W108 - 1972 280SE 4.5 - Do I need new brake cable? - PeachParts Mercedes-Benz Forum

Baxterdown · #1 10-11-2014, 11:12 AM

Hi guys,

When I bought my car, the PO told me that someone had pulled on the manual brake and snapped the cable, so that the light would be permanently on. He offered to fix it after he returned to FL after the summer, but hasn't happened.

The other day, while under the car with my mechanic he mentioned the brake cable "is bad" and pointed to a rusted cable in the undercarriage that goes to the rear tires. He said the only way to fix the dash light is to replace the cable.

Any thoughts?

R72benz · #2 10-11-2014, 10:38 PM

Can't offer an opinion on the parking brake cable except that it would be very important for me to have it working properly. However, on the brake light always on, I had the same problem when I purchased my 280SE 2 years ago. The problem turned out to be the rear brake fluid sensor at the fluid reservoir. I pulled the connector, but watched my fluid levels carefully.

When I found the time to investigate further, the problem turned out to be the plastic float of the sensor. The mechanism is fairly simple with a float lifting a metal plate off of two contacts. You can purchase a new float mechanism, but I found it simple to fix.

The float had become full of brake fluid and would no longer lift the plate off the contacts. I had to drill a small hole in the bottom to drain the fluid which I then sealed with epoxy. I have watched it closely for six months and it works fine.

Just something else to check.

vandor · #3 10-11-2014, 11:05 PM

Hm, I thought the switch was by the handle inside the car, so one would think that if the handle is pushed all the way back, the light should go out.

Try disconnecting the electrical connections by the brake fluid reservoir to see if the light goes out. If it does, then it's one of those sensors.

Baxterdown · #4 10-12-2014, 08:46 AM

Thanks guys!!!! I never thought it could be anything other than what the PO told me. And as with quite a few other things, it has turned out to be nothing like what he said. I'm gonna try what you guys suggested.

Jose

Baxterdown · #5 11-27-2014, 01:01 PM

Hey guys,

I finally got around to looking into this. I disconnected the fluid sensors at the reservoir and the brake light went off! You guys just saved me a HUGE headache by not having to replace the brake cable (which is useless in flatland Florida!).

What do I need to fix the sensors? A new reservoir?

Jose

Jub · #6 11-27-2014, 06:16 PM

Careful when parking without a parking brake: If your shifter bushings are worn, it can cause your car to slip from park to neutral and roll (happened to me as I was stepping out car). Since then I always park my car with the parking brake (even after replacing/fixing my shifter bushings). It is a common problem (google it; someone did a write-up on it on this forum, I believe).

Jub · #7 11-28-2014, 07:36 AM

Here's the write-up (this is for a floor shifter):

DIY: W123 console shifter bushings

When I owned my 72 280SE it was a column shifter, so not sure if this is an issue with your model or not?

R72benz · #8 11-28-2014, 08:05 AM

You shouldn't need a new reservoir unless it is leaking. Both float mechanisms lift out easily after you remove the cap. Check the floats to see if they are full fluid as mine were. If the floats are fine, I would check the contact points for corrosion on the flat plate on top of the push rod. Hopefully this will be an easy fix for you.
Good luck
Ron

Baxterdown · #9 11-28-2014, 01:16 PM

Thanks Ron! Do the caps just pop out? I tried turning them and popping them out, but was afraid of braking them...

j.

Idle · #10 11-28-2014, 06:48 PM

During that era Germany required all cars to have a 'low brake fluid' light. Some could even be tested for function by pushing on them to see if they lit up.

But some just ran the light from a switch in the brake fluid res, like Mercedes did, and this saved them the trouble of installing a new light somewhere on the dash.

I'm glad it turned out to be such an easy fix.

Tomguy · #11 11-28-2014, 07:27 PM

No, they unscrew. They have a hex head on top and you may need a 6 point socket if you can't undo them by hand (though I seem to recall being able to do it by hand on mine).

I forgot to add: The floats are connected to the rods, but if the MC ran out of fluid at any point they can detach from the float, meaning the light is always on. Rather than buying new float sensors, re-attach the old ones. That's all I had to do for mine.

R72benz · #12 11-29-2014, 07:58 AM

Jose,
On mine the mechanism the electrical connector attaches to just lifted out of the reservoir (with a little paying) after removing (unscrewing) the plastic caps that do have a hex head for removing with a tool. Tomguy is right about the floats. Once you take of the electrical connector mechanism the floats will probably come to the top and need to be reconnected on installation.

I recently replaced two sets of brake pads so took out fluid to back out the plungers. I used the opportunity to check the low fluid sensors. I now have them back and working as designed. Good luck, hopefully this will be an easy fix for you and you won't have to do the black tape over the light solution.

Tomguy · #13 11-29-2014, 11:34 AM

worst case is either leaving them unplugged or putting a piece of elec tape on the "rod plate" (for lack of better terms) that shorts the contacts upon low level.

Lucas · #14 11-30-2014, 10:39 PM

There's a little device for a stretched brake cable that will tighten it. It's a universal thing and slips over and will pull a little "U" type shape in the cable. If that makes sense.

It has to go an exposed part of the cable.

I once had a truck with no parking brake, manual transmission, and broken shutoff for the diesel motor. Sometimes I had to get creative and find things to rest against so I could get out and pop the hood to turn it off.

Baxterdown · #15 12-02-2014, 06:56 AM

Hey guys, thanks for the info! I unscrewed both reservoir caps and found the floater and rubber grommet floating on the left tank. Nothing on the right tank (metal pin, floater, and grommet are missing).

I tried to fix the one set I have but the rubber grommet is literally disintegrating in my hand and will not hold the floater in place. The metal pin slides right out as soon as I put it on the metal pin.

I looked on EPC, and the parts are kind of cryptic but I think I was able to figure it out. The sender unit comes as one set and the part number is: A0025429917. Nothing for it on peachparts.com or eBay. A Google search yielded a website, which has a list of online store listings that apparently sell it. It also has pictures to confirm what the part looks like. They list of about $45 each.

Doing further research, I found a used brake master cylinder on EBay for $30. The seller confirmed that the floaters, metal pins, and rubber grommets were there and in good working order. I don’t need the whole thing, but for $30!?!? So I bought it! The listing said it came out of a 1969 280S; but it looks identical to mine. I hope it works.

I’ll report back when I get the part and install the floaters.

Jose