Rack & Pinion

Discussion in 'Gen 1 & 2 - Suspension, Brake Systems, & Body' started by sperold, Jun 22, 2019.

  1. sperold

    sperold Last to Know Supporting Member

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    90 SHO, currently has non VAPS rack and pinion.

    Can the VAPS rack and pinion unit from a 94 be swapped into this car. Would capping off the VAPS tapped hole be the way to do it?

    The 94 rack and pinion is quite a bit cheaper and there is no core charge, which is handy when you have to ship across a border.

    Looking for advice, and thanks in advance.
     
  2. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    as I recall, they physically swap. However, the vaps rack defaults to high boost, which will be more than your non-vaps rack provided. So, the car will steer too "light" at high speed and be a little twitchy.
     
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  3. NoSlo

    NoSlo GoldMember

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    If you get the VAPS module also (located under the dash above the pedals) and chop its harness and the rack harness plug wiring, you can even wire up the VAPS system to work with little effort. Don't think you'd want one without this.

    After wiring in key power, ground, and the four wires to the rack, the only new input the module needs is from pin #3 on the ECU harness for the VSS signal. You could find a place for the module in the engine compartment so you don't have to go through the firewall.

    To see if it's working, ground pin 13 (for the data link connector you don't need) and for 90 seconds after you start the car the steering assist will go from high to low.

    [​IMG]
    [​IMG]

    (the rack connector pinout is not given, you would have to mind the colors.)


    One note - when reconnecting the pressure and return lines, you can get new teflon seals, which need to be stretched a bit before installation over the threads.
     
    Last edited: Jun 23, 2019
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  4. sperold

    sperold Last to Know Supporting Member

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    Thanks Rubydist.

    In the far distant past, I can remember a discussion (may have been with Terry) where, under a special circumstance, the rack can be fooled into making the default something other than maximum boost.

    I have no idea where this VAPS thing gets it's electrical signal to reduce the boost, but since I have no signal, can I remove the module, cap it off, and carry on?

    The racks are identical otherwise, as I have swapped the on-rack delivery lines from one to the other in the past.

    To be honest, with both systems in my stable, I have never noted the benefits of the VAPS system, but that may be just me.
     
  5. sperold

    sperold Last to Know Supporting Member

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    Thanks NoSlo.

    I am not nearly as proficient in altering wiring and tapping into modules as you are, and I am a little nervous about altering things.

    But great write up and a big help if I get ambitious.
     
  6. NoSlo

    NoSlo GoldMember

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    The racks are different enough that the service manual says a VAPS rack can't be serviced, and must be replaced as a unit, vs. the normal one with service procedures for mechanics. That should indicate there is more to it than just the external servo and pressure fittings, that one shouldn't just plug up the hole.

    The assist valve will likely be at the high assist setting, unless the vehicle got into a crash that disabled the battery before the VAPS could detect the car stopped.

    The previous method is to disable it when driving. From ShoTimes:

    First locate the VAPS module it is on the LH side of the dash to the right of the column. There should be a purple with orange stripe wire going to it. Cut this wire and splice in a switch to turn it on and off. Next here is how it works. According to the manual the motor is infinite in adjustment but there are four basic control modes.

    Idle- this is max boost for parking and Reverse
    20 mph- first adjustment made to lower boost
    40mph - next adjustment made only about 1/3rd boost
    60mph- last adjustment should no boost or very little

    after you have the switch in place get up to the speed you like hold it steady for a few seconds and turn the switch off. Now slow down and see what you think. Once you play with it for a few minutes you will find out what you like. Everybody will be different. My self I want a little more boost at speed because of larger tires and UDP's that slow the P/S pump my car requires a little more effort to turn through the curvy canyons that I drive in. My brothers SHO that is bone stock on the other hand felt better with less boost. So to each his own.

    With the VAPS module and it wired up, one could instead run the self-test, and disable it quickly with a switch when it reaches the desired assist.

    With the VAPS module, and the ability to simulate the VSS signal, one could avoid the driving part also.

    There is no clear documentation of how to manually operate the primary and secondary stepper motor actuators in the servo without a VAPS module. Setting to conflicting positions could cause problems. We know at most from the service manual that when testing the two module wires to either actuator (when parked), one wire should measure above 10V and the other under 2V (which one - not documented). With the hoses disconnected, one can view a spring that moves a bit inside the bottom port when the diagnostic goes through the motions (if you can get a view of that with a borescope, etc)
     
    Last edited: Jun 23, 2019
  7. BaySHO Performance

    BaySHO Performance SHO Member

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    All this talk about VAPS modules is all very well, but this is a '90 that doesn't have a VAPS module.
     
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  8. SHOdded

    SHOdded SHO Member Supporting Member

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    He's swapping a VAPS into a non-VAPS system :)
     
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  9. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    iirc, the 1/3 boost setting is the one you want if its not being adjusted - that's the closest to the non-vaps rack assist level as I recall.
     
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  10. sperold

    sperold Last to Know Supporting Member

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    Wow, a lot of information here.

    My dream of plugging the VAPs port and using the late model rack has been dashed. I had no idea these things were this complicated.

    I see that the pump for my 90 is recommended for 90 and 91s, while the 94 pump is listed for 90 to 95.

    Is there any chance the pump on my 90 is a lower pressure pump? Which might make it more compatible with
    a VAP rack stuck on maximum boost. I am reaching here.
     
  11. NoSlo

    NoSlo GoldMember

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    napacanada.com has non-VAPS non-sho (no stops) rack for a 90, part RAP22214, for $160 looneybux, no core. "call store for availability."
     
    Last edited: Jun 25, 2019
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