Brake issue '77 450SL - PeachParts Mercedes-Benz Forum

ncgirl05 · #1 09-11-2012, 07:49 PM

Hi All,

Twice in the past year while driving my '77 450SL the brakes would suddenly not be there, as in pushing the pedal almost to the floor to get the car to stop. It didn't happen every time, just those two times, and they would return to normal immediately afterwards. My mechanic said my master cylinder was going out. I had the master cylinder replaced 3 weeks ago, brakes flushed and brake fluid reservoir cleaned of "gunk".

Today, driving home from work (had to take it - the weather is far too lovely this week) I lost brakes just like before - and they stayed bad. Fortunately I was a mile from home and made it safely.

So I ask you - what could possibly have caused this?? If it wasn't the master cylinder that caused it, what else could it be? Unfortunately, my mechanic was getting ready to move the week after he worked on my car and was going into semi-retirement. I have no way to get in touch with him so I am seeking help in diagnosing. Good mechanics are so damn hard to find....

Thanks in advance!

Leigh Anne

rs899 · #2 09-12-2012, 07:03 AM

Still sounds like the master cylinder is the place to look. Unless you are confusing high pedal effort (which could be a bad brake servo) with low pedal, it still is a hydraulic issue.

Could be a bad replacement part, or there is air still trapped in the system somewhere.

mbboy · #3 09-12-2012, 07:26 AM

Quote:

Originally Posted by rs899

Still sounds like the master cylinder is the place to look. Unless you are confusing high pedal effort (which could be a bad brake servo) with low pedal, it still is a hydraulic issue.

Could be a bad replacement part, or there is air still trapped in the system somewhere.

I agree. Probably the master cylinder, In fact, when I replaced mine a few years ago, the ATE I got was bad right out of the box.

I would, however, check the brake booster -- the big, black cylinder on the firewall on the driver's side -- too make sure it hasn't rusted through, or is leaking fluid.

Imo, if there was air in the system, you wouldn't have had a high pedal to begin with.

rowdie · #4 09-12-2012, 08:27 AM

Check the fluid level. If full and the pedal goes to the floor it is the master cylinder. If empty there is a leak in the system. Ruptured hose, rusted line or maybe leaking caliper. Most likely MC as the other should have caused the brake warning light to come on and both front and rear should not fail at the same time.

ncgirl05 · #5 09-12-2012, 11:39 AM

Thanks all - I am going to check the fluid level when I get home today. I had the same thought that perhaps the new MC I bought was bad. I noticed that after the mechanic had worked on my brakes that they felt kind of "hard" - not real hard, just not much of that nice, firm travel you typically feel with good brakes.

meltedpanda · #6 09-12-2012, 08:16 PM

or put in incorrectly , or the wrong one, or air in the system , or a bad hose, connection.
Really not something to be driving until you sort it out

ncgirl05 · #7 09-13-2012, 05:16 AM

Quote:

Originally Posted by meltedpanda

or put in incorrectly , or the wrong one, or air in the system , or a bad hose, connection.
Really not something to be driving until you sort it out

Agreed. It's parked for now, regrettably. The fluid reservoir was full. My mechanic has worked primarily on Mercedes for over 30 years so I trust his work implicitly. I also took special care to order the proper MC according to VIN number. I believe now the part was bad.

ncgirl05 · #8 03-09-2013, 03:07 PM

Just a quick update on this as I hate threads without resolution - come to find out my mechanic must have been drinking or high or something - the master cylinder that was in the car was the same one that was supposed to have been replaced! Instead of taking it to the mechanic who had worked on it (who went into semi-retirement after working on my car) we decided to change it ourselves. Imagine our surprise when we realized this was not the replacement I had bought but the OLD master cylinder that was bad.
We replaced it, brakes are great. The only gremlin I have left to tackle are my turn signals. They are under a separate thread. Thanks to all who responded and gave their thoughts in this thread - much appreciation!

Leigh Anne
'77 450SL