It looks like you've narrowed down your problem to worn out brake hoses. I'll bet the smoking problem will go away once the new hoses are put in. This is a typical failure pattern for brake hoses. The inside wall deteriorates, then acts as a one-way valve, allowing brake fluid to pass through under the high pressure of applying brakes. Then it won't let fluid pass back under the low relaxation pressure, and the brakes can't properly release.

Since you're doing the master cylinder and brake hoses, why stop there? Why not rebuild all calipers? Then the whole system is refreshed.

If the brake fluid is that bad, I wonder what else has been neglected over the years. I too have an old car, and old cars require constant attention. There's not a lot of parts - namely seals - that are still original. I plan on replacing many of them in the near future.

Your car looks great, but you'll have a job ahead of you addressing issues with old seals and gaskets.

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95 E320 Cabriolet, 159K

I'm really only looking for a fix that will do the job for now. I plan to sell this car in the near future, so investing alot into on my budget wouldn't be wise, in my opinion.

But if I wasn't in this finacial/time postion, I probably would go all out with the breaks.

I'm just hoping the new master cylinder and the brake hoses do the job.

Your theory about the "one-way" hoses, seems likly.

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'77 300D 387,000 Miles . . .

'69 280S (SOLD)

'79 300CD (SOLD)

You seem to be tackling the repair the correct way, but you need to go further and inspect/repair caliper pistons and seals.

I respectfully suggest you should not be driving this vehicle on the highway - you really are tempting fate and while your life is your own -you are of course potentially risking the lives of others.

Can you not just leave the car on your mechanics premises?

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NormanB
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K

I could have left the car on my mechanic's premises, but I still would need a car. Installing the brake hoses and master cylinder, shouldn't be a major problem. I plan I doing the master cylinder today, and brake hoses when they come in on Monday. I'll inspect the calipers, but don't plan On replacing them, unless I have to. I do though plan on replacing all the pads, and cleaning the rotors.

About the, risking your life and the lives of others...I can't really argue with that, you have a case against me there. But i'm confident the break system, will be in good shape after I replace the hoses and master cylinder. I havn't driven the car since I drove it back from the mechanic, not only for safty reasons, but I also don't want to damage any other component, as a result of the high heat/pressure.

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'77 300D 387,000 Miles . . .

'69 280S (SOLD)

'79 300CD (SOLD)

Guys,

It seems like a plausible argument, that the brake hoses can hold back enough pressure to keep the pads in contact with the discs. However, as I noted earlier the amount of fluid that actually flows through the hoses is minimal. To maintain pressure as the brake heated up the hose would have to be a 100% effective one way valve. Those are hard enough to make on purpose. Any "leakage" past the blockage in the hose would allow the pressure to be relieved since the system is filled with an incompressible liquid. A very small volume change will effectively eliminate the pressure differential.

The original problem I thought was the master cylinder seals leaking, preventing the piston from returning to its "off" position. If this has not been fixed, there is likely no reason for the brakes to work any better today than the day you had your harrowing experience. If the problem persists after the master cylinder seals have been replaced, or you get a new/rebuilt master cylinder I would suspect the caliper seals, as they are directly involved in the mechanical release of the contact pressure between the pad and the disc.

Between the age and the torture these seals just experienced with the brakes overheating the seals are likely hardened from their intended condition. This will preclude them from being able to store the energy needed to pull the caliper piston back into the cylinder bore when the brake pedal is released. Which means the brakes will continue to overheat. This problem usually affects only one caliper at a time, and if all of yours were invovled in the original event, it is unlikely all the calipers failed in this manner simultaneously. The same for the hoses - if they can cause the brakes to stick "on" it is unlikely they all failed at the same point in time. The master cylinder, on the other hand, can fail and will affect all the brakes from that point on. Which is why the master cylinder should be rebuilt/replaced first.

The caliper kits from FastLane cost $17 and change for the fronts (the cost is for a set of new seals for both front calipers) and $18 and change for the rears (also a kit for both rear calipers). If you are going through the trouble to replace the hoses then you will have the calipers nearly off. Rebuilding is restricted to replacing the seals and cleaning any rust/dirt from the surfaces other than the cylinder bore and piston outside diameter that slides against the cylinder bore. These surfaces are matched for a specific fit that is not within the typical automotive shop to measure accurately, much less attempt to repair.

The key surfaces are typically chome plated for corrosion and wear resistance. Any evidence of plating degradation, rust or other surface defects of significant length or circumference will render the caliper useless. Honing thr bore, or abrasively cleaning the piston outside diameter or any other method involving metal removal will ruin the caliper. Loose rust, scale or deposits that can be removed with a soft wire brush (brass) are ok. The grooves the seal and rubber bellows or boot fit into can and should be thoroughly cleaned, including scraping to remove adherent deposits.

I agree with one of the comments above concerning the safety of brakes. Without adequately functioning brakes you are risking the lives of innocent people on the road as well as your own. I would not drive the car until the brakes were restored. Good luck, and I hope this helps. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Okay...I replaced the master cylinder about an hour ago. I didn't try them out because, I'll install the hoses in the next few days, and didn't want to waste time pumping out the breaks, when I will have to do it again.

I'll write back once I replace the hoses.

__________________
'77 300D 387,000 Miles . . .

'69 280S (SOLD)

'79 300CD (SOLD)