For some time now the van engine has been making a "clicking" noise, and as the revs rose, so did the speed of the clicking. To me it sounded like it was coming from the top of the engine, so I assumed a sticky tappet.
But upon further research it turns out that it is quite common for the brake vacuum pump to click, as it runs off the camshaft via a push rod into the pump itself. The rod can wear or the spring in the vacuum pump can weaken over time - both introducing slack into the system - hence the clicking noise.
There is a quick way to tell if it is the vacuum pump by repeatedly pressing the brake pedal inside the van. If the clicking noise goes away, or changes note, then its an indication that is where the problem lies. This is what happened on mine, so I set about having a closer look.
So the first job was to remove the pump itself. 2 bolts hold it in place at the front of the engine, so after removing the engine belly pan, access to the pump is straight forward.
One bolt is accessed via the top of the engine, and another at the bottom of the engine. For the bottom bolt you will need a crows foot spanner, as access is a little restricted. The photos below show where the two bolts are.
With the bolts removed, its just a case of wiggling the vacuum pump from underneath the van and it will come away. Now it might have some oil in it (mine did) so have a tray handy to catch any oil that might drip down from the engine.
With a bit more research on the net, I found that excess oil in the vacuum pump can also cause the clicking, as the pump diaphragm cannot return fully each time as the oil cannot be compressed.
The result is a clicking noise as the pushrod cannot return fully. I actually left my pump upside down in the tray for half an hour to drain the oil from it, and quite a bit came out.
I also took the chance to clean up the pump and the area on the engine that the pump came from.
The photo above shows what it looks like with the vacuum pump removed from the engine. The "circle" in the centre of the photo (just below the black pipe clip) is the end of the pushrod that passes through the cylinder head.
The push rod has a slight flat edge on one side to allow the oil run down and lubricate it. This is how the pump ends up having oil building up in it over time!
It was now time to turn my attention to the top of the engine, so I removed the rocker cover to expose the camshaft and tappets.
In the photo on the right, you can clearly see the push rod, and how it is activated via a lobe on the camshaft. You can also see the flat edge on one side of it, which allows the oil to run down one side to lubricate it.
The push rod on mine wasn't moving as freely as it could, so I removed it by pushing it down from above, and catching it in a rag that I had placed underneath. I then gave the rod a good clean, and the hole in the head that it travels through. I then reassembled it using a healthy smear of clean engine oil.
You can buy new push rods, and two lengths are available, so if you do, check with a dealer that you get the right size for your age of Transporter. For me I just re-used my original pushrod.
All that was left to do was reassemble everything. I put my original vacuum brake pump back on again, and used the original pushrod too - but everything was now much cleaner, moving freely and the oil drained from the pump.
So it seems to have worked, no more clicking!
Update: Already a month in and there is still no clicking! Very pleased!