Brake Pedal Softness/Responsiveness
 

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...

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.

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.

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

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.

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...

Bleeding Brakes
 

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.

Brake Hoses
 

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?

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.

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.........:rolleyes:

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

What started the problem?
 

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.

edit

Sorry I've not replied in a few days, havent been in front of a Pc that much..

Alright.

My lines are in fact stainless steel. Here is a Pic of the front setup. Its a bit dirty/rusty up there..I do live in the rustbelt after all...that pic was from 3/2009 when I put new rotors/pads on...

As to the "bulge" visible..I'll have to get back to you on that...


http://i98.photobucket.com/albums/l250/MafiaNicky/IMG_9005-1.jpg

What does that mean exactly? I've not heard of that before...maybe that is the cause...


I do have a preference for the firm feel of the SD...It has been mushy since the master cylinder was replaced in 07...

A combination of loud squaling from the pads and the fact that I had a set of brand new textar pads on my shelf has motivated me to actually fix the problem or atleast conduct research into it.

the car is a 190E 2.6 with a 3.0L m103 in it. The 2.6 blew its head gasket at 215k and it was cheaper to drop in a 3L than to fix the 2.6

MC=500E
FRONT=E430
REAR=SL600
Stainless Lines

When I did the work in March I did pump a few quarts of Typ 200 fluid though it..almost 3 when I ended the process...

When I first bought the car in 2006 the brakes were nice and firm and it was the setup as I've described above, I didn't change anything with the exception of installing the 500E master cylinder....

THe pedal seems to get hard at time and apply the brakes high in the stroke real firmly and other times it'll get soft and I'll need to drop it down low to really apply them to stop..

Question: The check valve on the booster vac line..what are symptoms that it has gone bad? what exactly does it do?

-Thanks

Kris

The mixture makes things harder to troubleshoot, but assuming everything more/less fit before and you haven't done anything odd like put non-vented rotors into a caliper that is sized for vented rotors (from the pic it they look vented), you should be able to return the system to good order.

Did you replace the gaskets from the booster to the MC when you swapped it out? It's possible you have an air/vacuum leak there.

Or, since the problem showed up when you replaced the MC, you might a) have a bad MC; or b) have trashed the seals in the new MC by using full pedal travel in the two-man bleeding process.

I'd focus on troubleshooting the MC or outright replacing it to restore proper feel and safety.

This assumes the basics in the bleeding process were done, like never letting the reservoir get empty while bleeding. Three quarts is a LOT of fluid to push though. Maybe pints, in the small bottle?

"Bedding in" or "seating" pads may mean slightly different things to different people. My understanding is you're getting the piston/pad/rotor relationship correct after you've installed a new pad/rotor since the distances have changed. "Bedding in" takes up the slack in the system caused by depressing the piston in order to make room for the new thicker pad or rotor. It may also refer to wearing away the edges of the pads or rotors if they weren't a perfect fit and you didn't have them turned; for example the outside edge of the new pad might just touch a small ridge on the old rotor. The slight difference may require more pedal travel to create stopping force until the ridge wears away or a groove is formed on the pad. If you've had the problem for two years, I don't think this would be your problem.

I had the shop replace the Master cylinder with one I got from ********..I dont recall if they replaced a gaskget or not...

Today I was stopping in a parking lot doing less than 10mph and my ABS kicked on...
that and my brakes started squealing really loud again..randomly not all the time though...

I do wonder if using the 500E master with a 2.6 brake booster could be the entire problem?

Could the booster not be able to accommodate the larger 500E master cylinder?

I would think that the pedal would be really difficult to press down? Is not that how a booster works? It helps make the pedal easier to apply? If it was not working / not enough the pedal would be really difficult to press down?

I don't know about the effects of mixing the booster and the MC. Putting that many different model parts together just doesn't seem like a good idea to me without doing some heavy research on what can adequately supply to downstream components and how you maintain that system.

However, the ABS and the squealing sound like a different problem. That's new since you just installed the textar pads recently, correct?

It sounds like you've got something put back together wrong or the complications of different components are coming home to roost. Are you sure that the caliper size and rotor size and the pads are compatible? Did you disconnect an ABS sensor and not get it back in right?

I do know that a number of people are running the same setup as I have...There was some heavy research done by other members who started the big brake upgrade (2Phast is one of them)

I agree ABS/Squealing sound like a different problem.

I did just put in Textar pads this past weekend. I used some anti-squeal paste on the back of the pads (CRC BrakeQuiet iirc) when I installed them.

As to the caliper/rotor/pads compatible...I am running E430 front calipers/rotors/pads...Im not sure if thats what you're getting at... Everything visible fits down there..

As to the ABS: I've not disconnected any sensors or anything. What exactly triggers the ABS to engage? Perhaps since my brakes arent "fully braking" and I have to press the pedal down futher the system is interpreting that as something else?

Just some thoughts...

Update:

At the suggestion of Hit Man X ( I was talking to him on AIM) I "degelled/deglazed" the rotors...

He had mt take 300 Grit Sandpaper and go at the rotor/pads and then break them in using the 10-stop, drive for a bit, 20-stop drive for a bit, etc..method. This seemed to help my squealing problem but not my brake pedal response feeling/issue.

I might be inclined to believe this is a master cylinder issue or perhaps calipers...

fluid transfer pressures
 

'pretty much the only thing to effect your symptom-ology.
AND the MC / Booster conniption is certainly possible.
The pedal travel issue points to the MC.
BUT the ABS ain't happy with SOMETHING.(Or the ABS is ill)
[do we have any diagnostics that can be applied to the ABS?]

I swear, I'd still wanna verify the brake hoses inner lining has not de-laminated
and/or started acting like a one way valve internally.
(How old are the hoses ,and from whom did you acquire?)

The Hit man is/was correct.If pads/rotors are not properly "seated"against each
other problems result.Except for Ceramic pads,the bedding in process is an
increasing speed use of the brakes (without ever coming to a complete stop).
[But,if you're reusing rotors they must be "deglazed"as in X man's instructions]
(Bedding in is the transfer of materiel from the New pads to the rotors surface,
AND cannot properly be accomplished without a fresh rotor surface.)

I would have to agree with you..fluid transfer pressures...

Like today for instance.. When I left this morning, my pedal felt sturdy, solid..it has a little bit of play in the beginning and then you pushed into it and it was solid all the way to stopping...

Later on in the day it wasnt as this...It became kind of soft in the middle..

When I came home today, I pulled into my driveway then drove in to the garage ( <10mph up the drive) and when I braked the fronts groaned something awful and the ABS kicked on. That seems to be the only time it comes on when I'm trying to come to a full stop when traveling at a low speed.

When I'm going 20+ the ABS doesnt do anything it shouldnt and there is no squaling. Just Low speeds to stop...

I'm wondering if the issues are tied together? I.e. not having enough "stopping power" makes the ABS think it should take over?

Does any of that sound like Master Cylinder issue?

ABS
 

It's "Eyes" are the speed sensors on the Axles themselves.
It "Sees" one or more sensor(s) reporting a different deceleration rate from the
others and takes action.
SO,Either It's "Off it's Feed"
OR it's telling you ONE or MORE WHEELS are out of synchronous Braking action.


The front brakes groaning,along with the ABS kicking on, is the "Lotto Win" for
you diagnostically...Unfortunately, I am not expert DIY enough to be able to interpret the SIGNS.

I would repost this over on the TECH side with the new info.
stevebfl,AD or P.Hiedary may have run into this and know the exact cause.

Thanks for the heads up...

I was just looking around my garage for something and I found 4 brand new brake lines for my 126...low and behold they are the same p/n for my 201 so if it ends up something with my brake lines I've got 4 new ones..

repost in tech? Isnt this the tech subforum?

bump?

Good news:

I went to the local junkyard and pulled a brake booster and master cylinder

http://i98.photobucket.com/albums/l250/MafiaNicky/IMG_9229.jpg

I power bled the system and braking is much better than it was before.

The pedal feels more solid.

I believe the problem stemmed from the fact that I had a 500E master cylinder hooked up to a 190E 2.6 booster. The 2.6 booster has an amplification factor of 4.5 where as the 500E booster is 5.6.

I do have a concern about my front calipers / rotors:

http://i98.photobucket.com/albums/l250/MafiaNicky/IMG_9239.jpg

There appears to be a blue streak on the rotor (from getting hot?) and the rotor is heavily rusted (or atleast to me it is) and its only 6 months old...Its a PBR rotor by the way.

I am wondering if either my rotors are just crappy. I've got brand new pads on (textar)... that or my calipers are just "weak" and not really applying them hard?