Slow servo build up cdti

[2.2-600-vtec]

Hi i have had problems with the brakes on my zt being well poor,
at first if you press the brakes not a lot happens, but after a very short time the brakes start to bite, i have driven it like this for awhile as not really had a chance to give the girl some stick and they seemed to work when pottering about day to day.
This weekend i had a empty car bar a very light but empty little trailer, so i decided to have some fum on a little but of road i know well,

Now no matter what i done and how hard i braked there was not a hope in hell the brakes would bite enough for the abs to fire, on one occasion i had nothing but a solid pedal after braking hard 100yards previous, it was not a real problem at the time as the handling is sublime for such a large car.

After about 200 yards or so the brakes where back as before (as in it slowed it down abit) so pottered back home very dissapointed.

i looked at brake temps when i got back and there was no heat of any concern in them, when compared to my old zs vvc on the same road, ( i had those on fire and lighting up the road on all 4 corners on that road once, mind you it had the ti conversion big brakes, but with standard pads and smaller discs than the zt).

Pads where all good with loads of life, discs are grooved so glazing should not be a problem, i checked the vac pipes for leaks and blanked off the egr pipe altogether to isolate that,

If you start the engine with your foot on the pedal it takes a good 30 seconds to drag the pedal down hence the looking at the pipes,

tonight i disconected the vac pipe from the pump and ran the engine, i found that the vac appeared very poor as in youcan put your finger over the hole and easilly pull it off, there is a vac there but compared to a petrol engine i would say its very poor,

is it possible that the vac pump is worn out? i always thought that diesels had a far stronger vacuum than petrols as its a dedicated pump?

any thoughts?

Thanks
Nathan

[RodgerD]

Originally Posted by 2.2-600-vtec

Hi i have had problems with the brakes on my zt being well poor,
at first if you press the brakes not a lot happens, but after a very short time the brakes start to bite, i have driven it like this for awhile as not really had a chance to give the girl some stick and they seemed to work when pottering about day to day.
This weekend i had a empty car bar a very light but empty little trailer, so i decided to have some fum on a little but of road i know well,

Now no matter what i done and how hard i braked there was not a hope in hell the brakes would bite enough for the abs to fire, on one occasion i had nothing but a solid pedal after braking hard 100yards previous, it was not a real problem at the time as the handling is sublime for such a large car.

After about 200 yards or so the brakes where back as before (as in it slowed it down abit) so pottered back home very dissapointed.

i looked at brake temps when i got back and there was no heat of any concern in them, when compared to my old zs vvc on the same road, ( i had those on fire and lighting up the road on all 4 corners on that road once, mind you it had the ti conversion big brakes, but with standard pads and smaller discs than the zt).

Pads where all good with loads of life, discs are grooved so glazing should not be a problem, i checked the vac pipes for leaks and blanked off the egr pipe altogether to isolate that,

If you start the engine with your foot on the pedal it takes a good 30 seconds to drag the pedal down hence the looking at the pipes,

tonight i disconected the vac pipe from the pump and ran the engine, i found that the vac appeared very poor as in youcan put your finger over the hole and easilly pull it off, there is a vac there but compared to a petrol engine i would say its very poor,

is it possible that the vac pump is worn out? i always thought that diesels had a far stronger vacuum than petrols as its a dedicated pump?

any thoughts?

Thanks
Nathan

Diesels don't produce vacuum like a petrol car. The vacuum comes from an exhauster, a mechanically driven suction pump. Like any mechanical item they can and do wear out. Check all the pipework from the exhauster to the servo first to exclude the possibility air is getting in.

[andrewinpopayan]

Why does everyone who needs help live so far from me? I have instruments and gauges, while not in themselves expensive, the cost of sending them back and forth is?

[Mike Noc]

Originally Posted by 2.2-600-vtec

is it possible that the vac pump is worn out? i always thought that diesels had a far stronger vacuum than petrols as its a dedicated pump?

any thoughts?

Thanks
Nathan

Possible but unlikely. Haven't heard of one wearing out on here, and the one in my car has done over 365,0000 miles and still going strong.

The vacuum is also used for the EGR valve, so trace the pipe up to the EGR actuator and on to the valve itself and look for any splits or damage.

Often the pipe can rub against the engine and over time wear through with the vibration.

The actuator sits above and behind the starter motor on the front of the engine, more often than not it is dangling on a fractured bracket on high milers, another reason the pipes can split.

Cable tie it to the starter motor and it will be fine.

[2.2-600-vtec]

Thanks for replies guys

EGR has been disabled and i blanked the pipe that feeds the actuator from the main pipe, the servo pipe appears all ok i have traced it back to the servo,

The car has only seen 116k miles but i have no real idea of service, even thought the book is stamped up to 100k that was a few years ago, would lack of use kill the pump?

I have a set of motorcycle carb balancing gauges, would they read enough vacuum or would the mechanical pump draw more than a petrol engine?

[andrewinpopayan]

Originally Posted by 2.2-600-vtec

Thanks for replies guys

EGR has been disabled and i blanked the pipe that feeds the actuator from the main pipe, the servo pipe appears all ok i have traced it back to the servo,

The car has only seen 116k miles but i have no real idea of service, even thought the book is stamped up to 100k that was a few years ago, would lack of use kill the pump?

I have a set of motorcycle carb balancing gauges, would they read enough vacuum or would the mechanical pump draw more than a petrol engine?

Any vacuum pump cannot evacuate to more than -1 Bar, 760mm mercury, it's how fast it does it. your bike gauges will be ok. I suspect a leak somewhere.

[2.2-600-vtec]

Thanks for that, any ideas how quickly it should build as it is not that fast with my finger over the end of the vac pump,
i will try and test the vac tonight

Thanks

[Mike Noc]

If it is the pump you should be able to pick up a used one cheap enough and it will be a safe bet - as mentioned they are usually bullet proof on these engines.

If it checks out and the pipework and connections are all OK then you may have a problem with the servo itself. If you can get a long enough bit of pipe you can try running it from another vehicle.

[2.2-600-vtec]

Right i have just been out and checked the vacuum, and it appears to be ok,
annoying as ordered a replacment which i will replace anyway.

On a plus note the test has checked all pipes and the vacuum so it would appear that the servo is down, with the engine running you get one slightly assisted pump then a lesser one then gone all with the engine still running, wait a while and you can do the same again.
it must be sealed as i get full vacuum pressure on the line, so must be something else internally? i take it they are sealed so if the diaphragm has split it would still hold a vacuum of sorts?

Thanks

[andrewinpopayan]

I had a servo on an Astra that a small hole had corroded in the bottom of it.

DPO was too enthusiastic with the brake fluid, it stripped the paint, exposing the steel to corrosion.

Vacuum should build up really quickly, no more than a couple of seconds AND stay there for a good while when you stop the engine.

Andrew