C4 - Hard barking peddal updates - findings - need help

[lancia58]

Hi

Car is Citroen a petrol C4 1.6 with auto gearbox ( AL4)

Some updates to the following thread

http://www.frenchcarforum.co.uk/forum/v ... =3&t=55504

The hard pedal happens only when the car is stopped and the revving at around 800 RPM.


In order to sort this I took the car to a certified Citroen garage ( never before go to a certified garage but as it is wife's car I wanted a fast remedy ) . They did the following things that didn't help

1) Replaced the vacuum hose ( part number 457884)
2) One way valve ( part number 459931 )
3) Replaced the brake amplifier ( AKA booster )

Than they replaced two valve hydraulic lifters ( part number 94293 ) that according to the garage were a bit seized, called me and say that the problem is sorted. They also claimed that this is due to dirt in the oil system and suggested to flush it. Happily I went to take the car. I checked it and it looks better. Two hours after I parked the car, I had to drove it and the hard brake pedal is back.

I did some more checking and here is my findings ( N is gear in Neutral , D gear is in Drive ) :

A) When the car stops and the N is engaged the brake pedal is almost normal, when pressed it travels around 3/4 of the full travel. Staying in N and revving to 1500 and up the brake pedal when pressed travels all the way
B) If then the D is engaged and I release the pedal brake and press it again it is rock hard. So it looks that when the engine is under load ( engaging the D ) the vacuum to the brake amplifier decreases results in hard braking pedal.
C) I measured the cylinders compression pressure , two cylinders read 170 psi and two 130 psi.

Can the low compression pressure affect that dramatically ?

I guess the above is related two my thread http://www.frenchcarforum.co.uk/forum/v ... =3&t=55642. Regarding this thread the as Simon suggested they say that the cause is a failed torque converter . Can a failed torque converter be the cause for the hard brake pedal or it is more likely the engine is weak ?



Zohar

[xantia_v6]

I would not think that a torque converter fault could affect the brakes, but Simon's suggestion of a blocked catalytic converter (causing low vacuum at idle) could be a sensible explanation.

[lancia58]

Hi

If the cathalytic converter is blocked how comes that when the gear is in N the vacuum is OK and when in D the pedal is hard ? The car past the mot in January with no problem. I took the car to an exhaust specialist and he said that the air flow is OK i.e. no blocking. Having said the above I suspected the cathalyticc convertor and I am not sure that the above contratdicts this. Is there an easy way to check out the cathalytic convertor ?

Regards
Zohar

[Paul-R]

Does the car have an electric parking brake? I notice on my C5 that the pedal goes hard after the parking brake operates.

[lancia58]

Hi

No it doesn't have an electric parking brake

Thanks

[lancia58]

Hi

Any ideas ?

Thanks
Zohar

[demag]

My son had a Peugeot 306 1.9 DW8 with a blocked catalytic converter and it wouldn't run. There was just too much back pressure.

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