by email. HTH, Johannes (99 GL '81)

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