Ugh. Brakes. Hate. Fail.

Girlfriend's car got a new master cylinder and 4 new brake lines today.

Problem before replacement: Soft pedal and poor stopping.

Problem after replacement: Soft pedal and poor stopping.

The front calipers have been rebuilt, there's newish rotors on it, the rear calipers are ok. So we figured there must be air in the system. Vacuum bleed them again, pedal go.t worse. Vacuum bled them again, zero pedal. I mean zero pedal and no stopping. Pump and hold bleed them, got some pedal back. Turn the car on, no pedal at all. Turn the car off, pump a couple times, get the smallest inkling of a pedal. Turn the car on, no pedal. Disconnect vacuum line to booster with car on, get an inkling of pedal. No fluid in the booster, booster appears to work when tested. Hold vacuum line up to booster with car on, no pedal. Hold vacuum line up to booster and pull it away over and over, get pedal then no pedal over and over.

I'm stumped. I'm angry. Save me.

ABS?

3 things to try:

Manually bleed the brakes using a helper on the pedal

Ditch the vacuum bleeder and build a pressure bleeder.

http://faculty.ccp.edu/faculty/dreed/campingart/jettatech/bleeder/

or do the gravity bleed solution:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2075307

No ABS.

Brakes have been vacuum bled thrice, manual bled twice, gravity bled once. I have a pressure bleeder.

I think the sudden change from "brakes, but crappy brakes" to "pedal straight to floor with zero pressure" is indicative of a failed component and not more bleeding. I just at a loss as to what.

Did you bench-bleed the master cylinder before installing? Air trapped in the master is really difficult to get out of the system. Of course, the empty master cylinder points to a fluid leak somewhere, possibly a defective hose or caliper. Or, sometimes you can run the master cylinder dry using a pressure bleeder or vacuum bleeding if you don't keep an eye on the fluid level. I'd say just retrace your steps and you will find the problem. Or, you have a defective proportioning valve.. Or, well eventually you run out of parts in the system to replace

Vacuum bleeding is way more effective when you slightly engage the pedal. Pretty much just a tiny amount of pressure on the pedal. I use a brake pedal depressor.

My favorite way to bleed is a gravity bleed. I always get a good pedal. Plus it's the lazy man's way. Open the bleeder and let it run out. Can't get much easier.

If you get a ton of air in the system, normal bleeding procedures can be ineffective. I've seen it when changing lines or many components at once. I normally open the bleeder and slowly and smoothly depress the pedal. Then close the bleeder once the pedal is down. Need two people but it's quick and pretty effective. The fast pumping action most people use when bleeding doesn't work well when moving lots of air.

When I grenades the rear on the z28 and replaced it, I couldn't get the rears to bleed for E36 M3. Had way too much air in the system. Ended up getting it done, by opening a bleeder putting my finger tightly over the hole and having a friend pump the pedal. Air will be pushed our past your finger but not sicker back in. Same concept as a speed bleeder. Pretty quick we had fluid in both calipers and finished it off with a gravity bleed.

what type of vehicle is it? After a big brake repair I'm gonna bet air in the lines. It shouldn't have gotten worse, that's why I think it's air.

In reply to 06HHR:

The master isn't empty (or at least the res isn't), the pedal just feels like it is.

There isn't a proportioning valve, 3 chamber master.

To Opti: It's a Mercedes 190e.

replacing all those lines probably still has air in the system, either in the Master cylinder or the lines... When I redid all the lines on my jeep, I bled that sucker 7 bajillion times... Finally got a good hard pedal, but you'll be surprised at home much air is in there. Keep manually bleeding it and check for leaks.

Try a reverse bleed.

Defective master cylinder? I rubbed through the rear brake line on my bike doing a open testing day before a race weekend at NHMS. Replaced the line then spent hours with the same symptoms, 4-5 hours. Ended up breaking down the rear master as no spares could be found, cleaning it good(twice). Finally at 7 pm, just before reg closed got a petal. Steve

There has been more than one occasion where I went through multiple parts store rebuilds before getting a good one. Sounds like that is your issue too.

I'm with the crew that thinks it could be a defective master. By this point, you should be seeing an improvement...

As frustrating as it is. Just saying you have a new/replaced part is no guarantee. If it walks like a duck and quacks like a duck......

Sounds like a bad master cylinder.

I would try a reverse bleed, that is, push fluid up from the calipers to the MC. If that doesn't work then its likely a bad MC. A lot of the industrial vehicles that I work on will only work right if the are reverse bled. Bouncing the pedal (not a full stroke) while pushing the fluid through helps work the air out faster.

KyAllroad wrote: As frustrating as it is. Just saying you have a new/replaced part is no guarantee. If it walks like a duck and quacks like a duck...... Sounds like a bad master cylinder.

You have to watch out for those duck based ABS systems. You really have to squeeze them to get all the air out.

I have seen air bubbles trapped at the top of a curve in a brake line before. Also, on real 'hard cases' I've had to open the bleed screws for the rear, put tubes on them into jars etc leave them open then bleed the front end first using the buddy method. Once the front is bled, go back and re bleed the rear. It once took a buddy and I two and a half hours to bleed his Midget that way!

Reverse bleeding is a good thing too, you can get large syringes that you fill with fluid then connect to a bleed screw then force fluid uphill.

http://www.amazon.com/Easy-Glide-Syringe-Sterile-Catheter/dp/B007S97UIG

You can get them at drugstores too, they are generally called catheter syringes. A turkey baster can work but they are a bear to handle.

I use one of these for reverse bleeding. I bought it at HF, and washed it out with alcohol before putting the brake fluid in it.

In reply to Curmudgeon:

Good point.

TSC has them syringes too in the vet section, prolly cheaper too. 3ml and up.

I use 'em for a lotta stuff. Evacuating MC of old fluid. Shooting grease or lube. Apply Kroil a drop at a time. Best was prolly measuring paint, reducer and hardener in ratio w/ 3ml syringes for use in an air brush for touch up paint. Less waste and very accurate.

Also used 'em for measuring the accelerator pump shot on VW AC carbs when attached to the shot nozzle w/ small dia. hose. Dead nuts vs other methods.

sounds like defective MC out of the box. you said "new" but is it really a new part or is it a reman? reman's have an appetite similar to hennessy honda of woodstock.

my vote is air in the lines. I had to leave my car gravity bleed for a few days to get all the air out.

Agree with both/either bad new master cylinder and air trapped in a high spot in the lines.

I recently bled the air out of a system that had been open and was dry. first time I'd done that, was always a caliper replacement or single line, flush, etc. It took FOREVER. I bought a new MC, because I couldn't believe there was still air coming out after suction bleeding for a long time. Seriously, cycled two of those large brake fluid containers through it. After the MC replacement.

Consider the brake pads. My mom's Honda Odyssey had cheapo Car Quest uber-low dust specials installed by the local gas station mechanic and the first time on the road, the 'Van went right through a stop sign with the brake pedal to the floor. After installing new higher quality brake pads on there, everything is back to normal.

The last brake problem I saw that looked like a MC really was worn out caliper pins that let the caliper move up when the brakes were applied.

May have a solution, will be checking in the morning.

The res doesn't have a traditional 2 chamber design, nor does it have a shared chamber. It has a partially shared chamber. There's a smaller res inside the main res for the rear brakes. If the main res is not completely topped off, you can run the rear chamber dry and the res still looks full of fluid.

This I think explains why the pedal has been getting worse with more bleeding. So far, if the master res has been half fun, I've been thinking that's enough fluid. I think this also explains why the brakes have been so E36 M3ty for the longest time. The first time I bled the brakes (months ago), I ran the master dry. I'm unsure if there's been fluid in the rear chamber since then.

What this does not explain is the onset of zero pedal yesterday. If this was the main cause, there should still be some pedal from the front brakes (right?).

I like this solution not only because it fits, but because it seems to be Mercedes specific and blatantly simple but not painfully obvious. These are two things I've been suspecting, since a hydraulic system should be just a hydraulic system.