Brake vacuum pump: buzz on press, buzz on release. Normal?

veektor · Post by **veektor** » 04 Mar 2018, 08:56

Please forgive me if this is a dumb question, but I'm going to have a lot of those in these early days of learning Volvo things. I am not driving this car yet, have some engine and transmission service to do before I take it on the road. As I am looking over the car, I am always listening for unusual sounds. I noticed a buzzing sound for about a second when brake pedal is pressed, and about the same when released. I also noticed it happening without brake input with warm engine idling.

I think it is coming from the brake vacuum pump, which is a first for me. Is it supposed to work the way I described? I know that in general the vacuum booster or its hose can leak and cause vacuum issues, but I have no idea what behavior is supposed to be with a pump in the mix.

Post by **jimmy57** » 04 Mar 2018, 09:52

when the car is first started cold that is normal. the variable valve timing controls and ignition timing are manipulated for emissions improvements and manifold vacuum is very low. pump is fitted for this reason. if it is busy like this all the time there is something else going on. an issue that you can prevent is the pump vac switch breaking and costing you $100+.
the switch is clipped to front of air filter box and is the junction of 3 hoses. the end with electrical plug can pop off when plastic tabs age and break. pull the hoses off and disconnect electrical plug. you can use JB QUIK-WELD to secure it. new ones come this way. mix the jb weld and give it 2 minutes to firm up. it is 5 min cure time. spread the jb weld around the perimeter of the electric switch end where you see the housing halves latch tabs. (if this area is already "glued" together then it has already been replaced, stop, no need to do anything) once you have the jb weld applied then use electrical tape and go round that area to make a mold of sorts to keep jb weld in place and to make it look nicer too. on the side where tabs are located use something to pack jb weld around tabs. this assures this never flies apart ever.
note: you may find the switch end is crooked where it is already breaking. this can cause irregular pump running. in this case you can use a c clamp to press switch together for the repair.

Post by **abscate** » 04 Mar 2018, 10:19

Jimmy - if I remember right if you let this thing fly apart you lose the spring and/or valve internals so then you are in for new parts.

Ill check my 2005 to see if it has this pump and valve system - good to get in front of repairs which cost only a tube of JB weld

Post by **oragex** » 04 Mar 2018, 11:25

Does it sound like this ? Note that I replaced my switch but the pump still runs for some (wrong) reason. Maybe a leak at the brake booster, at the master cylinder, or may air trapped into the ABS valve unit. Or even a problem with the ABS controller unit.

veektor · Post by **veektor** » 04 Mar 2018, 13:43

Thanks for easing my mind. I'll keep an eye/ear out for erratic cycling, but sounds like activation with brake pedal is normal. I still have the "DSTC SPIN CONTROL OFF" message that I can't change using "Reset" button, but I haven't had a chance to inspect all of the brake sensors yet, which I read is the likely culprit for this issue.

Cookie-the-Swede · Post by **Cookie-the-Swede** » 04 Mar 2018, 21:07

Mine did this so I replaced the pump (and switch). Afterward, it still buzzed briefly whenever I depressed and released the brake pedal but it was much quieter. It's annoying. I eventually unplugged the electrical connection on the switch. Now it doesn't buzz anymore but the brakes still work the same.

Post by **oragex** » 05 Mar 2018, 06:23

Cookie-the-Swede wrote: ↑04 Mar 2018, 21:07 Mine did this so I replaced the pump (and switch). Afterward, it still buzzed briefly whenever I depressed and released the brake pedal but it was much quieter. It's annoying. I eventually unplugged the electrical connection on the switch. Now it doesn't buzz anymore but the brakes still work the same.

I am not sure about this, but the switch and pump roles are to prime the brakes. If this part of the system is off, when doing an emergency braking - 'jump of the pedal' as we say - the brakes may not react as fast as usually.