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348 The Steering Rack, an engineering exploration

Discussion in '348/355' started by steved033, May 11, 2019.

  1. steved033

    steved033 Formula 3
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    Apr 12, 2017
    1,489
    Atlanta, GA
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    Steve D.
    For the sheer love of engineering, and the fact that we own an engineering design company where we do product development and reverse engineer some parts, I've taken a "free time" interest in the NLA/obsolete parts, I purchased a bent steering rack for the express interest of disassembly. So if you're curious too, here goes:

    1. The patient arrived safe and sound. Lots of good parts here. all the bushings are in really good shape, the inner rod ends don't have any slop, and the ball joints are in good shape.

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    2. The business end has seen better days.

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    3. It's a TRW 37502289 rack.
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    A 13mm wrench loosens and removes the seal, shims, and spring.

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    5. The same 13mm wrench removes the pinion cover.

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    6. With a firm press, the pinion and bearing come out. There is a bearing on the top side that I did not remove.
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    7. There aren't too many parts that make up the inner workings of the rack. All those shims attest to the precision that a rack is built with. (Your shims may vary)

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    8. What does it take to get the inner tie rods off? Are they left thread? Do you have to cut through the stake more? (there's no pic)

    9. The rack so so bent that even if I did the the ITRs off, it wasn't going to come out, so I cut it.

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    10. Now the moment you've all been waiting for: The end bushing was intact, and CANNOT be removed without disassembling the rack.

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    more to come....
     
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  2. steved033

    steved033 Formula 3
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    Apr 12, 2017
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    Steve D.
  3. Qavion

    Qavion Formula 3

    Feb 20, 2015
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    Ian Riddell
    Are those spiral gouges in the pinion normal? (7th photo)
     
  4. steved033

    steved033 Formula 3
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    Apr 12, 2017
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    Yes, it's the runout from the helical cut. I'm honestly not sure if the helical gear is cut first then machined off to make the bearing surface, or if the gear is cut after that bearing ID is cut

    sjd
     
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  5. Ferrarium

    Ferrarium Formula Junior
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    Jul 28, 2018
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    Eric
    Those flats on the bushing allow air to pass in and out or the boot would want to balloon or cavitate.
     
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  6. QSA

    QSA Karting

    Jun 3, 2011
    135
    Kingwood, TX
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    Quinn
    Curious to how rack rebuilding shops replace this bushing. Anything off the shelf, or do they all have to be custom made?
     
  7. Ferrarium

    Ferrarium Formula Junior
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    Jul 28, 2018
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    Eric
    Round sleeve with nylon insert I see most often. Aldo solid Delrin. I made them in Delrin and aluminum. As far as I know shops make them too. Aluminum would be optimal, no flex and softer than the rack and wont disintegrate like the nylon one does. There is places that sell the original bushing though, I have actually seen them.
     
  8. steved033

    steved033 Formula 3
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    Apr 12, 2017
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    Steve D.
  9. Ferrarium

    Ferrarium Formula Junior
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    Jul 28, 2018
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    Eric
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  10. steved033

    steved033 Formula 3
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    Apr 12, 2017
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  11. Ferrarium

    Ferrarium Formula Junior
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    Jul 28, 2018
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    Ahhh good I did not see that, I recall the ID needs to be 23 mm? It would be good to track down a cross ref part number. Most places use a round sleeve with a set screw when rebuilding.

    I'm dead sure if you did a run folks here would buy them and stick em in the parts bin for later. :)

    What did you measure as OD and ID? I recall 30.5 OD and 23 ID?
     
  12. steved033

    steved033 Formula 3
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    Apr 12, 2017
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    Yes, the ID is 23mm.

    The part number on the bushing itself seems to be 36019804

    The round sleeve with screw is great because you don't have to take the rack completely apart to slide the rack clear of the bushing.

    sjd
     
  13. Ferrarium

    Ferrarium Formula Junior
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    Jul 28, 2018
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    When I did mine the bushing was gone it had disintegrated. I had nothing to look at. An aluminum 2 piece with 2 set screws could be used without taking anything apart. Just clam shell together and pound it in then set screw it. I have a post out here where I did mine made Delrin and aluminum with the cad.

    I like the idea of flat spotting the bushing instead of machining grooves in for air flow like I did, mine was a sleeve. If I ever did it again I would definitely use a 2 part 6061 sleeve.
     
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  14. redwedge

    redwedge Karting

    Sep 30, 2012
    224
    London
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    Steve C
    Interesting - Quaife makes a quick rack kit for the X1/9 - I wonder if the parts would fit a 355? (given the 355 manual rack is, I believe, a 348 rack)
     
  15. QSA

    QSA Karting

    Jun 3, 2011
    135
    Kingwood, TX
    Full Name:
    Quinn
    ID 23 mm
    OD 30.5 mm - is that the width of those tabs, or the body? Do you have both diameters?
    Length?
     

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