65mph & No Brakes (w108)
 

Yeah, it got pretty scary when all of a sudden I had completly no brakes and I was moving at about 65MPH. Seconds before the brake failure, I noticed gray smoke coming from the front wheel wells. There was none/vey little from under the hood. Although, I was still doing 65MPH, the smoke was still easily seen, so it must of been alot of smoke.

After I managed get the car off the freeway, using a combination of low gears and the parking break, I looked the car over. nothing brake fluid leaking, plenty of brake fluid in the little tanks above the master cylinder. The only miss was that the cap of the two brake fluid tanks was soaked with brake fluid, but not enough to make the brake fluid level go below min. I waited and waited hoping that the brakes would have to cool off, and that would ragain that pressure. But, that didn't work.

So, what could have happened. The brake failure was all-a-sudden. No warning, no sounds, just no brakes.

The model is a '69 280S (w108). I've had it for about a month.

That's pretty scary- glad you're okay.

Did you peek underneath to see if you lost a brake line or something up front? I suppose you'd see more fluid if so, but maybe it would only come out while activating the system. If the inside of any of your tires are covered in fluid, then you certainly lost a brake line.

Reminds me of the time in my old 70 280SE when, after kicking it down a gear to pass, the throttle linkage got stuck fully open. That was an exciting few minutes worth of driving... But losing all brakes is certainly scarier. Good luck-

JAS

No brakes at all, or marginal brakes?
I believe even your car has at least 2 'channels', meaning the rear brakes should do something even if the front channel goes out.

The smoke makes me suspect that one of the calipers stuck, and overheated, which in turn causes the brake fluid to boil, and the front channel to fail.

Does the pedal offer any resistance now?

Nice car, BTW!

Once had a caliper seize on a 450se. Plenty of smoke.
I was able to limp home with the caliper removed, and that line plugged with big screw and a hose clamp. Worked, but do not try this at home! I'm older and more risk-averse now...

First - what a beautiful car, so glad you were able to bring it to rest without further incident.

You say you have no pressure when pedal depressed yet there is no loss of fluid from the brake resevoir - that is confusing.

I say right now I have no experience of your particular model but here goes.

If you are not developing pressure and without loss of fluid I would guess your master cylinder is shot or at least one of the internal seals.

But then there is the smoke - but no loss of brake fluid - must have been something else then OR did your brakes overheat and you have 'boiled' moisture in the brake fluid leaving a compressible oil/vapour mix that has compromised hydraulic efficiency - hell I don't know - the smoke business is confusing.

In the first instance I would buy a quart or so of brake fluid and run that through the system bleeding each line in turn (For routine do a search here loads of advice). If that does not restore system pressure you are going to have to delve deeper.

After a failure like that I would want to have a good look at master cylinder and each wheel caliper/piston/cylinder arrangement.

One thing for sure - you have had a lucky escape maybe you need to pile some dough into the braking system!!

Good luck

NormanB

yes, totally no brakes.

The brake pedal has some resistence, but only when the car is off. When the car is on, the only resistence seems to be from the friction in the pedal.

Pumping the brakes makes no difference.

I ordered a master cylinder, I'll install it ASAP.

I'll keep u guys posted.

Mike,

It sounds very much like a master cylinder failure. Once the seals fail, brake fluid gets behind the piston and it will not come back to its normal "off" positon. This causes the brakes to stay on, which causes them to overheat as you experienced. The net effect is for the pressure to build in the system, which makes the brakes burn hotter and faster, and so on until the pads wear down enough to reduce the contact pressure on the disc. Pumping the brakes has no real effect as the pistion is not coming back in the master cylinder. You are likely only exercising the mechanical linkage and pedal return spring.

Given the high heat and extreme stress of the event, the rubber seals in the calipers are probably shot too. I would also think the discs are probably no longer the same hardness they were from the factory. So, I would replace the caliper seals too and give the discs a good examination. I would also take a look at the grease pack in the wheel bearings.

The rubber seals are an integral part of the caliper function. If you look inside the caliper there is no return spring to pull the pad back from the disc when you take your foot off the pedal. And by design the master cylinder piston draws fluid to fill the void as it moves back from the brake fluid reservoir so it does not "suck" the piston back into the cylinder.

In actuality there is very little brake fluid flow when you apply the brakes - the fluid merely serves to transmit the hydraulic pressure, and other than the swelling of hoses and other pressure containing parts as the pressure rises, there is no significant flow of fluid (which is good or the rate at which the brakes responded would be based on the length and configuration of the flow path - which would be really dangerous as each wheel responded when it felt like it).

The return force to pull the pads away from the disc is provided by the seal. The seal is engineered to have a high coefficient of static friction with the piston, so when you push on the pedal and the piston moves out of the cylinder bore slightly to squeeze the pad against the disc, this seal (a square cross section "O"-ring) deforms. When youlet off the pressure, the seal relaxes and pulls the piston back slightly, unloading the pads from their contact with the disc. The actual travel is very slight.

If you have aged the seals they will no longer perform this function, and they may even leak. If they stop pulling the pistion back, you will burn up another set of pads as the pads will stay in hard contact with the disc. So, I would examine all the elements of the system to make sure they are ok. I am not sure about the availability of seal replacement kits for your car, but they are available for most and cost a few dollars.

The job is not particularly difficult, but you need a spot to clean your calipers good before reassembly. Cleanliness is vital when these go back together. And you need some patience as the external rubber boot (a new one is typically part of the kit) can be tricky to get on. I have done this recently and relearned to swear in languages I thought I forgot. The key is to be patient and it helps to do the job with the piston aligned to the cylinder bore in the vertical position, with the boot on the piston, but dangling off the end of the piston going into the cylinder bore first. Use only brake fluid to rinse, lube and rinse and lube the parts. Good luck, and I hope this helps, Jim

Thanks for all the deep thought into the issue, JimSmith. Good thing I have a break form school, so I can tackle this brake problem. As soon as I get these brakes fixed, I can't wait to sell the car. :(

JimSmith has it outlined

I have to say that the brakes on the 108s have been great almost no problems.

the master muts be the cause -- the system is so simple that it must be it -- let us know.

Also must say the car looks very nice - the white 108 is just a great Mercedes.


I will also say that a total failure of the system is very rare -- one must remember that this system was way ahead of its time. I also would say that rebuild is easy in this car -- the calipers were designed to be rebuilt.

I just reread the post -- SELL IT.

Why do that -- This thing can become a member of the family.


I spent all of my school days driving 108s -- the first one was not as nice as the one you have now.

They really are great cars -- I know that this brake thing is not fun -- but it is very very rare -- I have not ever seen it in a 108 MB -- that is why I would like to know what the outcome is.

Once you get them setup they are great -- you must change the oil and you must lube it - other than that it is very forgiving.


If you do sell it PM me

yeldogt,

I love the car, the whole brake issue is only a set back to me. The main problem I have with the car is the 10-12MPG. I'm a full time student/ work part time. I'm struggling to pay from my rising tution, and simply can't afford the luxury of owning a gas guzzler, no matter how much I enjoy. If the car did atleast 18MPG, I would consider keeping it, but currently it's killing me.

So, don't get me wrong the W108 is a great car, but simply doesn't fit my daily driver needs. And I can't afford to have it as a car on the side. So... I'm sorta forced to have to let it go. Hey, but if you wish to take it off my hands, please be my guest. Atleast I'll know it will be going into good hands.

New Developments:
I tried to pump the air and whatever else out of the brake system. The only place that reacted to the pumping was the right front. Nothing came out of the rest. I also pumped the resivours. Now I have a little brake power. My plan now is to drive it (easy) to a MB shop about 15 miles away, during the middle of the night. This way there will be less traffic for me to worry about. The MB tech at the shop is a family friend, and is confident he can fix the problem, with all his pro tools. I'll write back, as soon as I can, with what I learn.

I have often wondered about the durability of the master pump and whether there is a recommendation for a service or replacement interval.

Most of the forum members would have cars at least 20 years old, and critical safety components with rubber seals in them surely will fail at some time. Although I regularly inspect brake pads and replace the brake fluids yearly, the issue of the master cylinder is usually ignored. The several times I broached it at my workshop, the argument is that failure is rare, and even in that event, the dual circuit setup preserves safety.

From your experience, this does not appear to be the case. Does anyone routinely include the master cylinder in the regular service?

It's smart that its a double circuit, but i'm sure there are classic MB drivers from this forum, using their second seal in the master cylinder. Seal kits or new/rebuilt master cylinders, are penny's in comparison to a costly accident, as a cause of a brake failure. I was lucky to get away from my experience, but had the driving conditon been different....I may not be writing right now.

Re: 65mph & No Brakes (w108)
 

It's a good thing your okay.....:eek: :eek: :eek: :eek: :eek: :eek:

New Developments:

I along with the mechanic tied bleeding the brakes again. The only one that blead anything, was the right front. Than we used an air pressure hose and pump to try to unclog the lines. All of them cleared up, except for the rear right. Eventually we took of the thick rubber brake hose that runs to the break, and cleared it out with copper wire. After intsalling it back, that side blead. We drained out the old nasty brake fluid and replaced it with new brake fluid.

The mechanic ordered 4 of those brakes lines, since the rest of them are probably in bad shape. They should come in Monday. I picked up the master cylinder today, and hope to get it installed this weekened.

One Problem Though....

On my way back from the mechanic, my brakes worked well. Except for the fact that they seemed to overheat, anjd smoke. I'm assuming there is too much break pressure in the brake system, even when not braking. While I waited for the brakes to cool off, I called the mechanic, and he said that installing the new master cylinder will solve this problem.

Does everything he said add up? Any theories as to what the problem maybe? Any questions?

Maybe that's why your getting bad mpg's? Just kidding but I have heard people here talk of losing efficiency when brakes are wacked.
David

It looks like you've narrowed down your problem to worn out brake hoses. I'll bet the smoking problem will go away once the new hoses are put in. This is a typical failure pattern for brake hoses. The inside wall deteriorates, then acts as a one-way valve, allowing brake fluid to pass through under the high pressure of applying brakes. Then it won't let fluid pass back under the low relaxation pressure, and the brakes can't properly release.

Since you're doing the master cylinder and brake hoses, why stop there? Why not rebuild all calipers? Then the whole system is refreshed.

If the brake fluid is that bad, I wonder what else has been neglected over the years. I too have an old car, and old cars require constant attention. There's not a lot of parts - namely seals - that are still original. I plan on replacing many of them in the near future.

Your car looks great, but you'll have a job ahead of you addressing issues with old seals and gaskets.

I'm really only looking for a fix that will do the job for now. I plan to sell this car in the near future, so investing alot into on my budget wouldn't be wise, in my opinion.

But if I wasn't in this finacial/time postion, I probably would go all out with the breaks.

I'm just hoping the new master cylinder and the brake hoses do the job.

Your theory about the "one-way" hoses, seems likly.

You seem to be tackling the repair the correct way, but you need to go further and inspect/repair caliper pistons and seals.

I respectfully suggest you should not be driving this vehicle on the highway - you really are tempting fate and while your life is your own -you are of course potentially risking the lives of others.

Can you not just leave the car on your mechanics premises?

I could have left the car on my mechanic's premises, but I still would need a car. Installing the brake hoses and master cylinder, shouldn't be a major problem. I plan I doing the master cylinder today, and brake hoses when they come in on Monday. I'll inspect the calipers, but don't plan On replacing them, unless I have to. I do though plan on replacing all the pads, and cleaning the rotors.

About the, risking your life and the lives of others...I can't really argue with that, you have a case against me there. But i'm confident the break system, will be in good shape after I replace the hoses and master cylinder. I havn't driven the car since I drove it back from the mechanic, not only for safty reasons, but I also don't want to damage any other component, as a result of the high heat/pressure.

Guys,

It seems like a plausible argument, that the brake hoses can hold back enough pressure to keep the pads in contact with the discs. However, as I noted earlier the amount of fluid that actually flows through the hoses is minimal. To maintain pressure as the brake heated up the hose would have to be a 100% effective one way valve. Those are hard enough to make on purpose. Any "leakage" past the blockage in the hose would allow the pressure to be relieved since the system is filled with an incompressible liquid. A very small volume change will effectively eliminate the pressure differential.

The original problem I thought was the master cylinder seals leaking, preventing the piston from returning to its "off" position. If this has not been fixed, there is likely no reason for the brakes to work any better today than the day you had your harrowing experience. If the problem persists after the master cylinder seals have been replaced, or you get a new/rebuilt master cylinder I would suspect the caliper seals, as they are directly involved in the mechanical release of the contact pressure between the pad and the disc.

Between the age and the torture these seals just experienced with the brakes overheating the seals are likely hardened from their intended condition. This will preclude them from being able to store the energy needed to pull the caliper piston back into the cylinder bore when the brake pedal is released. Which means the brakes will continue to overheat. This problem usually affects only one caliper at a time, and if all of yours were invovled in the original event, it is unlikely all the calipers failed in this manner simultaneously. The same for the hoses - if they can cause the brakes to stick "on" it is unlikely they all failed at the same point in time. The master cylinder, on the other hand, can fail and will affect all the brakes from that point on. Which is why the master cylinder should be rebuilt/replaced first.

The caliper kits from FastLane cost $17 and change for the fronts (the cost is for a set of new seals for both front calipers) and $18 and change for the rears (also a kit for both rear calipers). If you are going through the trouble to replace the hoses then you will have the calipers nearly off. Rebuilding is restricted to replacing the seals and cleaning any rust/dirt from the surfaces other than the cylinder bore and piston outside diameter that slides against the cylinder bore. These surfaces are matched for a specific fit that is not within the typical automotive shop to measure accurately, much less attempt to repair.

The key surfaces are typically chome plated for corrosion and wear resistance. Any evidence of plating degradation, rust or other surface defects of significant length or circumference will render the caliper useless. Honing thr bore, or abrasively cleaning the piston outside diameter or any other method involving metal removal will ruin the caliper. Loose rust, scale or deposits that can be removed with a soft wire brush (brass) are ok. The grooves the seal and rubber bellows or boot fit into can and should be thoroughly cleaned, including scraping to remove adherent deposits.

I agree with one of the comments above concerning the safety of brakes. Without adequately functioning brakes you are risking the lives of innocent people on the road as well as your own. I would not drive the car until the brakes were restored. Good luck, and I hope this helps. Jim

Okay...I replaced the master cylinder about an hour ago. I didn't try them out because, I'll install the hoses in the next few days, and didn't want to waste time pumping out the breaks, when I will have to do it again.

I'll write back once I replace the hoses.