Brake problem

[Gregerz2010]

I have a S type, 2.7 diesel 2005
I have a problem with brakes/servo/vacum pump, can anyone help?
Brakes work when I first apply pressure to the pedal, then pedal goes stiff as if servo assist not working, I can hear a slight hiss when pressing brake pedal, not sure if that has always been there and I only noticed it because of the brake problem!
How much suction should there be on the vacum pump, there is not much on mine but again not sure if this is normal?
I am a new member and would appreciate any help I can get.

[J44EAG]

Have you noticed any drop in brake fluid level in the master cylinder? It is not unknown for a cylinder to fail and the servo fill up with brake fluid. Leads to exiting drives!

A hard pedal does not sound good. A small hiss can sometimes be heard.

Can`t be too careful where brakes are concerned. Do you have a local main or independent repair man you can take advice from?

Regret rather difficult to diagnose without being sat in the car. Let us know how you get on.

Mike

[Gregerz2010]

Thanks for your reply Mike
There has been no drop in brake fluid or leaks, the brakes work at first, it is if you keep your foot on the pedal applying more gradual pressure the servo assist seems to stop working and you then need to brake very hard to stop. Checked all the vacum pipes & they seem ok.
Not found anyone local as yet, without it costing a small fortune.

Dave

[J44EAG]

I have it in mind there is an NRV on or near the servo. I`ll have a look tomorrow. Mike

[Gregerz2010]

ok, thank you Mike

Dave

[Gregerz2010]

Brakes now done, it was the brake servo, a simple job to fit, done in about 1 1/2 hours, garage was going to charge a small fortune to fit it, so a big saving doing it myself servo cost £385 (with discounts!) from Jaguar ouch!

[rosemary]

Hello All
Sounds like I have the same problem as Gregerz2010 on my 2005 S, 2.7d with the brakes. Happened today stopping at the junction at the end of our road, the brakes worked initially then I had to apply great pressure on the pedal to finally stop at the junction. It was as though all assistance had gone and the brakes had faded away. So in to my local garage to see what's what. I'll check the fluid level in a minute as suggested in Mike's post.
Dave

[rosemary]

Hello Folks
Well I've checked the Brake Booster Vacuum pump and Vacuum Pipes for leaks and operation. No leaks and the pump is sucking pretty well.
The brakes/vacuum assistance still fades away and the pressure needed on the pedal to finally stop is excessive. So suspicion falls on the Booster Unit itself. On one of the diagrams there is reference to a NRV to maintain vacuum but no hint as to where, in or on, the unit this is. There are two electrical connections on the Booster unit, one for "pedal travel" and the other referred to as "booster solenoid" Question:- Can anyone shed any light on, where the NRV is and what these electrical connections do particularly the second, the first seems self evident, I can't find any descriptions in the Workshop Manual nor do I have any warnings indicated on the instrument panel. I note on ebay and other sites the cost of a Booster Unit varies between £390 and £580 for a new unit and these are not Jaguar prices, which I dread to think, so not a cheap repair when fitting cost is added, I note there are plenty of used units for sale as well. Is this indicative of a common component failure. Seems we are heading to a repair near the value of the car again, good job I still like it.

Dave

[Montana5]

Have a read through here, some of this might help...
http://www.jaguarforum.com/showthread.php?t=81670

http://www.jaguarforum.com/showthread.php?t=87639

Doug.

[rosemary]

Hello Montana
Thanks for the pointer, Now I know where the NRV is (check valve ) in the diagram, so I'll check for air flow.
I'll just have to work out a method to pressurise and suck the pipe.

Dave

[rosemary]

Hello All
One further question:- Is the NRV (check valve) part of the brake booster unit or part of the vacuum tube.

Dave

[rosemary]

Hello Doug

I am now convinced after studying the Jaguar Forum in your post and my experience in my car with the characteristics of the problem that my defect is with the Brake Booster (Servo) or the NRV (stuck) which resides as part of the Vacuum Hose assembly. All the reports point to the same characteristics with the braking effect on the cars. A defective Servo vacuum function. the cause of which could be a leaking diaphragm within the servo or a stuck NRV. The Vacuum pump seems an unlikely culprit. So the choice is get a new servo and or a replacement vacuum hose. The first has a price tag of:- from £735 fitted as reported in the link, or £25 for a second hand working tube with NRV and no major dismantling .
I'm going to buy a tube first and see.

Dave

[Montana5]

Hi Dave, It does sound like the Servo, however I would agree it may be worth trying a replacement hose & NRV first and I'd probably do the same, fingers crossed.

Doug.

[rosemary]

Hello Doug
Vacuum Tube arrives Tuesday, £25 from SMG Wolverhampton, so as you say fingers crossed I'll be reporting good or bad news.

Dave

[rosemary]

Hello Folks
Vacuum Tube arrived as scheduled from SMG, checked that it functioned correctly, fitted it. Brakes, although a slight improvement, are still the same, bad news, and I was all excited when I took off the existing pipe and looked in the NRV inners and saw fine rust coating it all and it was letting by slightly when I pressurised it.
Got to bite the bullet and get a replacement servo.

Dave