Brake bleeding not working - PeachParts Mercedes-Benz Forum

martureo · #1 06-03-2012, 09:24 PM

Alright, I've searched the forum and this is not my first rodeo when it comes to brakes. (I've been working on brakes for a number of years now and many different makes/depths of repair/replacement)

w123 300D 1984

Brake fluid looked dirty so I decided to change it. NO ISSUES PRIOR. None whatsoever other than a dragging caliper two years ago.

1)Pulled fluid from reservoir by way of Mityvac
2)Put fresh fluid in reservoir
3)Pulled fluid from driver's front wheel.
4)Pulled fluid from pass. front wheel.
5)Pulled fluid from pass rear wheel (I know, it should've been driver's rear but the jack was on that side of the car already)
6)Attempted to pull fluid from driver's rear, no fluid.
7)Then I checked the reservoir yet again (kept refilling it up to the top between wheels).
8)Removed bleed screw to remove junk and replaced bleed screw on driver's rear.
9)Attempted to pull fluid again. No luck. Ever after pumping for 5 good minutes.
10) Got someone to pump brake pedal and use push method. Fluid drips. But pedal does not become firm.
11) Just in case wheel method was wrong I repeated the other wheels in order. All other wheel bleed with mityvac and pedal method.
12) Tried again on driver's rear. Got some fluid but no stream and pedal will not firm up.

What the crap do I do now? I've currently got the bleed screw open slightly trying to gravity bleed that one wheel, but I need this car in the morning as it's my DD.

vstech · #2 06-03-2012, 10:08 PM

pull the rubber hose, and get a replacement. it sounds like a bad one to me.

martureo · #3 06-03-2012, 11:52 PM

Hose replaced. Now no fluid.

kmaysob · #4 06-03-2012, 11:57 PM

start at the master cylinder and work back. if you crack the lines at the mc and fluid comes out, its farther down the line. is it possible you sucked air through the mc when bleeding ?

vstech · #5 06-04-2012, 12:03 AM

... if you have fluid to one side, but not the other, the only thing it can be is the hard line between the split, the rubber line, or the caliper itself. the rear calipers get fluid from a single line, so one side getting it, but not the other, it's a line problem.
take the hose off the caliper, and verify if fluid is at least reaching it!

Govert · #6 06-04-2012, 03:55 AM

And the reservoir has to be filled to the neck, otherwise the fluid will not flow over the partition in the reservoir. Have you checked (with a flashlight) whether the both sections of the reservoir are full?

t walgamuth · #7 06-04-2012, 06:20 AM

I am not able to tell from your post that you are using correct bleeding process. After using the mitivac to pull fluid to the bleeders, you must close the bleeder and have a helper pump up the brakes. Once he or she begins to get resistance they must stop pumping and hold the pedal while you open the bleed. Wait for the pedal to go to the floor or very near it and close the bleeder, then repeat until a firm pedal is felt while working that bleeder. Then move to the next wheel.

Start with the furthest away from the master, in a lh drive car, that is the rr. Then lr, rf and finish with the left front.

Good luck.

martureo · #8 06-04-2012, 10:16 AM

I have fluid to the driver's front, passenger's front and passenger's rear. All three will bleed normally.

Both sections of the reservoir are full and have been so. I never let either section run dry, even when I was initially removing fluid.

No matter whether the engine is on, or under load there is no increase in brake pedal pressure whatsoever. And no fluid appears at the driver's rear caliper.

I replaced the hose with a brand new one. The old one did not appear to have any collapsed section, but I couldn't say if it had a leak or not. (It was Pirelli brand... I thought that was interesting...)

To those who were interested, I usually loosen the bleed screw to make sure it's freely moving, then seal the last gap between the exposed threads and the caliper with petroleum jelly or grease (whichever I have on hand at that moment). Then I attach the MityVac, pump the vacuum up to around 25inHg and then slowly open the bleed screw until I have a constant flow of brake fluid. I continue to pump to keep the vacuum as close to 25inHg as possible, I never let it fall below 10inHg with the bleed screw open.

Stretch · #9 06-04-2012, 10:57 AM

I guess it has already gotten a bit messy.

If you are stuck getting fluid out of the driver's rear caliper then you need to bite the bullet - disconnect the brake pipe from that caliper and see if you can push fluid out of the system => so that's from the hard brake line... you should be able to see if that tiny short bit of the hard brake line from the T joint to where the flexible pipe running to the caliper is blocked or not. (Probably won't be)

Next stage - with bicycle pump / foot pump / air compressor pressurise from the flexible pipe to the caliper with bleed screw open. See if you can get any air through that part of the system. Do not remove the caliper from the vehicle for this as you'll just pop the pistons out.

You need to find out which bit is blocked.

Zulfiqar · #10 06-04-2012, 11:00 AM

how about tapping split joint with a hammer, maybe something is blocking it.

Codifex Maximus · #11 06-04-2012, 09:45 PM

This is really weird. I would think you'd be seeing brake fluid at the driver's rear caliper. Have someone pump on that pedal and look for the leaking fluid. That fluid is gotta be going somewhere!

If the system, all except for the driver's rear, is getting fluid and is tight and not leaking then it could be an occluded pipe prior to the caliper. I agree with Army, disconnecting the pipe at the caliper and seeing if you can pump fluid out using pedal action is a good pipe diagnostic.

martureo · #12 06-05-2012, 12:17 AM

Tried once more after building the "homemade pressure bleeder" suggested on this site. This time I finally got fluid to the driver's rear caliper.

The only problem is that the fluid coming from each wheel now has a million tiny bubbles in it. The brake pedal is now firmer than before but still needs to travel almost to the floor until the brakes become effective. I'm going to wait until tomorrow night hoping the liquid will become less colloidal than it is now and it will give me the chance to get yet more brake fluid.

Stretch · #13 06-05-2012, 02:50 AM

I get the feeling you now need to buy brake fluid in bulk at bulk prices. Perhaps after you've pumped through 5 litres of the stuff you'll get a free T shirt?

vstech · #14 06-05-2012, 08:00 AM

bubbles?
odd.
you have full power bleeder, and it's connected to the MC, and it's pumping fluid through the driver's rear caliper... but it's full of bubbles?
I'd leave the bleeder open, and keep pumping fluid out until it clears up.
actually, I'd clean all traces of the petroleum jelly off all the calipers, and start at the rear right, and pump it up and flow fluid out until it's a clear stream, then go the the left side, and repeat, then go up front... it doesn't matter which front you do first, as they are independent.

Air&Road · #15 06-05-2012, 08:15 AM

I would recommend that you FILL the reservoir and keep it filled while going through the two man bleeding method with the engine running. Take all precautions with engine running. Set parking brake hard and make SURE that the pedal operator is a responsible adult that knows to not touch the accelerator or shifter lever while helping.

I have seen many of these particular cars that unless a stout person with both feet firmly on the pedal, you will not get enough pedal movement without the engine running. It's tough to overcome the booster once the vac reserve is gone.

Try it!