brake master cylinder bench bleed 79sd - Page 2 - PeachParts Mercedes-Benz Forum

vstech · #16 11-28-2010, 06:31 AM

most american MC's need to be bench bled. for some reason, the MB MC allows fluid to flow through it with no need for a bench. ya fill the reservoir, leave the lines loose, and wait for fluid to seep out. once fluid is out of each line, you tighten and proceed to bleed the lines at each wheel.

rosenfe · #17 11-29-2010, 12:01 AM

okay here is an update,i installed new mc and hoses and good used calipers and new pads on rear.i first tried to bleed useing pressure bleeder,but brake fluid kept coming out of resoirvoir at caps where plugs go in,some pressure at bleeding screws ,but not much fluid,it made a mess.pedal still soft going to floor ,but also hard when backing up and even foward,so i had helper do the pedal pressure while i opened bleeder screw,better,more fluid and some air came out,but pedal still pretty low and hard at times.i realized that i did not change out o ring from mc to booster-possible vac leak there.i did more research and found out that best way to bleed new mc is to install and then loosen each line a half turn while pedal pressure is applied.i will try tommorow as well as install new o ring.ill update after im done,im not giving up.

Stretch · #18 11-29-2010, 08:25 AM

Quote:

Originally Posted by rosenfe

okay here is an update,i installed new mc and hoses and good used calipers and new pads on rear.i first tried to bleed useing pressure bleeder,but brake fluid kept coming out of resoirvoir at caps where plugs go in,some pressure at bleeding screws ,but not much fluid,it made a mess.pedal still soft going to floor ,but also hard when backing up and even foward,so i had helper do the pedal pressure while i opened bleeder screw,better,more fluid and some air came out,but pedal still pretty low and hard at times.i realized that i did not change out o ring from mc to booster-possible vac leak there.i did more research and found out that best way to bleed new mc is to install and then loosen each line a half turn while pedal pressure is applied.i will try tommorow as well as install new o ring.ill update after im done,im not giving up.

Well keep going...

Look out for brake fluid spills on your paint work - you know it will eat it away don't you?

If you have the brake lines correctly seated in the master brake cylinder and they are tight you shouldn't get any leaks there... unless of course you are applying way too much pressure with your pressure bleeding kit.

What pressure are you applying? You are following the instructions aren't you?

rosenfe · #19 11-29-2010, 01:07 PM

when pressure bleeding i get it to about 8 lbs (im not sure what dial is useing -lbs ),its coming out of fluid resoirvoir at rubber caps to each chamber -where float is for electrical switch.on my sdl i did not have this problem.i may try vacume at calipers instead,but to bleed mc im going to apply pedal pressure -not too much and open brake line a bit,bleeding directly at mc and then go back to calipers.

Alastair · #20 11-29-2010, 01:25 PM

The way I've always bled brakes is start at the furthest from he MC, attach a tube to the nipple, undo a good 1 turn or so, the other end of pipe in jam-jar with some fluid in. Then with completely full MC reservoir, do Three FAST pumps--stamping on pedal, followed by three slow pumps. Check reservoir level and repeat.

--Its easier with a helper to check for bubbles at the wheel end, but I normally end up doing it alone.

The fast strokes followed by long strokes seems to shift even the stubbornest air in the system....

Stretch · #21 11-29-2010, 01:47 PM

Quote:

Originally Posted by rosenfe

when pressure bleeding i get it to about 8 lbs (im not sure what dial is useing -lbs ),its coming out of fluid resoirvoir at rubber caps to each chamber -where float is for electrical switch.on my sdl i did not have this problem.i may try vacume at calipers instead,but to bleed mc im going to apply pedal pressure -not too much and open brake line a bit,bleeding directly at mc and then go back to calipers.

I guess that is 8 PSI - pounds per square inch. If it still leaks at this pressure and you're sure it is all well connected perhaps you could try it at 5 PSI (or even lower) especially if you are combining the effect of the power bleeder and pushing down on the foot pedal.

rosenfe · #22 11-29-2010, 02:05 PM

im not pushing on pedal and useing pressure bleeder at same time,ill try less pressure again,but it did not push much air and fluid as compared to foot pumping.im going to start with mc,see how that affects the pedal and go from there.thanks for the reply-i ll keep thread updated

vstech · #23 11-29-2010, 04:39 PM

so, fluid is leaking out the reservoir switches? the rubber caps must be cracked or damaged somehow. fluid should not leak out there.

rosenfe · #24 11-29-2010, 11:36 PM

yes out of the switches with rubber cap, the front one furthest away from firewall,your right it shouldnt leak out of there it didnt on my sdl,on that cr i could get 10-15 psi

t walgamuth · #25 11-30-2010, 06:04 AM

I tried bench bleeding a mc once, and got brake fluid all over my garage, since then I don't and have no troulble bleeding it in place. I crack the hard lines and bleed them by letting them sputter a bit.

rosenfe · #26 12-06-2010, 12:33 PM

update and embarssed about how stupid i can be.

ive been trying to get air out and also deal with hard pedal as original post described.i finally gave up and brought to my indy.

turns out when putting calipers on rear i put them on wrong side with bleeding nipple up ,this allowed air to rise and not come out,also i had put an o ring on back of mc to booster ,thinking there was not one there,but apparently there already was one with new mc and this created an additional space for vac to leak out and create hard pedal.my indy also took mc out to bench bleed-thats what he does with installs of new mc.so i feel pretty stupid and emabrrased,but i dont plan to stop working on my car,i learn with everyone of these episodes,but my indy must think im an idiot-though he is always polite to me ,probably laughing with his buddies about this crazy do it yourself mechanic.now ill have great brakes

tangofox007 · #27 12-06-2010, 12:54 PM

Quote:

Originally Posted by rosenfe

turns out when putting calipers on rear i put them on wrong side with bleeding nipple up ,this allowed air to rise and not come out

"Up" is where the bleed screw should be. And for the reason you stated: air rises.

rosenfe · #28 12-06-2010, 12:57 PM

yes your right, up is correct.

Junkman · #29 12-06-2010, 04:00 PM

FWIW, per consultant Roy, when the caps over the fluid level switches leak, connect them with a plastic hose and seal with hose clamps. I think 1/2" clear plastic is what I have on there until I finish.