Brake booster: Small mechanical victory, HUGE psychological victory

[123boy]

So, bought an '83 240D a couple months ago, 200K on the clock. The car had been "sitting" for a few years. Was able to get it running, short "test drive", and drive it home (after changing the oil at the sellers house). About a 15 mile drive.
The brakes never felt quite "right". Very hard, heavy pedal. Weak brake action. Felt like poor manual brakes. Could be attributed to many things, right?
Started checking through the brake system: Decent pads, rotors "ok", no stuck pistons. Vacuum pump checks good, ditto main vacuum line from pump to booster. No other vacuum related issues. After trying to pull a vacuum on the booster with my trusty "MiteyVac", and not able to, I faced the reality that the booster was probably shot.
Keep in mind, earlier in the day, I was reading a post on here about NLA parts. Also, the phrase "nothing more expensive than a cheap Mercedes" kept popping into my head. And thinking, I need this car like I need a hole in the head. Getting a little discouraged about the whole "process".
Then I remembered one of the many "Kent Burgsma" videos I had seen. Now, I know Kent gets "flamed" on here quite a bit. And, I get that. But ya gotta admit, he knows a thing or two about these cars. Shares a ton of knowledge. Had a good idea and is capitalizing on it. Puts a lot of time/effort into all of it, obviously. Dude's in his 70's fer cryin out loud...lol.
Anyhoo...back to my booster situation. Kent mentioned in the video about a small o-ring between the master cylinder and the booster (as is common on most vehicles). He said don't assume you need a new booster until you check that o-ring.
Removed the master cylinder mounting nuts, cracked the brake line flare nuts (after placing rags beneath to catch any dripping brake fluid) pulled the master cylinder back (forward, actually) enough to see where the 0-ring lives and wuddya know? The o-ring wasn't cracked, dried out and broken. It wasn't even THERE!! No trace of it!
Put a new one in there and my brakes now operate normally! Man, was I ever pumped. I'm sure I would have found that same info on this site, eventually, but you never know when something you heard or saw in the past will come in handy.
Also, and this is something I've been hearing my whole life in relation to car repair (hell, any type of repair), always check the simple things first. Many problems initially may appear big, but often boil down to something simple. Like this!

[meltedpanda]

good for you ! , but realize every rubber bit and vacuum line and connection is the first place to look , Your car is 30+ years old lol Enjoy the ride . We are here to help

[123boy]

Thanks "meltedpanda". Really appreciate the support. Yes, you are 100% correct. As I mentioned, often times it's the simple things. I don't know what "jarred" my memory, but I had totally forgotten about the small o-ring (and it is SMALL) between master cylinder and booster. Don't know if it's human nature or just my nature to wanna make something more complicated than it is? Probably the latter.

[aluminum]

The Hook up to pedal Linkage related to Free play Clearance is very important .
if their is no adjustment right at the Master Cylinder push rod then the adjustment is under the dash . if you see a Eccentric Bolt that hook's up the Linkage you want to turn the slash mark toward the rear . ( now this is the case for earlier model's I know but perhaps yours as well not 100 % on that .
Sometimes Booster to Booster change out requires a Brake switch Adjustment as well.
Your correct on the Rubber Seal Gasket that fits between Booster and Master cylinder .
Most often they are fine but new is always better . Check all the Rubber Vacuum lines with motor running for leaks . I use water spray .

[123boy]

I agree 100% with your brake pushrod adjustment assessment. It can take a while to get it right, sometimes.
As far as the booster o-ring is concerned. Yes, "most of the time" they ARE fine. This is the first time, in many years, I came across one that not only wasn't fine, but was completely missing!
When I finally remembered to check it as a possible contributor to my hard pedal, I was thinking "this is a waste of time, these o-rings are never a problem". And also, " I know I'm gonna hafta get into the booster swap headache".....can be such a PITA. This was the first time I found a missing part on a car and was actually happy about it. The o-ring wasn't dried out, cracked or rotted...it was completey gone! No traces of it ever being there. Which I find strange. Strange because this car was driven right up to a few years ago....not sitting idle in a garage, field, barn or someone's back yard rotting away. Also, where did it go? It's not like the o-ring can just "fall out"? As you mentioned "new is always" better. In this case, new is always better when an important part is completely missing lol
Thanks for the response and tips "aluminum". Good stuff. Appreciate it!

[vwnate1]

Thanx for this as I've been wondering about the freeplay adjustment on my '84 300TD graymarket .

-Nate

Originally Posted by aluminum

The Hook up to pedal Linkage related to Free play Clearance is very important .
if their is no adjustment right at the Master Cylinder push rod then the adjustment is under the dash . if you see a Eccentric Bolt that hook's up the Linkage you want to turn the slash mark toward the rear . ( now this is the case for earlier model's I know but perhaps yours as well not 100 % on that .
Sometimes Booster to Booster change out requires a Brake switch Adjustment as well.
Your correct on the Rubber Seal Gasket that fits between Booster and Master cylinder .
Most often they are fine but new is always better . Check all the Rubber Vacuum lines with motor running for leaks . I use water spray .