I have an 87 300 sdl, and the other day, the brakes seemed to quit. I started loosing pressure on them, and it started to take more and more stroke to make the car stop, and I'd have to pump the brakes to get pressure. I let to car cool down, and when I tried again, I had next to no brakes. I thought it was the master cylinder, but when I replaced it, similar things were happening. but something was interesting. I could build pressure and have the car hold it when it was shut off, but when the car was running, I coudl build pressure, and it would slowly drop. The pedal woudl slowly go to the floor, but that didn't happen while the car was stopped. Any Ideas what is wrong??

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Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

I've had similar issues with the '86.

It comes down to three possibilities:

1) Air in the lines.

2) Bad master cylinder

3) No fluid in rear reservoir causing air to be drawn into the lines and the need to thoroughly bleed the rear brakes......yet again. This is the most likely culprit because you get about 10 strokes of the pedal and fluid is needed in the m/c to prevent exhausting the fluid in the rear reservoir.

It's impossible to see the level in the rear reservoir from the driver's side, due to the design. You must look at it from the passenger side.

all 3 of the resivours were full when I took it off. I'm wondering about the brake booster?? Could it have a torn diaphram?? I'll go out in about an hour and bleed the brakes. Can the brakes be bled before the abs controler??

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

You have two reservoirs.

The brake booster doesn't sound like the culprit. The brakes would work fine with a very stiff and high pedal.

Since you replaced the master cylinder, did you properly bleed it before installing it?

Brakes are normally bled at the wheels, but, the m/c needs it's own bleed prior to doing the wheels.

how do you bleed the MC?? I didn't know that it needed to be bled. Maybe guys like me should stick to air brakes. no bleeding involved.

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

Yep, that's your problem.

Normally, you bleed them with some tubes that fit the outlets and route the fluid back into the reservoir.

But, with the unit all connected up, I'll give you one other possibility to try if you have two people:

1) Get a pile of rags. Put them beneath the outlet fittings.

2) Crack one of the outlet fittings and have the helper press down on the pedal as far as possible. Tighten the fitting and release the pedal. Repeat about 10 times.

3) Repeat step 2 for the second outlet fitting.

Make sure the brake fluid doesn't leak all over the underhood area.

It's a messy job doing it this way, but it does work.

works now. thank you very much brian.

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

Good job.

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