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#1
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78 300sd brake pedal going to floor after master cylinder replace and bled
I have a 1978 300sd with brake issues. The pedal slowly goes to the floor when the engine is running but not when off. I have replaced the master cylinder twice, both rebuilt form auto parts store, and bled the system from the brake cylinders. I have checked the vac at the pump and get 25inHg. The booster is holding vacuum also. I have looked for fluid leaks and find non. Now i am at a loss. Could air in the system cause this?
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#2
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You usually need to bench bleed the m/c prior to installation to ensure there is no air. Bleeding at the wheel cylinders won't free the m/c of air if any is trapped within it (likely).
I've successfully bled it on the vehicle using a kit from Napa. Tubes are connected to the outlets of the m/c and routed back into the reservoir. |
#3
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agreed. also in question is quality of rebuild... used is better than mcparts junk
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#4
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Why would a used master cylinder be better? Replacing a 30 year old wear item with another 30 year old wear item means you're likely gonna be back in there replacing that sucker again in a short period of time.
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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate Sooner or later every car falls apart, ours does it later! -German Narrator in a MB Promotion Film about the then brand new W123. |
#5
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I did bench bleed the m/c prior to installation.
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#6
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Quote:
if you bench bleed, and flushed the lines, and got all the air out of the calipers, then the only thing left is bad MC.
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#7
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Thanks. Plan to try full bleed tomorrow. If that does not work another m/c i guess.
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