1979 300 sd brake nightmare - PeachParts Mercedes-Benz Forum

lovedieselsd · #1 06-12-2006, 01:20 AM

the 116 brake system on my recently purchased 79 300 sd is a nightmare. the disc on the driver side is warped, I had it machined twice and now it sort of stopped wobbling al the rubbers and ball joints around it to dust. still touches the pads at points when rotating it manually though. problem not really solved so to speak.
that's 1. now also the booster is not giving pressure... so when braking hard, and letting go shortly and then pushing the pedal again it needs way more pressure. vacuum gives 15 pounds, even when you take the hose of the booster and put your thumb on the end of it. so no vacuumleak there. when in D or R and letting go of the pedal a bit it needs much more force to stop the car than at first.
can I just change to calipers and discs of a 123 chassis? non vented ones? that would be so cool. any tips on that 'unique' booster? is it the same as on the 280?
thanks. Help, I'm learning...

ok, so I'll start with taking the master cylinder of a similar car at pull-a-part to see how it works and to not mess up my own

and I'll try that with the booster too. although that seems to be a french-engineering kinda way of being attached to the body acc to RS899... looking forward to that one..
thanks guys. still odd how that rotor stays warped after machining it though.

Ara T. · #2 06-12-2006, 01:32 AM

Your rotors are warped because you had them machined, twice. Usually these suckers last long enough that you just buy new ones (they're pretty cheap) instead of wasting time getting them machined. I have a brake booster issue as well. What did mine in is that the old master cylinder leaked brake fluid into it which I suppose ****ed it up. So If I do one good hard stop and try to do another one I wont get power assist. Basically what im saying here is make sure your master cylinder is good. Not only will you stop much better but also you will stop drowning your booster in brake fluid.

lovedieselsd · #3 06-12-2006, 01:45 AM

but the machining was recommended by the local mercedes gods, aka the garage that does the maintenance on all the benzes around here...! anyway the booster/ master cylinder needs checking. is it difficult to get that enormous unit off? any repair-kits available? does it need replacement or just tlc?
thanks

Ara T. · #4 06-12-2006, 03:55 AM

I am afraid I only know how to do it on a W123. I first removed the Master Cylinder which was simple, 2 nuts and the brake lines and after that i just pulled it off. The brake booster was harder but still wasnt bad, just awkward. I had to pull the plastic underdashthing under the steering wheel (where the drives knees are near) and grab the two nuts off there (needed a nice flex head for my socket wrench and a nice long extension) and disconnect the lil clip that attaches to the brake pedal. Not too bad. It is probably a little different for your car but I hope any little bit helps. I would say replace the MC with a new unit if its almost 30 years old. If youre down there you might as well do the rubber brake lines that attach to your brake calipers. And of course you'll be bleeding the brakes for a while with nice clean brake fluid. The brake booster you can get away with not replacing, it doesnt really affect stopping distance, just how hard it is to press the brake pedal. I mean for me, one good power assisted shove on the brake is good enough.

rs899 · #5 06-12-2006, 11:18 AM

The W116 is pretty much the same as the W123, except that the booster almost seems as if it were manufactured in place. It takes a lot of fiddling and pulling and prodding to get it in there.

There are 4 nuts under the dash that hold the booster to the firewall. Two of them are virtually inaccessible. PITA.

Rick

Brian Carlton · #6 06-12-2006, 11:23 AM

Quote:

Originally Posted by lovedieselsd

but the machining was recommended by the local mercedes gods, aka the garage that does the maintenance on all the benzes around here...!

........time to find another Mercedes god. That one needs to be replaced.

rs899 · #7 06-12-2006, 02:33 PM

oh, and that unique booster is virtually the same as the W116 280SE . I think on the one I had the hole that attaches the pedal was larger or smaller. I ended up using one from a W126 that works fine.

lovedieselsd · #8 06-12-2006, 05:55 PM

just came back from pull a part junkyard and took a closer look at the way the booster is attached in a 280 se. it's true, you can virtually not get the f##ker out. unless you want to take the whole dash out, and some of that stuff will break because it's all so brittle. pretty depressed now. I think I'll just push the pedal a bit harder... would it help to just replace the master cylinder and drain the system? since the car pulls to the right too. on top of that warped disc that is! otherwise maybe a 126 booster when I have a few days time...

rs899 · #9 06-12-2006, 06:18 PM

This is probably one time when money for a rebuilt brake booster may be money well spent. Don't ask me how I know. I installed 2 good boosters - one each in a W123 and W126, And I threw 4 bad ones away....

There's lots of crap under the dash on the W116 that's in your way. But I think you need to fix it-you've got a lot of metal to stop.

Rick

lovedieselsd · #10 06-12-2006, 06:24 PM

well, this beater is just not worth the time. it brakes fine, as long as you don't let go of the brake a couple of times...

lovedieselsd · #11 07-02-2006, 01:36 PM

It is actually not such a nightmare I've found. unlike the french cars I worked on the rotor can be separated so I got 2 for $62 (free shipping even) from brembo, put them on and all is good. still the booster problem though, but those nuts aren't as difficult to get to as one person here said. just take off the panel underneath the steering wheel and do it. I might do that in the future, I'm starting to like this beater...

thanks for all the support by the way guys