Brake pedal gets very hard to press at times

[carboy2017]

I had the issue of my brake pedal getting very hard and stiff when trying to engage it especially after driving steady at 70pmh for maybe 20 mins and the workaround was to gently tap the pedal a few times and it returns to normal

I took the car to the local garage and they could not diagnose it,I took it to the Mitsu dealers and they said its the front caliper on the left thats sticking and causing it

I changed the left front caliper ,got new pads and it was ok for a some time and then came back but not as bad as before

So I replaced the front right caliper and changed the brake fluid last month but during constant use over the bank holiday weekend I noticed the same fault coming back (but not as severe as before) and im at a loss as to whats causing this on my Mitsubishi Lancer

Anyone had the same problem or know whats causing this?

[E-bmw]

Likely cause will be the brake servo, don't know why a garage would be unable to diagnose that.

[untakenname]

Check the return valve in the pipe between the brake servo and the engine they can sometimes fail, had it on my WRX where over a certain boost pressure the valve wouldn't work so instead of vacuum assisting with the braking I had boost pressure actively resisting.

[carboy2017]

E-bmw said:

Likely cause will be the brake servo, don't know why a garage would be unable to diagnose that.

I tried the local as well as the Mitsubishi dealer but no success!

[carboy2017]

untakenname said:

Check the return valve in the pipe between the brake servo and the engine they can sometimes fail, had it on my WRX where over a certain boost pressure the valve wouldn't work so instead of vacuum assisting with the braking I had boost pressure actively resisting.

thanks for the tip

[stevieturbo]

Stick a vacuum gauge as close as possible to the servo to monitor vacuum.

And also check pedal adjustment if any where the pedal interacts with the servo.

Changing calipers etc on that description seems a bit bonkers. Do some testing around the servo.

[carboy2017]

I tried to search for the brake servo return valve or even the whole unit (brake servo) but so far none available,only used ones on eBay

Any idea where I can buy a brand new brake servo unit for a 2006 Mitsubishi Lancer saloon

[stevieturbo]

carboy2017 said:

I tried to search for the brake servo return valve or even the whole unit (brake servo) but so far none available,only used ones on eBay

Any idea where I can buy a brand new brake servo unit for a 2006 Mitsubishi Lancer saloon

Try Mitsubishi ?

Have you proven whatever is actually wrong, will be fixed by another servo ?

[Smint]

You've checked the rear calipers are working freely? If the fronts have had issues the rears won't be any better.