Technical 2013 1.2 500 - brakes have too much servo assistance

[sicarumba]

Afternoon all

Had the 500 in for service and MOT a couple of weeks ago. When I collected it and drove home, I noticed the brake pedal felt spongy. I was almost home so rather than turn around I decided I would call the garage when I got back. The more I used the brake pedal the more convinced I became that rather than just being spongy like there was air in the system, it was actually applying too much servo assistance; the brakes were much more sensitive, requiring less pressure to apply than before. It was possible to push the pedal to the floor which was why it felt initially like air in the system, but the brakes were unusually sharp and could be applied with very little effort or pedal travel. It's my wife's car so I don't drive it all that often for it to be immediately obvious, however she tried the brake pedal and agreed it was a lot more sensitive.

The service was a simple oil/filter and air filter change, no brake work, so I decided to lift the air filter and check for any vacuum pipes to the servo which were kinked, loose etc.. Everything looked fine, so I poked around the servo itself and disconnected (what I presume to be) the pressure sensor to see if it was a loose connection. Didn't appear so, so I put everything back together. Went for a little drive and the brakes were back to normal, pedal became firm way before the end of travel and brakes were more progressive as they should be. I assumed the garage had not put something back on properly and all was well, brakes fine ever since...

...until today, as Mrs Carumba messaged me from work to say "the brakes are snatchy again". I'll be looking at the car again when she gets home, and if I can't figure it out tonight I'll drop it back at the garage in the morning for them to have a look. Google suggests sensitive brakes could be an overfilled fluid reservoir, but I would have thought this would perhaps move the brake biting point and change the pedal travel rather than increase the boost.

Has anyone else had anything like this before? I'd like to check as much as possible myself, so at least I can give the garage all the information if I can't find the problem. I have MES and cabling and I'll be looking at the brake pressure sensor output and anything else I can find...

 

[John202020]

I would look at the front pads and discs first, it's very unlikely it's a servo issue? They, servo, either work normally or not at all

 

[sicarumba]

Well I had the car back today and the garage say they can't find anything wrong. They had it on a rolling road and said "it would pass an MOT". They checked under the bonnet, looked at everything I said I had tampered with and checked the four corners but can find nothing out of the ordinary, and say the pedal feels fine. I collected the car and it feels exactly as it did when I dropped it off, brakes are very strong but no longer very progressive (need to be much more careful when applying them), and the pedal travels way further than it used to.

 

[vexorg]

Have you checked the pedal linkage in case there's something up there?

 

[eeeno]

Well garage says it'll pass MOT, so it's fine until it's not.

I had aggressive brakes when front discs were almost gone with new brake pads. The previous owner thought that it wouldn't need new discs. Also brake reservoir was filled above max.

Also stuck sliding pins can cause similar behavior. This car has emergency braking system which applies maximum power when you move your foot from the accelerator to the brake pedal fast enough. It takes time to get used to.

 

[varesecrazy]

Hi..

Just a thought..
Has it got the 'Body Control Kit'?
Where the Body Module effects braking

That presumably something you wouldnt see an effect with at 0.00 mph on a ramp.. or 15 on a roller


But your description of 'pedal to the floor' just sounds wrong..

Like a basic mechanical fault...

As you say..odd that your 20 minute tinker made a difference

 

[sicarumba]

I would look at the front pads and discs first, it's very unlikely it's a servo issue? They, servo, either work normally or not at all

My understanding of the servo is the same. If anything, I would expect the opposite to be true; if there were a servo problem it would be less effective, making the pedal stiffer and requiring more force. That's why I am a bit stumped, the only way I can describe the pedal feel is that it's like the servo is much stronger, allowing the pedal to be pushed further with less effort. I also noticed the engine stumbles when I press the brake pedal, which again suggests vacuum leak and would normally make braking harder.

Have you checked the pedal linkage in case there's something up there?

Not specifically, won't hurt to give it a look when it gets light, thank you

Well garage says it'll pass MOT, so it's fine until it's not.

I had aggressive brakes when front discs were almost gone with new brake pads. The previous owner thought that it wouldn't need new discs. Also brake reservoir was filled above max.

Also stuck sliding pins can cause similar behavior. This car has emergency braking system which applies maximum power when you move your foot from the accelerator to the brake pedal fast enough. It takes time to get used to.

Interesting, is that EBD? Could the EBD cause excessive braking or does it just alter the bias? The garage tell me they've checked the brakes so I'd have hoped the discs are fine. I checked the fluid reservoir after reading about an over-filled one could cause the brakes to drag, but it's below max.

Hi..


Just a thought..
Has it got the 'Body Control Kit'?
Where the Body Module effects braking

That presumably something you wouldnt see an effect with at 0.00 mph on a ramp.. or 15 on a roller


But your description of 'pedal to the floor' just sounds wrong..

Like a basic mechanical fault...

As you say..odd that your 20 minute tinker made a difference

I have no idea. Is there an easy way to find out? Presumably with MES, I remember seeing "body control module" listed but I don't know if it does anything with the brakes. The pedal to the floor is indeed wrong, it's why I initially thought the garage had done something to allow air into the system. It was only when I drove a while did the whole thing feel different, as air in the system wouldn't make the brakes harsher. Could my tinkering have been a coincidence? Perhaps, but why would a basic mechanical fault simply reverse itself?

 

[eeeno]

I'm afraid that diagnostics won't show you anything useful about the brakes as they're mostly hydraulic/mechanical and this symptom what you describe is common sign of the brake system needing an overhaul. Probably brake liquid changed and bled, caliper pistons pumped out a bit, cleaned under the rubber gasket and then pressed in, sliding pins checked and cleaned of all previous grease and only tiny amount of brake sliding pin grease applied. Also brake disc and brake pad wear checked. Rear brake drums cleaned and checked.

It's probably nothing severe as it is not losing brake liquid, so just the usual maintenance is needed. Before starting the car, without key in, can you pump the brake pedal stiff, so that it does not fall to the floor? Keep a little pressure on the pedal and if it falls to the floor, you have a serious issue.

 

[z rider]

I have not looked, how the 500 system works in detail, but vacuum brake servos normally fail in two different ways.
1. No vacuum is applied - the pedal feels hard, You have to use more force to brake the car.
2. Too much vacuum applied - the pedal feels lighter and can bee depressed deeper. Worst case is that the brakes are applied without using the pedal at all.
The servo has an internal control valve the regulates the brake force according to the pressure You put on the pedal. Perhaps this is what causes Your issues

 

[sicarumba]

I'm afraid that diagnostics won't show you anything useful about the brakes as they're mostly hydraulic/mechanical and this symptom what you describe is common sign of the brake system needing an overhaul. Probably brake liquid changed and bled, caliper pistons pumped out a bit, cleaned under the rubber gasket and then pressed in, sliding pins checked and cleaned of all previous grease and only tiny amount of brake sliding pin grease applied. Also brake disc and brake pad wear checked. Rear brake drums cleaned and checked.

It's probably nothing severe as it is not losing brake liquid, so just the usual maintenance is needed. Before starting the car, without key in, can you pump the brake pedal stiff, so that it does not fall to the floor? Keep a little pressure on the pedal and if it falls to the floor, you have a serious issue.

I can pump the pedal stiff and it does not fall to the floor, only when the engine running does it do that.

I have not looked, how the 500 system works in detail, but vacuum brake servos normally fail in two different ways.
1. No vacuum is applied - the pedal feels hard, You have to use more force to brake the car.
2. Too much vacuum applied - the pedal feels lighter and can bee depressed deeper. Worst case is that the brakes are applied without using the pedal at all.
The servo has an internal control valve the regulates the brake force according to the pressure You put on the pedal. Perhaps this is what causes Your issues

Interesting. Number 2 is exactly what I feel like I have, too much vacuum applied. It's not applying the brakes without using the pedal. I'm surprised I can find no information on this valve, whether for a 500 or any other car, but I may well look into the feasibility of changing the whole servo anyway if it's not too expensive or I can do it myself. Thank you for this.

 

[vexorg]

I didn't think vacuum on servos was regulated, just as much vacuum as possible.

 

[portland_bill]

Whilst the brake pedal is on the right, the servo is mounted over to the left, in its usual LHD position. There is a linkage across the car, under the dash. Above the passenger's feet is a pivot. That area needs to be checked, to ensure the mats, if fitted, are not interfering with the linkage, and then that the linkage is all correct, with no loose mountings or pivots. Also check that there is some free play when the pedal is fully released.

The brake light switch also needs checking for correct position and adjustment. (There are threads about this, including a reset procedure) First check the brake lights. Not just are they working, but how far down the pedal moves before they illuminate. They should illuminate soon after the pedal moves, and ideally before the free play is all used, so the lights illuminate before brakes are applied. There have been cases where the switch can hold the pedal, preventing a full release.

When the problem occurs, are there any unusual hissing sounds from the servo?

The front brakes do need an annual clean. The pads tend to gather dirt, and sometimes a little rust around the edges, causing them to stick a little. If not moving freely, they can stick, requiring more pedal travel next time. Working well on the MOT brake roller tester is not an indication that all is perfect.
Front discs with run-out will push the pads away, leading to excess travel at each application, but this tends to be more consistent.

The rear brakes have self-adjusters. (I'm assuming drums here) If they are not holding, allowing excess travel, the pedal will have to move further to take up the movement. How is the handbrake? If the self-adjusters are inconsistent, the handbrake will be too, needing more travel to apply. A leaking wheel cylinder will lose fluid, slowly, which can give inconsistent braking, as first application will have more travel, but then be better for the remainder of a journey, gently leakign again as it sits.

 

[z rider]

The control valve is an internal part of the servo, its not sold separately (if not part of a rebuild kit). Its absolutely no bad idea to look for the brakes that nothing is stuck, it should be part of regular service. You can do a quick check for sticking pads. With the car on even ground push it a little bit with no handbrake or gear applied the car should move easyly. Then apply the brakes with good force and try again after release. If it's now harder to push the car, You know some brakes are sticking.

 

[DaveMcT]

Grip each rubber brake hose while someone applies the brakes. You should feel a pulse but an obvious expansion of the hose needs new hoses. It's also possible for the hose lining to separate using all sorts of strange effects.

I had soggy pedal issue on my Panda 100HP so decided to fit HEL braided hoses. They initially felt over-sensitive but (having had motorbikes) knew what to expect. I much prefer the braking and costs were reasonable. At the back, I have one long hose (each side from the under-body flare nut connector right to the brake. Each one deletes two hoses and a length of steel tube. The fronts are direct replacements of the old rubbers.

WIfe's 1.2-60 Panda had new rubber hoses because she didn't like the 100HP brakes. Her's were much less soggy with new rubber hoses.

 

[sicarumba]

Went out to check today and on my test drive the brakes have (annoyingly) returned to normal operation. Followed the advice above, checked the linkage for obstructions, checked the brakes are not sticking after pressing the pedal a few times, but with the brakes operating normally it's not so easy to find an obvious problem. When I get more time I'll start taking wheels off and checking everything for appropriate operation. I thought I could hear something like a hissing sound near the servo but with the engine running it's difficult to tell if I'm just imagining it. Whatever happens I'll be sure to conclude it here.

 

[John202020]

Do you know anyone who has a 500, get them to drive yours and see what they say?
I would strip down(not totally) all the brakes to confirm they are working correctly on each wheel ?

 

[sicarumba]

Bringing this thread back to life, the brakes have been operating normally for months, save for a single occurrence which again went away as soon as I removed the air filter to investigate further. I've inspected the individual brakes on all four corners and can see no problems there.

Today, my wife called me from a layby to say the brakes had gone again only this time they were locked on. The pedal was barely moving and she was only just able to limp to a safe space with the brakes applied. By the time I / the AA got there it had released and so he was similarly unable to suggest the issue. After I explained what has happened in the past he suggested, like me, that it sounded like the servo was applying too much pressure or was not able to release it. On her way home this evening it happened again very close to home so when I got there I felt the pedal was rock solid. I pulled the brake servo check valve out and received an almighty whoosh of released vacuum and the brakes immediately returned to normal.

I think I'd like to replace the check valve and failing this, replace the servo. Nobody else on the internet seems to have had anything like this happen to them so it's time to throw money at it. Anyone know where I can get a new check valve before I order from eBay? Seems I can get one for a 0.9 easily enough but the 1.2 is elusive...

 

[John202020]

If in doubt dealer part?

 

[z rider]

It's not the check valve, it's the servo. The check valve rarely fails and if gives another mistake. It really is the servo at fault. Removing the check valve makes your car operative but there will be no assistance to braking, so be careful if you bring your car home this way.

 

[John202020]

It's not the check valve, it's the servo. The check valve rarely fails and if gives another mistake. It really is the servo at fault. Removing the check valve makes your car operative but there will be no assistance to braking, so be careful if you bring your car home this way.

Maybe just buy a second hand servo?