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  #1  
Old 07-13-2008, 01:32 PM
winmutt's Avatar
85 300D 4spd+tow+h4
 
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Brakes bled, bench bled, still soft pedal.

Replaced the 2 rear brake lines, fronts are newish as well and show no cracks. I have bled the system several times and as of this weekend bench bled it 2x. It certainly locks up pretty well now but the pedal is still super soft/spongy. MBC? Booster? Something else I noticed. Some of the calipers when the bleeder screw is open will just pass fluid right through without pumping. Is this bad?
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  #2  
Old 07-13-2008, 01:59 PM
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I really do not know much about this. However years ago I replaced a master cylinder. The directions said to bench bleed before installing it and I ignored the directions. Sure enough I could not get good brake pedal even after bleeding the brakes several times. I had to remove it, do a bench bleed, and reinstall the master cylinder then rebleed the brakes. Perhaps you need to remove the master cylinder and do a bench bleed out of the car (if in fact you did not do this), then re-bleed the brakes.

Just my experience.
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  #3  
Old 07-13-2008, 02:10 PM
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On W123, it's easy to mount the left rear caliper on the right side & vice/versa. And in this case, you will never get all the air out of the lines, so I suggest you check the calipers for r to r & l to l.
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Old 07-13-2008, 02:58 PM
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you must have air in there somewhere...
get a new smallish plastic garden sprayer with a plastic wand, and cut the end off and attach a parts car MC cap to it, or use a rubber stopper and strap it down. then fill the sprayer up with brake fluid, and pump it up a few times, don't go too high.
open up the furthest bleed screw and let it bleed until you are SURE the fluid is flushed all the way from the front. keep the pressure sprayer full of fluid, and repeat on the rest of the wheels.
this way, you are TOTALLY sure all the air is out of the lines.
have fun!
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  #5  
Old 07-13-2008, 03:15 PM
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Quote:
Originally Posted by vstech View Post
you must have air in there somewhere...
get a new smallish plastic garden sprayer with a plastic wand, and cut the end off and attach a parts car MC cap to it, or use a rubber stopper and strap it down. then fill the sprayer up with brake fluid, and pump it up a few times, don't go too high.
open up the furthest bleed screw and let it bleed until you are SURE the fluid is flushed all the way from the front. keep the pressure sprayer full of fluid, and repeat on the rest of the wheels.
this way, you are TOTALLY sure all the air is out of the lines.
have fun!
And remember to be mindful while using this rig of the effect splashed brake fluid will have on your paint job

I realize we aren't talking about a brake fluid bath of the whole car here, I'm just saying if something goes wrong, pressurized brake fluid wouldn't be my first choice for the mistake to happen.
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  #6  
Old 07-14-2008, 12:34 AM
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Quote:
Originally Posted by 280EZRider View Post
On W123, it's easy to mount the left rear caliper on the right side & vice/versa. And in this case, you will never get all the air out of the lines, so I suggest you check the calipers for r to r & l to l.
Well the bleed was on top which makes me think its correct. This is a wagon.

I have bench bled and rebled the system 3 times now and every time it is soft.

So when I opened the bleeder and fluid came out this is normal? It was enough to flow freely through the one man bleeder.
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  #7  
Old 07-14-2008, 12:40 AM
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Normal OPs

Opening the bleeder screw and finding free flowing fluid is normal...The MC is
above all else in the system and Gravity is still King on Earth.
Someone I know who turns wrenches for profit actually suggested bleeding
the brakes in this passive manner(Too much running back and forth for me).

I haven't any suggestions other than those offered.

I know the pedal should be rock hard.
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  #8  
Old 07-14-2008, 03:17 AM
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winmutt,

i do some off roading, so its crucial our brake fluid is changed correctly and somewhat frequently. take a look at my writeup here: http://4runners.org/writeups/brakebleed/index.htm

a couple of key tips:

1) two people always seem to work better
2) baaarely crack the bleeder screw. you dont have to see alot of fluid come out.
3) have your friend pump the brakes but have him put a wood block behind the brake so he does not damage the MC piston
4) when you are finished with one side, have your buddy pump the brake once more, have him hold it, and then you tighten the bleeder valve. if he lets the brake go, air gets sucked in.

me: lots of trial and error and that writeup above is the culmination of some very frustrating attempts over two to three weeks

bob
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  #9  
Old 07-14-2008, 12:26 PM
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I replaced the right front caliper and all 4 hoses on my 126 3 months ago. I ran into the same problem. I gravity-bled the system 3 tumes - still crappy pedal. Since it was 9pm, I drove an S8 home. Next night, I vacuum bled it. Better but not as it was. I cracked the m/c lines with someone pressing the brake pedal for me and re-bled the system again. Perfect.

Did you have someone helping you foot-bleed it ? Did they press the pedal to the floor ? If so, then the primary seal in the m/c may have been damaged. I usually put my left foot under the brake pedal when foot bleeding as to not press the pedal to the floor.
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  #10  
Old 07-14-2008, 12:41 PM
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Quote:
Originally Posted by bustedbenz View Post
And remember to be mindful while using this rig of the effect splashed brake fluid will have on your paint job

I realize we aren't talking about a brake fluid bath of the whole car here, I'm just saying if something goes wrong, pressurized brake fluid wouldn't be my first choice for the mistake to happen.
agreed! with these non ABS cars, it takes VERY little pressure to flush the system free of air. really, just a couple pumps, 4 or 5 with a quart of fluid in a gallon sprayer is fine.
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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!
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  #11  
Old 07-14-2008, 01:12 PM
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Quote:
Originally Posted by AdvisorGuy View Post
I cracked the m/c lines with someone pressing the brake pedal for me and re-bled the system again. Perfect.

Did you have someone helping you foot-bleed it ? Did they press the pedal to the floor ? If so, then the primary seal in the m/c may have been damaged. I usually put my left foot under the brake pedal when foot bleeding as to not press the pedal to the floor.
I will try cracking the MC lines. I certainly pushed it to the floor and all the way when I was bench bleeding it. If cracking it doesnt work I will replace the MBC. Sigh.
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  #12  
Old 07-14-2008, 01:58 PM
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Maybe I am missing something but I think bench bleeding is something that can be done only with the master cylinder out of the car; that is why it is called "bench" bleeding. So do not understand your comment about putting the pedal to the floor. If you do not bench bleed it per instructions, you will never get it to work properly in the car.
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  #13  
Old 07-14-2008, 02:08 PM
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naw, bench bleeding is simply done in the car or out.
it just refers to bleeding the mc prior to installing the brake lines.
all that's needed it the bleeder lines and for somebody to push the pedal.
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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!
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  #14  
Old 07-14-2008, 02:11 PM
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You cant bench bleed in the car unless you jack up the back end until its MBC is flat. In my case I have a rotating vise so I bled it at many angles.
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1994 E320 Cabriolet
1995 E320 Touring
2001 Eurovan FOR SALE
1985 300D car, sold and missed.
OBK #42
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  #15  
Old 07-14-2008, 02:57 PM
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Quote:
Originally Posted by winmutt View Post
You cant bench bleed in the car unless you jack up the back end until its MBC is flat. In my case I have a rotating vise so I bled it at many angles.

I have never bled one on a bench. i use the clear tube kit that comes with the MC (in US MC you always get one) or go buy one for $5 at NAPA for the MB MC (not included). you can see the tubes with the hood up and sitting in the driver seat, just pump the pedal until the bubbles go away. never had any issue doing this many, many times in the past
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