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Matt, Engineer
Category: Australia Car
Satisfied Customers: 21995
Experience:  Automotive Engineer for 20 years, BEng hons degree,
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I have a Nissan patrol 2000 3lt diesel. My pedal went spungy

Customer Question

I have a Nissan patrol 2000 3lt diesel. My pedal went spungy without warning. I have replaced the master cylinder and bled all wheels. The pads are almost new. The pedal is ok with the engine stopped. As soon as the engine starts the pedal goes almost to the floor. I have rebled the system several times.
Submitted: 1 year ago.
Category: Australia Car
Expert:  Matt replied 1 year ago.


This could be a flexible brake line is ballooning under pressure, this can't always be seen from the outside so to test this use a hose clamp on each line in turn to close off then lines one at time . Push the pedal in between and see if you can feel any difference as each line is closed off.

if this doesn't help then its possible that you need to run the ABS pump to move any trapped air inside

the dealer method is to use the diagnostic tool to cycle the ABS during bleeding

however I've had good results buy just taking the car for short drive and stamping on the pedal at low speed to lock the brakes and trigger the ABS

and then re-bleed

Customer: replied 1 year ago.
G'day Matt
I have tried what you recommended and the result was the same. The pedal still goes to the floor when the engine is started. i can still pump a hard pedal with the engine stopped. I don't know anything about the ABS system but it feels to me that when the engine starts some thing in the ABS system allows the fluid to recycle back to the master cylinder. Sounds a bit odd but so is the problem
Expert:  Matt replied 1 year ago.


if you've triggered the ABS and rebled and its still no different

then the next step is to pull the ABS fuse and see how that effects the issue as this should make it a 'dumb' system

Customer: replied 1 year ago.
I tried that still no differance
Expert:  Matt replied 1 year ago.


Ok when you replaced the master cylinder there's some adjustment available if you to remove the master cylinder again and have your assistant push down on the brake pedal to expose the pushrod as it exits the servo

on the end of the pushrod there should be a little adjustment nut

try screwing this in a turn or two and put it all back together

this adjustment takes out free play at the pedal so its better to have a little bit of play rather than too tight