XC70: Wheels/Brakes possible brake (vacuum?) issue

[JonnyA]

HI

I think that i may have an issue with the brakes on my XC70 (2012 D5) and would like to pick the collective brains here.

Generally the brakes work very well but I have found that if i brake very hard lift off then re-apply the brakes the pedal goes hard and i have 'almost' no braking.
This would seem to be a sympton of using up the servo vacuum.
I have had two occasions where i have experienced this (other than specifically trying to do it), the first time; braking at the top of a hill as i caught up a slow vehicle then having trundled down the hill a short way had to brake again as they stopped to turn off without indicating.
the second time; braking hard to slow rapidly then allowing the car to run on breifly to a passing place before braking to a stop. in both these situations the second pedal press was solid and it felt as though i had no stopping power.
I have taken in to my local indie (volvo specialist) and they have found it hard to replicate, although they said they managed to get the pedal hardish on one time in a test run and have detected no vac leaks. They think it is probably OK - but suggest a manual change down on steep decsent to improve vacuum pump speed... not convinced this should be necessary and would not help when i am driving normally.

I cannot beleive that the car should use up all the servo 'power' in one hit on the brakes so think there is a problem. Am i right??

I gather that there is a vacuum pump (end of cam shaft, im told) but have no idea how the system works or how to test it or if this model has another pump etc.
Can anyone offer any advice.

[green van man]

The standard test is to pump the pedle hard with the engine off, then with foot still on pedle start engine and pedle should creep down as vacuume restored.

As there is no leaks on the system reportedly I would be looking at a weak vacuume pump, indeed a higher engine rpm in a lower gear would produce more vacuume and I belive the resevour should give 5 brake applications before being exhausted so your second does seem rather low.

Servo brakes without Servo are a real frightener and I would also be looking for improvement were it my car. Being a Volvo throwing bits at it will be expencive but for piece of mind I would be investigating and a new vacuume pump would be high on the list of possible remedies.
Having said all that, I have no problems with my servo brakes on either of my cars, however my landrover has a known problem of oil leaking from the vacuume pump which I monitor closely, any evidence of said fault and a new pump will be fitted asap.

Paul.

[37 RUBY]

Originally Posted by green van man

As there is no leaks on the system reportedly I would be looking at a weak vacuume pump.....

So is there a figure set in Vida for what vacuum the pump should be drawing at idle, mid range and at max rpm?

Originally Posted by green van man

Servo brakes without Servo are a real frightener....

....you should try cable brakes with four grown men inside. Underpant colour changer.

JonnyA, here is a video from a respected Volvo forum member that may assist....https://m.youtube.com/watch?v=-lgYAS3GoiE

[green van man]

Originally Posted by 37 RUBY

So is there a figure set in Vida for what vacuum the pump should be drawing at idle, mid range and at max rpm?




....you should try cable brakes with four grown men inside. Underpant colour changer.

JonnyA, here is a video from a respected Volvo forum member that may assist....https://m.youtube.com/watch?v=-lgYAS3GoiE

I learned to drive on no servo drum brakes all round with 1 in 4 hills common, I fully understand the underwear problem.

Paul.