Brake Pedal Softness/Responsiveness - PeachParts Mercedes-Benz Forum

JamesDean · #1 09-05-2009, 03:29 PM

Hey everyone,

First off:
1993 190E 3.0
Front: 94 E420
Rear : 96 SL600
500E Master
SS Lines / ATE SuperBlue...

Now: My situation is: the brake pedal feels softer than I remember it being when I first bought the car...The brakes dont seem to engage very high in the pedal stroke...they seem to engage about somewhere after 1/4 pedal or half pedal. In situations where I need to stop I usually go down to 3/4 pedal and ease up to half pedal.

When I first bought the car it had the stock 190E 2.6 master on it, it died about a year later so I opted to put the 500E master on as it was actually cheaper than the 190E one...

Now, my 300SD's--which has a new master and new front calipers--pedal feels MUCH more firm (allbeit less powerful) than my 190's...

I'm not really sure if I'm describing the whole thing as accurately as I can..

I've bled all 4 corners via the 2 man method. I even bought a power bleeder and used nearly three quarts on a full bleed of the system...

I put on new rotors this past spring, PBR rotors to be exact.

If anyone can help me out I'd appreciate it. I'm not really sure what the problem could be...

slk230red · #2 09-05-2009, 03:37 PM

The only time I've ever experienced what you are describing, besides being a defective master cylinder or air in the brake lines, is when one of my front pads wasn't properly seated in the caliber assembly. The brake pedal had too much travel after bleeding the brakes.
Upon further inspection I found the problem, replaced the pads, and since then the brake pedal has very little travel.

JamesDean · #3 09-05-2009, 03:43 PM

Hm...

I'm fairly certain they are seated properly. I just put in a new set today (textar)...

Perhaps there is still air in the system or the master is defective, its been like this since it was install in early 07 though...so perhaps air?

If it is air..I'm not sure how to go about removing it, I've done the powerbleeder method used a few quarts of fluid too. Is there anything special one needs to do to bleed a car with ABS?

slk230red · #4 09-05-2009, 03:52 PM

Quote:

Originally Posted by JamesDean

Hm...

I'm fairly certain they are seated properly. I just put in a new set today (textar)...

Perhaps there is still air in the system or the master is defective, its been like this since it was install in early 07 though...so perhaps air?

If it is air..I'm not sure how to go about removing it, I've done the powerbleeder method used a few quarts of fluid too. Is there anything special one needs to do to bleed a car with ABS?

Nothing special, I use a Mighty Vac and it works great for bleeding brakes. I've used it on my MB's and Corvette.

JamesDean · #5 09-05-2009, 03:55 PM

I've got one of those guys. Used it when I first flushed the system. I'm pondering using it today to try to get this air out of the system and if there is any special bleed point for the ABS block.

slk230red · #6 09-05-2009, 04:00 PM

Quote:

Originally Posted by JamesDean

I've got one of those guys. Used it when I first flushed the system. I'm pondering using it today to try to get this air out of the system and if there is any special bleed point for the ABS block.

Not that I'm aware of, I just start with the furthest wheel and work my way to the front. Make sure you shut the bleeder screw before the vacuum goes all the way down and keep the reservoir full.

Good luck,

Dave

JamesDean · #7 09-05-2009, 04:00 PM

what if my master cylinder was never bench bled?

slk230red · #8 09-05-2009, 04:07 PM

Quote:

Originally Posted by JamesDean

what if my master cylinder was never bench bled?

The air should work its way out. You could do it on the car if you have a helper. Pump the pedal and crack the lines (1 at a time) at the master. Be sure to use a rag around the fitting to contain the fluid so it doesn't spray.

JamesDean · #9 09-05-2009, 06:17 PM

alright, I bled the master, and all 4 calipers. starting with the master then the rears and etc...

Some air bubbles came out, maybe 3-5 per caliper, then i let it run for a but to see if any other bubbles came and nothing happened.

I didnt feel any substantial change in the pedal. There is still a bit of pedal travel before actual braking occurs...

compress ignite · #10 09-05-2009, 06:37 PM

CLEAN the top of the MC reservoir area, completely.
1. Get "New,Fresh,cheap,plastic turkey baster[tube with a bulb on the end]"
2. Remove master cylinder reservoir cap.
3.Remove the Filter Screen insert.
4.Evacuate all the Old Nasty BF you can with the "Turkey Baster"
(you will not be able to remove fluid from the rear portion of the reservoir)
5.Refill the MC reservoir with fresh clean (UNOPENED container) BF.
6.Attach the Pressure Bleeder cap to the MC reservoir and pressurize to 15PSI.
7.Using bleeder nipples with the appropriate "Catch Container",BLEED the brakes.

There are instructions in the search function on how to make a Pressure Brake Bleeder with a $9.95 garden sprayer from your favorite Big Box Store.

All this "Pumping" or "Directing an Assistant" or using a Mighty Vac to bleed
the brakes is 19th century...This can be a quick Solo 20 minute job every Spring or ....Masochism.

compress ignite · #11 09-05-2009, 06:40 PM

Jimmy,

How old are yours?
Are they "Rubber" or Stain-Less Steel braid with a Teflon inner liner?

When you step on the brake pedal with the engine running ,do the Brake Hoses
"Bulge" visibly?

Ferdman · #12 09-06-2009, 06:53 AM

As mentioned it's best to use a pressure bleeder rather than pressing the brake pedal which can cause problems with the master cylinder since the piston goes beyond its normal travel. Bleeding sequence is RR, LR, RF, LF. Be sure the rear chamber of the master cylinder is filled with brake fluid so as not to introduce air into the system.

tinypanzer · #13 09-07-2009, 10:46 PM

MB spec is to flush/replace brake fluid every year on that car, so ya might as well start with that and see if it fixes the issue. It certainly wouldn't hurt to inspect all brake hoses since you will have to bleed yet again if you find a bad hose afterwards.

James Dean? I thought you were partial to Porsches.........

Chas H · #14 09-07-2009, 10:55 PM

Quote:

Originally Posted by JamesDean

Hm...

I'm fairly certain they are seated properly. I just put in a new set today (textar)...

Perhaps there is still air in the system or the master is defective, its been like this since it was install in early 07 though...so perhaps air?

If it is air..I'm not sure how to go about removing it, I've done the powerbleeder method used a few quarts of fluid too. Is there anything special one needs to do to bleed a car with ABS?

Have you properly bedded in the new pads? Your symptoms suggest you have not.

Yak · #15 09-08-2009, 10:59 AM

I'm confused. What work was done that started the problem? Did you begin to feel mushiness/travel and decided to change the fluid, or some repair that then resulted in mushiness/travel? Or a preference for the firm feel in the 300SD? You say it's been mushy since '07?

Can you clarify your system - the car is a 190E 2.6 or 3.0? The MC is from a 500E, the front calipers are from an E420 and the rears are from an SL600? And you've got stainless lines on it? And you've pumped 'quarts' of fresh fluid through it?

I had SS lines on an Audi I owned and started getting a mushy pedal and more travel when the lines were about to fail. SS are great when new and fresh - excellent feel, firm pedal - but they wear out just like rubber lines.

But - if I understand your system correctly and the symptoms have been around since '07 - I'd guess that the mixing of components has a lot to do with the lack of feel and pedal travel. You may simply need 1/2 travel to pump enough fluid through the calipers to engage the brakes.