Tandem Master Brake Cylinder?

[bpossel]

I recently replaced my master brake cylinder and fluid reservoir.  As part of this service work, I bled my entire brake system with my “power bleeder”.  I was able to obtain a nice flow of fluid through all 4 calipers.

Last night, I removed the left front caliper to clean and inspect the pistons.  I then re-installed.  I didn’t want to bleed the system again until I did the same process on the right front caliper.  In the process of repositioning my car in the garage to make room to complete the right front caliper, I noticed that my brake pedal went ALL the way to the floor, as if I didn’t have any brakes.  (note: still had plenty of fluid in the reservoir, both chambers…).  I ended up using the parking brake to carefully re-park the car.

Ok, I wasn’t expecting a good brake pressure, since I had removed & reinstalled the left front caliper (without bleeding the air out) …  but…  I was expecting that the rear brakes would work and that I could have used the rear brakes to reposition the car…  not!  

 :?: Question: the fact this car has a dual (tandem) master cylinder, can anyone think of why my rear brakes didn’t work?  Why my brake pedal went all the way to the floor?

  Thanks!
Bob


bpossel
Memphis, TN.
1971 280SL
1997 E320

[ja17]

Hello Bob,
The rear circuit kicks in very close to the floor when the fronts are out. It was probably there but so low and unfamiliar that you may have thought the pedal to be on the floor. If it happens again force yourself to keep pushing on the pedal. If you do not have some rear braking then you do have a problem.

One note of caution; always always pump the break pedal up before attempting to drive away after any brake work. It takes several pumps to fill the brake calipers as the pistons move outward and seat against the rotors. This must be done even after simple brake pad replacement.

Joe Alexander
Blacklick, Ohio

[A Dalton]

<<One note of caution; always always pump the break pedal up before attempting to drive away after any brake work. It takes several pumps to fill the brake calipers as the pistons move outward and seat against the rotors. This must be done even after simple brake pad replacement.>>

 To add to that caution.
 While pumping to refill the calipers, keep an eye on the fluid level in the res .. as you fill the cal., you are deleting the res., and if the res gets down low enough to allow air into master, you have to start all over again.....always top the res after any bleeding/brake work..........

 

[bpossel]

Thanks Guys!

I think I will start over and re-bleed entire system from back to front.  Its only time and some fluid.....  It has to be some trapped air somewhere....

Regards,
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[jeffc280sl]

Bob,

If your bleeder system is  a vacuum system and you haven't already tried this, place some teflon tape around the bleeder fitting threads so that it doesn't leak air.  If the threads permit air to pass it could cause you to blead and blead thinking tiny air bubbles are in the brake line when in fact the air bubbles are entering the system at the blead fitting itself.

Jeff C.
1970 280SL 4-speed

[A Dalton]

Originally posted by Lax882@aol.com

Bob,

If your bleeder system is  a vacuum system and you haven't already tried this, place some teflon tape around the bleeder fitting threads so that it doesn't leak air.  If the threads permit air to pass it could cause you to blead and blead thinking tiny air bubbles are in the brake line when in fact the air bubbles are entering the system at the blead fitting itself.

Jeff C.
1970 280SL 4-speed

 Which is why a pressure bleed is best...
 A nice single person bleeder I use is simply get a hand squeeze inflator from an old blood pressure cuff set-up.
 Hook the hose to a master cap with a fitting.
 These work slick cuz you can only pump them up to a few lbs, they have a open/close valve right on the pump squeezer, and they hold enough pressure to do a couple of wheels with each pump.
The other thing I like is their volume is not enough to drain the master down before they reach zero pressure, so you do not have to watch the res so closely.  I then use a clear plastic hose on the bleeders so you can see when the line is clear fluid/no air/new color.
 Slick , homemade,cheap, and flawless...