Brake Clunk....?

[Andrew280SEL]

My 350SE has a strange fault in the brakes, and I'm wondering what you guys think.

Now, the brakes work wonderfully in day to day use. The ability to stop such a heavy car so quickly is mighty impressive to me.

The scary thing though, is I've realised holding the brakes hard-ish for a long time (say, 5 minutes maybe) at a standstill is they will suddenly fade....
But will pump back up easily enough.

But that's not what this thread is about. I suspect I'll need to replace the master cylinder to fix that problem, which I would have on another spares car.

Everytime I touch the brakes when driving however, there's usually a noticable little "clunk" when I take my foot off. Doesn't affect anything really, it's just noticable and isn't particularly desirable to have.

Just wondering what you guys might think this is, and is it possible it's somehow related to the fading problem?

 

[B13]

check your control arm and subframe bushes.

Also make sure you have the right sized pads and anti-rattle springs installed in your brakes... my RX7 was missing the anti-rattle springs on its front brakes, so the pads were secure enough and worked, but when you pressed the brake pedal they moved upwards approx 1.5mm (the front calipers are on the cabin side of the disc, not on the bumper side) due to the turning of the disc, and then when you took your foot off the brake they'd "fall" back down with a noticeable clunk...

Jack the front of your W116 up and have a helper turn a wheel while softly applying the brake to check.

I.

 

[s class]

I had these symptoms of 'pad movement' on my 280SE from aftermarket pads at the rear. I switched to MB supplied pads and the problems went away.

 

[Styria]

Hi Andrew280SEL, I'll go with B13 on this one as far as bushes, ball joints etc. are concerned. I presume the 'clonking' is coming from the front and I would suggest that you also look at your disc rotors to see if they are unduly worn. Regards Styria

 

[BAR]

My own experience indicates that clunking comes from ball joints.

A loose pad would 'clink' a ball joint 'clunks', worn rubbers 'squeak'.

Fading, when at rest... do you mean that when the car is stationary and you have your foot on the brake pedal, the pedal slowly sinks to the floor?

This would indicate one of three possibilities to my mind:
1. Water and or air in the brake fluid - bleed and replace the brake fluid
2. Leaking brake cylinders at the wheel(s) - inspect each wheel for fluid leaks
3. Master cylinder - inspect for leaks

If it is 2 or 3, you should notice that the master cylinder fluid level drops quickly after a top up.

 

[John S]

Keep in mind that sometimes a master cylinder may leak internally by flowing past the seal, so there is actually no loss of hydraulic fluid.

 

[Andrew280SEL]

Thanks guys, I'll check what's been suggested as soon as I can.

Fading, when at rest... do you mean that when the car is stationary and you have your foot on the brake pedal, the pedal slowly sinks to the floor?

This would indicate one of three possibilities to my mind:
1. Water and or air in the brake fluid - bleed and replace the brake fluid
2. Leaking brake cylinders at the wheel(s) - inspect each wheel for fluid leaks
3. Master cylinder - inspect for leaks

If it is 2 or 3, you should notice that the master cylinder fluid level drops quickly after a top up.

Yes, if I keep my foot on the pedal long enough it will sink to the floor. However I wouldn't say it's slow. From memory it sunk pretty quickly once it happened, but it takes quite a while to actually happen, if that makes sense.

Now it doesn't chew through brake fluid...but it has lost some. I've only ever topped it up once, and the level is definately lower, though only a tiny bit. Whereas, the entire time I've had my 280SEL (since August 2006) the brake fluid level has never moved in that car.

 

[WGB]

My first thought is that you have water in you brake fluid.

When you hold on hot brakes the fluid boils and hydraulic pressure is lost.

Try a simple brake fluid change first and see what happens.

Bill

 

[Styria]

It would seem that Andrew is dealing with two problems here - the clunking bit and the dropping of the brake pedal after prolonged holding his foot on the pedal. He says (from memory) after several minutes.

As far as the clonking is concerned, I think that Bar describes it pretty well - he is speaking from first hand experience. With the Brake Master cylinder, another test that Andrew could perform is to hold foot on pedal whilst starting the engine. If the pedal goes down slightly, this to me would indicate a faulty Brake Master cylinder. Regards Styria

 

[BAR]

Sounds like your problem isn't one of leaking, given that there is only a minimal loss of fluid. This would be normal and reflect the wear rate of the brake pads, thus fluid level drops as pads wear down.

It woul appear that you have loss of pressure at the master cylinder, not unlikely given the age of the vehicle.

This can be 'reconditioned' with a kit or get one that has been done already. I'm sure Styria can provide this for you.

Don't forget to bleed the system after replacing any brake cylinders or master cylinder.

 

[SELfor50]

Andrew, I occasionally get brake 'clunk'. After replacement of 'reco'd' calipers and a good overhaul I still get it occasionally. Just get some new anti-rattle springs / clips and chuck em in.

It's intermittent right?? Doesn't happen 'all' the time??

 

[Michel]

Sounds like a master cylinder on it's way out Andrew....

Be careful, eventually, it will simply let go...

 

[Andrew280SEL]

Sounds like a master cylinder on it's way out Andrew....

Be careful, eventually, it will simply let go...

Thanks for your concern Michel, you are certainly correct there and it worries me a little.

Thankfully though, I don't drive it that regularly and I have my 280SEL to use instead while I fix it. I might as well fix that while I get the valve guides and seals and timing chain replaced as well.

It's intermittent right?? Doesn't happen 'all' the time??

It's hard to call it intermittent, because I guess it happens very often. But at the same time I don't think it definately happens all the time.

I'd say it happens a lot more the harder I press the brakes, which probably makes sense I guess.

 

[AM1961]

Hi all. I was going to start a new thread, but a quick search found this old one.

Not the clunk, but the soft/long pedal. I think my question is answered.

On my way home from the city of Melbourne this morning, about 3 km from home, I noticed the pedal felt a bit 'soft'.

The next application of the brakes and the pedal went further to the floor before starting to do it's job.

On the fourth stop, the pedal ended up on the floor just as the car stopped.

Only 500m to go, and a bit of pumping of the pedal, I made it into the carport.

Quick check of the brake fluid reservoir and around the wheels showed no sign of fluid loss.

After reading this thread, I have come to the conclusion that it sounds like the master cylinder.

Does this seem correct, or are there any other thoughts/suggestions?

Regards Andrew.

 

[Michel]

Hi all. I was going to start a new thread, but a quick search found this old one.

Not the clunk, but the soft/long pedal. I think my question is answered.

On my way home from the city of Melbourne this morning, about 3 km from home, I noticed the pedal felt a bit 'soft'.

The next application of the brakes and the pedal went further to the floor before starting to do it's job.

On the fourth stop, the pedal ended up on the floor just as the car stopped.

Only 500m to go, and a bit of pumping of the pedal, I made it into the carport.

Quick check of the brake fluid reservoir and around the wheels showed no sign of fluid loss.

After reading this thread, I have come to the conclusion that it sounds like the master cylinder.

Does this seem correct, or are there any other thoughts/suggestions?

Regards Andrew.

Sounds about right.

The brake fluid must have gone somewhere.

 

[Styria]

If you have lost brake fluid, I would suggest that most of it would be sitting in the brake servo unit. It's my hunch you have two problems - firstly, the Master Cylinder, and now also the servo unit. In my opinion, you will also be faced with having to rempve/rebuild the servo unit which will be at least a $300.00 operation. That's just the servo unit.

If you are going to remove the servo unit (a little awkward), I would recommend that you replace the anti sway bar bushes on the firewall, and also clean up/paint the inner chassis member below the servo unit. I have documented all of that in my Gleaming Beauty report thread some three weeks ago. Regards Styria

N.B. Maybe others would like to come in on this problem.

 

[WiSeGuYY]

UHH , brake is essential item in the car , i don't know about you guys but i would run inspection on the master cylinder and the four brake pads ( i usually use ATE) and check the leakage of brake fluid and test the circuit before the car back in the street.

REGARDS

TAREK