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Drum Brake Squeak

September 24, 2010 | Troubleshooting & Repair

By David Jones, Dick Weiss, Alan Klingen

[Editor: Just installed new pads and your drum brakes squeak? Not sure about how to "break in" the pads? Here's advice from three experienced 356ers.]

David Jones: There are plenty of procedures written about breaking in disc brake pads and rotors but very little about drum brakes any more because they are not very common now. As I raced a car with drum brakes it was common knowledge that one could not go out with new brakes and expect them to work perfectly immediately so there was an established break in procedure and as I mentioned we always put a 45 degree chamfer on the leading edge of the shoe as Porsche also recommend for brake shoes, this lowers the propensity for brake grab and chatter. I would use the brakes  early and lightly for the first few dozen applications so as not to overheat them and cause them to glaze over which can cause the squealing. Gradually increase pedal force over the first 500 miles and then they can be considered bedded in. This of course is doing it by the book but use good judgement and sensible brake use and they can be considered bedded in much sooner. I would also examine the drums very carefully to see if there was any component touching the drum which could cause the squeal.

Dick Weiss: The shoes should have a flat surface (including the lining's edge) to contact the little pads on the face of the backing plate;  some relined shoes have only the steel edge in contact and will tend to wear into the pads unevenly if the drums aren't truely round. There should be a chamfer one each end of the linings (allowing changes to either side for direction) and suggested by a tech bulletin to add 2-cuts across the linings (but NOT completely to the steel backing!) to divide the lining into 3-segments.   Slot width=about 2,5mm (I use double blades in the hacksaw).  The slots act as dust collectors, but allows the linings to meet the drum's surface easier.  There were times where the slots were cut at an angle to be self-cleaning if aimed outward and discharged to the vent holes in the drum's face--mostly in 'B' drums, but a bulletin was issued to add the holes using a template for the 'A' drum. Braking-in the linings will take place w/in 50-100 miles BUT they must be arced as close as possible to match the drum's ID and NOT 'lightly' using the brakes will minimize glazing!

Alan Klingen: Check the basics; drum cut true, no leaks, and the shoes arced correctly. The shoe arc should be so that there is a slight "rock" in the shoe as you lay it in the drum. In other words the radius of the shoe arc should be slightly smaller than the arc of the drum. If you lay the shoe in the drum and hold one end of the shoe against the drum the other side should show a slight lift, 1 mm would be good and more is not too bad. If all these are good then its a lining issue. Is the shoe old? I have had great results with the lining that NLA provides. Not an empty plug, they really are good linings.

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