What type of braking problem is this?

[Leon2012]

Hi,

I've recently got a Leon 110 SX TDI and it's got Ferodo DS Performance front brake pads on it. The rest of the brakes (front + rear) are standard.

The problem is that sometimes the brakes don't work properly, and I'm trying to work out what's causing it.

It's some kind of brake fade, but I think it's pedal fade rather than pad fade.

For example, I did a spirited run through the countryside tonight for about 10 miles, going up to 77 (etc.....) and down to 40-50 for corners, then slow right down for sharp corners, and the brakes worked well.

But then towards the end, I was coming to a swooping downhill right, with metal posts with red reflectors on the left. As I came down the hill at speed, I applied the brakes firmly but didn't stamp on them, and the best way I can describe it is they went hard, you can feel it more on your foot and the brakes didn't work properly. They just about slowed me down and I nearly crashed basically - I got the feeling like it was a close one with your heart going a bit harder, etc. I's happened before, so want to sort it out.

Very shortly after the brakes came back ok and when the car had standard pads, this happened so much that I stopped driving fast as it was too dangerous stopping.

Now with the DS Performance pads on, braking is usually very good, with a good feeling of braking power, with the nose diving slightly.

It's just that if I can work out what's going on, then I can get a solution sorted.

If it is pedal fade then a bleed would work, and possibly stainless steel braided hoses. If it's pad fade, a bigger brake conversion + DS2500s would be in order, but I don't want to do anything without knowing what I'm dealing with.

Cheers

 

[Seatmann]

Check the pipe from the servo, it's probably cracked or just leaking somewhere, usually where it goes into the vac pump on the end of the cam.

 

[Muttley]

Sounds like you are losing servo assistance. There was a thread on here ages ago about a non-return valve in the vacuum line to the servo which sometimes fails and gave similar symptoms. Sorry I can't be more helpful, it's never happened to me.

 

[Slimy]

I've had this on motorway driving. If I'm going from one motorway to another, or A road, or anywhere where I have to come from 70 to zero several times in a few minutes. I can do it once perfectly fine and stop on a dime. The second time seems to take a bit longer but is still fairly safe. The third time I basically have no brakes, and there is more braking effort from the gearbox.

When this happens, my front discs are usually brighter than my headlights, and there is a strong burning smell going on. Once they've cooled down I'm back to normal.

If I were to look at fixing it, I'd look at DS pads (as you have done), but then perhaps a slotted disc to grip on to? I guess larger brakes would also help, but I can never justify the cost.

This isn't just my current car, from memory any of my previous cars that had decent brakes had the same eventual problem. The only cars that didn't were things like 1.2 Nova's and the like, where 70mph in the first place was strictly optional!

 

[Leon2012]

Hi and cheers,

It's a hard one to describe, but I'll try and elaborate:

Normally when I press the brake pedal, gradually more and more, it goes from a 'good brake feel' which continues while slowly down, and by the end I either have stopped, or more likely right at the end of some heavy braking I get this 'metallic/hard' feeling in the ball of my foot, and it's like the brakes lock up at the last minute, causing ineffective brakes.

This used to happen all the time before I got the pads changed. I must also add that the previous garage who fitted the standard pads did a shoddy job, which was pointed out by the recent mechanic who did a proper job on fitting the new DS Performance pads.

This feeling of having almost no brakes towards the end of slowing down is obviously dangerous, and it does seem like the brakes locking up, as I've had this before on a Peugeot 205 without ABS, however I thought with ABS this was not supposed to happen?

If there was a problem with the servo, wouldn't it be the same with the old and new pads?

The new pads are definately a lot better, but it still happens under the heaviest/most prolonged braking.

BTW, about the brake pads making a strong burning smell, this happened on the way TO my destination yesterday through the countryside, but I didn't suffer the above problem, however on the way back, I didn't get the burning smell but did get the ineffective brakes problem.


I hope this helps to nail it down,

Cheers

 

[Slimy]

Normally when I press the brake pedal, gradually more and more, it goes from a 'good brake feel' which continues while slowly down, and by the end I either have stopped, or more likely right at the end of some heavy braking I get this 'metallic/hard' feeling in the ball of my foot, and it's like the brakes lock up at the last minute, causing ineffective brakes.

That sounds like you're hitting the limit of the pedal travel, which I think could be a master cylinder issue. If you immediately pump the brakes, do you get brakes again or does it take a bit of time before you are able to stop again?

 

[Leon2012]

Thanks Slimy, I'll have to try that when I get a chance & will report back

Cheers

 

[Leon2012]

Update:

I've had a bit of a chance to test the brakes some more, and am thinking that it might actually be the tyres losing grip at the end? I can get full pedal travel, and on a quiet road I went up to 40 - 50 and did emergency stops. The car stopped well and had a little bit of a hard feeling at the end with a skid. Then I pumped the pedal again immediately as suggested - most of the time it came back, but a few times it went quite hard and I couldn't really press it + the brakes weren't fully effective, then releasing and pressing again I got the brakes back again.

The tyres are Dunlop Wintersport 3D on the front with approx. 4-4.5mm tread and Avon Ice Touring on the back, also with 4-4.5mm tread.

I have recently changed them, about 6 weeks ago and had the DS Performance pads fitted a coupld of weeks after that, so thinking back, the terrible stopping ability before December on budget looking pads and budget brand tyres may have been due to the tyres.

And now, the brakes a so good at the front, especially since I bedded them in nicely, so now the weak link is the lack of tread on the tyres?

I did buy them as part worns off eBay, and the old tyres were part worn too when I got the car, so I've not got any benchmark to work from.

 

[rsmith]

How can u not tell the difference between your tyres not stopping u or a brake mechanism degradation! I would have thought that to be obvious to most, when's your last fluid change btw and mileage or wear on your discs?

 

[Slimy]

If the tyres lost grip you'd feel the ABS kicking in, and that's a VERY distinct feeling!!

However, if you are currently on winter tyres then hard braking just isn't really an option. I'm having real trouble even in dry conditions on my Goodyear Ultragrip 8's. Admittedly it's exactly the same on ice so that's where the benefit is, but they are so far below my summer tyres it's unreal.

I'd say take it easy until you can get back to sticky rubber, then see if you still have a problem.

 

[Leon2012]

Well as far as I'm aware, the ABS hasn't kicked in, as I've had no lights show up, and I don't think a 'very distinct' feeling as you put it.

The front brakes are in good condition - new performance pads, standard discs quite new and hardly used, new pads fitted by specialist, so mechanically sound, and the rears are in average/functional condition which came with the car.

I don't know when the brakes were last bled, I asked my previous mechanic to do it, but he forgot.

That's one of my next jobs to do, but I wanted to make sure to understand this problem before going forward. The brakes felt good when I tested them last night and the only problem seemed to be a bit of skidding at the end sometimes. However, after braking many times I get the fade problem, so was wondering whether it was a certain problem, and if I can correct it if it's a mechanical fault or if I can get away with a bleed, maybe stainless braided cables and new rear discs + DS Performance pads, or whether I should bite the bullet and get a full brake conversion (which is v.costly for my car as I need hubs, carriers, calipers, discs and pads!..for each corner!).

BTW: taking it easy until spring isn't really an option, because I didn't buy the car for that. I want to enjoy it and do some spirited runs sometimes


Cheers

 

[Slimy]

Oh, I didn't suggest waiting until spring, considering the weather I've had near me I'm tempted to change back to summer tyres next week!

The ABS kicking in sends pulses up the brake pedal that you would feel, about ten a second or so? It's also incredibly noisy, I believe one person panicked because they expected it to have been a broken driveshaft rather than just the ABS kicking in!

One point, you mention braided brake lines. Standard brake lines are already braided, they're just coated in rubber to protect them. So unless you can see any damage, you won't gain anything by switching to HEL or similar.

 

[Leon2012]

Thanks for the info Slimy & it's really cold at the moment, so I'll be keeping the winters on for a bit yet..

Yes I'm aware that stock lines are braided, I just thought getting some new stainless ones might help, but probably not you're right.

Cheers