1983 300D. 3 symptoms:

1) Very slow (4-6 months) brake fluid leak. Brakes work fine, but have to add brake fluid to keep rear reservoir in proper range.

2) When I turn the engine off after a long drive, I hear a bubbling noise through the firewall in front of me, i.e., where the master cylinder is. Bubbling eventually subsides about 10-20 seconds after engine is turned off.

3) Flushed brake fluid this past weekend. Rear brake flush went well, but could never get front brakes air-free. Instead, every pump of the brake pedal by my assistant resulted in same bubbling noise I hear when the car is turned off, and I could see half air half fluid going out through my clear bleeder hose and into waste receptacle. So, front brake lines are flushed, but not bled.

Despite all of these symptoms, when I drive the car, all four wheels seem to brake fine. (In other words, if the fronts weren't working, it would be easy to make the back tires skid with a hard brake, but that doesn't happen, the car just stops quickly even under hard braking conditions).

Defective master cylinder? Or could it be a bad brake booster? I don't see any fluid leaking between the booster and the master cylinder.

Any thoughts on most likely cause(s)? Thanks, fellow-MB diesel fans.

Gene

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Gene

1983 300d (133k)
1983 300sd (118k)

Could be leaking out the end of the M/C (the end you can't see) into the booster.

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

Rear seal on the MC leaking into the Power Booster...
There will be all your "Lost" brake fluid.

New Booster Time.

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'84 300SD sold
124.128

I'll agree a new M/C or rebuild kit is in order.
Remove the brake fluid from the booster.
I doubt that has failed.

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83 SD

84 CD

Thanks for the suggestions everyone. I was thinking I would need a new master cylinder. Boosters are expensive, so I think I'll get a new master cylinder on there and see if that works by itself, and only get the booster if the new master cylinder doesn't do the trick by itself.

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Gene

1983 300d (133k)
1983 300sd (118k)

if you do not replace the booster, at LEAST pull it and get all the fluid out of it.
it's nasty stuff, and the booster is not designed to have fluid in it. it WILL fail!
and it's kinda hard to stop the car without it!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Does it matter what brand of brake fluid you put in a 1984 300TD? Mine is low, so I'll have to go get some. I haven't put any in before, so don't know whether the brand matters really.

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" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles

^^I use Valvoline Full Synthetic Dot 3 & 4.

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83 SD

84 CD

Any DOT 3 or 4 should work. I just use the Napa stuff, I get a good discount there. DOT 4 supercedes 3, but 5 is different stuff.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth