Screen washer pump question

Well today I thought it would be fun to clean up the windscreen washer pump assembly on my 140 and paint it black.

Didn’t get very far because I now think the vacuum chamber may be black painted over some kind of zinc coloured plating, on its top half, while the bottom half of the vacuum chamber seems to be a dark grey coating over unplated brass.
Please see the picture.

Black paint peeling off of the plated brass top half
Grey coating on the brass bottom half

Can anyone advise on a correct finish on the pump vacuum chamber?

The lid which screws onto the glass bottle is black painted steel.
Thank you in advance.

I’ll bet it was semi-gloss black, but I don’t know that for certain.

You’re correct that the vacuum chamber consists of 2 different materials. Depending on whether made by Trico England or a later Trico USA replacement version, the top dome is a die cast made of an aluminium alloy and the original version for your XK 140 will show the name Trico in raised letters.

The lower half is always made of brass. The difference in material is the reason you see the different “ageing” behaviour of the paint. The original versions had a satin or semi-gloss black paint.

Bob K.

Hi Bob,
Thank you for the information, very helpful.
This vacuum chamber top dome does not have any lettering, so it would be a replacement version (I got it on eBay, maybe 15 years ago).
It still works perfectly, so I will go ahead and paint it black and continue to use it.
Thanks again

I have one of these on my XK120 FHC, has never worked or I should say that the whole system does not work. Please can someone give the diagram of the pipe routes. I am assuming this was not standard on my car as there is nothing in the manual about a screen washer?

I have a new vacuum part, on top of the water bottle with two pipes in. Also what looks like a similar small pipe to the inlet manifold. On the dashboard there appears to be a little chrome button with a sort of soft push feel to it like a pump ? Not sure I understand the whole system ?

No, it was standard on later FHCs. Its in the Body section of the Parts Cat.
My early FHC does not have it, so perhaps you can guess from the hose descriptions or others will know more.

Hello John,
first of all I have to say, that I have never seen a disassembled pump unit. But I am quite sure that the function is as follows:

The pump unit consists of two chambers separated by a membrane or piston. The upper chamber is filled with air, the lower with water. In passive state the membrane is pressed down by whatever so that the water chamber is empty. If vacuum is applied to the small tube on top of the pump unit, the membrane is sucked up against the load. With that the water chamber is filled with water sucked out of the glas bottle. Breaking of the vacuum causes the membrane to be pressed back down and discharging the water chamber. Due to a nonreturn valve the water can’t flow back to the bottle but is pressed instead through the lateral pipe to the washer jets. Presumably there is another nonreturn valve which prevents backflow of air from the washer jets during filling of the water chamber.

The connections of the hoses are as follows:

  • a vacuum hose from the inlet manifold of the engine to the inlet of the control button in the dash board
  • a vacuum hose from the outlet of the control button in the dash board to the top tube of the pump unit
  • a water hose from the lateral tube of the pump unit to a tee-connection and from there to the two washer jets

Operation is as follows:

  • Press the control button in the dash board for a certain time to fill the water chamber of the pump unit
  • Release the button and the water chamber is emptied to the washer jets


Rob and Joerg, thank you both for the details and explanations. Now that we all have time to work on cars, I look at sorting this out.


If you allow me, I would like to recommend these pieces of information on the subject under the motto: Everything you ever wanted to know about …well eh…Trico washer pumps.


Bob K.

That was actually an interesting read. It helped confirm the originality of my 150. Thanks for sharing that.

Bob K, thanks very much for info. I will have a look at all the tubes and see where the connections are not attached or not right, thanks John