I bet anyone who cares to take me up on it, a lunch that a properly bleed and installed master cylinder will fix said problem.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

on an 83 all the rubber bushings under the whole car need replaced...
This would cost over a grand if you paid someone.... also calipers can be
rebuilt.... DIY.... and you dont have to do all 4 brakes in one day... do one today... and then do one tomorrow...just work your way around the car.

mercedes diesels are awsome cars... and even if you have a stuck caliper... once its pushed back into position at least half the caliper will work....until you get the new caliper or rebuild kit...

hatterasguy is right... on his car it would be the master cylinder...
because his brakes are well maintained and his pads and rotors are
fairly new and his calipers have been serviced....

but on the one i fixed today... the caliper was frozen to the rotor and the rotor had broken off of the hub of the rotor making a free floating metal ring that sort of looked like the round thing that Xenia Princess warrior throws.
I will take pictures and post them tomorrow...maybe...

also, I put it back together with only half the caliper working until I could rebuild it....I put in new pads, new rotors, and I will rebuild a couple or calipers over the next few weekends...

I'm just saying that from what I have seen of stuck calipers brake feel is fine, except you either get pulling, or a horrible metallic screach if the pad is down to the backing.

The caliper would have to blow out completly IE fluid dripping from the wheel in order for the pedal to go to the floor. The original poster said he found no leaks.

Lets see how he fixes it, my bet is still on master cylinder.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Had a similar problem with my Miata - Drive 10-15+ miles, go for brakes & pedal would drop to floor, but would pump up & then work fine... Take off back down the highway; next time taking off-ramp, pedal dropped but would pump back up... Problem not resolved after installing new master cylinder, all 4 new calipers, new hoses & rotors -

Any takers as to what the root cause of the problem was?

bnc

on a well maintained car it would be the master cylinder... but on a 24 year old car with original rotors and calipers.... and really old worn out pads... its not...

the pistons can go out so far and then they rust... and dirt and rust is brought back into the caliper.... I actually pulled dirt out of a master cylinder with a turkey baister today on a 300sd...(but I guess that was not possible since brake fluid does not circulate)

I have the exact same problem right now on an 83 300sd and if i replace the master cylinder I will let you know...

On newer cars there is a brake fluid distribution box...
located under the car.... cutting the system into two section for
safety.... probably that box.....

here is a real good article on brake fluid...

http://www.xs11.com/tips/maintenance/maint1.shtml

On the Miata, it was... drum roll please -

bad wheel bearings -

enough wear in the bearings to cause minor wobble in rotors, which causes the caliper piston to be pushed slightly farther back into caliper housing - Thus, when brake pedal was applied, it dropped down to floor trying to push piston & pads against rotor. Pistons had to travel farther distance than 'normal', and pumping pedal would displace enough fluid to return piston to normal position. Turns out that it's very common occurance for bearing wear/wobble in raced/aggressively driven Miatas.

Even after installing factory new Miata MC/calipers/pads/rotors/hoses, it still dropped pedal after highway run - baffled the beejeebers out of me until I chased down the bearing issue!

bnc

Because this was your problem doesn't mean that it is common. If you had been checking your fluid level (look at it when you check the oil), you would have caught this. Also, you could have see the leakage, had you inspected the calipers, which is harder to do.

The seals in the calipers deform under use, and don't slide along a bore like the master cylinder seals or seals in the slave cylinders of drum brakes, which we don't have. The pistons proceed through the seals very slowly, and are very unlikely to fail before the piston sticks for other reasons.

Don't fall into the trap of thinking that your bizarre problem is what affects everyone else.

guys.... its the calipers......he has a stuck caliper that has been stuck and rusted for years.... his system is loaded with water and crud and rust and dirt because of this....he is experience a brake fluid boil....

Where I am wrong is that over the years i have said leave your brake fluid alone... well... i was wrong... you need to change it... it collects water and dirt from those old calipers.....

Some European car manufacturers specify DOT 4 brake fluid. Like DOT 3, this is a glycol-based fluid, but it has a higher boiling point. DOT 4 boils at a minimum of 446 degrees F. This higher boiling point is necessary on vehicles expected to generate a lot of heat in the braking system. When brake fluid boils, vapour bubbles are created in the sealed brake systems. When you step on the brake pedal, the brake pressure compresses the bubbles, not applying the brakes with full force. Braking performance decreases and the pedal feels soft or spongy.
One of the problems with glycol-based brake fluids is that they are hygroscopic. They attract moisture out of the air into the fluid. Leave a can of brake fluid open on the bench or leave the cap off your brake master cylinder and the fluid becomes contaminated with water. Moisture can even be absorbed slowly through the seals in good braking systems. Water boils at only 212 degrees F (100C), so this significantly lowers the boiling point of the brake fluid. DOT 3 fluid with only 3% water in it boils at only 284 degrees F. This is 115 degrees lower than clean brake fluid. DOT 4 fluid boils at 311 degrees F, 135 degrees lower than clean DOT 4 fluid. You probably wouldn't notice this in every day driving, but if you had to brake hard, then the additional heat in the brake system could boil the fluid and you find yourself with poor performing brakes.

oh the miatia was experienceing brake fluid boil as well...

same with the fellow with the bad caliper...

[QUOTE=blueranger;1288891]oh the miatia was experienceing brake fluid boil as well...

Well, BlueRanger - truth is that there never was a fluid boil issue on the Miata -

But as a kid, I loved your fights against the Putties & the Tengas...

Attached Thumbnails

 

...You're full of it. He wasn't going down the side of a mountian.

It's his master cylinder.

in these old cars the fluid is 20 years old.... its has more then the
3% water it is designed to hold... its filthy and contaminated... and
its boiling point is 200 deg vs 400 deg for new... the stuck caliper
cause the boil when you press the brake and it cools quickly and you
have brakes in just a few seconds....

my experience is when a master cylinder goes bad the pedal always goes
to the floor.....

but, I am just the guy who is doing the benz brakes....