Suspected vacuum leak - brake booster

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Jan 16, 2019 | 10:15 AM

Nedoerr

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From: California, USA

Suspected vacuum leak - brake booster

Hi all,

It feels like my brake booster vacuum isn’t holding as I near a stop while braking (lunge forward right before I stop). I understand this is often caused by a vacuum leak. I would like to test for a vacuum leak using a smoker. What is the easiest vacuum line to access on a supercharged XJL? As I’m new to diagnosing vacuum leaks, a picture might help too.

I realize there are other brake booster tests I can perform, but I have multiple reasons for wanting to run a vacuum test. This is just the latest one.

Thanks in advance.

Jan 16, 2019 | 03:23 PM

dmchao

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I believe the line with the check valve is still designed similarly to older model years. If you soap bubble test the line actually pulling vacuum you could see if there is a seal going bad, before delving into evaluating the whole system or master cylinder/booster assembly

Jan 16, 2019 | 03:43 PM

XJsss

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From: Reynolds Lake Oconee, GA USA

The x351 has a brake vacuum pump that is driven by the engine. I can't help you with the location, but mine was just changed by my dealer as it had developed an oil leak.

Jan 16, 2019 | 09:50 PM

Nedoerr

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From: California, USA

Quote:

Originally Posted by XJsss

The x351 has a brake vacuum pump that is driven by the engine. I can't help you with the location, but mine was just changed by my dealer as it had developed an oil leak.

Good to know. Did you have any symptoms, or how was it diagnosed? Thanks.

Jan 17, 2019 | 09:11 AM

XJsss

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From: Reynolds Lake Oconee, GA USA

I had my XJ on tor it's six year service and had complained that I had an oil smell when parked in my garage, but no issues that I could tell in the braking system. Mat, my tech, at Hennessy North Atlanta Jaguar made the diagnosis and replaced the vacuum pump, I had, also, complained about chain rattle noise when the engine was cold, so Mat replaced the timing chain tensioners and guides. All was covered by my Assurant Extended Warranty purchased through my Jaguar dealer.