Tdi noisy vacuum pump overhaul
 

The vacuum pump on my 190k 1998 V70 tdi has been making the usual annoying tapping noises (taps loudly and stops temporarily when you press the brake pedal) so I decided to remove it and have a look.

Getting the lower nut off is the most difficult part. I tried several things including various sockets, curved spanners, internet research, three dimensional trigonometry, computer aided design, and having exhausted all that modern facilities had to offer, ………….. in the end, I used a 13mm ring spanner with stiff wire wound on it. Firstly I straightened the spanner in the vice as the ring end was slightly cranked and wouldn’t fit on the nut without the spanner catching on the fuel pipes. It needs to be nearly straight.

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I fed it down from the right, so I held the wire above the fuel lines and then used my left hand down the left of the pump to push the end of the spanner on the nut. One flat at a time but at least I got it off.

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As you pull the pump away from the engine studs, the push rod comes out so be ready to catch it.

I took the clamp off the vacuum line but couldn’t pull the pipe off, so I used a 22mm spanner to undo the brass fitting to get the pump free.

I dismantled the pump by taking off the six screws and the bottom cover plate and then undoing the bolt through the spring. I then washed all the bits in paraffin and laid them out as in the photo.

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There are some more valves still in the body which I later pushed out to wash in paraffin.

Unfortunately, I didn’t make a note of exactly where each valve came from and which way up it went, so re-assembly was fraught! Make sure you draw a diagram!

The piston is a flat disc which has a recess around the edge. There is a rubber seal in the recess and then a copper piston ring so that the squashed seal holds the copper against the cylinder wall. I cleaned the copper ring with fine emery cloth but be careful as it’s soft and bends easily.

The valves are nylon discs held in a little metal cages with a spring under the disc.

I inspected everything carefully and expected to see wear marks or burring but there was nothing visible. Something was stopping the piston returning to the top of it’s stroke before the cam hit it again. I can only conclude that the valves were blocked with thick oil and so the vacuum created below the piston was holding it down. This is pretty amazing when you feel the strength of the spring!

So I re-assembled, oiling the piston and ring, and then struggled to compress the spring. Eventually I hit on using my vertical drill stand and was able to compress it easily with one hand and put on the nut with the other.

I fitted the pump back on the car and now there’s no knocking! I think it will only last until the little valves become oiled up again though. What is amazing is that there didn’t appear to be any wear at all, so I think there must be many owners who have changed their pump for a new one when it wasn’t really needed.

If you think about it, my car has done 190k miles, say at an average of 35 mph. So the engine has run for 5429 hours. Say this is at an average of 2000 rpm. That means it’s done over 651 million revolutions! It’s quite amazing that the pump is still working let alone showing no signs of wear – even on the copper piston ring!