I, evidently, started my research and post before you posted and made my post after you posted. So, I did not gain the benefit of you post.

Thanks for the info. I suspected as much.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

Damnit, so this could kill my booster? Looks like I will get the reman on order to swap out and do it the first of next week.

FWIW, my pedal feel is fine.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Chances are that the DOT4, combined with the lack of driving, is what's killing MCs. DOT4 is extremely hygroscopic, much more so that DOT3, and that water causes corrosion in the bore. When the seals ride over this corrosion, they get damaged, and cause leakage.
If you don't rely on this car as a DD, then I would pull the master that's on it, and rebuild it myself. Pull it, disassemble, and check the bore the whole length with a T gauge. If it's within specs after being honed, then get a kit for it, reassemble, and be done with it. If you still use DOT4, make sure to get a compatible seal kit. Replace your grommets and fill cap seal at this time as well.

Hmmm, well the car is driven at least a few times a week. Brakes are flushed in the spring due to the absorption of water...

Interesting observation that the DOT4 is breaking it down, but would make sense I suppose as it is a US supplier that remans the units probably only specs the seals for DOT3 as almost all US stuff uses it.

Appears that my best bet is to return for refund and install a new one from FTE. At least the oil change today went easy.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Can you provide more info on DOT-4 being more hygroscopic than DOT-3? I thought they are both glycol based and equally hygroscopic. The only difference between the 2 is DOT-4 has a higher boiling point.

__________________
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

AFAIK it is what, 25-50°F difference in boiling point?

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Quote:
"From:

Pontons With Brake Boosters (power assisted brakes):
Do you have brake fluid disappearing slowly and you cannot see where? The master cylinder can leak slowly and the fluid dries up before you notice it. Or, the fluid is being drawn into the brake booster (if fitted). Rapid loss of fluid through the booster usually gets burned in the engine and makes it look like you are fogging mosquitoes. To stop the loss, unplug the vacuum line to the booster. Get the fluid out of the booster immediately. Brake fluid will ruin the rubber diaphragm inside the booster. Remove the vacuum check valve and drain the brake fluid out of the booster. Better yet, remove the booster from the car, undo the J-hooks holding the can on the booster, remove the can, and wash the diaphragm with alcohol or lacquer thinner. If you have a leather diaphragm, wash as above and soak in mineral oil. Are you bleeding the brakes after a brake job where you changed everything but the booster and the brake pedal never gets hard and you still get bubbles out of one of the wheel cylinders? Then, the booster is probably leaking. Pull the vacuum line under the booster (above the pedals) and check if the vacuum line is wet. When installing newly relined brake shoes, cover the lining with masking tape to keep grease off. When screwing all pieces of the brakes back together, if you cannot use your fingers to get the nut, bolt, or bake line screwed in most of the way, then stop. Something is wrong. This is especially true of the fine pitch brake fittings and the bolt screwed into the backing plate, through which the long thin pin passes and is held by a cotter pin. "

The Pontons is what, from the 50's? From the description above, it sounds like the booster design is very different than one from the W123. It even mentioned a "leather diaphram" and also a "vacuum line under the booster (above the pedals)".

I also had a mystery DOT-4 (than DOT-3 because it was cheaper) leak for a couple of months, with no external leaks. The mystery was solved when I pulled the MC and found it almost filled to the level of the MC. I sucked it all out with a syringe and stuffed Bounty towels in there to soak up what's left and put the used MC from my 240D parts car in there and the brakes has been working fine since. The vaccum line on the W123 is on top of the booster as I recall so will not suck all the brake fluid which has leaked in there, just whatever gets splashed up to the vac hose. I meant to check the booster with a Mightyvac to see if it has developed any leaks due to being half filled with brake fluid (DOT-4 then DOT-3), which has not caused a catastrophic failure of the booster yet, but haven't gotten around to it since the brakes has been working fine. Maybe I'll do it soon.

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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

I've had that first seal start leaking oil inside the car onto the floor. Didn't notice it until the carpet got saturated and my feet started slipping off the pedals.

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5 speed '91 190E 2.6 320,000 mi. (new car, fast, smooth as silk six, couldn't find any more Peugeots)
5 speed '85 Peugeot 505 2.5l Turbo Diesel 266,000 mi. (old car, fast for a diesel, had 2 others)
5 speed '01 Jetta V6 (new wifes car, pretty quick)
5 speed '85 Peugeot 505 2.2l Turbo Gas 197,000 mi. (wifes car, faster, sadly gone just short of 200k )
5 speed '83 Yamaha 750 Maxim 14,000 mi. (fastest)
0 speed 4' x 8' 1800 lb Harbor Freight utility trailer (only as fast as what's pulling it)

I dealt with it in school, but for the life of me I can't find the info now. I remember having a conversation about it with the instructor in the brakes class because my CB400 required DOT4. He told me that it has higher boiling points both wet and dry, but absorbs more water and risks more corrosion.

FWIW, there are DOT3 fluids out there that exceed the DOT4 requirements.

I have been using the DOT4 as it is stamped on the brake fluid cap last time I have checked it.

FWIW, my other 126s ( and BMWs, trucks, the Volvo) have no issues with the same DOT4... I really just assume I have been receiving ****ty remans.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

funola:

There's still a seal that exist between the MC and the booster. If this seal is failing/failed, fluid WILL leak into the booster.

Well if this is only Pontoon, can we stop discussing Pontoons in my thread? I am trying to narrow my issue, not compound something else that would make me question more parts.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

You may be past this point, but the first thing I would to is a little trouble shooting. Have you tried removing the lines leaving the master cylender and installing plugs, and stepping on the brake peddle? If you are questioning the master cylender as a unit this will disable the rest of the system so you know for sure that the leak in internal. the peddle should not move because there is no where for the fluid to move to. If it moves at all then one of the seals in the master cylender is bad.

hope that helps, good luck

__________________

That was my point....this seal also exist in your car. The physical parts are different from the Pontoon, but the concept still applies to our cars.

NEW master cyl arrived today, will probably install this weekend.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]