Hard brake pedal V70 D5 Euro4 Manual

[TurboDiesel2006]

Car is Volvo V70 D5 185 Euro IV with manual gearbox.

I am getting a very hard brake pedal after a two depressions. I push the pedal once - ok, then the second time the pedal gets hard at the end of the travel and if I try a third time it is very hard and retardation is poor. If I release the brakes then a couple of seconds later it is ok but goes into the same cycle.

From other threads and internet search the symptoms are indicative of a lack of servo boost.

My car has the mechanical camshaft driven brake vacuum pump on the LHS of the engine. Whilst replacing the swirl flaps I noted this was leaking oil, so took it off and replaced the seals. All seemed ok.

I had not used the car between replacing the vacuum pump seals and experiencing this problem (see rear brakes comment below) so my immediate suspect was the pump.
I have checked the vacuum from the brake vacuum pump and am getting;
Servo Outlet - 29psi (59 inhg, 199pka), steady reading at engine idle
Engine Mount Outlet - 10psi (20.3 inhg, 68 kpa), steady reading at engine idle.
I have no idea if these figures are good or bad. Can anybody advise please before I buy a new vacuum pump?

I have just finished replacing the rear discs, pads, handbrake pads, levers and cables and used new slider pins well lubed so I don't think it is this causing the hard brake pedal. I bled the entire system at the same time and have no sticking pads. The front calipers were renewed in 2020.

Any ideas please.

[TurboDiesel2006]

Update - I should have read my vacuum gauge more carefully. The results were in fact;
Servo outlet - 29 inHg (I think some may refer to this a primary outlet)
Engine mount outlet - 10 inHg (I think some may refer this to the secondary outlet)

I think this means that the vacuum going to the servo is correct (from other threads I think it should be > 25 inHg) but the engine mount outlet seems low to me. As they are from the same pump mechanism I would have expected then to be the same but I am not an expert on this so can anybody please advise.

If the engine mount (secondary outlet) was below spec could this indicate a fault in the pump whereby it was somehow leaking at this outlet and that was also venting the servo outlet which would explain the car's inability to maintain vacuum to the servo?

[TurboDiesel2006]

When I took the brake booster pipe off after the car had sat overnight there was a hiss of air which I think says the booster is not leaking. I have now taken the pump off again, cleaned it and checked the primary (Brake boost) and secondary (engine mount) one way valves on the pump. The brake one was open but started to work after I cleaned it using carb cleaner, the secondary was ok. The vane inside the pump was ok and moved correctly. It is difficult to see what could go wrong as it is so simple but when I re-assembled it and tested the secondary take off I was still only getting 10 inHg. If I revved the engine it went up to 15 inHg but I then noticed oil in the test vacuum pipe. Also if I released the vacuum it didn't get above 2 inHg at idle unless I revved it again when it went back to 15 inHg.

I was testing at the connections to the pump so as to take the pipes out of the equation. For completeness I put 25 inHg on the secondary take off pipe and it held fine. I also check the front engine mount and that was ok. I then put 20 in/Hg on the pipe from the vacuum pump to the brake servo and that held ok. I did however note that there was oil on the inside wall of the pipe.

A test drive confirmed unsurprisingly that nothing had changed.

My conclusion from this is that the pump is broken in some way (valves faulty, vane excessively worn after 225k miles) and the only solution is a new pump but I am far from convinced on my hypothesis.

Does anybody have any suggestions, advice or guidance before I buy a new pump. Thanks

[dave c59]

I'd suspect the vacuum lines - could the one to the mounts be split and losing pressure, is the mount itself leaking? I'd disconnect the pipe and blank it off and see if that makes any difference. Does yours use vacuum to control the turbo? Could be another line leaking.

Good luck.

[Kev0607]

No vacuum lines to the turbo on these engines. Its all controlled electronically.

It sounds like a vacuum pump problem, but you don't want it to be a parts cannon either (spending money on parts it doesn't need). I'd advise getting it properly diagnosed by a garage, ideally a Volvo specialist.

[TurboDiesel2006]

Thank you for the suggestions.

Problem now fixed. After my last entry I decided to bite the bullet and ordered a new vacuum pump, in my case a Pierburg unit from Autodoc. It took a week to arrive but having fitted the new unit I checked the vacuum at each outlet and was now getting 22 inHg at the the engine mount (secondary) outlet. Previously the servo (primary) outlet was ok but the engine mount (secondary) was only 10 inHg. The brake pedal is now back to normal.

So to conclude if you have a hard brake pedal on your 2005-2007 Euro IV D5 with a manual gearbox (I think the auto box cars have an electric pump) check the vacuum at both outlets of the engine driven vacuum pump. Both should be more than 22 inHg. If they are not then it is probably time to replace the pump.