Air in Brake system
 

Hi,

I replaced the rear brake lines, hoses, calipers & pads on my 90 300D (w124) last week. When i bleed either of the rear brake calipers there is a constant flow of air bubbles on both sides along with brake fluid. I emptied two full quarts but still the bubbles don't seem to stop.

I checked the rear compartment of the reservoir and it is full. The brake lines are tight at the T junction in the back and absolutely no leaks. I am stumped. Could the rebuilt calipers be bad out of the box ????? I got these rebuilt ATE calipers from O'reilly's for $73 a piece. Please advise.
Thanks

smk_texas

How are you bleeding the brakes ? That may be the problem.

I used the Motive (one man) power bleeder. I pressurized it up to 15 psi and loosened the bleed screws at far right caliper first. There is a good constant flow of brake fluid but the air bubbles don't seem to stop. I got frustrated after wasting almost 3qts of DOT4 bf. I closed the closed the bleed screws and pumped the brake pedal. It seems to build pressure initially but the pressure fizzles out and the brake pedal goes down. There is no movement in both the rear calipers. Only the front brakes are working. Thanks

first the rear compartment of the reservoir is for the front brakes.it is back to front.try using close off pliers on the front brake hoses so that you can get all your pressure at the rear.how old is the master cylinder? i have seen them go bad when a lot of pumping is done to clear air.if you have no leaks and the reservoir is full [both compartments]then i would think the air is coming from master.

This may help
 

It is possible to inadvertently mount the left caliper on the right side and vise versa (on the back brakes). In this case, the rubber lines will have a tighter loop, the bleed screw will be in the wrong position, and it will impossible to bleed all the air out. No need to ask how I know this.

Hi David,

The original mc was bad so i replaced it with a used one along with the calipers, lines & pads. May be the replacement mc is bad ???? Thanks