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  #1  
Old 07-13-2018, 10:59 PM
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Brake Tail Lights Always On!

Dealing with my endless lack of brakes in a 300CD, i changed the master cylinder and have some improvement, but just noticed that THE BRAKE TAIL LIGHTS ARE ON WHENEVER THE IGNITION SWITCH IS IN THE RUN POSITION, WHETHER THE BRAKES ARE STEPPED ON OR NOT! I jacked up each wheel to see if it spun freely, both with and without the engine running, and all four spin freely. Tried pulling the electrical connectors off the reservoir, made no difference. Am baffled, and wondering if there is some connection with the brakes working so poorly despite nearly every part in the system having been replaced, and repeated attempts at bleeding the brakes. Where is the switch that controls those lites? Thanks!
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  #2  
Old 07-13-2018, 11:52 PM
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You're not the first to struggle with bleeding brakes on these cars. My experience has been that 2 people are required (one operating the pedal, the other cracking/sealing the bleeder port) or a pressure bleeder is required for good results. A one-man show simply won't cut it.

The brake light switch should be above the brake pedal. I really haven't looked at the Mercedes switch, but a friend of mine had his brake lights stick on due to a rubber bumper falling off the pedal arm of his Hyundai.

Quickie DIY page for a changeout from the forum sponsor:
https://www.pelicanparts.com/techarticles/Mercedes-W123/63-ELEC-Brake_Light_Switch_Replacement/63-ELEC-Brake_Light_Switch_Replacement.htm
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  #3  
Old 07-14-2018, 12:24 AM
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Quote:
Originally Posted by sun tortise View Post
Dealing with my endless lack of brakes in a 300CD, i changed the master cylinder and have some improvement, but just noticed that THE BRAKE TAIL LIGHTS ARE ON WHENEVER THE IGNITION SWITCH IS IN THE RUN POSITION, WHETHER THE BRAKES ARE STEPPED ON OR NOT! I jacked up each wheel to see if it spun freely, both with and without the engine running, and all four spin freely. Tried pulling the electrical connectors off the reservoir, made no difference. Am baffled, and wondering if there is some connection with the brakes working so poorly despite nearly every part in the system having been replaced, and repeated attempts at bleeding the brakes. Where is the switch that controls those lites? Thanks!

1) Which lights seem to be the problem; the tail lights, the brake lights, or both?

2) In any event, both the tail lights, and the brake lights are very sensitive creatures, and will behave badly when shouted at.
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Old 07-14-2018, 12:28 AM
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I think it is just a switch on the pedal, like all my other cars, though I don't recall ever looking for it on my W123 cars. There is generally an adjustment. It should sense the pedal motion without affecting it, i.e. pedal shouldn't bottom-out on the switch. Good it is only powered in "run". In many cars, it is always powered, meaning the battery runs down overnight if the brake lights stay on.
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  #5  
Old 07-14-2018, 12:41 AM
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I was shouting at the brakes

and cussing even. Thanks for the link to how to get at that switch. Very clear pictures. I was bleeding the brakes with the tube in a jar method, which has worked for me in the past. maybe i will try to make a pressure bleeder out of a spray pump as i saw in another post.
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  #6  
Old 07-14-2018, 12:50 AM
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Post Brake Lights ON

The take away here is very simple :

Unplug the brake light switch, if they go out, either the switch is out of adjustment or it's bad, easy fix either way .

Now, back to bleeding ~ I use a pressure bleeder, co$t me $50 for a Motion Pro brand one, maybe your F.L.A.P.S. has one as a loaned tool ? .
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Old 07-14-2018, 09:17 AM
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Quote:
Originally Posted by sun tortise View Post
I was bleeding the brakes with the tube in a jar method, which has worked for me in the past.
That's worked for every other car I've ever touched. Has failed miserably on both Mercedes, and I do mean miserably. Left the SL with brakes that wouldn't stop the car and the SDL with a a spongecake for a brake pedal. A 2-man setup worked for the SDL, but the SL required a pressure bleeder. Not sure why Mercedes brakes are so hard to bleed, but the tube-in-a-jar method does NOT work.
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  #8  
Old Yesterday, 12:53 PM
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Brake pedal low

Finally got someone to help me bleed the brakes. Got a good fluid flow on all of them, but the pedal still goes way low before the brakes engage. Wheel calipers and pads were replaced by P.O.



Wondering if there is some kind of an adjustable arm that affects how much the pedal needs to be depressed to activate the brakes.
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  #9  
Old Yesterday, 06:33 PM
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Is there a pedal freeplay adjustment on these cars? Maybe someone else who has been in there will chime in. I haven’t replaced booster or master on my benz, but on my truck there was an adjustment in the rod going through from the pedal to the booster. When you fixed the lights, did you move the switch closer to the pedal? If so, maybe the pedal wasn’t coming all the way up. Also, I presume you did a bench bleed an the master before install?
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  #10  
Old Yesterday, 07:26 PM
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Post Proper Brake Bleeding

It requires -both- a pressure bleeder and the bottle with rubber hose connected .

Yes, those of use who do brake bleeding on a regular basis can usually do it single handedly without the jar by feel but this still sprays corrosive brake fluid underneath the vehicle's chassis and is simply lazy and bad practice .


The order in which wheel is done is also very important and not mentioned by the O.P. .

For satisfactory results one must dot every 'I ' and cross every 'T', every time .
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1982 240D creampuff 370,000 miles
1978 300CD back from the dead&1980 300CD ~ SOLD
1984 300CD KEEPER ! 428,XXX miles
1984 Euro 300TD Fully optioned SWMBO's
1974 350SLC 4 speed stickshift SOLD & missed
Krazy Kommie Ural Motos (3)
BMW Moto R60/6 Barn Find, 8,000miles
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  #11  
Old Yesterday, 11:26 PM
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Orange brake warning lite on too!

Got enough brakes to take it for a spin, and the pedal goes almost all the way to the floor, and the orange brake warning lite comes on. Really baffled, as almost every thing brake related was replaced, bled, etc.
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  #12  
Old Today, 12:08 AM
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Post Brake Troubles

? Can you post a picture of the master cylinder and resivoir ? .
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-Nate
1982 240D creampuff 370,000 miles
1978 300CD back from the dead&1980 300CD ~ SOLD
1984 300CD KEEPER ! 428,XXX miles
1984 Euro 300TD Fully optioned SWMBO's
1974 350SLC 4 speed stickshift SOLD & missed
Krazy Kommie Ural Motos (3)
BMW Moto R60/6 Barn Find, 8,000miles
1959 VW #113 Deuxe Beetle, 36hp engine, stock
Junk, Rust
Arthritis, Crushed Spine,Broken Neck&Back
Memories &Peace Of Mind
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