R107 450SL brake padal went along way down

[RaceDiagnostics]

After about 30mins of driving today the brake peadal went soft and travelled a long way down before the brakes were applied, they recovered when pumped a couple of times but next time it was the same. The braking effeciency did still seem good although there was a lot of travel before pumping.

10 mins later, all was back to normal, another 10 mins on, the long travel was back etc....

Any suggesting on what could be at fault.

 

[Druk]

Master cylinder.

 

[RaceDiagnostics]

Repair or replace?

 

[Druk]

Replace. Speak to Sean at ECP Edinburgh. Get an ATE one.

 

[219]

It does sound like the master cylinder most likely .

A slim possibility is that your brake fluid could be boiling if a heat shield is missing and you have a brake pipe running near a hot exhaust manifold - I had this with the clutch on my W114 280E - it only happened in very hot weather , but in my case it was because RHD manual 280E's were very rare beasts and the pipe to the slave cylinder ran very close to the downpipes - not an issue on LHD models .

Thinking of the very hot weather we are having right now - could just be an issue with your brakes .

 

[Number_Cruncher]

Other things beyond those already mentioned that can cause this sort of problem include -

- collapsing wheel bearings which push the brake pads and pistons back

- pistons or pads binding, and locally boiling the fluid in the caliper

With a serious symptom like this, I would be tempted to have all the wheels off, throroughly check all the brakes (pistons and pads) for free movement, remaining friction material, disc condition (check for blueing marks), check all the wheels for looseness in the bearings, and renew all the brake fluid. If after that, nothing obvious is found wrong, I would fit a new master cylinder.

 

[RaceDiagnostics]

Other things beyond those already mentioned that can cause this sort of problem include -

- collapsing wheel bearings which push the brake pads and pistons back

- pistons or pads binding, and locally boiling the fluid in the caliper

With a serious symptom like this, I would be tempted to have all the wheels off, throroughly check all the brakes (pistons and pads) for free movement, remaining friction material, disc condition (check for blueing marks), check all the wheels for looseness in the bearings, and renew all the brake fluid. If after that, nothing obvious is found wrong, I would fit a new master cylinder.

I inspected all of this today, there was no sign of any problem. Also brakes worked perfectly today, although I only did about 4 miles or so.

 

[LTD]

Given you are handy around a car, I would consider overhauling everything associated with the brake system.

It'll be cheaper and less-stress inducing than repairing the front end of your car.

 

[RaceDiagnostics]

I'm going try to get hold of a replacement master cylinder for next week end and change it.

However I am sure that as soon as I try to remove the brake lines they will shear off.

 

[Stratman]

Given you are handy around a car, I would consider overhauling everything associated with the brake system.

It'll be cheaper and less-stress inducing than repairing the front end of your car.

And the back end of somebody else's

 

[RaceDiagnostics]

Quote for the part from MB, £251+vat,

quote for the part from ECP, £57+vat, so ordered it there.

 

[RaceDiagnostics]

Other things beyond those already mentioned that can cause this sort of problem include -

- collapsing wheel bearings which push the brake pads and pistons back

- pistons or pads binding, and locally boiling the fluid in the caliper

With a serious symptom like this, I would be tempted to have all the wheels off, throroughly check all the brakes (pistons and pads) for free movement, remaining friction material, disc condition (check for blueing marks), check all the wheels for looseness in the bearings, and renew all the brake fluid. If after that, nothing obvious is found wrong, I would fit a new master cylinder.

I reinspected each wheel before changing the master cylinder once all the brakes were hot and the brake travel problem reapeared, and found that the right rear was binding when hot. After inspection I could see that one pad was 95% worn and the other 50%, indicating a sticky piston. I gues this must have been suficient to boild the fluid in the caliper and cause the symptom. Anyway after a lot of levering I was abale to free off the cylinder and get new pads in and so far no repetition of the issue.

I'll now need to try to swap my new master cylinder for a new brake cliiper at ECP.

 

[Druk]

Me still thinks the master cyl is the cause of the original issue. Change them both and the flexibles and bleed once.

A stitch in time etc etc.

 

[Frank O' Phile]

Did you renew the brake fluid in all lines?

 

[RaceDiagnostics]

No, I hadn't planned to till I did the clliper.

 

[Frank O' Phile]

If it hasn't been changed for a few years it may have an amount of water contamination as it is hydroscopic(?).

As the calipers heat up the water vapourises and you have a gap which results in no brakes. After a cooling down period, it all returns to normal. That is, until the next time it heats up.

I had this in a car where I'd replaced the rear drums that were a bit too tight over the shoes and the heat generated by the friction left me with no brakes at a roundabout on a dual carriageway. By the time my heart rate returned to normal so had the brakes.

If your not losing any fluid then...?