[murph3001]

Hi, N18 MCS (2011) very occasionally I get a hard brake pedal with no assistance - only seems to be in stop/start traffic at low revs and is fairly infrequent but none the less unnerving.

I ordered a vaccum tester and removed the pipe off the top, then plugged the tester straight onto the vacuum pump, it read approx 5\hg vac at idle. I gave some revs and go a reading of 25/hg vac. Video link below:

Can I therefore assume the issue lies elsewhere? or is there a more comprehensive test I need to do?

Thanks if anyone can help.

 

[mike1967]

think i would be scanning the abs system before vac side, geoffsnook on here had a issue with brake pedal went to floor randomly and turned out was a problem abs pump he has a countryman cooper s , simple scan might flag abs codes at least you have a start point, will add these vac pumps when they fail they can be a engine killer, ie the bearing over heats sometimes get a warning of a eml for exhaust camshaft jammed or out of time as it slows the camshaft and effects the time just before they take the chain out and jump teeth, i had one on 1.4 prince engine a few weeks a go done that and had a hard brake pedal

 

[murph3001]

think i would be scanning the abs system before vac side, geoffsnook on here had a issue with brake pedal went to floor randomly and turned out was a problem abs pump he has a countryman cooper s , simple scan might flag abs codes at least you have a start point, will add these vac pumps when they fail they can be a engine killer, ie the bearing over heats sometimes get a warning of a eml for exhaust camshaft jammed or out of time as it slows the camshaft and effects the time just before they take the chain out and jump teeth, i had one on 1.4 prince engine a few weeks a go done that and had a hard brake pedal

Interesting, I read that thread re. abs pump. I haven't had the pedal go to the floor and no codes flag up on my (old and basic) scan tool so ruled that out. As the pedal goes hard maybe only 1 in 50 times I am a unsure if this is a sign of the vacuum pump on it's way out.

Should the pump give out a constant 25/hg vac when the engine is warm regardless of revs?

 

[mike1967]

Interesting, I read that thread re. abs pump. I haven't had the pedal go to the floor and no codes flag up on my (old and basic) scan tool so ruled that out. As the pedal goes hard maybe only 1 in 50 times I am a unsure if this is a sign of the vacuum pump on it's way out.

Should the pump give out a constant 25/hg vac when the engine is warm regardless of revs?

dont know for sure on n18 pumps , they earlier n14 and n12 engines pretty sure they do run 25 all the time i know the diesels do ,

 

[GEOFFSNOOK]

Hi when i first had the car my pedel went solid once or twice but thought it may have been me imagining it never lost fluid or anything my stop start never worked either until mike replaced the bosster sensor the only reason it went to the floor was the fact all the fluid decided to exit stage right lol

 

[murph3001]

Hi when i first had the car my pedel went solid once or twice but thought it may have been me imagining it never lost fluid or anything my stop start never worked either until mike replaced the bosster sensor the only reason it went to the floor was the fact all the fluid decided to exit stage right lol

That's maybe a good starting point!... Because my stop/start also has never worked since ownership (not that it bothers me)

I assume its the boost pressure sensor? eg:

Boost Pressure Sensor

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[Stu E]

Servo started to leak on my car, start stop stopped, very occasional hard pedal and a hiss from servo when taking foot off brake pedal.

 

[murph3001]

Servo started to leak on my car, start stop stopped, very occasional hard pedal and a hiss from servo when taking foot off brake pedal.

Cheers appreciate that! I think Servo next check after I replace the sensor - havent noticed any drop in fluid so started with the vacuum pump.