so, the pressure differential switch on my MC is lighting up the BRAKE warning constantly. FSM 42-035 says that this means the two brake circuits have more than acceptable pressure difference, but offers no remedy. what should i do?

__________________
'77 240D, 504H, OM617.952, etc.

Start by making sure the fluid level is correct in both parts of the reservoir.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

thanks. i should have said, this is a one-chamber reservoir.

__________________
'77 240D, 504H, OM617.952, etc.

No divider in the middle of it? Where did you get that?

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

i think it was original equipment in the first couple of years.

__________________
'77 240D, 504H, OM617.952, etc.

I suggest you look again for the divider. The rear reservoir is hard to see but is probably there and low. Did you check for leaks around your brake flex lines?

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

thanks again folks. no leaks at the soft lines are apparent, at least at a cursory glance (next step: jacking the car up to look more closely inside the rear wheels?).

i took a look at a two-chamber reservoir and mine is different. what do you all think?

__________________
'77 240D, 504H, OM617.952, etc.

Check FSM 42-315, page 7. There are a couple of seals (item #36) that may have become compromised. You may be able to solve the problem by cleaning the bore for the pressure differential shaft with alcohol.

The bottom of page 2 gives a pretty good diagram of how it works.

http://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Chassis/42-315.pdf

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

In that picture the front reservoir chamber is below the add mark. The rear one looks like it might be full. Is that the car from the original post?

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

SD, thanks for the reference. that is some serious reading i'll have to do, to understand what i'm taking apart below.

Skippy, yes, same car. the reservoir is overly full front and back, but i am still not clear about the chambers. unlike the later model there is only one float and reset button, and of course only one filler neck.

by wiggling the reservoir in my hand i can see air bubbles at the same level up top front and back. not sure what caused the darker color seen in the picture. can the reservoir(s) being too full cause this issue?

additional info: an indie shop had the booster out a couple of weeks ago in order to swap the swaybar. those idiots installed it with the original bushings. maybe they also bolloxed up some aspect of the brakes?

__________________
'77 240D, 504H, OM617.952, etc.

i read the FSM section again and since mine is the same as the one pictured, it must be "tandem", i.e. two chambered. i misunderstood what the number of floats meant.

now, what does it mean for an MC to be "stepped"?
42-315 Disassembly, inspection and assembly of stepped tandem main cylinder

__________________
'77 240D, 504H, OM617.952, etc.

A stepped cylinder has two different bores. The front one will be smaller than the rear. Does it say you have a stepped one? I don't think I have seen a benz with a stepped cylinder.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

thanks tom. no, but 42-315 describes only stepped ones, 42-310 nonstepped ones. per those titles, only the former can be disassembled. SD Blue, any idea which cars got those?

i haven't found a leak, so maybe i have a clog in a brake line? my MC was somehow missing the filter in the filler.

__________________
'77 240D, 504H, OM617.952, etc.

How does the car stop? Maybe it's the switch misreporting on you.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

stopping is OK. there have been a couple of isolated moments when the pedal seemed soft for a second, but if braking is at all impaired, it's not very much so.

i also thought to blame the switch but no replacement seems available. checked it out with the multimeter and got some moving contact lubricant in there, it seems to work a bit more smoothly. maybe there are three positions the pin can be in, where the outer two show about 20 megaohms (open) and the innermost one 0.1 ohms (closed). the pin positions really were axial when i thought they would be a swinging arm of some kind. unfortunately, even the poster foldout schematic, which has resistance values for the fuel level sender and A/C switches, doesn't say what the proper value should be. the BRAKE light is still on after this test.

__________________
'77 240D, 504H, OM617.952, etc.