No Brakes! Wait a minute (well actually an hour) there back?

[PeterW113]

Hello all,

This morning on my way to the 96 Club gathering in London I experienced total brake failure. The brake pedal went to the floor with no resistance at all, and no braking! Fortunately, I was traveling at low speed in the usual London traffic and was able to safely pullover with no damage done.

Looking under the bonnet (hood) I could see some fluid had leaked from the reservoir where the reservoir attaches to the master cylinder, or so it appears to be, however there was still plenty of fluid in the reservoir.

After an hour by the roadside, and then to be told by the RAC that a recovery truck would be another four hours, I tried the brakes again and behold with engine running the brake pedal resistance was back to normal.

I turned off the engine checked the reservoir, and although there was the evidence of a leak the fluid was still at a similar level so I gave up on the RAC and cautiously drove home with the brakes working all the way.  This was a huge relief but also leaves me confused.

I plan to replace the grommet which joins the MC and reservoir, but has any one experienced something similar and could it mean that the Servo or MC are on the way out?

I am going to be reading related posts but if any one has any thoughts that would be appreciated.

Cheers

Peter

[Pawel66]

Horrifying experience - I think you were very very lucky... Reliefed to read "no damage done".

I do not know what happened, but I would carefully clean/rinse the painted areas where fluid leaked for now.

[PeterW113]

Thats a good point, I have washed the car down as its raining, but off to the garage to make sure no damage is being done.

Cheers

Peter

[450sl]

I would replace the mastercilinder asap.
Leakage is of little or no concern.

[stickandrudderman]

Agreed. Intermittent pedal failure can only be master cylinder.

[PeterW113]

Stick, 450sl and Pawel66

Thank you all for your comments and advice, I will replace the master cylinder as well.

Cheers

Peter

[450sl]

In the masterbrakecilinder are seals.

At some point they get tired , and start to give problems like a soft pedal -no pedal-low pedal.

Often the short term cure (as a lifesaver ) is repeatable pumping the pedal to get some brakepressure back ,  but definately a sign to replace your mastercilinder rightaway.

[ja17]

Fluid leaking from between the master cylinder and the booster is usually caused by a defective master cylinder. With a dual system like ours are, complete brake failure is still rare.

If your brakes overheated somehow (stuck caliper, plugged brake hose, or driving with the emergency on), then the brake fluid will overheat.  If the fluid is old and has enough moisture in it, the fluid will overheat without you knowing it. The brake system will fill with air and you will have no brakes. Flush brake fluid every two years.

[A Dalton]

 When one finds a master  w/rear seal leaking, it is good practice to  check the booster for fluid while the master is off.
 Easily done by sticking a rubber hose to the bottom of the booster , thru the master mounting hole and applying suction .

Failure to check for  fluid remains in the booster will eventually ruin the boosters inner works.
I have seen some of  them fill right up b/c the owners just keep adding fluid, unaware as to where it is going.

[PeterW113]

Many thanks for that tip, I will certainly check the booster for fluid.

I have started to remove the master cylinder though not yet finished the task. I am not familiar with the process, such as should I separate the resovoir before removing the MC, so checking out the Technicle Manual before going further.

Cheers

Peter

[Kevkeller]

I guess I quoted the wrong post on an earlier post so I deleted it.

I think people are not reading what the OP wrote. He said his leak was between the reservoir and the master cylinder not the master cylinder and the power booster.

He described his problem was the pedal completely going to the floor without the brakes working then after letting the car sit for a while they worked fine.  That doesn’t sound like he was pumping the brakes to build up pressure again. I can’t think of a reason why this would occur.
Did I misread the description?

[PeterW113]

You are correct with your interpretation, however I have since noticed that there are rust stains running down the booster at the point where the MC attaches.  I hope to remove the MC this weekend and will report back.  I am hoping that any leak or wear is limited to the MC.

 I have also concluded that the reservoir is press fitted into the MC so it just needs to be gently prised off.

[Mike K]

Empty the reservoir with a large syringe. 
You can gently prise the reservoir off the MC with a long flat tip screwdriver.

Also make sure that you place some old rags underneath & around the base of the MC to collect any fluid runoff. The fluid is highly corrosive to paint.

Best
Mike

[Mike K]

Here's an old post I wrote when I replaced the MC.
I did a bench bleed on the new MC prior to installing.

https://www.sl113.org/forums/index.php?topic=22964.msg164152#msg164152

Hope this helps.

Best
Mike

[suavemechanic]

Plus one for moisture in the fluid allowing it to boil ,give the system a bleed and some fresh fluid

[PeterW113]

Thanks for all the advice. The MC is now removed having been drained first as suggested. There was a slight whoosh of air as it separated from the servo. I assume this was a good thing indicating the servo was holding it’s vacuum?  In side the servo looked clean and dry.

New MC and brake lines are now on order.

Best

Peter

[Pawel66]

There is this oring between MC and booster - do not forget to replace it...

[PeterW113]

Just want to say thank you for everyones assistance and advice.

The master cylinder has been replaced, including seal, for a modest circa £120. Flexible brake pipes changed and fluid flushed through. I used the Sealy brake bleeding kit (recommended on the forum) which worked a dream.

So all sorted, thanks again and happy New Year.

Peter