2002 CLK500 Brake failure

[Monty5150]

Good evening all.

I have had a CLK500 for the last year, it was CAT C'd back in 2008 and put straight back on the road with all the correct paperwork. MOT'd & serviced by an Indy Merc garage 3 months ago, currently 86k on the clock. Last week whilst in the outside lane of the M25 the brakes completely failed, as in no resistance on the brake pedal and full travel to the floor. The BAS & ESP lights came on and i managed to get over to the hard shoulder & stop. Whilst being recovered the brakes went back to normal and the warning lights went off. The car is currently at the Indy & so far they have found nothing to cause the fault lights. They are keeping it for a few days and will run about in it to see if anything changes but as it stands all they can do is give it back to me. Understandably i don't trust it now.

I've done some research and know that it does not have the SBC system that has plagued other models and that there are a number of possible causes such as the brake pedal switch, battery, steering sensor etc. I have not tried swapping any parts yet although did try the steering lock left/right/left and restart fix which did not immediately extinguish the warning lights. I believe that another possible cause can be the master cylinder which it would seem has a circa 10 year life. Of possible relevance i had to carry out an emergency stop a few days before the failure.

I'm happy to try replacing parts etc but my issue is that if this is an intermittant fault how do i ascertain whether a replacement part has fixed it before i take it back on the road? I assume that replacing all possible parts will not be viable due to the value of the car. It was bought as a fun car and i have £6k invested in it but at present it's scrap as i won't take my family in it & will not sell it as it is. Short of breaking it for parts what are my options? I've wanted a V8 since i was old enough to appreciate one and after a short ownership it looks like my dream has come to an end. Any help gratefully appreciated.

 

[star]

I would think you have a caliper/brake sticking on slightly, resulting in boiling of the brake fluid.

 

[Monty5150]

I would think you have a caliper/brake sticking on slightly, resulting in boiling of the brake fluid.

Thanks for the prompt response. At the time we looked at the fluid resevoir to check the level and whilst that was fine there was a light coating of fresh fluid on the top. No sign of a split, could the fluid boiling overcome the seals enough to force it through the filling cap? The brakes feel as they were before which one would assume means that the fluid has not been contaminated with vapour/moisture through boiling or other causes? I'm assuming that the garage has already checked the brake operation and fluid but will confirm when i speak with them later today.

 

[John Laidlaw]

As Ian above, you might want them to check that (sticking calliper) When you say fresh fluid, it's not mixing?
I'd get that changed anyway for the minimal cost involved..
Boiling fluid will migrate nicely.....

 

[Monty5150]

John/Ian, many thanks. I'll enquire as to how closely they inspected the calipers and see what they say. As you say a fluid change isn't big money so will most likely get that sorted. I can't see any receipts in the paperwork for a fluid change so most likely it's over 2 years old anyway. The fresh fluid was actually on top of the resevoir around the cap ie externally. My assumption is that its been forced through the cap. I'm certain it was clean prior as i'd cleaned the engine bay after making a mess polishing scratches out of the headlights. I shall probably swap over the brake switch as well for what it will cost as that is the most common cause.

 

[star]

The fluid around the cap is from when the bf got hot and expanded, pushing excess out. Brake light switch will not make a difference.

 

[mercedes13156]

Can I suggest that it's water in the brake fluid that's boiling? A friend of mine, many years ago, when I was on the bikes, sailed past me during a very heavy braking session and went straight through a bend at over 120mph injuring himself quite badly. He reported that the brake lever went straight to the bar after about half a second of braking. The Police tested the brakes about half an hour later and they appeared perfect but there was a mess of brake fluid around the reservoir cap where some had been squeezed out past the seal. We worked out that water in the brake fluid had flashed into steam as the temperature of the fluid exceeded 100 degrees after a series of very fast approaches to some tight bends. A few seconds after the crash, the steam condensed back to water and the brakes were working again.

As others have said previously, change the fluid immediately and look for any abrasion in the rotating parts that would cause heat which could transfer up the brake pipes. The brake fluid is isolated from the disk and pads by the piston and the caliper. There would have to be a tremendous amount of heat in the caliper for this to happen. The more likely reason is the constant compression of the water and brake fluid under braking, or constant small but high frequency compressions from a warped disk, which will heat the brake fluid up in much the same way that air in a diesel engine heats up on compression.

 

[Monty5150]

Can I suggest that it's water in the brake fluid that's boiling? A friend of mine, many years ago, when I was on the bikes, sailed past me during a very heavy braking session and went straight through a bend at over 120mph injuring himself quite badly. He reported that the brake lever went straight to the bar after about half a second of braking. The Police tested the brakes about half an hour later and they appeared perfect but there was a mess of brake fluid around the reservoir cap where some had been squeezed out past the seal. We worked out that water in the brake fluid had flashed into steam as the temperature of the fluid exceeded 100 degrees after a series of very fast approaches to some tight bends. A few seconds after the crash, the steam condensed back to water and the brakes were working again.

As others have said previously, change the fluid immediately and look for any abrasion in the rotating parts that would cause heat which could transfer up the brake pipes. The brake fluid is isolated from the disk and pads by the piston and the caliper. There would have to be a tremendous amount of heat in the caliper for this to happen. The more likely reason is the constant compression of the water and brake fluid under braking, or constant small but high frequency compressions from a warped disk, which will heat the brake fluid up in much the same way that air in a diesel engine heats up on compression.

Thanks, i'll do just that as soon as the garage rings me back. Can anyone clarify the situation regarding the braking system and electronics? Initially & following a quick google search at the time i had put this down to a faulty sensor/switch as this seemed a common fault. My first reaction was anger as i thought it was ludicrous that a simple sensor failing could result in a complete loss of brakes. I mentioned this to the garage and they said that this could happen but surely it should failsafe to bog standard hydraulic brakes in the event of an electrical malfunction?

 

[LostKiwi]

The brake system is a basic hydraulic mechanism. Fluid in a cylinder forced down a pipe to piston in a caliper.
No sensors are involved in it nor cause the pedal to go to the floor.
The ABS sits in the pipes and has a bunch of pistons that can compress the fluid in the pipes going to each wheel. If that happens ABS will pulse the fluid and the pedal but again it will not go to the floor (in fact it feels like the opposite).

As above - the symptom you have is classic fluid boiling as its water content is too high.

 

[Monty5150]

The brake system is a basic hydraulic mechanism. Fluid in a cylinder forced down a pipe to piston in a caliper.
No sensors are involved in it nor cause the pedal to go to the floor.
The ABS sits in the pipes and has a bunch of pistons that can compress the fluid in the pipes going to each wheel. If that happens ABS will pulse the fluid and the pedal but again it will not go to the floor (in fact it feels like the opposite).

As above - the symptom you have is classic fluid boiling as its water content is too high.

That's the answer i was hoping for! Seems i had a bit of a bum steer from my garage. Had no reply from them yet so will set them straight when i do. Given the weather i should imagine they are currently driving a BBQ & had an early one!

My sincere thanks to all that have replied & enjoy your weekend.

Keith

 

[John Laidlaw]

You too Keith - it will be fixable then you can get back to enjoying it!

 

[star]

It's hard to boil the brake fluid whilst on a motorway as the brake do not get overly hot unless one is sticking on.

 

[grahamcol]

I had an incidence once with a newly purchased 202 where the brake pedal suddenly felt very odd and needed pumping several times in order to stop the car. Upon getting out I found the nearside rear brake was extremely hot and this had obviously caused the brake fluid to boil. Strange thing is this happened just the once and my Indy couldn't find anything wrong with the brakes. I owned the car for a further two years and experienced no further problems.

 

[om613]

+3 for the stuck piston.
The key bit here is that when cooled down, brake pedal is hard as normal. The fluid's boiled, whether it has water in it or not, and when it boils, it expands, losing its normal incompressibilty.

No point changing just the fluid, it will do it again.
You need the caliper either stripped and repaired or replaced (easiest option).

 

[mercedes13156]

+3 for the stuck piston.
The key bit here is that when cooled down, brake pedal is hard as normal. The fluid's boiled, whether it has water in it or not, and when it boils, it expands, losing its normal incompressibilty.

No point changing just the fluid, it will do it again.
You need the caliper either stripped and repaired or replaced (easiest option).

If you have water in the brake fluid, it's going to happen a lot sooner at 100 degrees C than Dot 4 at 235 degrees C

 

[Craiglxviii]

+3 for the stuck piston.
The key bit here is that when cooled down, brake pedal is hard as normal. The fluid's boiled, whether it has water in it or not, and when it boils, it expands, losing its normal incompressibilty.

No point changing just the fluid, it will do it again.
You need the caliper either stripped and repaired or replaced (easiest option).

Recon rear caliper on my E320 S211 Avantgarde just cost me £103, so not a massive cost.

 

[Naraic]

Wouldn't the fluid boil at the caliper end? And if it does...do our cars no longer have dual circuit brakes to provide a fail safe in such a n instance?

 

[om613]

If you have water in the brake fluid, it's going to happen a lot sooner at 100 degrees C than Dot 4 at 235 degrees C

With a seized piston, such high temps will happen ... slightly later.
At your finger's peril, give the disc a prod. I'll give that one a 'Stelvio Pass'.

 

[Monty5150]

Just an update, have picked up the car following the brake fluid change and the garage confirmed that there was nothing wrong with the calipers or discs so assume then that the only cause was water in the fluid. The discs and pads have still got a little life in them but will opt to change them all now anyway. I will also send the calipers away for refurbishing for peace of mind. It's a few £ but i plan to keep the car a while. Am i right in saying that the calipers are made by Brembo? Would this mean then that the discs/pads are Brembo too? My previous car was a CLK320 diesel and to my knowledge the OEM parts on than were Pagid. Thanks again to everyone that has replied so far.

 

[Naraic]

They could be Brembo.