Hello everyone! Happy Fall.
The brakes went to about 5% effectiveness while driving at 50MPH on my 74 280 (of course it was rush hour!). Pedal went all the way to the floor. Luckily I didnt hit anyone!

I replaced the front pads about 2 months ago and had flawless operation until this misshap. I believe I have traced it to a siezed front caliper (passenger side). So my plan is to rebuild it and replace front hoses (i think Mark Di or Diesel Dog recommended I do this and of course I didnt-silly me).

My experience with brakes says I should replace rear hoses, do rear pads and maybe attack the master cylinder also; a complete refreshening. Note: Have not found any leaking and Master cyl is still full but that caliper makes a Groaning ship like sound ala "Das Boot".

What frightens me is the price of a brake booster. How do you tell when that is gone and will the renewed pressure of rebuilt brakes blow it out if it isnt allready?

Ahh geez...that one owner 91 300E with 82K and all records for 7G's sure is looking good right now.

Thanks,

Mark - 1974 280 Blue - Blue rasberry slurrpy color....4 barrels and 4 speeds=thirsty!

Brake pedal going to the floor is most likely a fluid leak, either interal in the master cylnder or external in a leaking metal brake line, brake hose or caliper. In some cases, if a seized caliper gets hot enough, the brake fluid can boil and may cause a low pedal.

Usually if the brake booster fails, it will cause a very hard brake pedal and require heavy pressure to stop, sometimes accompanied by a rough engine idle due to a major vacuum leak at the failed booster. I wouldn't worry until it fails.

If they haven't been done in the last 10 years or so, I recommend all new brake hoses. They can look OK outside but be swollen shut inside, holding fluid pressure and causing the same effect as a seized caliper. Recheck the calipers after hose replacement. If any are still seized, rebuild or replace them in pairs, to maintain equal braking on both sides of the car.

Happy Motoring, Mark

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DrDKW

yes, this definetly does not sound like a seized caliper, as you'd have 3 other wheels which still had brakes and, if anything, the pedal would go down LESS as less fluid goes through the system (Since that one caliper won't take any).

You have air in your lines (maybe low fluid), a leak in your system, or a bad master cylinder. Almost ANYTHING else brake-related and you'd still have SOME pedal and stopping power (as in >5%)! I'd say one of your lines is probably cracked or split, causing fluid to seep out at the previous brake usage, and air to fill in its spot when you let off the pedal, causing such poor stopping power. If you pushed the pedal that hard and your rear wheels didn't lock up, I'd suspect a hose back there leaking somewhere.

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

I would start with the Master Cylinder as likely culprit for pedal to the floor action. Usually what happens when MC rubber seals wear thin is that first you can force the pedal to the metal slowly with lots of pressure, say while standing at a red light. Then the pedal occasionally goes to the floor with less and less pressure. Finally you are double pumping the pedal to stop.

Bad booster just give you a hard pedal and stalls the engine, won't make the pedal go to the floor.

If you can recover the brakes by a quick pump, it's for sure the master cylinder. Rebuild kit is cheap, job is easy if you can find one, sometimes you can't and have to replace the MC instead. Do so at once -- rebuild or replace.

I would also strongly recommend new brake hoses and caliper rebuilds. The caliper rebuilds are easy when they aren't stuck yet, and if the hoses are hard and starting to crack, so are the piston seals and dust boots.

You will be amazed at how good the brakes are when you get done!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I replaced the brakes on my 73 280C (also 114) not too long ago. They're amazing easy to work on. I would give you this tip, in addition to what's already been said: don't bother trying to rebuild the calipers unless you know they've been rebuilt or replaced recently. I went down to my local import car parts store and bought rebuilt ones (good as new, really) for $50.00 a piece. Before that I did try to rebuild one but it was so rusty and scored inside that it wasn't worth saving the $30.00 in price over a rebuild kit ($20.00?). Also, while you've got the wheels off the car you might as well replace the rotors. You can find them for about $25.00 a pair NEW on eBay or some of the internet parts houses (e mail me if you want some recommendations).

When you mention "expensive" for a master cylinder, what do you mean exactly? I bought one a year ago (internet parts house) for $125.00 and I've seen them go cheaper on eBay. This is probably comparable to buying one for most Chevys or Fords.

Indeed, I have to say that one of the surprising things I found about owning an old Benz is that you can find parts easily (because MB tended to use the same parts for, say, 30 years) and they're no more expensive than most other, more pedestrian cars. I used to own a number of Peugeots -- now THOSE are expensive parts -- at least 2X-3X what I pay for comparable MB parts.

Good luck!

Catrinus
73 280C