Brake woes

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Jan 1, 2018 | 06:34 AM

Jaydee

Thread Starter

Junior Member

Joined: Dec 2017

Posts: 7

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From: Norfolk

Brake woes

Hi all and happy new year. After reconnecting battery after an overnight charge to try to reset handbrake fault I did the calibration steps but now I have a bigger issue.
when at low speed like in a line of traffic the brakes are almost non existent. No codes no warnings. At higher revs when brakes applied all ok. How can this have happened by reconnecting battery.
thanks in advance
Jaydee
2004 2.7 D SE

Jan 1, 2018 | 10:29 AM

Mikey

Joined: Oct 2009

Posts: 11,057

Likes: 2,272

From: Perth Ontario Canada

plying wtih t battery connections will not correct an EPB warning, nor will it affect the hydraulic side.

You seem to have two unrelated faults.

Jan 1, 2018 | 11:23 AM

Jaydee

Thread Starter

Junior Member

Joined: Dec 2017

Posts: 7

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From: Norfolk

Quote:

Originally Posted by Mikey

plying wtih t battery connections will not correct an EPB warning, nor will it affect the hydraulic side.

You seem to have two unrelated faults.

thanks Mikey I was reconnecting battery after a charge. Now I realise that i have brake fade, suggesting a servo problem maybe

Jan 1, 2018 | 12:04 PM

Mikey

Joined: Oct 2009

Posts: 11,057

Likes: 2,272

From: Perth Ontario Canada

NO, not a servo problem either since the brakes wor when at normal speeds.

i'd suggest finding a qualified garage.

Jan 1, 2018 | 03:12 PM

kr98664

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Joined: Oct 2012

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From: Oregon

Quote:

Originally Posted by Jaydee

when at low speed like in a line of traffic the brakes are almost non existent. No codes no warnings. At higher revs when brakes applied all ok. How can this have happened by reconnecting battery.

2004 2.7 D SE

Please define "non existent". Does the pedal sink to the floor, or pedal travel is normal but extra force is required?

If the pedal sinks to the floor, that would indicate something wrong in the hydraulics, which doesn't seem very likely as you say the brakes recover with higher engine speed.

I'd suspect a problem with the brake booster, as the power assist reduces pedal effort. On a gas engine, the boost muscle comes from intake manifold vacuum. The vacuum varies with engine RPM and load, so the booster has a built-in reservoir to provide assist when the vacuum supply is low.

You have a diesel, right? I've zero experience with the Jaguar version, but on other diesels on which I've worked, the brake booster got its muscle from either an auxiliary vacuum pump, or the booster was a completely different design that used hydraulic pressure from the power steering system. If the Jaguar version is either of those styles, the muscle force is RPM dependent. If so, you could have a problem with the muscle supply, or a problem with the internal reservoir designed to compensate for periods of low muscle supply.

It may just be a coincidence this happened after reconnecting the battery.