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Freddie

Member Since: 21 May 2014
Location: Cape Town
Posts: 46

Intermittent brakes and charging

Hi Everyone,

Forgive me; I have trawled the internet for answers, and although there is lots of info out there on this topic, none that I have found seem to help.
Before I spend a small fortune on a new alternator/ vacuum pump, I was hoping that I could pick your brains...

A few months back, I posted on the forum that the brakes on my 2004 Defender TD5 being less than useless.
http://www.defender2.net/forum/post469358.html

I needed to replace pads, disks, callipers as it was but with little effect.
I then replaced the brake master cylinder and servo. Since the new cylinder and servo, the brakes have been MUCH better. However, they are intermittent.

When I am going uphill (at high rpm), the brakes are sharp and fierce, with very little pressure that needs to be applied to the pedal to slow the car.
However, there are times (e.g., sitting in traffic) when I apply the brake, and my foot travels further than normal before the vehicle slows at a comparable rate. More often than not, removing my foot and placing it back on the pedal (once) makes it sharp again, but this can be rather disconcerting.

I have bled the brakes best part of a dozen times (no exaggeration)
There doesn't seem to be any leaks or corrosion in the piping.
The wheel bearings all seem to be fine.

If the vehicle is stationary (and off), I get about six pumps through the brake pedal before it goes hard. If I then start the car, while applying gentle pressure to the pedal, it doesn't move. However, when I release my foot and place it back on the pedal, it feels as it should.

I have removed the pipe from the servo itself, and there seems to be good suction.
It feels the same as another Defender TD5 (with good brakes) that I used for comparison.
(both vehicles are international spec / don't have EGR's or EGR piping)

I cannot hear or feel any suction leaks in the servo piping either.

This, therefore, has me completely stumped and wondering whether the vacuum pump is on its last legs?

It is my understanding that the vacuum pump is part of the alternator on the TD5's? Coincidentally, I have noticed that my batteries are always fairly low on power:
When off, they sit around 12v.
On ignition (fuel pump running), it dips to 11.8v.
Then on idle, the vehicle can be anywhere from 14.04v-14.50v which seems very erratic.

The other TD5 that I checked, using the same method as above, was,
Off @ 12.39v
Ignition @ 11.8v
Idle @ 13.9v

I'm at a loss. Any help or suggestions would be greatly appreciated!
Many thanks in advance!

6th Sep 2016 1:29pm

gazman

Member Since: 17 Aug 2015
Location: Liverpool
Posts: 652

I can't really it to landrovers, but I've just changed the master cylinder on my motorbike because the lever was using too much travel to get any power. I could pump them up, but as you say they would be rubbish in to time at all. I tried bleeding them off the bike and then fitting, changing fluid, bleeding and bleeding till it went out of fashion.
In the end I came to the conclusion the seals in the master cylinder must have been worn and was allowing fluid to pass to the secondary/dust seal. so I could build up the pressure in this chamber and it would be firm but would then would loose this pressure to the expansion bottle when not used. So would be spongy again until pumped.

Anyway I've changed the master cylinder and the brakes are awesome again 2014 - current ..... 2003 defender td5 90 (my car)
2009 - current .... 2005 zx10r

6th Sep 2016 4:50pm

Freddie

Member Since: 21 May 2014
Location: Cape Town
Posts: 46

Many thanks for the reply Gazman!

I've just replaced the internals of the master cylinder with a kit.
I knew that I should have purchased the entire unit when I placed the order. That said when I got it apart everything looked to be in great shape, no obvious signs or wear on anything. Nice fit - couldn't be better.

The fact that the brakes are good 9 times out of 10 is what gets me.
When the vehicle's revving high there's never a problem but freewheeling downhill the pedal is nowhere near as responsive.

crazy!

6th Sep 2016 6:11pm

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