Solid brake pedal

Tony_D · Unread post by **Tony_D** » 07 Feb 2009, 14:42

I've got a 98 Megane Coupe 1.6 8 valve.

Drove to the shop this afternoon; stopped at the first junction fine. Drove up to a queue of cars at a set of traffic lights; went to press the brakes and the brake pedal was rock solid. The roads are still slippery, but I managed to stop with the handbrake just in time.
I tried the brakes again and the pedal would not move. There were no lights on, on the dashboard. I turned the engine off and re-started the car and the brakes are now working fine!
In 12 years of driving I have never had a problem like this! I don't want to drive the car until I find out what's wrong.

Thank you,

Tony

ACTIVE8 · Unread post by **ACTIVE8** » 07 Feb 2009, 15:02

When a pedal does not move, it can point to no servo action, making the pedal very heavy, and therefore very hard to move.

Tony_D · Unread post by **Tony_D** » 07 Feb 2009, 20:17

I'm going to take the vacuum pipe off the servo to see what difference it makes? I assumed I'd be able to stop the car even without a servo though? My Corsa rally car has no servo, neither has my FIAT; the brake pedal takes a bit more effort to push but nothing like what happened in the Megane today.

Some people have said the brake fluid could have frozen? Strange that the brakes worked the first time I used them but not the second time?

Others have simply said "it's a Renault; scrap the bloody thing"

AndersDK · Unread post by **AndersDK** » 07 Feb 2009, 22:23

What ever the problem, get it sorted asap.

Cant believe its ice, even though your brake fluid would be overdue (more than 2 yrs old).

Its more likely a mechanical problem with the pedal to cylinder/servo linkage.

Tony_D · Unread post by **Tony_D** » 07 Feb 2009, 22:34

It wouldn't harm to change the brake fluid in it; I don't know the full history of the car.

The car will be off the road until I can find the problem! Looks like I'll be bouncing to work in the rally car on Monday

ACTIVE8 · Unread post by **ACTIVE8** » 07 Feb 2009, 23:13

On a car designed to work without a servo there will be different designs in the system I.E. bigger master cylinder, mechanical leverage ratios will be different etc.

So a direct comparison should not be made because, a servo can make a vast difference with its assistance.

Brake fluid is hydroscopic, and will therefore absorb moisture over a period of time, therefore I agree it would be best to change it, especially when you do not know when it was last changed.

Given the fact that the car is ten years old I would agree with Anders, in that it would be a good idea to carry out a proper assessment of the mechanical components in the braking system.

Tony_D · Unread post by **Tony_D** » 08 Feb 2009, 18:50

As far as I can tell the servo is working correctly. I'll wait for better weather and change the brake fluid.

Thanks for the help guys.

Tony_D · Unread post by **Tony_D** » 10 Feb 2009, 17:06

The servo appears to be working. The brake fluid has been changed and they system has been bled.
I have normal brakes at low speed, but when I increase the rpm the brake pedal goes solid. As the car slows down through engine braking the brake pedal moves slightly but is notchy way. Even when the brake pedal moves as the car slows down the brakes are terrible.

My only thoughts now are to change the master cylinder and maybe the ABS unit?

I noticed on the VOSA website that there were some recall notices for Meganes. Does anyone know what was done to the brakes during the recall - my local Renault dealer is a complete waste of time!

AndersDK · Unread post by **AndersDK** » 10 Feb 2009, 18:17

I suggest you find the fuse for the ABS system and remove it. Remember the ABS system PREVENTS the wheels from braking ONLY. It does not in any way produce braking forces.

That would instantly tell you if it is our ABS system locking out the brakes, as now the brakes should work OK.

Tony_D · Unread post by **Tony_D** » 10 Feb 2009, 23:57

Great idea! I'll give it a go. Thanks for the advice.

Tony_D · Unread post by **Tony_D** » 11 Feb 2009, 17:35

I removed both fuses for the ABS system and tried the car again.

The brakes pedal still goes hard; but I have noticed that it only occurs when the car is doing more than approx. 25 mph. I've even tried free-wheeling at 30 mph and trying the brakes, but the pedal still remains solid.

AndersDK · Unread post by **AndersDK** » 12 Feb 2009, 20:59

That is indeed very strange ...

I could only think of some weird problem in the vaccum assist servo.
At a certain vacuum, the membrane may pull the rod sidewards locking the brake pedal -

or something like that.

If that is true, you may still try another test :
find the vacuum hose to the servo, unplug the hose and prop the open hose end, not to disturb the engine.
That should of course give you a harder brakes pedal, but any faults caused by the vacuum assist pulling to help you, should now disappear.

Take care, do not overdo it, drive very careful with a hand on your handbrake lever

Tony_D · Unread post by **Tony_D** » 12 Feb 2009, 22:38

Thank you Anders, I'll have another look at the car tomorrow.

ACTIVE8 · Unread post by **ACTIVE8** » 13 Feb 2009, 22:42

Good luck with sorting this one, because as Anders says " it's strange! "

ACTIVE8 · Unread post by **ACTIVE8** » 15 Feb 2009, 16:52

Hi Tony_D

What's the latest braking

news on this thread?