Brakes work only when they want to

Hello!

I'm trying to prepare my 2002 TD5 disco 2 manual for a little christmas roadtrip, but things got a little complicated yesterday. I changed glow plugs and I was happy that finally a job went without any problems (apart from one bolt and part of my fingernail sacrificed to the engine compartment). When I started the car and drove around the city to test it I noticed a little "whistle" noise present for the first 100 meters and then it dissapeared. after around 3km when i tried to brake, the brake pedal got really hard but fortunetly it started working after ~3 seconds so I didn't crash into the car in front of me. I drove home and everything was ok, but just in front of my house it got hard again, but again, fortunetly I was driving really slow so nothing bad happpened.

I'm guessing that the problem is vacuum related, but the fact that it sometimes work and sometimes it doesn't really confuses me. I checked and greased the brakes not long ago, and everything was fine. I have the three amigos and had them for a year now (I did the bypass, but it didn't help) and everything was working fine.
Here are my questions:
-Could it be ABS related?
-How to check the hose from the vacuum pump to the servo? it seems very hard to get to
-does anyone know part numbers for the vacuum pump hose/ brake booster check valve? i can't find them anywhere. or maybe the parts from the defenders fit?

or maybe someone already knows what could be the issue?

I really appreciate any help, i'm really confused.

Cheers!

The bypass mod only helps when its a shuttle valve fault.

brianconwy said:

The bypass mod only helps when its a shuttle valve fault.

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Good to know, thank you! i will check the faults as soon as i can

If you believe its a vacuum issue, then remove and check that the one way valve at the servo is working, as they can “carbon up” just clean with brake cleaner and refit, the same at the valve on the other end of the vac pipe, if there is one fitted with TD5s.

With engine off, press and release pedal a few times to empty vacuum. Then keep pedal down and start motor. If the booster is OK, the pedal will travel further down as the vacuum builds up. Release pedal with engine running and check if it returns to normal when you press it again.

The part # for the check valve is STC780, which according to here - https://www.johncraddockltd.co.uk/stc780-non-return-valve-disco.html - seems to be cross compatible with various LR models.

Thank you for help!!

When I went to check the check valve (which seems fine) i noticed that the vacuum hose disconnected from the vacuum control solenoid, which also could explain the whistling noise. I must have dissconected it when changing the glow plugs and somehow didn't see it (lesson learned, rain and 1*C is not ideal for fixing things). I will go for the test drive today and see how it goes. Thanks again for help, I was worried that i would have to cancel my plans.

Maciej said:

Thank you for help!!

When I went to check the check valve (which seems fine) i noticed that the vacuum hose disconnected from the vacuum control solenoid, which also could explain the whistling noise. I must have dissconected it when changing the glow plugs and somehow didn't see it (lesson learned, rain and 1*C is not ideal for fixing things). I will go for the test drive today and see how it goes. Thanks again for help, I was worried that i would have to cancel my plans.

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Hope it what ever works for you. Don’t be a stranger to the Forum

I went on a test drive today and everything worked perfectly! well, almost everything, because my issue with black smoke at 1000-2000 rpm returned, but at least brakes work.