ThE B l e E d I N G edGe

[pizza_king]

Let it Bleed. OK, I have a W124 '93 300E 3.2L. Project is to replace the rear wheel set of brake pads and well worn dics. Mistake I made, discovered after I replaced the pads, was that I completely removed the caliper and split the 2 sides (opened) to access the old pads for removal. Should have knocked out the 2 guide pins and removed pads, which would not have allowed air into the lines. I thought the air would be easy to bleed out, which I've easily done before on countless makes and models. Problem is while using the brake pedal to bleed the brakes per standard procedure (rears calipers only) very little air and fluid is coming out of the brake bleed screw, sometimes nothing at all. The brake pedal just mushes down to the floor without any firmness building up. I removed one of the rear wheels to observe the caliper/brake pads while brake pedal actuated, but the caliper pistons did move. Next plan is to bleed the front calipers, thinking air traveled to the front brake lines. Any advice would be very much appreciated. Thanks! Mike

[Xsbank]

Are you sure that the caliper is sealed properly?

Unfortunately, bleeding the brakes by pumping the pedal, the age-old way of doing it, also makes the main piston in the master cylinder travel through parts of the bore that it may never have been before. The result of this is, or can be, a master cylinder that's rubbish.

The brake fluid is supposed to be changed every (2 years?) because it absorbs water (hydrostatic? That doesn't sound right I'll have to look it up), so if the PO did not do that, there could be corrosion in the bore of the M.C. which will hasten its demise (hmmmm, talk about a bore).

I would get a mighty-Vac, or make a pressure bleeder, to bleed what's left of the brakes to see if it will bleed properly and to see if the master cylinder has had it. Pressure bleeding is the only way to go, apart from saving a dodgy M.C., but its much faster and much less fussy.

[Arthur Dalton]

Hygroscopic

Some master reservoirs have an interior sectional divide for front/back brake fluid..you have to fill the front completely before the fluid will go over the top of the divide into the rear section..check that closely..very common mistake..
...and never , ever split a caliper..

[aldedmon]

pizza king what was your final solution. I have same problem

[Stoney]

I use a Pressure Bleeder that forces the new brake fluid through the system under 15 PSI of pressure. It does a great job of clearing any air bells in the system.
Motive Products is the maker.

Originally Posted by pizza_king

Let it Bleed. OK, I have a W124 '93 300E 3.2L. Project is to replace the rear wheel set of brake pads and well worn dics. Mistake I made, discovered after I replaced the pads, was that I completely removed the caliper and split the 2 sides (opened) to access the old pads for removal. Should have knocked out the 2 guide pins and removed pads, which would not have allowed air into the lines. I thought the air would be easy to bleed out, which I've easily done before on countless makes and models. Problem is while using the brake pedal to bleed the brakes per standard procedure (rears calipers only) very little air and fluid is coming out of the brake bleed screw, sometimes nothing at all. The brake pedal just mushes down to the floor without any firmness building up. I removed one of the rear wheels to observe the caliper/brake pads while brake pedal actuated, but the caliper pistons did move. Next plan is to bleed the front calipers, thinking air traveled to the front brake lines. Any advice would be very much appreciated. Thanks! Mike