Mercedes-Benz Forum banner

Caliper replaced - no air, and no caliper movement

2K views 16 replies 7 participants last post by  tuttebenne 
#1 ·
Here's a weird one...
So while replacing the pads, the bleed screw on the right front caliper twisted and destroyed the threads on that caliper. So I replaced that caliper and while using my MityVac, I ran the reservoir dry. Nice.
So, filled it up, bled that side, got the air out, and I can move the caliper towards and away from the chassis by about 1mm, and the rotor spins free, which means the piston has not moved and it has no pressure.
I bled some more, then my MityVac's internal seal broke and shot brake fluid all over me when I pulled the trigger. Great. Now, made a pressure bleeder from a bike pump and other bits, and pressure bled that caliper. Still no more air, and no pressure at that caliper. WTF.

I gave it a few days to let the car think about what anxiety it's causing me, to which it couldn't have cared less, and hit it again today. This time I bled the front right caliper and got a little bit of air out after pushing through maybe 1/4 pint, and then all seemed good as far as air goes. Bled the "trouble" side again, and no go. Still no freakin' pressure!

I know this system is separated from front to rear, so I haven't touched the rear (didn't do those pads anyway) and that little portion of the reservoir is at max anyway and has never dropped. What I'm fearing is that there is some air stuck in the ABS pump, but if there was, how would I get a hard actuation of the front left caliper and none at the right, and no air coming out either side?
I have bled well over a quart of fluid through the system now.

Should I put a piece of wood between the seat and the brake pedal, depressing it, and bleed again with the ignition turned to on to open the ABS circuit? Would that even work?


HELP! AAAHHHH!!!!

(It's a 1990 300E, US spec)
 
See less See more
#2 ·
You have to use a pressure bleeder and bleed at 2 bar (30psi). If there is a slight leak from the homemade bleeder you won't get the required pressure required to bleed.

I suggest you get a Motiv bleeder. Nothing else works right
 
#3 ·
I've always used a 2nd person on the brakes ,on all my cars with no problems whatsoever , may need stronger pressure on the pedal,or you may have gunk in that line,when I did the PB Booster on Dieter,had to remove MC,it had tons of crap at the bottom,cleaned it out .
 
#11 ·
+1...plus you run the risk of taking your master cylinder seals to uncharted territory using the 'foot/helper" method. Yes turning the key on will help in bleeding because it activates the ABS pump. Not necessary, but helpful. Hard to say what the OP is doing wrong without being there...just suggestions from those of us that have done this successfully.

Kevin.
 
#6 ·
The bleeder I have works well, and I pressurize between 15 and 20psi. Anything more and I'm nervous of it bursting. It's an old car ya know.
I get fluid moving out and there doesn't seem to be any obstructions at the master or caliper. My thought is that I may have a bad new (they're rebuilds) caliper at that corner. I have had a new part from O'Reilly's go bad almost out of the box. I am trying the new one tomorrow.
 
#8 · (Edited)
You need to bleed hole system even the rear caliper the brake system is split in two systems (diagonal), one front caliper and one rear caliper the reason is when you brake you stay in a straight line with the car even when one line is loosing the brake fluid.
Otherwise you should spinn around if you only have rear brakes and they would have different pressure on each wheel.
I have bleed the brake system with a air pressure vacuum bleeder works fine, I have change the 12 years old fluid.
 
#9 ·
I replaced the caliper with another new one and pressure bled it at 30psi. No change.

Would turning the ignition on or pressure bleeding with the pedal held down do any good? I'm very tempted to drive it to a shop and pay them to bleed it and figure it out.
This is a ridiculous problem and shouldn't be this much of a hassle. And, I have no reason at all to believe that any air is in anywhere but in that line or somehow in the ABS.

Any other ideas?
 
#12 ·
Good info on the ABS, if there is a bleed screw, I'd love to try that.
Not my first time bleeding brakes, but I've never run into such an issue. I'm not doing the manual method with a helper on the pedal, only doing the pressure bleeder and previously the MityVac until that POS broke :^).

I'll try with the ignition on. If anyone knows anything about the bleed screw possibility, I'd like to try that.
 
#13 ·
Some ABS pumps have a bleed screw and some don't. Mine does not. It seems to usually be visible if you take the top plastic shroud off. Look for the procedure in the 124 SM....it shows location. I can't help there because I don't have one-as of '92 TE models. MityVac will NOT produce enough vacuum to pull through the pump. You don't want to do it that way though...you want to push through the pump.
Kevin
 
#16 ·
FIXED:

I knew I had to have all the air out of the master, lines and calipers, (I even bled out the opposite side in the front) so that led me to believe I had air in the ABS, somehow.

I knew I was getting adequate pressure from my bleeding method since I was using my home-made pressure bleeder and pumping up to 20psi, with spikes to 28 or so, and I ran about 2 quarts of fluid through total. The caliper was new, and then replaced with another new one to make sure it wasn't a problem with a seized piston.

So I put down the bleeder, put the wheels on and took it for a drive. I found some long patches of gravel and lit up the ABS about 6 times and took it back.
I popped the wheel off of the passenger side, pumped the brake pedal a few times, and the caliper was starting to work! It wasn't super tight, but it would put resistance on the rotor.
I then bled that side and wouldn't you know, bubble city. Pushed another pint through the problem side and then a half pint through the driver's side, buttoned it all up for the last time, and took it for another drive. Brake feel was back to normal and everything felt great.
Problem solved.

FYI, there is no bleed screw on a 1990 300E's ABS unit. You have to do what I did and activate it.

Thanks for all your input, and I hope this helps someone someday!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top