yea the lock system is all plugged off.I now will unplug the booster from the vacuum line and see if it makes a difference in my driving.

If you unplug the BIG line from the booster, you wont have any brakes.
RE-READ what I wrote

Maybe go thru those diagrams so you get a better understanding

This is false, you will still have brakes, just not power assisted brakes.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Sorry for the mis-information.
The whole point is to test the booster
Please let us know what your conclusion is
I will now bow out....
Take over guys

Yeah, no power brakes on a system that is designed to have it = VERY difficult stopping power.

The thread is getting long, I thought I read where the booster was tested, hook up a city-vac to the booster itself, pump a million times, if it holds vacuum, it's good.

dg85300D, keep posting, we're all here to help each other and learn. No one has ALL the answers.

__________________
83 SD

84 CD

I think those diagrams will be of benifit.
When I first got my D, whunter told me to replace gromet in
Booster first, flush fluids and replace rubber brake hoses. I should have listened to him, I ended up buying and
Installing a whole new booster, good learning experience for me but
Waste of money.
The rubber pieces just rot, once those all are replaced
His car will be good to go!

Hmmn, I didn't think that's how the Mercedes vacuum system works. My understanding is the vent provides clean air to the inlet of the vacuum pump only, not to the vacuum consumers, which needs vacuum only, not air. The air side and vacuum side of the vac pump is totally isolated. In a diaphragm pump, the isolation is via the diaphragm, in vane pumps, via the vanes.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

You are probably correct, my point is that the system needs a source of relatively clean air, that is what the vent does.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Back to the original problem: hard brakes. I have two 124 cars, an '87 wagon and a '95 sedan, and the brake pedal feel is remarkably different between the two. The wagon is a very firm hard pedal, practically no pedal movement after the initial application, and I like that. The '95 is on the softer side, much more like American cars, and I don't like that. I have replaced the master cylinder on the '95, as well as flexible brake lines, and bled the brakes two different ways, but no change in the pedal feel. I suspect this is a "feature" of the '95.

My point is that the OP may be experiencing a brake pedal feel that is normal for his car, and chasing a problem that doesn't exist (like I have).

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Very true, my 1979 300D took markedly more pedal effort than any other car I have driven, my w126,w124,w210, w202 and w203 all took much less effort by comparison. I replaced several components trying to fix the same this in it, I eventually stopped before replacing the booster. I seem to remember mine held vacuum just fine, and my MC was new and it was still harder than I was accustomed too....

Some people have replaced the w123 booster with a w126 one for increased braking power.

I think a comparison between two cars may not be a bad idea here...

OP, is there any chance you have access to another w123 for comparison?

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Symptom: hard brakes

Causes: multiple (vacuum leak typically)

Do not forget to rule out if the rest of the brake system is in good shape too. It's possible your car has multiple issues where the vacuum leak is making you think it's just that, when in fact there may be other issues with the brakes.

Suggestion: plumb all vacuum lines properly, isolate and diagnose each "system" or vacuum consumer, to see if there are any leaks. Isolate and re-test until you've diagnosed what the issue is.

At the same time, look over the entire brake system to see whether there is anything else amiss.

My car for the longest time had what I would say are hard brakes. I didn't realize they were hard because they stopped the car fine, until I heard a hissing noise after shutoff. Turns out it was a leaky booster, so I replaced that and the brakes now feel different. The brakes are definitely now grabbier and bite with better feedback.

Like you I had nothing to compare it to previously but after finding an observable symptom (hissing sound) and diagnosing thoroughly, I found the culprit and resolved the issue.

"Hard" brakes is a subjective term, try comparing it like was suggested, with a different but similar condition w123.

__________________
http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Any results with the brakes?
Dont leave us hangin

sorry. thought i posted something here!


So the booster is completely fine as well as the master cylnder. I flushed all the brake fluid and replaced all the lines and the brakes feel more responsive now. Still somewhat stiff, but i think this is how they are supposed to feel. Checked the pads and calipers (no sticking calipers and pads look fine for now).

For the ultimate test i drove it around San Francisco last weekend going up and down numerous hills. Stopped like a pro and never once slipped or felt wrong. The braking is much more stiff compared to a newer german car or Japanese car but i think this is one is solved.

Thanks everyone!

Nice to have good brakes!!

I notice a distinct difference brake wise between our 1977 300d and the 1984 300d. My two 240ds seem about the same as the 84 300d. The 240s are a 1979 and a 1983.

My assumption is that the brake systems where not upgraded during the 123 period. So at some point will have a serious look into the 1977 300d.

You can live with the brakes on the 1977 300d but at the same time they are not what they should be. So there are faults or a fault to be found.

The weirdess thing but not unknown is when we got the 1977 300d the rotor had separated at the thinner area of the hub and was only held in place by the caliper but obviously contributed nothing to the braking system. No unusual noises either.

Sounds like you should find another 123 to compare the brakes with still. Pedal feel is differant between brands but should be similar in all 123s. One test I do in frequently is to read the temperature of each opposing wheel after a run. Sometimes it can give some clues. Also your problem can just be some aftermarket brake pads that have materials incorporated that have poor coefficients of friction.

Personally I prefer the older types of pad composition as to me they grab on to the disk better even though they wear faster and do not seem to wear the disk as much as metallic pads do. I drive my cars in a reasonable fashion as well so besides the additional brake pad dust they are fine. Getting harder to find the softer composition pads as time moves forward. Metallic pads do tend to require more pedal pressure I expect and glazed pads quite a lot more pressure.

These cars originated thirty years or more ago. To me they have decent brakes for the time period and are still pretty decent when in good shape for todays conditions. I have no pre considerations of what I will find when I eventually get into our 1977 300d. It may be just one thing or multiples. Oddly enough I suspect the booster on that 1977 car of ours. I will do the comparison test as mentioned below in my evaluation of the brake system.

One test I can think of in your case is to put your brakes on with the engine off and the vacuum system drained by a couple of applications. Then start the car holding the pedal down. Two 123s should act the same pedal wise. If yours is different from the test car maybe the booster needs changed out with one from an auto wreckers. Believe my when I say I know what a 1977 300d feels like when the brakes are not really great but can be gotten by with. If we did not own three other 123s I probably would not know the difference. Just attribute it to an older brake system design.