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Thread: Cast turbo rear arm transplant

  1. #1
    Isn't chemistry always nano?
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    Cast turbo rear arm transplant

    It is my understanding that the turbo arms are shorter like the RSR to work with revised pickup points. I can't find any measurments but for a comparison pic in Bruce Andersons book.

    Anyone know if the turbo arms can sub for the steel ones in a 67?

  2. #2
    Senior Member 911quest's Avatar
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    Here is a picture of both back to back... let me if you need any measurements. The SWB arm is flatter if that makes any sense.
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    Tony Proasi

    52 split window coupe

  3. #3
    Isn't chemistry always nano?
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    Wow!

    911quest:
    Thanks! Talk about having stuff lying around...

    I see what you mean by 'flatter'. Makes sense as the torsen tube pickup point is raised on the RSR/turbo. I would assume that wouldn't matter as you would just rotate the spring plate a few more splines to set the chosen ride height. What would be the interesting measurments would be the spring plate mounting point to the inside brake disk as the turbo arm looks 'thicker' and would push the wheel out. My car has spacers with the 4.5" steels, I don't recall how thick. I would think the other important dimension would be the distance from the torsen pivot to say the center of the axel... or whatever would compare total length.

    Looks close though.

    Any thoughts?

  4. #4

    Cast turbo rear arm transplant

    I trust you realize the turbo arms are shorter. The welded torsion bar mounts will have to be lengthened and raised slightly to mount the turbo arms. The turbo supplement to the shop manual gives the exact dimensions. In addition the turbo arms are for the long wheelbase cars so you will need to move your fender opening rearward and use longer springplates.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  5. #5
    Isn't chemistry always nano?
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    logic?

    Well, here was my thinking... and wrong it might be, on many levels

    So the -68 SWB cars differ from the 69- LWB cars since the torsen bar tube was moved ~2-3" towards the front of the car. I assume the wheel base between the models is the same as I have been assured that RS flares would fit my 67 just dandy but for having to weld up the torsen bar hole and move it closer to the wheel. So the wheel base should be identical between the two cars. Thus the LWB arm must be 2-3" longer than the SWB arm. So I saw in B. Andersons book that the turbo arms are 1.9" shorter due to using the RSR locating points that are 0.9" farther appart and 0.4" higher along with being moved back.

    I was getting ready to remove the ones on my car and have them powder coated and came across the picture in BA's book and thought I would ask. No rusting and a bit more robust are good things. Seems like the length is in the ballpark but the critical dimension is that the turbo arms are too wide vs the SWB.

    Am I missing something? Thanks for the replys.

  6. #6
    Senior Member Aldo's Avatar
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    LWB's are longer in wheelbase, hence the name. That is achieved not by moving the torsion bar tube location, but by using longer control arms/swing plates. The torsion bar opening on the fender looks further forward only because the wheel opening is moved rearward.
    Alan Domme
    Austin, TX
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  7. #7
    Moderator Chuck Miller's Avatar
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    Thumbs up

    Allan is of course right...

    Another way to look at it, and what I and others have had a hard time getting a hold of is, that the half shafts (in plan) start in the same position at the transmission in both SWB and LWB. On the SWB 911s where the half shafts end is directly in line from where they started. From '69 on where the half shafts end is different rearward by about 2 3/8 inches...

    Also with that, all LWB 911 CV joints start off and are ALWAYS in rearward 'tension'....... and last for a REALLY LONG time......

    Hope this helps...
    Chuck Miller
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  8. #8
    Isn't chemistry always nano?
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    facts wrong. right conclusion?

    Ok, so torsen tube/bar is a fixed location along with the inner CV joints. LWB and SWB are differnet by 2.375 inches. So the turbo arms being 1.9" shorter than the LWB or 0.475" longer than the SWB arms would move the center of the axle ~0.5" to the rear of the car.

    I think you would be hard pressed to notice that on inspection of the wheel location.

    Do I have this correct now? Thanks again.

  9. #9
    Senior Member Aldo's Avatar
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    Don't forget that the swing plates are longer too. I remember a photo I saw somewhere of a SWB car with LWB rear suspension. It was VERY obvious
    visually.
    Alan Domme
    Austin, TX
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    '16 VW Golf R
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  10. #10
    Senior Member boba's Avatar
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    Quote Originally Posted by 912-2.8 View Post
    Ok, so torsen tube/bar is a fixed location along with the inner CV joints. LWB and SWB are differnet by 2.375 inches. So the turbo arms being 1.9" shorter than the LWB or 0.475" longer than the SWB arms would move the center of the axle ~0.5" to the rear of the car.

    I think you would be hard pressed to notice that on inspection of the wheel location.

    Do I have this correct now? Thanks again.
    No,
    the pick up point for the Turbo trailing arm has been relocated rearward. Here are some pics of the pickup point mods to fit turbo arm to a LWB car. I do not have any photos of the mod on a SWB.
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