Recently, the XJS sometimes stalls, but only when in reverse. Yesterday, I took it to get a smog check, and it stalled on the technician as he was reversing onto the rolling road.

He said, "you might have a vacuum leak which is causing the stall in reverse and the brake pedal seems like it might have weak vacuum."

Does anyone have any suggestions or tips about how I would go about looking for vacuum leak?

Never done it before, so all advise is most welcome and appreciated.

 

Use some start pilot or even some brake cleaner and squirt it in areas where hoses attach. If the engine sound changes you've found your leak.

 

Mac Allan,

Your brakes don't have a vacuum attachment so I would treat his comment about the brake pedal with some caution.

Paul

 

Thanks, that is part of why I posted the thread, hoping for enlightenment or clarification.

I had thought the Tevis ABS system was purely power assisted by the ABS pump/bulb pressure system. However, in looking at the parts diagrams for the brakes, it looks like it might *also* have vacuum assist.

Clearly not an expert on this, so I appreciate any guidance.

 

It can still have a vacume leak, not the brakes but the engine resulting in the stalls...

 

The later Teves mark iv used vacuum power, the earlier mark III (your system) did not.

 

What provides brake boost? Or what could cause the pedal to feel like there is a lack of boost?

Thanks. You guys are great.

 

Hi Mac

How do the Brakes feel during normal driving, are you having to push the Brake Pedal any harder than you normally would.

 

Mac Allan,

The Teves Mk II uses an electric pump to provide powered assistance to the brake circuits.

People sometimes use conflicting phrases to describe vacuum assistance. A traditional vacuum servo will provide assistance to the brakes thus making the pedal feel easier to push. So a lack of vacuum makes it harder to push the pedal to achieve the same retardation. When your mechanic described "a lack of vacuum" did he really mean that? in other words was he describing the pedal as having a hard feel, or did he mean exactly the opposite ie a soft pedal, which might indicate air somewhere in the system?

Cheers

Paul

 

Since I replaced the front pads, the brakes just haven't felt quite right, so when the smog tech mentioned a vacuum leak, I had a brief "Eureka" moment, until I remembered or thought I remembered how the system worked.

Here is my previous thread from several months ago:

https://www.jaguarforums.com/forum/x...estion-161610/

I've bleed the brakes now several times, and had renewed the fluid in the last 12 months. If I only drive the XJS, I get used to it, but if I go from one of the other cars I notice it.

If I were to describe the problem, the pedal has to travel too far before the brakes start to engage. However, it doesn't feel like a soft pedal (air) and pumping the pedal doesn't change the feel.

I'm stumped.

 

Bumping this in hopes that someone has a suggestion of things I can check.

Thanks.

 

What condition is the brake pressure bubble? Is your ABS pump working all the time? Turn the ignition to ON but don't start the car. You shouöd hear a pump running (opposite side of the car). It should switxh off after a few seconds. If it doesn't switch off, the pressure bubble has shot. If it turns off, press the brake pedal a few times. Again, engine left off! If I remember correctly, something like 7 or 8 presses on the brake pedal should switch it on. If it turns on earlier, then the bubble is shot or is dieing...

 

You might be on to something.

With car off, I pumped the brakes 10 times to relieve pressure. After start, it took 14 seconds for the Anti-Lock and Brake warning lights to go out. After four strokes of the brake pedal, the Brake warning light illuminates.

It looks like the bulb is on it's way out.

 

That can explain your spongey feel. New bulb is available... The same as in many Saabs (900) and Buicks (Regatta).