Technical Hard Brake Pedal - Brake Booster Vacuum?

[Guerciotti]

Hi,
2016 Fiat 500 1.2. Brake pedal has gone hard. Car still stops ok but you need to apply a lot of force to the brakes so I'm thinking an issue with the brake booster.

Did some research and apparently most common cause is a vacuum leak rather than a failure in the brake booster unit itself. Does this sound about right? Is there any warning code that will help diagnose the problem further?

Thanks in advance for your help.

 

[jackwhoo]

I think you are right to suspect the brake servo (vacuum booster) or the vacuum pipe that connects the servo to the inlet manifold . Check the vacuum pipe.

 

[Guerciotti]

Thanks. Had a quick look with the pipe still in the car but wasn't obviously split or hanging loose. In order to test properly I guess I need to do a smoke test by pulling the pipe off from the brake booster end and seeing if there are any leaks?

Thanks

 

[jackwhoo]

Hi,
Gently remove the vacuum pipe at brake servo and with the engine at idle speed you should feel strong vacuum by putting a finger over end of pipe.
The pipe is just a pipe that connects to the inlet manifold.
Let us know how you get on.

 

[Guerciotti]

Thanks. I removed the vacuum pipe at brake servo and with the engine at idle speed and the good news is that there is strong vacuum there.

Based on that what do you think the next test is? Is it necessarily a problem with the brake booster itself or maybe there is an air leak between it and the brake fluid cylinder? Or other? The brake booster is TRW if that helps.

Thank you.

 

[jackwhoo]

Check the brakes at each wheel.
If wheel brakes are all good I'm thinking you need a new or used brake servo.
With the engine at idle can you hear a hissing sound where the drivers or passengers feet normally rest?

 

[jackwhoo]

It is unusual for brake servos to go bad but it does happen

 

[CapnChaos]

Hi 2011 Fiat 500 Twinair here with a similar brake issue - in that it’s very hard to press and operate.

 

[jackwhoo]

Hi 2011 Fiat 500 Twinair here with a similar brake issue - in that it’s very hard to press and operate.

Carry out suggestions a already made-report results. If you can't carry out suggestions take it to a garage - report back. Brakes are important don't ignor problem.

 

[Guerciotti]

Check the brakes at each wheel.
If wheel brakes are all good I'm thinking you need a new or used brake servo.
With the engine at idle can you hear a hissing sound where the drivers or passengers feet normally rest?

Thanks. I put my head in the footwell on both sides (car is LHD) and couldn't hear any sign of a hissing noise with the engine at idle. Is this a good or bad sign?

 

[jackwhoo]

Thanks. I put my head in the footwell on both sides (car is LHD) and couldn't hear any sign of a hissing noise with the engine at idle. Is this a good or bad sign?

If you heard a hissing noise it would have confirmed servo fault.......but no hissing does not mean servo is ok.

 

[z rider]

You should hear a hissing sound, it belongs to the operation of the servo. IIRC it comes on releasing the brakes. If you cannot hear it inside the car you should open the engine bay and have a second person operate the brakes while you are listening.

 

[jackwhoo]

You should not hear a hissing sound when the brake pedal is not pressed.

 

[z rider]

Correct. The hissing sound comes when you operate the brake. You have a short hiss when you release the brake, after that there should be no hissing sound anymore. If there is no hiss at releasing the brakes, no vacuum has been applied to the brakes.

 

[bugsymike]

If you pump the brake pedal several times with the engine off so the pedal is quite hard, whilst keeping your foot on the brake pedal start the engine , if servo is working the brake pedal will drop.
Many years ago at college a lecturer said the job of a brake servo is to reduce pedal effort, it doesn't make the car stop any quicker in it's own providing you can duplicate the pressure by harder pedal effort.
Sometimes with engine running on idle it can be possible to hear a vacuum leak, with bonnet up or as engine turned off it may be possible to here a leak as vacuum runs out.
Another test may be to spray brake cleaner or similar around the vacuum hoses and servo, if engine revs pick up you have located the source of leak.
Some times a servo can leak where the master cylinder is bolted to it, this could often be proved by holding a cloth around the flange if hissing or smearing plastercene/body shop dum dum etc. around the flange. Often if that was the case a new servo was the only cure as the seal was not available.
An ageing rubber vacuum hose can collapse causing the issue, on diesels a vacuum pump fault can cause low vacuum also.
As @jackwhoo says "Brakes are important don't ignor problem."
I had a customer who knew his daughters car had a servo leak (when engine off it quickly lost vacuum) she had to move her car and did it without starting the engine, the result was she didn't press the brake pedal hard enough or start the engine and trapped my leg between her and her fathers front bumpers, the bolt pushed in as far as my bone and went septic, I was off work for three months.

 

[John202020]

I would, if you have the experience, check every wheel, partly strip the brakes down confirming each wheel is working correctly.
It's possible it's a master cylinder issue, have a professional look at the car don't wait! My old Mazda suffered total brake loss at the mot testing station, I was so lucky as I had my children in the car moments earlier

 

[Guerciotti]

If you pump the brake pedal several times with the engine off so the pedal is quite hard, whilst keeping your foot on the brake pedal start the engine , if servo is working the brake pedal will drop.
Many years ago at college a lecturer said the job of a brake servo is to reduce pedal effort, it doesn't make the car stop any quicker in it's own providing you can duplicate the pressure by harder pedal effort.
Sometimes with engine running on idle it can be possible to hear a vacuum leak, with bonnet up or as engine turned off it may be possible to here a leak as vacuum runs out.
Another test may be to spray brake cleaner or similar around the vacuum hoses and servo, if engine revs pick up you have located the source of leak.
Some times a servo can leak where the master cylinder is bolted to it, this could often be proved by holding a cloth around the flange if hissing or smearing plastercene/body shop dum dum etc. around the flange. Often if that was the case a new servo was the only cure as the seal was not available.
An ageing rubber vacuum hose can collapse causing the issue, on diesels a vacuum pump fault can cause low vacuum also.
As @jackwhoo says "Brakes are important don't ignor problem."
I had a customer who knew his daughters car had a servo leak (when engine off it quickly lost vacuum) she had to move her car and did it without starting the engine, the result was she didn't press the brake pedal hard enough or start the engine and trapped my leg between her and her fathers front bumpers, the bolt pushed in as far as my bone and went septic, I was off work for three months.

Hi. Apologies for the delay in replying.

I just performed the first test above (pumping brake pedal until hard then starting engine with foot on the pedal) and the pedal does drop after starting the engine so that would imply that the servo is working..?

 

[Guerciotti]

Correct. The hissing sound comes when you operate the brake. You have a short hiss when you release the brake, after that there should be no hissing sound anymore. If there is no hiss at releasing the brakes, no vacuum has been applied to the brakes.

Hi. I just did this test with the bonnet up and my ear near the servo when my wife applied the brakes and I did hear a short hiss (which sounded like pressure being released) when she took her foot off the pedal that that plus the other test above would imply that the brake server (booster) is working fine.

I will now take apart all of the brakes at each side and see what I find and will let you all know.

Thanks again for all of your help.

 

[John202020]

Hi. Apologies for the delay in replying.

I just performed the first test above (pumping brake pedal until hard then starting engine with foot on the pedal) and the pedal does drop after starting the engine so that would imply that the servo is working..?

Generally yes working

 

[Guerciotti]

Hi. I just did this test with the bonnet up and my ear near the servo when my wife applied the brakes and I did hear a short hiss (which sounded like pressure being released) when she took her foot off the pedal that that plus the other test above would imply that the brake server (booster) is working fine.

I will now take apart all of the brakes at each side and see what I find and will let you all know.

Thanks again for all of your help.

Hi,
I am currently trying to take off the rear drum but is stuck. According to the Haynes manual "if the drum is binding on the brake shoes screw two M10 bolts into the locating stud threaded holes in the drum, and progressively tighten them against the hub flange to push the drum from the hub"

I've tried to do this without any luck but I guess it depends on the position of the hub as there are different parts of the rear brake that you could be pushing on. I have tried the 'ten to four' and the 'quarter to three' positions...any trips greatly appreciated !

Thanks again