Freelander 1 Brake Servo Operation

Recently my TD4 has given a new symptom.
Brakes and pedal pressure feel fine until engine switched off for short period. 10mins ish. Then the brake pedal is very hard to press like the Servo is not working. After engine running for 10 mins it all comes good again.

Is there a non return valve? Could it be vacuum pump on the way out?

Checked for leaks and all good, new pipes a few months back.

Anyone had this??

Thanks

andyfreelandy said:

Brakes and pedal pressure feel fine until engine switched off for short period. 10mins ish. Then the brake pedal is very hard to press like the Servo is not working. After engine running for 10 mins it all comes good again.

Click to expand...

It's loosing it's vacuum.

andyfreelandy said:

Is there a non return valve? Could it be vacuum pump on the way out?

Click to expand...

Yes. There's a non return valve built into the plastic pipe connection on the servo.

Sort of forgot about this as TD4 has been off the road getting its rebuild!
Took it out today to test for rattles, clonks and general feel and all good.
Except, while doing a few brake tests I noticed the above problem again.
3 brake pedal presses with engine running seem o.k. The 4th feels like no servo assistance at all.

I appreciate the reservoir is small but is this normal? I rarely drive on the brakes so maybe it has always been like this.
Otherwise is it a servo problem?
No leaks that I can hear or see and all small pipes replaced last year.
Other than this niggle it drives like a new car now and handles better than it has ever done!!

I wonder if your vacuum pump is not pulling enough to keep up with system usage?

That is my thought. Can you confirm that other vehicles can maintain 5 or more pedal presses without loss of servo assistance?

Thanks

Hi Andy:
Engine stopped: hard pedal.
I start the engine at idle: pedal Ok. I step on more than 10 times and continue well.
Engine stop: at the third step it gets hard.
I replaced vacuum pipes and reservoir because I broke an outlet (very fragile). As Nodge says, it carries a check valve.
I have a 2005 Td4
Good luck.

I'd say 4 to 5 pushes would be about right, before the vacuum has exhausted and needs to rebuild. Don't forget the vac pump is only small, and so can only pull a vacuum at a low rate.
A petrol engine on the other hand has basically unlimited vacuum (the vac pipe flow rate being the limiting factor really), but a diesel is reliant on a pump, so vacuum ability is reduced.
I've noticed that the servo assistance on the TD4 is lower than the petrol engine FL1, so this shows that there's less vacuum available from that little pump.


The test for checking the servo is easy.

With the engine off, pump the pedal until there's no more vacuum, the pedal will rise on each pump. When the pedal stops rising, push the pedal with reasonable force (like slowing down normally), and start the engine. As soon as the engine starts, the pedal will start to go down, as the vac assistance increases. It should only take a second or two for the pedal to stop going down. If this is the case, the then vacuum system is functioning correctly, or at least correctly enough to pass an MOT.

Thanks for the clarification. Servo is working it is just how long it should keep working with repeated brake applications in quick succession that I feel has changed.

I'll try the same test in another TD4, it may be just the way it works!!

Repeated applications isn't a real design criteria, as in the real world, it doesn't happen very often. Under sustained braking, the vacuum will or should hold, as only releasing the pedal results in vacuum depletion in the servo.