Technical Ducato 2001 - Hard brake pedal, sometimes...

[Peter81]

Hi,

I have recently bought a 2001 Ducato based MH with the 1.9 TD engine.
I have an issue with the brakes which I can't really make sense of, the brake pedal is rock hard, but as it seems, only sometimes.

So I changed the vacuum pump, it felt like it got bit better. Unfortunately the brakes are still not working properly.
When driving and revving over 2000 rpm and brake, the brakes seem to work normally ie. the servo seems to be operating and the brakes are light as they should be, but if you have to brake twice within a short time frame the pedal goes rock hard.
When driving slowly, for example in city traffic at low rpm, the brakes can sometimes work normally and sometimes you have to put your full bodyweight on the pedal to be able to stop.
I also noticed that there seem to be a kind of a gurgling sound sometimes when pressing the brake pedal hard with the motor running. (hard to explain the sound)

- Last MOT no significant difference in brake power between left and right wheels, so I think the calipers are moving as they should (nothing stuck)
- Brake fluid, I have no record when it was changed the last time.
- Vacuum hoses seem to be intact, no chafing or bending what I can see.
- The pedal seems to be going down a bit when pushing the pedal and starting the engine.

How many PSI/BAR of vacuum on idle measured on the pump? Could the new aftermarket pump be faulty? (I didn't buy the more expensive original Bosch pump)

Could there be a problem with the servo? Anyone had similar problems?

Any ideas please?

 

[jackwhoo]

Yes you could have a servo problem.
Check servo not full of fluid.
With engine running can you hear hissing sound behind brake pedal?

Check hose not perished or holed between pump and servo.
Check non return valve in hose at servo.

-12 psi ish on vacuum line

 

[Peter81]

Thank you for your answer, much appreciated!

I will have a look at this according to your suggestions.

 

[Peter81]

Had a chance to look at this now, the vacuum and hoses werw ok, now it seems like the Ducato motorhomes from 2001 have a very expensive brake servo (Bendix 900 euro) and none second hand anywhere to be found.
I could check the newer Ducato 2002 -> Bosch servo (which I can find plenty of second hand), this seems to have the same distance between the mounting bolts on both sides of the servo and the same attachment on the brake pedal, but the actuator that goes into the brake cylinder seems a bit shorter.
Anyone have any idea if it would be possible to use the newer brake cylinder? The brake pipes might need rerouting I guess, but it would be a considerably cheaper solution...

EDIT: And regarding the sound in the previous reply, I can't hear a hissing sound but a clear gurgling sound when braking. Sounds a bit like when you drain a sink

Thank you!

 

[rolandbrindley]

Before you spend big money just check the one-way valve that keeps the vacuum up inside the servo tank. If you can get it out clean it thoroughly, use petrol then blow through with an air line.

Try blowing into it the blocked way to see if it is bleeding air through slightly. If you can buy one separately then change just that before changing the entire servo.

 

[Peter81]

Thank you for your answer.
I removed the white check valve and cleaned it, it is not letting any air through the blocked way. I also tried a second one with the same result

 

[Peter81]

Hi all, back at this again.

Today I replaced the brake servo with another second hand, replaced the vacuum hoses and measured the vacuum at the white checkvalve and at the pump. Vacuum was rising slowly to about 8 psi and stayed there, then after raising the rpm the vacuum dropped to 12 psi pretty much instantly and stayed there. I had the same measurements at both the pump and the white checkvalve.
Could the new vacuum pump be faulty?