Brake problem - sometimes hard pedal

[jonnyboy93]

Hi

Been having some issues with the brakes on my 2002 S40 T4 recently. I have had a search through the forum for similar issues, but nothing I can find quite the same.

The issue - For a while now, the brake pedal has been very high and hard. Very little travel, and it feels like you have to really put in the effort and that the braking power is reduced and the car takes longer to stop. Other times the pedal feels more normal, in that there is more travel and more progressive braking.

When there is longer travel on the pedal, at times it feels like there is a notch half way down where there is some resistance, and this then gives way.

Also, a few times, when the pedal has been really hard, and have been braking, the pedal has then given, and dropped all of a sudden.

I have done the standard test to check the servo, pump a few times with engine off and the pedal is firm (not many/any pumps required), and then with foot on the pedal start the engine and the pedal drops.

Its a little worrying as its not all the time, so you are never sure how the brakes are going to perform. For example, on a longish journey yesterday, they were fine to start out with, a couple of times along the journey the pedal was very hard and required a lot of effort to stop the car, then it was back to normal, and then towards the end of the journey, had the pedal being firm then dropped after a bit of pressure was put on it.

I have had all the wheels of and had a visual inspection of the discs and pads, and can see nothing out of the ordinary or uneven wear. All the pads and discs were replaced about 18 months ago.

Any ideas what this could be? I'm leaning towards intermittent servo performance myself, but am interested in others views before I source a replacement for this

Cheers

Jon

[pierremcalpine]

There is a vacuum hose with a check valve that connects to the brake booster which is a common failure point. The main symptoms there that I have heard of are: very difficult braking when we first starts up when cold. Not sure if that helps you though. It’s an easy fix/test if you can get your hands on a working hose....

[bobthecabbage]

Mine is a bit like that, very similar in fact but I'm used to it. All of my brake callipers have been replaced so its not that.

It is worth checking the pistons can move freely and the slide pins aren't binding/seized. A hole in the boot protecting these can lead to it failing fairly quickly.

To maintain/improve braking I find it useful to occassionally activate the ABS by finding a bit of wet muddy road/grass/gravel/ice. Be careful, don't crash, use private land etc and any other caveats you can think of.

Also I find it helps to brake firmly whilst going down a steep hill a few times to help adjust up the rear brakes and give an improved handbrake.

I still don't know what causes the firm pedal and the notch that you sometimes have to push through to get adequate braking. I think some of it is due to the ABS setup.

[V40T4R]

Hi,
What Pierre said or maybe brake booster failing.

[martin93]

Well mine has never had a firm notchy pedal. And hate to sound like a knowitall Bob, but rear disk brakes should not need a hard stamp in order to adjust up the handbrake. This should only apply to cars with rear drums which have an auto adjuster in them. Rear disk brakes adjust naturally when the pedal is released, which is why as the brake pads wear, the fluid level gradually drops as the growing space between the caliper piston and bore is taken up with fluid.

I would third on it being a brake servo issue rather than a caliper problem. Although I would check the caliper sliders aren't seized just to make sure, as to me greasing these up are a yearly service item.

Biggest issue I've found with servo's on older cars is the brake master cylinder leaking fluid into the actual servo causing all sorts of problems. I would check the one way valve first as pierremcalpine suggested, and make sure there are no leaks on the hose and its connections. Then have a look for any signs of fluid on the vacuum pipe going into the servo while you're there.

So to conclude, I would say it's a brake servo or master cylinder problem.

[jonnyboy93]

Thanks for all the replies so far.

I had a look yesterday and checked the operation of the check valve, and all appears to be fine with that. All other checks appear to show the servo is operating properly, i.e. you can pump the pedal with the engine off and it gets solid, then drops once engine is started.

Had no issues with the brakes this morning on a 60 mile drive so will keep an eye on things.

Got a bit of spare time next weekend with the bank holiday so will have a proper look at the calipers all round and check for ease of operation etc.

[magnuz]

I also sometimes get this problem ! but in my case, if i crawl under the dashboard and squirt some penetrating fluid in to the back of the servo where the pedal pushrod goes through some sort of air filter in to the servo & work the pedal with the engine running to help to get the fluid through ,.. it does seem to make an improvement. There is a valve just inside the servo, that i suspect gets some dirt in it & causes my problem ?
Also worth giving the brake light switch a squirt whilst under there, as this switch also tells the ABS that the brakes are being applied !

[bobthecabbage]

Originally Posted by martin93

Well mine has never had a firm notchy pedal. And hate to sound like a knowitall Bob, but rear disk brakes should not need a hard stamp in order to adjust up the handbrake. This should only apply to cars with rear drums which have an auto adjuster in them. Rear disk brakes adjust naturally when the pedal is released, which is why as the brake pads wear, the fluid level gradually drops as the growing space between the caliper piston and bore is taken up with fluid.

I would third on it being a brake servo issue rather than a caliper problem. Although I would check the caliper sliders aren't seized just to make sure, as to me greasing these up are a yearly service item.

Biggest issue I've found with servo's on older cars is the brake master cylinder leaking fluid into the actual servo causing all sorts of problems. I would check the one way valve first as pierremcalpine suggested, and make sure there are no leaks on the hose and its connections. Then have a look for any signs of fluid on the vacuum pipe going into the servo while you're there.

So to conclude, I would say it's a brake servo or master cylinder problem.

Depends how you drive your car. I use a lot of engine braking and rarely use hard or firm braking to slow down. I've never had to adjust the handbrake travel on my car which had handbrake failures on most its MOTs before I bought it.

The piston in the calliper is held by the rubber seal and does not move in and out in relation to the seal but just flexes the rubber seal when you brake. So as the pads wear the handbrake becomes slacker and brake travel longer until a firm or harsh application of the pedal shocks the piston free from the grip of the seal.

If I deliberately do this the handbrake and brake pedal travel decreases.

The notch people feel is perhaps the EBD kicking in as the rear wheels start to slow down faster than the fronts and the ABS pump opens up a valve to allow more brake pressure to the fronts. This is apparently how the ABS systems of this era were set up.

As a side note, I believe EBD was only fitted to phase II cars from 2000-2004.

[Baffler]

Originally Posted by jonnyboy93

I had a look yesterday and checked the operation of the check valve, and all appears to be fine with that. All other checks appear to show the servo is operating properly, i.e. you can pump the pedal with the engine off and it gets solid, then drops once engine is started.

Had no issues with the brakes this morning on a 60 mile drive so will keep an eye on things.

Probably because you disturbed the check valve seal on the servo. Given its location it's subject to heat rising from the exhaust manifold so might be perished and letting air past. Next time you notice a hard pedal try a shot of silicone spray or better still replace it...probably cheaper than a can of silicone spray.

Originally Posted by bobthecabbage

Depends how you drive your car. I use a lot of engine braking and rarely use hard or firm braking to slow down. I've never had to adjust the handbrake travel on my car which had handbrake failures on most its MOTs before I bought it.

The piston in the calliper is held by the rubber seal and does not move in and out in relation to the seal but just flexes the rubber seal when you brake. So as the pads wear the handbrake becomes slacker and brake travel longer until a firm or harsh application of the pedal shocks the piston free from the grip of the seal.

If I deliberately do this the handbrake and brake pedal travel decreases.

The notch people feel is perhaps the EBD kicking in as the rear wheels start to slow down faster than the fronts and the ABS pump opens up a valve to allow more brake pressure to the fronts. This is apparently how the ABS systems of this era were set up.

As a side note, I believe EBD was only fitted to phase II cars from 2000-2004.

Did you mean Dynamic Stability Assistance Bob? All T4's from '97 onward have the DSA option.

[bobthecabbage]

No, I was talking about Electronic Brake Force Distribution. I believe it was fitted to all phase twos.

It is covered in the manual.

It works by sending full braking pressure to the rear brakes until the wheels are detected slowing down more than the fronts. Apparently it also limits braking pressure to the fronts until the rears start losing grip.

This system means that if the car is fully loaded you get maximum braking efficiency from the rear brakes compared to a car without the system which may bias front to rear 60:40 to avoid the rears constantly locking up and activating the abs.

Also cars with EBD become dangerous when the EBD and ABS aren't working because the rear wheels will lock up and cause the driver to lose control.