Posted by HH56 On 2016/5/23 12:57:56
If the pedal is slow to return it's possible the pedal is mechanically binding or something has happened to the rubber seal in the valving and vacuum is still being partially applied to pull the piston down. I think most likely would be something in the canister around the leather piston seal has either hardened or become sticky.
There is a single spring inside the unit which pushes the piston and attached pedal back to the top. Anything that provides resistance to the spring such as dry lube or even a gummy surface caused by deteriorating lube or worse, hydraulic fluid leaking into the vacuum side would make things slow to return.
I would check the fluid level to make sure vacuum has not pulled the level down. If that is OK let the car run awhile to heat the unit up and then work the brakes several times and see if things start freeing. If not then it is time for more comprehensive troubleshooting.
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