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Souster

Is this a servo or vacuum pump problem?

Hi there, yet again the brakes on my 300tdi defender 1997 have come to my attention as they are poor. The reason its come to mind is i had to do an emergency stop the other day and only just missed the other driver as it takes so long to stop. When i do an emergency stop i cant lock the wheels no matter how hard i try, and the force i am applying onto the peddle is alot, im nearly of the seat! They are just not up to scratch when braking hard.

I have checked the brake vacuum pump for suction where it attatches to the servo and its sucking a fair amount to feel it on my thumb. Whern the engine is started, the pedal does sink, so does this mean that the servo is working? As soon as i turn the engine off i loose total servo assistance instantly... Whereas i thought the vacuum is maintained for atleast 10 mins?(correct me if im wrong). Another thing i have noticed, is a hissing noise when the brake pedal is depressed and when the engine is turned off after it being running you can hear air escaping from somewhere when the pedal is depressed. I have checked for cracks in the servo and i cant seem to see any and ive also checked the seal between the master cylinder and servo and that seems fine.

6 months ago the defender had a new master cylinder but there are bubbles coming up out of the reservoir when the pedal is depressed (is this normal then). Its also had new brake pipes all round including flexis, new brake pads and i rebuilt the rear brake calipers. The system has been bled that many times that it cant be any cleaner;) .... (but that was a previous brake problem that is now sorted)

Any help would be greatly appreciated folks, thanks in advance
V8Ian

It sounds like the servo diaphram is leaking. It can be dangerous to attempt a DIY because of the spring pressure within the servo
frog

Re: Is this a servo or vacuum pump problem?

Hello and welcome to LandyTown

Souster wrote:
As soon as i turn the engine off i loose total servo assistance instantly...


This isn't normal, there's a no return valve in the system that should maintain vaccum for a while (hours) after you've switched the engine off.

Does the pedal kick back when you kill the engine ? If so I suspect the valve or the servo are at fault.

With engine off, pump pedal until rock solid. Keep your foot pressed on pedal and start engine. Pedal should sink a little then stay, if it carries on going down, air is being let into the system.

Are you finding you need to pump the pedal to get pressure ? A possible reason for this are worn wheel bearings which spread the pads when driven.

Hope this helps.
Greg
Souster

Re: Is this a servo or vacuum pump problem?

Thanks for your help folks. I have taken off the no return valve and tried to blow through it both ways.. but only could blow through it the one way!

No, the pedal doesnt kick back... by this do you mean rise to how it was before the engine is started?

When the engine is off, then the pedal is pumped to be rock solid, then i start the engine the pedal sicks a bit, but then stays and doesnt travel any further. Does this mean air isnt getting into the brake fluid?

All wheel bearings are fine, checked at replaced recently.
frog

All this suggests there's nothing wrong with your servo   Not sure about the air bubbles though

Have you tried someone else's defender, the brakes on them aren't sports car sharp so maybe it's a matter of getting used to them and leaving a larger gap with the vehicle in front.

I'm not sure I've ever locked up the wheels on mine.
Souster

Thanks frog. So whats a servo diaphram? is that basically the servo, or am i missing something. And where is the vacuum pressure leaking from when the pedal is pressed each time and as soon as the engine is turned of while the predal is pressed.
rangerovering

Personally I would (VERY carefully) try driving the car with the servo pipe off - ie a quiet road somewhere with very little traffic. Even an empty yard somewhere would be ideal.

You don't need to go quickly, try and establish how much more difficult it is to stop without the servo assistance.
If there is little difference then you definately know there is a problem. If there is a big change then it would suggest there is not much problem with the servo assistance, when connected it is doing its job!
Souster

i have actually done exactly that, disconnected the vacuum pipe, and it is almost impossible to stop the land rover at 10mph!
Dakar

Of course, Stumpy's not always that clean   ..............

frog

Souster wrote:
Thanks frog. So whats a servo diaphram? is that basically the servo, or am i missing something.


It's inside the servo.

Is yours a 90 or 110 ? Loaded or empty ?
Souster

Its a 90, which is very rarely loaded. Allthough, i wouldnt fancy loading it too heavy with how the brakes are!    Thanks for the reply frog.
frog

I noticed in your first post that you say the rear calipers have been rebuilt. Can you tell if they work or not ?

One thing you could do (since you're a bit of a test driver  ) is to clamp the rear hoses temporarily and see if braking is worse. Could try the same for the fronts. That's just to exclude a problem with front/rear system.

Whereabouts are you ? Anyone near you got a spare servo you could try ?
V8Ian

It sounds to me like a perferated diaphram, resulting in reduced vacuum and inability to retain vacuum. Being a diesel, does it run a vacuum pump, does it work efficiently? My first thought re the diaphram appears justified by fact the check valve is operational.
Souster

thanks folks again, the rear brakes do look to be working quite well, i dont think i can clamp the flexis as they are braided hoses! so is there anyway of servicing/repairing the diaphram or is it just the case of a new servo?
Souster

yeah, the vacuum pump has been tested and is working perfectly, as well as the non return valve. cheers
frog

iirc, the first response to your question suggested a servo's not really a DIY repair. I don't have experience of attempting it so can't say, I guess finding spares could be a challenge.

Not sure where you're located, but I have a second hand one you could try before going for a new one (no guarantee it would work any better than yours though, I've never driven the vehicle it's come off   )
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