504 brake pad change

[cane toad]

What is the correct procedure for changing the front brake pads on a 79 504 sedan and what necsitates the machining of the discs regards cane toad

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[Lennix]

If its just the basic task of changing them, you just take off the wheel, remove the clips holding the disc in place, retreive the old ones and put new ones in the way the old ones sat. Its important that you dont depress the brake pedal while you do this. One done drive slowly in a safe place with no suddent obstacles to test the brakes before heading into traffic. If you get the correct disc there shoudl be no need for machining them. It is recommended to clean (with fine sandpaper) and inspect the disc before fitting new pads + inspect hoses etc..

[John505]

Only use methylated spirits or brake fluid on the brake caliper piston rubber seals. When you have removed the small bolt holding the twin rods that secure the pads in the caliper, remove the rods using screwdriver/pliers etc & attempt the remove pads. If they are stuck by a wear lip of metal on the edge of the rotor, you will need to push the piston back a little to provide more room to pull the pads out, one at a time.
With the pads out, check the rubber seals - if there are any brake fluid leaks past the seals or the seals are badly torn, then they will need to be replaced, which means the caliper must be removed & dismantled. Can be DIY if you know what you're doing - otherwise a brake repair shop job.
To install new pads the main trick is to push the piston all the way back into the brake cylinder. I use an excellent tool made by Kingchrome for this, or you can use small piece of wood & lever. Watch for overflow of brake fluid from the brake master cylinder.
After pads in place refit the holding pins & use some medium strength threadlocker on the small holding bolt. Reinstall anti-rattle clips & depress the brake pedal a couple of times to seat the brake pistons/pads.
Overall fairly simple DIY - but if either seals or rotors need changing there is a lot more to it! Fortunately 504 brakes are not like later generation Pug brakes where there is an ongoing need to renew rotors as well as pads.
John505