300E Rear Brake Bleed Problem
Thread Starter
Newbie
Joined: Aug 2008
Posts: 7
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'95 S600, '77 300D
300E Rear Brake Bleed Problem
hello,
i have a '93 300E stubborn brake problem that needs some peer review and advice. the history is as follows:
1) replaced REAR brake disks and pads, opened the brake calipers - my mistake! 2) attempted brake bleed using standard pedal pump with that resulted in spotty fluid discharge with apparent air stuck in the lines, 3) thought problem was master cylinder and rebuilt it accordingly, 4) still not able to pedal pump and bleed the brakes, 5) in frustration took the car to a local inde shop and they bled the brakes using shop vacuum bleed tool, 6) since then the brakes have been working fine except about a week later noticed pedal travels about half way down before braking especially during first start up of the day and as car is driven more the pedal pressure/travel acts normally. 7) yesterday i adjusted the parking brake shoes. while there i decided to try and bleed the REAR brakes again thinking there was still air trapped in the lines. this time i used a Mighty Vac tool. initially i started on the right rear wheel and had good fluid flow out of the line but then only air. moved over to the left rear wheel, started bleeding and only spotty burst of fluid and mostly air. the vacuum pressure is good. in fact i can hear gargling air suction coming from the master cylinder fluid reservoir. i find that puzzling how the brake line can be sucking air from a fully topped up reservoir.
i feel something is missing here, i'm doing something wrong, in the bleed procedure. trying to avoid another $100 expense if taking it back to the inde shop. by the way, i have successfully bled the front brakes with good fluid flow - no air.
appreciate your input on this problem!
mark
i have a '93 300E stubborn brake problem that needs some peer review and advice. the history is as follows:
1) replaced REAR brake disks and pads, opened the brake calipers - my mistake! 2) attempted brake bleed using standard pedal pump with that resulted in spotty fluid discharge with apparent air stuck in the lines, 3) thought problem was master cylinder and rebuilt it accordingly, 4) still not able to pedal pump and bleed the brakes, 5) in frustration took the car to a local inde shop and they bled the brakes using shop vacuum bleed tool, 6) since then the brakes have been working fine except about a week later noticed pedal travels about half way down before braking especially during first start up of the day and as car is driven more the pedal pressure/travel acts normally. 7) yesterday i adjusted the parking brake shoes. while there i decided to try and bleed the REAR brakes again thinking there was still air trapped in the lines. this time i used a Mighty Vac tool. initially i started on the right rear wheel and had good fluid flow out of the line but then only air. moved over to the left rear wheel, started bleeding and only spotty burst of fluid and mostly air. the vacuum pressure is good. in fact i can hear gargling air suction coming from the master cylinder fluid reservoir. i find that puzzling how the brake line can be sucking air from a fully topped up reservoir.
i feel something is missing here, i'm doing something wrong, in the bleed procedure. trying to avoid another $100 expense if taking it back to the inde shop. by the way, i have successfully bled the front brakes with good fluid flow - no air.
appreciate your input on this problem!
mark
Senior Member
Joined: Jul 2004
Posts: 462
Likes: 3
From: Boulder, CO
86 W124
The reservoir seems full or to have enough but it doesn't, you're pulling in air. When I do it, I re-top every other set. Basically it has to be full to the very top otherwise you'll get just a bit of air and it screws everything up. The res is also chambered so it only seems full.
Try that or you might have a vacuum issue.
Try that or you might have a vacuum issue.
