Frau Frankenbenz not stopping on a dime
 

The last couple of days it seems the brakes are mushy and it is taking more pressure to stop. Where should I start looking - vaccuum or physical brake pads or something else? I've never dealt w/ brake issues before. It is getting worse every time I drive - as of today I can't stop quickly at all.:eek: I will take back roads on the way home today. Thanks in advance for your help.

Does the pedal feel mushy or is it stiff and you need more force to press it? Mushy pedal points towards a leak, worn pads or a bad master cylinder. Is the fluid level correct? If the booster/vacuum system is bad, the pedal gets stiff and it feels like it is pushing your foot back. Do you have any other issues with your vacuum system (door locks, engine shut off, etc.)? Test the brake-booster by pressing the pedal very hard and hold it and then shut off the engine at the same time. If it keeps running, the booster is probably bad (vacuum leak).

IP Shutoff works fine. Pressure is less than normal when pressing on brake pedal. Door locks don't work, but are disconnected from the system. Fluid level does not appear to have gone down. Put in new master cylinder last year.

What car is this you are talking about first of all?

It could be that your brake master cylinder is leaking brake fluid past its seal and letting it into your brake booster. This is what happened to me... I changed the master cylinder but the brake booster was damaged and puts out minimal assist... buit the car stops very well regardless... much better than your typical modern econocar. Econocars I have noticed though, overboost the hell out of the brakes and make them very touchy and this tends to give these drivers a lot of false confidence... what it translates into is you're going on the freeway and someone ahead of you touches their brakes, so you give yours a little nudge and lock your wheels up and go over the side of the road...almost lost control of my dad's 2000 Accord this way. Anways im getting off the subject here.

You might want to take your MC off and check it out if it hasnt been replaced... if youi change it out do the four rubber hoses as well... one per brake caliper. You should be able to stop from 40 mph to 0 mph with very little brake pedal pressure, and should be able to lock them up if you give them a good stomp. Not that locking up your brakes is a good thing for your pads or stopping distance, but it is a good guage of performance.

Sorry, the car is an 83 240D body with an 84 300SD engine/240D manual tranny.

Less pressure when pressing the pedal sounds more like a hydraulic problem, not vacuum. Check brake pads and discs for wear, check all calipers and brake lines for leaks (rust!) and check your MC. Bleed the system, maybe it's only air from extensive use. (have you been driving in the mountains?) In this case I would also change the fluid.
BTW there is a nice thread somewhere in this forum about bleeding the brake hydraulic system by connecting it to the clutch hydraulic system at the clutch slave cylinder. 100% mess free workplace and 100% air free brake AND clutch hydraulics.

Hmmm
 

Data #1. Mushy brake pedal.
Data #2. Master cylinder replaced, NEW or REBUILT???
Data #3. Fluid level not falling, verify this, try filling reservoir???
Data #4. It is getting worse every time you drive, DANGER: safety issue???

* Remove all wheels, inspect ALL brake pads.
* Look for damp/wet lines/hoses.
* While the car is raised, have someone HOLD the brake, and try to spin each tire.
* While the car is raised, have someone PUMP the brake several times, then release, with brake released, try to spin each tire.

took it to the indy...
 

Decided life safety issues are best dealt with someone with experience. I checked the reservoir, I was mistaken before. It was bone dry. After filling with brake fluid and driving a few miles, it was clear that fluid was leaking b/t the master and the booster. Drove to my mechanic, he said the master was prob. bad, and possibly an additional leak at one of the brake lines - still investigating as of last phone call. The master I am fairly certain was a new unit from Autozone, although my mechanic said he had experienced many bad mc from them before. Thanks for all your help.

Theres your problem right there...i wouldnt put my life in the hands of an AUtozone part! :o

$$$ later and still doesn't work!
 

Well, I have lost faith in my indy. I went to pick up my car after they replaced the m/c and the 4 hoses , and now it appears that the vacuum/booster system is screwed. I have a very hard pedal and and the shut-off doesn't work. I checked the suction at the hard line straight from the vacuum pump, and I'm pulling about 27" hg, so vacuum pump is good. I will continue to search the forum, but is there a "best" starting point to start locating the leak? Thanks in advance!

it sounds to me
 

like he fixed the fluid leak problem and dislodged or misinstalled a vac related problem.

give him a chance to make it right. should be no charge for it.

tom w

Thoughts
 

Vacuum seal between master cylinder and booster missing or damaged,
shutoff valve line came loose.
Both issues are easy to fix.

more info, please help
 

OK, so I checked the vacuum hose just before the booster with all vacuum accessories attached. Vacuum at the hose is 20" hg. Plugged the same line and tried to turn the key to shut off engine - engine shuts off fine. So - that leaves the seal b/t the m/c and the booster, or the booster itself. Is there any other diagnostic to descriminate b/t the two? Or should I just get a new booster? I assume any further testing will require the removal of both the m/c and the booster. Please verify. thanks in advance.

It is very simple.
 

It is very simple.
Remove the nuts holding the master cylinder to booster.
Ease the master cylinder away from the booster.
Replace the vacuum seal between them.
Install the master cylinder to booster.
Install and tighten the nuts.

Test the system.:)

Yeah..I bet you find the Indy forgot to put that O-ring between the mastercylinder and the booster.

ohhhhhhh-ring!
 

OK, so I pulled the MC away from the booster. No sort of rubber ring to be found. A-Ha! You guys are the best. There are a couple of grooves on the M/C where it touches the front face of the booster, and then there's the cylinder itself that sticks into the booster. Which location does the o-ring go to? and, who knows what size ring I need? The haynes manual doesn't say, and the steaky site is down :mad: . I asked at Autozone, and of course their computer sez "we don't carry that seal..." If this is something I can buy @ a generic place that would be great, since this car is my daily driver. Thanks againg for all your help.

it fits over the protusion of the mastercylinder....measure that and you have the size you need from your hardware store. I don't have one I could measure right now.

Answer:
 

Attached pictures.

Our 83 had no seal ring of any kind when we took off the M/C, but the brakes worked fine, and were VERY powerful. What does that mean? :D ;)

We are putting one on when we reinstall it however...

booster vacuum seal ring: 1 5/8" ID, 1 7/8" OD
 

Just measured it FYI, those are the measurements for the booster vacuum seal ring. Needs to be 1/8" thick I think, best in some brake fluid resistant material. Now I just need to find the darn compass and cut one from the make your own gasket material... Thanks again guys.

It means you didn't look close enough......and the old O-ring was flat as a pancake....because that is what seals the Booster vacuum in.....you WOULD have a massive vacuum leak without it.

pick up a generic O-ring at the parts or hardware store .....many have those kits that will sell you a single O-ring from....

o-ring from napa, $0.75, stopping and shutting off, priceless
 

Picked up a 1 5/8" id rubber o-ring from napa, tightened it down and voila! Brake booster sucks the pedal down a little on start up, and the engine shuts off with key. Hurray. Nothing like successful pre-work repairs to start your Monday off right.:D