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#1
10-07-2003, 02:14 PM
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Brake seizure problem
I am looking for a solution to a problem that my 1963 220SEb Vin# 111.023 120 39550 has developed. This 111 model has front disc brakes and a non-tandem master brake cylinder. Even though my factory Mercedes maintenance servicer manual covers 1959-67 models, it discribes only tandem master cylinders and not non-tandem. Apparently my master cylinder's internal design does not require a special check valve to relieve pressure on the front disc but does have a primary check valve to trap fluid going to the rear drum brakes. This design is quite different when compared to the illustrated later tandem master cylinder, which includes a "special" check valve on the line to the front disc brakes, which releases pressure on the discs once the brake application is removed. I recently had the Master Cylinder and the remote ATE50/26 Power brake accumulator/slave rebuilt. Now I am experiencing occasional brake lock up! The only clues that I can provide is that once the brakes lock up: 1. I can free them by opening a bleed valve on the boost accumulator slave cylinder. 2. While it is locked up, if I unscrew the hydraulic line going from the master to the booster, fluid slowly dribbles out, but if I unscrew the line from the booster returning to the master cylinder it spurts out under pressure. On the surface I would assume that my problem is not with the rebuilt master cylinder but somewhere in the rebuilt booster or slave cylinder that is maintaining pressure in that booster to master return line. If that is the case, where in the booster/slave is my problem? Does anyone have any thoughts?
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#2
10-08-2003, 10:29 AM
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Gregg,
Don't know if your booster to master return line is metal or rubber but I once had a VW front brake line swell almost completely closed and would not allow fluid to return to the master cylinder after application of the brake pedal. Jerry
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Jerry - If you don't learn something new every day, you aren't paying attention!! 1971 108 280SE 2.8 "Ronnie" 1985 300TDT (76,904 Original miles  ) "Sadie" (Sold-went back to Arkansas)1984 300DT "Green-go" (Sold) 1984 300DT "Silver Bullet" (Sold) 1956 220S Ponton 1985 300D (Sold) 1984 300D
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#3
10-08-2003, 01:07 PM
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Jerry,
Thanks for the input. The return line is metal as are the other lines in the system including flexible lines (at the wheels) that had been previously replaced with teflon lined stainless steel, so this would eliminate the collapsing hose theory. Today I isolated/ bypassed the booster and the brakes are responding normally (no seizure), although of course without boost, so I am assuming that the rebuilt booster or its slave are at fault and will return it to the rebuilder under warrantee.
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#4
10-08-2003, 08:36 PM
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Gregg:
Double check to make sure you don't have any air in the system up front -- I had fits with my old Toyota Crown with a remote front brake booster, and that was the problem. A little air in the front system (from the leaking proportioning valve) would cause the front brakes to seize -- stamping on the brake pedal a couple times would cause it to finally release. You might try that, just to be sure. The saftey bypass system around the remote booster can also trap air, and this will again cause the slave cylinder at the booster to keep the brakes applied when you release the pedal. Huge pain in the sitting part, I didn't regret selling THAT part of the car. I did like the power and handling, though.... Peter
__________________
1972 220D ?? miles 1988 300E 200,012 1987 300D Turbo killed 9/25/07, 275,000 miles 1985 Volvo 740 GLE Turobodiesel 218,000 1972 280 SE 4.5 165, 000 - It runs!
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