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Old 12-28-2003, 07:29 PM
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Join Date: Dec 2003
Location: North Wales
Posts: 4
W123 Front Caliper Heat Shield/Piston Position

When istalling new pads I noticed that the heat shields on the pistons had deteriorated so I figured I would replace can only be had with a purchase of rebuild kit so I figured I would just rebuild the caliper. I have the official repair manual but I am confused about the position of the piston and heat shield. The manual says "the shields should be installed with an elevation on the piston facing upward. This elevation serves for one-sided contact of the break pads while braking which will reduce the tendency to squeal". The manual lists a "tool" to show the correct position of the piston and another tool for the installation of the heat shield and yet another for turning the installed piston so as to correctly position it. the piston position really that critical and is the use of the heat shields really necessary (Teves/ATE uses heat shields but other models of calipers (Bendix I believe) does not. I am concerned that I will get this job done and have the shields installed incorrectly. Lastly, the dust covers should be installed on the pistons first and then the pistons should be installed, correct? Is there an easy way to fasten the outer edge of the dust seal to the caliper?Thank you in advance for advice given.
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Old 12-28-2003, 10:13 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Pay attention when dismantling to the position of the piston, and do only one side at a time.

You can use the heat shield to help you locate the piston correclty -- just lay it over the piston to get the alignment right when you go to put the piston back in. This is the tricky part, as you must be very careful not to rotate the piston as it goes in, and it's somewhat difficult to get it started down the bore. Liberal amounts of brake fluid or assembly past (if you can find it, DO NOT USE anything except brake fluid or brake assembly paste!). I've had to pop the piston out more than once to get it in at the correct position. You aren't going to be able to rotate it without the special tool, I've tried.

Dust boot goes on after piston is installed, heat shield is last. MAKE SURE the piston is correct BEFORE pressing the head shield in, I've never gotten one out intact! Getting the dust boot down is a pain -- i use a square piece of wood and a hammer. I also use a similar but wider stick to push the piston down -- you can push it through the caliper and press straight down on the piston that way.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
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