hello .. got new petrol sedici .
is it normal when emergency braking when a wheel loses grip, that the brake pedal leaves your foot, it feels as if someone is pushing it for you ??
normal braking is fine . had brakes checked before this happened was told all ok .
can anyone help please
I'm guessing that 'new' means new to you, so is actually between '06-11'.
Here you're saying a wheel loses grip.
Having the brakes checked might just be a visual check of pads and shoes.
.... or I didn't explain it well enough....
When sudden braking (testing!) the pedal goes soft under foot, with no juddering, the pedal operates independently and goes down without my foot putting any pressure on it. Therefore, for a split second, it feels like I have no brakes. Once pedal is released, braking returns to normal.
Could it be the ABS unit not working??? If so, any ideas how I can check it. Ive not come across this in all my experience of motoring.
Cheers
Now you say no juddering, so ABS system not operating, depite wheel losing grip.
Is the pedal movng without you pushing? In which case, what changes when 'once pedal is released', as that surely is the same thing if your foot is no longer on the pedal.
Feels like no brakes? Is the car not slowing at that point, so the pedal is ineffective, or are the brakes operating, but only lightly and the pedal is soft?
Is it just less resistance than expected?
There could be several options here.
Soft or squishy pedal:
Air in the system.
Flexible hoses gone soft and expanding under pressure.
Master cylinder seals failing so not pressurising. This would allow the pedal to move with less effort than expected, and produce little braking effort.
Pedal moving with little or no effort:
Servo fault. Internal valving not sealing allowing servo to operate without effort from the driver, but this should put the brakes on hard.
Master cylinder seals as above.
If the ABS unit is not operating, it has not read the differing wheel speeds as one has lost grip. This should illuminate the ABS warning light if wheel sensors are not returning the correct signals. ABS light should illuminate when ignition turned on, and extinguish after 3-4 seconds after the system self-test. Does this happen?
After running, there should be a reserve of vacuum to allow 3-4 brake applications.
With engine off, press the pedal, gently. This should apply the brakes normally, with resistance underfoot after normal movement.
Repeat, several times until all vacuum is exhausted. Pedal should now be hard and give resistance higher in its travel. You should still be able to hold this pressure. Pedal should not sink.
With pressure held, start the engine. As it starts, vacuum is created, the pedal should sink slightly, after which you should be able to hold pressure again. Release and push again, should feel normal as vacuum is now present.
With engine off, and an assistant, apply pressure to the pedal, and as pressurised, examine each flexible hose in turn to check for any expansion.
Same test, but check that the calipers are moving as they should.
A tight piston in the caliper may let go and allow extra pedal movement.
If drum brakes on the rear, leaking rear wheel cylinders may allow excess pedal movement, then seal with a second application, similar to failing master cylinder seals.
Are you sure the reservoir has sufficient fluid? With many Fiats there is a black diaphragm under the cap, which can give the impression of a full reservoir. If it has been allowed to drop, it will have allowed air in. Would do no harm to bleed the whole system.
