Any connection in common that could have caused this?

Last weekend for 1st time the vacuum locking on the 300SD (81) stopped

working automatically. No hoses knocked off...so I figured lost vacuum somewhere.

Then when I first drove on Monday I have an obvious soft brake pedal, going to the floor...

Almost no brakes. My rears were just done 4 months ago, and the fronts were checked same time and were ok 4 months ago..

The brake fluid level is showing full So I assume no leaks......

Any suggestions for possible issue ? Is a connection possible ?

Thanks,

Austin

__________________
'87 924S
'81 280SEL

Sold ->

81 300SD -
93 300E w/ 3.2
85 300D-
79 300SD
82 300CD
83 300CD - CA
87 190E 5 spd
87 Porsche 924S

"..I'll take a simple "C" to "G" and feel brand new about it..."

This is the SD? Soft pedal usually indicates air in lines. Since the system is closed, assuming that you haven't opened the lines, expect internal leak in the master. Physically check front & rear calipers for leaks. Put a vacuum gauge on a line & measure vacuum from vacuum pump. I would expect a hard pedal if the problem were caused by lack of vacuum.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Unless you know what you're doing, trust me, you don't want to mess with your brakes.

Can you cite your reasons for not working on one's brake system.

__________________
1982 240D 4spd, 327,000mi

Wouldn't a lack of vacuum be a hard pedal, not a soft pedal?

__________________
1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
262,715 and counting

Needing to stop from 73 mph to 0 in a quick amount of time.

I don't mess around with my brakes. I have my indy do that stuff. I would rather pay the money to have someone who's done this before do it right then me be cheap and cause the death or damage to myself or someone else.

Granted practice makes perfect. If you want to go ahead and bleed your brake lines promise me that when you're all done you will put both of your feet on the brake peddle and push in as hard as you can. Then pump the brake and do a lot of slow and fast tests around your neighbor hood.

If you have a brake failure, have it occur when you're going slow near your house and not on the highway

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-Typos courtesy of my mobile phone.

Fair enough.

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1982 240D 4spd, 327,000mi

Locks and brakes are separate vacuum systems on that car- Locks are run by the pump in the trunk, brakes off engine driven pump.
If you had to make a hard stop recently, that could have caused the brake failure. In the master cylinder, corrosion builds up in the areas the pistons normally do not travel in. When you stomp on the brakes, the pistons go into this corroded area, and the corrosion (aluminum oxide or iron oxide depending on what the master is made from) cuts the seals allowing fluid to leak past. This results in extremely soft pedal and total loss of brakes in a short time.
For a test, with the car idling, put your foot on the brake lightly. If the pedal slowly drops, then the master is done and needs to be replaced. Having this failure, you should also replace all the rubber flex hoses in the brake system. Chances are they are just as old as the master.

Sounds about right...thank you..

__________________
'87 924S
'81 280SEL

Sold ->

81 300SD -
93 300E w/ 3.2
85 300D-
79 300SD
82 300CD
83 300CD - CA
87 190E 5 spd
87 Porsche 924S

"..I'll take a simple "C" to "G" and feel brand new about it..."

Baring an external leak or not enough Brake Fluid I vote the Master Cylinder also.

It could be an internal leak in the Master Cylinder or an external Leak at the rear of the Master Cylinder; that leak will leak into the Brake Booster where it is no visable.

If someone does not want to work on their Brakes that is OK. However, DIY on the Brakes next to an Ignition Tune-up, and Filter Changes has to be one of the most often done DIY items.

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84 300D, 82 Volvo 244Gl Diesel

Take note of 4x4 & Diesel !! they are on the money. Time to replace the master an flexible lines. Brakes tend to fail when they are used hard. Like in an emergency, you dont need that risk. Its ok to replace the parts yourself, Unless you know what you are doing I would suggest not trying to rebuild your master. Dont use second hand brake parts from a junk yard. Only new or professionally rebuilt parts.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

The rebuild kit for a Master Cylinder cost nearly as much as an exchange Master Cylinder and you get no warranty.

On the other hand I ended up with a rebuilt Master Cylinder that only lasted about 1 year.
I did exchange it under warranty but I did not put on the exchaned one. I bought a new FENCO Master Cylinder (at the time Autozone had a good price on it; has gone up since then). That has solved my problem. (I had the same Pedal to the Floor Problem as the OP.)

There is nothing difficult about rebuilding your own Master Cylinder if only the Seals are shot as the kit replaces the Seals and Pistons. The problem is if the Master Cylinder bore is rusted, pitted or erroded inside.
If the bore is not good putting a new kit it will at best get you buy for some months or at the worst not work at all.
The Merceds Master Cylinder has a pin the goes through a slot in the front Piston of the Master Cylinder. If someone wanted to rebuild it they would have to find some clever way to pull the pin out; or you cannot slide the Piston/Seal Assy. out of the Cylinder.

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84 300D, 82 Volvo 244Gl Diesel

1981 300SD at Mechanic NOW...

Waiting for another call back...........


So far NOT THE MASTER CYLINDER...........



ANY OTHER POSSIBLE IDEAS....HE IS CHECKING CALIPERS NEXT...


AA

__________________
'87 924S
'81 280SEL

Sold ->

81 300SD -
93 300E w/ 3.2
85 300D-
79 300SD
82 300CD
83 300CD - CA
87 190E 5 spd
87 Porsche 924S

"..I'll take a simple "C" to "G" and feel brand new about it..."

Any air leaks? Holes in the rubber lines at the wheel, worn out caliper piston seals, and even rusted through metal lines can cause problems.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

and the answer is............. .........leaking Rear Caliper ...Still under warranty

New one arrives tomorrow morning....No cost.


WHEW!......



..

__________________
'87 924S
'81 280SEL

Sold ->

81 300SD -
93 300E w/ 3.2
85 300D-
79 300SD
82 300CD
83 300CD - CA
87 190E 5 spd
87 Porsche 924S

"..I'll take a simple "C" to "G" and feel brand new about it..."