Rebuild a Type 4 mechanical fuel pump

Discussion in 'How To' started by mcswiggs, Apr 20, 2016.

  1. When I was at VolksWorld the other week I happened upon the Rage stall who were selling fuel pump rebuild kits; of course on closer inspection they were for Type 1 pumps but the trader said it's possible to rejuvenate a Type 4 pump too - so here's how...

    My guinea pig pump is my spare that I've already cleaned up using my degreaser of choice; pickling vinegar, for that tangy finish.
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    Strip the pump down to its components. Splitting the two halves can be difficult particularly if the diaphragm could be worth saving but a careful prod with a razor or Stanley blade should break the adhesion. Careful with the fuel filter too, it's delicate, and give it a good clean.
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    Taking the new kit, use a die grinder to remove the nib that holds the two discs that sandwich the rubber diaphragm together on its shaft. Try to leave as much of the nib as you can, you'll be needing it. Pry the discs apart using a soft wedge, working your way round until it pops apart. Do the same with the old diaphragm assembly too.
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    Right, time to swap the rubber diaphragms over. I used the old rubber on the new shaft to practice with first. Use a couple of clamps to reassemble the sandwich and give it a pop of weld on what was your nib to hold it all together. Slam it all straight into a bowl of water as soon as the weld is done so the heat doesn't have time to damage the rubber. My first attempt wasn't great as it wasn't properly clamped up. When you're confident enough, do the proper job with the new rubber on the old shaft. I chose to grind the weld back down a bit (to make sure there aren't any clearance problems when reassembled and running, and to reduce the moving mass) but I expect I'm being overly fussy.
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    Now, the smaller diaphragm assembly that forms the anti-siphon valve in the rebuild kit is rubbish quality and doesn't actually fit, so repeat the procedure to swap over these rubbers too. The kit also comes with a replacement valve flap, but again the quality is rubbish so I left the original as it was perfectly functional.
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    Clean all the component with degreaser and blow out with air line if you've got one. Reassemble, having packed the lever area with grease.
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    So, how well does it work? I bodged up a test rig driven off my drill in a stand. To simulate the cam I've put a couple of large thick washers eccentrically in a router bit and popped it all in the chuck. I can't pretend this is super accurate and engineeringly sound, but it gives some idea of performance and allows a comparison test between different pumps. Apparently pumps should suck at 10 Hg in and according to Bentley blow at 0.35 kg cm2. Here're the results;

    ..........................................................Vacuum on inlet (hg in).............Pressure at outlet (kg cm2)
    Another old pump..................................................15..............................................0.25
    Rebuilt pump........................................................ 25..............................................0.3
    New Chinese replacement pump.......................... 11.............................................. 0.22

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    Well, I'm happy with the rebuilt pump, and thinking about getting my money back on the new replacement pump as it doesn't really pass muster. The irony is the one on on the van at the mo is working fine, but at least I can carry a spare that I'm confident in. Good luck with yours!
     

    Attached Files:

    Last edited: Apr 23, 2016
  2. One thing I forgot. Looks like our pumps suffer a bit of creep with that cyclic load - the tabs on the upper shell half that the screws go through tend to bend so take the opportunity to flatten down both mating surfaces with some coarse wet and dry on a good flat surface such as a piece of glass or kitchen work top.
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    Last edited: Apr 23, 2016
  3. Thanks for that.

    question. Theres a rubber washer on the underside that seals the bottom of the pump from the oily side ie the plunger mech. Did you swap that? Seems to me that as the cause of my leak. Also on one pump there was a return spring under the plunger, actuator are, or whatever it is. This was missing on the other. Unless it escaped when i wasnt looking.
     
  4. The rubber seal thing has been in good nick on all the ones I've taken apart so far, it's unlucky you've got a duff'n.

    If you look closely at the photo of the seal on the new plunger/diaphragm you'll see it's actually split along one half of its diameter, so I'd say it'd be possible to cut out the old one and insert the split one. Either that or bodge the old one with sealer.
    If there's oil getting through have you checked the err-hum diameter of your rod? I think it just bleeds past its guides, so a new one for £10 might help. And is it all packed with grease?

    And yes, the spring underneath the diaphragm plunger needs to be in place. In those pressure tests I did the old spare pump turned out to have a broken, mangled spring which I think was why the readings were a bit low - other than that the pump was all intact.
     
    paradox, Buddy Hawks and Dicky like this.
  5. Why do I have oil coming from the breather pipe
     
  6. If it’s oil then it’s because is weeping from the sump, past the pump rod, into the base of the pump body and out through the little drain.

    You could take the pump off, check the diameter of the rod and replace if worn.

    If it’s fuel comping out of the drain then it’s because the pump diaphragm is perforated.

    Good luck!
     
  7. Many thanks for your suggestions. I have now replaced the pump after modifying various allen keys, etc and seem to have worked out a fairly straightforward way of removing and replacing the pump as the top bolt is a bit of a pig to get to. I removed three of the screws on the tinware that obscures the top bolt and eased it away so that I could get a fairly long straight drive onto the bolt, seems to have worked ok. I have also replaced the spacer, gaskets and the push rod which was about 3mm shorter than the new one, all back together again and so far seems to have cured the problem, fingers crossed.
     
  8. davidoft

    davidoft Sponsor

  9. I bought a new pump from VW Heritage, and replaced everything, spacer, pushrod, etc.
     
  10. davidoft

    davidoft Sponsor

    Where did you ge the replacement parts from ?
     
  11. I got all the necessary parts from VW Heritage.
     

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