Aack - Brakes - scary! - PeachParts Mercedes-Benz Forum

Prospector · #1 10-03-2014, 11:01 AM

Over the past few weeks, I've been thinking it was time to do brakes on the car. Things just didn't seem 'right' but i couldn't put a finger on it.

Last night I did my first oil change, and everything went well. Afterwards, I noticed a few drips on the ground and cussed myself for not being careful, then went for a drive around th eblock and found I had about 1/3 the stopping power I normally do. That was weird.

This morning the brakes were even softer.

When I got to work I popped the hood and noticed fluid leaking between the reservoir and brake booster. No wonder the brakes are going soft. I wonder if I leaned on something when I did the oil change and made a small problem bigger.

Anyways, I am now faced with a decision - according to ************** I should replace the booster and master since th efluid will bugger up the booster if it goes inside it. OTOH, best case would be that I only have to replace the gasket between the master cylinder and the brake booster.

I can't afford to be without wheels for more than a day or two. when I dig into this, how deep should I plan on going? Anyone else been through this?

I just ordered all the stuff for interior dashboard repairs. It doesn't rain but it pours. Good thing I got the garage cleaned out.

masc243 · #2 10-03-2014, 11:43 AM

Quote:

Originally Posted by Prospector

Over the past few weeks, I've been thinking it was time to do brakes on the car. Things just didn't seem 'right' but i couldn't put a finger on it.

Last night I did my first oil change, and everything went well. Afterwards, I noticed a few drips on the ground and cussed myself for not being careful, then went for a drive around th eblock and found I had about 1/3 the stopping power I normally do. That was weird.

This morning the brakes were even softer.

When I got to work I popped the hood and noticed fluid leaking between the reservoir and brake booster. No wonder the brakes are going soft. I wonder if I leaned on something when I did the oil change and made a small problem bigger.

Anyways, I am now faced with a decision - according to ************** I should replace the booster and master since th efluid will bugger up the booster if it goes inside it. OTOH, best case would be that I only have to replace the gasket between the master cylinder and the brake booster.

I can't afford to be without wheels for more than a day or two. when I dig into this, how deep should I plan on going? Anyone else been through this?

I just ordered all the stuff for interior dashboard repairs. It doesn't rain but it pours. Good thing I got the garage cleaned out.

Are you certain the master cylinder has failed. The reservoir quite literally just pops into 2 large grommet type seals and is held in place by friction. Maybe it was inadvertently popped off.

If the master cylinder were to fail, I don't really believe you would see fluid at the mating gasket as the fluid would be filling inside of the booster.

If the master cylinder truly has failed, Most will say, don't take chances with brakes, and I agree; You should replace the booster.

uberwasser · #3 10-03-2014, 12:02 PM

Fluid can leak at the master cylinder/booster connection, but if it does that usually means the booster has filled up with fluid. There are only two fasteners holding the master cylinder to the booster - I'd start by pulling that off and taking a peak inside the booster. Note that there is a rubber o-ring/gasket there that could be disturbed and you'll need to make sure it gets back in to its place or your booster will leak vacuum and you'll have another compounding issue.

Be aware that brake fluid will basically melt away any paint it touches. So you should rinse it off with plenty of water from any painted surface it touches.

Prospector · #4 10-03-2014, 01:38 PM

Shopping for parts, it appears there is an option for with or without pressure sensor. I can't see anything on my car that indicates whether such a sensor is on it or not. Reading other threads, it looks like it is safe to order a MC with the sensor, even if you don't need it just to be on the safe side - correct?? FWIW, my chassis is a late number and there is a #0323 cast into one side of the MC, and 987/2 cast into the other.

I do have a couple of wires running to the top of the reservoir, but I am not sure what they run. Maybe a level sensor???

My plan is to get a new MC sent express and install it regardless. While doing that I'll check condition of the booster. Then I'll get a booster sent if needed.

Yay car stuff!!

uberwasser · #5 10-03-2014, 01:59 PM

There is no pressure sensor on the W123. There are a pair of level sensors, one for each of the two chambers within the reservoir (one chamber holds the fluid for the front brakes, the other for the rear brakes). The reservoir is something you can re-use and so is separate from the master cylinder when it comes time to order it.

winmutt · #6 10-03-2014, 02:12 PM

Consider yourself lucky that it was caught with ease.

fahrvergnugen · #7 10-03-2014, 02:22 PM

The seal at the end of the master cylinder is where mine went bad; I hadn't ever seen that on any of my VWs, Audis, or any other car I have owned. Sad thing is the master wasn't more than 6-7 years old ( the car did sit for about 3 years).

Prospector · #8 10-03-2014, 03:25 PM

Well, I ordered the MC from PeachParts, and got a new oil pan and gasket; mine has hit the ground a few times. Then I ordered a valve cover gasket while I had them on the phone.

I just placed an order with DG for fuel lines so while the brakes are being bled and the car is in the air, I guess I'm doing the fuel lines too.

I should order new rotors, pads and wheel bearings and just keep going...

masc243 · #9 10-03-2014, 09:37 PM

Pads and rotors can be inspected; might not need to be replaced. What would concern me the most is the condition of the calipers and attaching brake lines. These cars are often parked and neglected before sale to an owner who is inclined to bring them back to a safe drivable state. Brake fluid will accumulate moisture over time and begin to cause corrosion (rust) in the pucks of the calipers. I would be performing a physical inspection; if all appears to function without hanging up, I would at a minimum be purging the old fluid and reservicing with the proper fluid. If the flexible lines at the calipers appear original, i'd replace those.

When i bought my 85 300d; the rear calipers were siezed. Ending up changing all the pads, all the calipers and flex lines, and the master cylinder.

Master cylinder will need to be bled. Lots of folks will bench bleed the MC, I chose to bleed the MC after mounting on the booster.

Rotors are fairly robust and should be able to be turned. Better to turn OEM rotors than to replace with aftermarket rotors from an unknown supplier.

Prospector · #10 10-04-2014, 12:14 AM

Thanks Masc - I've been driving the car for +/- 6 months. Before that, the PO had her as a daily driver. She ain't pretty, she just looks that way.

I do hear you on flushing the the system, I just don't know if I have the patience to go through with it. I probably should.

charmalu · #11 10-04-2014, 01:00 PM

Quote:

Originally Posted by Prospector

Thanks Masc - I've been driving the car for +/- 6 months. Before that, the PO had her as a daily driver. She ain't pretty, she just looks that way.

I do hear you on flushing the the system, I just don't know if I have the patience to go through with it. I probably should.

Get a Motive Power Brake Flusher. Comes with a MC Cap that fits the MB`s.
Screw it on, pump up the unit, and start with the R/R Caliper. It is a one man operation and just takes a few minutes.

Charlie

charmalu · #12 10-04-2014, 01:37 PM

Thought I would throw in this thread that was from a month or so back.

leak between master cylinder and brake booster

Charlie

masc243 · #13 10-04-2014, 05:12 PM

Quote:

Originally Posted by charmalu

Get a Motive Power Brake Flusher. Comes with a MC Cap that fits the MB`s.
Screw it on, pump up the unit, and start with the R/R Caliper. It is a one man operation and just takes a few minutes.

Charlie

Looks like a decent brake flusher. Had the one from Harbor Freight; Seemed create too much vacuum flow; just never seemed to work properly...
Might invest in that one.
Mike

leathermang · #14 10-05-2014, 09:20 AM

Quote:

Originally Posted by masc243

Looks like a decent brake flusher. Had the one from Harbor Freight; Seemed create too much vacuum flow; just never seemed to work properly...
Might invest in that one.
Mike

What do you mean ' too much vacuum flow ' ?
It should be producing a pressure flow of brake fluid....
and it is hard to imagine that with a hand pressure pump it would produce too much....as it will make MUCH less than a good correct procedure brake pedal flushing procedure.

leathermang · #15 10-05-2014, 09:26 AM

Quote:

Originally Posted by charmalu

....and start with the R/R Caliper. ......

Charlie may know that your car's brake lines are routed so that the Right Rear is the longest brake line distance from the master cylinder...
but for General Rules... in case someone has a car which is routed differently...and I have owned several in my life.... one starts with the longest line so that all the old fluid is flushed out completely... you have created a reservoir of clean fluid from which the other lines feed from...