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420A Power Steering Pump Modification

Posted by silvreclips, Apr 17, 2019

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  1. silvreclips

    silvreclips Proven Member

    Joined Jul 19, 2005
    Greenville, South Carolina
    Like the 4g63 PS pump, the 420a pump also has issues with the PS system loosing assist at higher RPM. This has turned out to be a bigger issue then I had originally anticipated. While I have autox this car for many years, I have never been aware of this problem until recently. One particular autox had a very fast slalom where I experienced the PS assist decreasing dramatically, to the point where it felt like I had almost no assist at all. After some research I found some articles that talked about this exact issue with the 4g63 PS pumps, however I could not find any info about how to fix the 420a pump to keep this from happening. With the help from the 4g63 instructions I was able to successfully mod the 420a in a similar way that eliminates this problem.

    **Shout out to @Calan for the How To for the 4g63 pump. That helped me understand where the problem was and how to fix it. **

    Link to article: https://www.dsmtuners.com/threads/how-to-rebuild-and-modify-a-power-steering-pump.345914/

    I was able to take apart the pump while it was still on the car, I had a syringe that helped me suck the fluid out as I went along to keep the spill to a minimum.

    Step 1) Remove as much fluid from the reservoir as possible.

    Step 2) Remove the high pressure line from the Pump, this is the banjo bolt on the top of the pump. The banjo bolt threads into the flow control assembly. While trying to loosen the banjo, that flow control assembly was also trying to loosen and spin the PS hose around. It took some work but I finally broke it free. (Save the crush washers or find new ones, I reused mine)


    Step 3) Remove the Flow Control Assembly from the pump.


    Step 4) Look in the large end (banjo thread end) of the Flow Control Assembly, you will be pushing that piece out with the 2 small holes in it. (Note how far it is pressed in) Under that will be a spring and then the sleeve that blocks off the flow to the rack. I used a punch and gently tapped it out with a hammer. The punch was small enough to get through the spring so I only hit the piece that is pressed in. It makes sense once you get it apart. That sleeve gets pushed up against the restrictor plug at higher rpm and starts to block off those 2 holes that feed fluid to the rack. You can kind of see it in the picture below.



    Step 5) I drilled out this sleeve with a 9/32" bit so even when the sleeve is up against the restrictor plug, it does not block off those 2 holes. There are other ways you can mod the flow control, you can also replace that spring with a spacer or maybe just shim the spring like the 4g63 guys do. I chose to drill it out because it was the easiest for me to do. I only went about 1/4" deep.


    Step 6) You will need to reassembly the Flow Control Assembly. I put the pieces back together and used a socket and a vice to push the restrictor back in place. Get it as close to its original position as possible.

    Step 7) Put the PS pump back together, refill with fluid, etc...

    Results: The high RPM cutout has now been eliminated.
    dsmcrzy, DogWhistle and ec17pse like this.

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