w116 300sd Mercedes Hard to brake

[Gito]

1979 300sd
Hard to brake and brake pedal feels mushy.
Pedal does not travel to floor when at a stand still so I don't think its the Master Cylinder(MC)

Just replaced the front/rear calipers, rotors and brake hoses.

Bled the brake lines using my motive brake bleeder.

Used Dot 4 brake fluid by Napa.

Started at the rear passenger side brake caliper and continued to move to the rear drivers side caliper, then to the front passenger side caliper and finally moving on to bleed the drivers front caliper.

Are these signs of a bad brake booster or a bad Master Cylinder?
Am I using the right brake fluid?
Should I switch brake fluids before looking at what else might be wrong?

Car had not been driven since September of 2015.
I actually think that the brakes today feel like the brakes from back in Sep 2015.
Just seems odd that I have to press on the brake pedal so hard with all new calipers, rotors and brake hoses.

I once read a post where some guy switched to a different brake fluid ( same Dot) and this ended up correcting the problem

Please advise

 

[RooflessVW]

I suspect you still have some air in the system. Does the pedal firm up when you pump it?

New pads can feel funny when they're brand new. Did you bed them in?

 

[eljefino]

I pulled a w123 out of two year storage and the brakes went bad. In my example the master cylinder didn't let fluid back UP so the calipers self-applied slightly and the heat roasted the calipers, boiled the fluid, and led to total failure.

You could also have surface rust on the rotors that will scrape off. Now is a great time to inspect all four corners and make sure they're all equally clean, inside and out.

After that, take the little pins out and make sure your pads are free to move and haven't rusted themselves stuck in a position.

 

[Chris142]

Calipers on upside down?

 

[Gito]

Originally Posted By: Chris142
Calipers on upside down?


Nope, bleeder on top and brake hose attaches to top of caliper

 

[Gito]

Originally Posted By: rooflessVW
I suspect you still have some air in the system. Does the pedal firm up when you pump it?

New pads can feel funny when they're brand new. Did you bed them in?


How do you bed the brakes?

Hope its not too late. I tested the brakes in my neighborhood. Drove up a hill and drove back down, never slamming on the brakes and gradually coming to a stop.
I then carefully got on the freeway, exited slowly, then jumped back on the freeway to 3 miles back to my home.

How do you bed?

 

[Michael_P]

Sounds like a dumb question; but do your vacuum power locks work?

 

[Gito]

Oops, I just read the cap on the reservoir and it reads DOT 3. Time to flush.

Is it going to make a difference?

Will using DOT 3 completely flush out the current DOT 4?

 

[Rand]

Originally Posted By: Gito
Oops, I just read the cap on the reservoir and it reads DOT 3. Time to flush.

Is it going to make a difference?

Will using DOT 3 completely flush out the current DOT 4?


That is not an issue they are fully compatible.

you probably have air somewhere, or bad master cylinder.

 

[Gito]

I always thought that a brake pedal that travels while already at a stop is a sign of air in the lines or a bad Master Cylinder (MC).

I do have a backup brand new MC but I don't want to jump the gun with this.

On a side note: there is some sort of sealer or caulking between the Master Cylinder and the Brake Booster

 

[Gito]

Originally Posted By: Michael_P
Sounds like a dumb question; but do your vacuum power locks work?


yes they do

 

[chrome]

Originally Posted By: Gito
1979 300sd
Just replaced the front/rear calipers, rotors and brake hoses.


New pads too? Or old pads? Did you bed in the pads/rotors? Usually when new pads and rotors are installed, the first few miles have relatively poor braking efficiency. It gets better as the parts bed in.

 

[JHZR2]

Re-bleed.

 

[Gito]

Can someone correctly explain how to bed the pads/rotors?

Yes, new pads. New rotors, new pads, new hoses, new calipers.

Yes, I will re-bleed

 

[The_Eric]

Mushy pedal is often times air in the system.

I wouldn't worry about bedding the pads. It can vary from manufacturer to manufacturer and some don't recommend it at all. At any rate, not bedding them in will eventually give the same results as bedding them in. It will vary from pad to pad and also by application how long it will take before they're up to full effectiveness but it usually doesn't take more than a few trips.

 

[Gito]

What type of brake fluid is recommended for my 1979 300sd?
AutoZ has a special on Prestone dot 3 for 5.99 per L.
I also saw their brand selling for 7.99L, that's cheaper than Napa's 9.99.

Just want to get fluid that meets the standard for Mercedes

 

[meep]

Originally Posted By: Rand
Originally Posted By: Gito
Oops, I just read the cap on the reservoir and it reads DOT 3. Time to flush.

Is it going to make a difference?

Will using DOT 3 completely flush out the current DOT 4?


That is not an issue they are fully compatible.

you probably have air somewhere, or bad master cylinder.


They are fully compatible, but....

When Dot 4 came out I switched my cars and a friend's truck to it. All ended up with a marginally softer pedal feel. Some time later moved back to Dot 3 and they went back to their old firmer feel. I wouldn't believe it myself - I'd think they weren't bled properly, except that I did the procedure 3 times, bled, and got the same results. I now keep dot 3 in dot 3 and dot 4 in dot 4.

PS - all those vehicles were 80's and 90's models

-M

 

[Gito]

Bled the lines again and used DOT 3.
Same feeling, hard to brake and almost seems like the brake pads don't grab but instead glide on the rotor surface.


Not driving the car until i get to the bottom of it.

Will swap out the Master Cylinder with a new one. Have a new MC in my cabinet.

Will I have to bench bleed the MC?

 

[Silk]

Mercedes didn't use wear indicators on earlier models, they use a pad stop. It almost sounds like you have worn pads hitting the stops.

 

[Gito]

I have brand new pads, brand new rotors, brand new calipers and brand new hoses, all the way around.
New fluid, Dot 3, and bled using my Motive brake bleeder pump.

One thing that I do notice is that after I bled the brakes, and after turning on the car, the brake pedal sort of travels slowly when depressing it to the floor. Almost feels like it would be the Mcylinder at fault but as soon as you begin to drive and come to a complete stop, the brake pedal remains in its position when and after depressing it.