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  • Wider Seating

    Ahoy! A bit 'cart before the horse' but I am open to suggestions (other than to lose weight, which I am) on how to increase the width of the drivers seat in a Marina based Roadster.(SWB)
    From the pile of bits recently acquired and previous experience I assume that the limiting factors are the chassis rail and the width of the diff. nose, which in turn gives a wide transmission tunnel ?

    The tunnel seems rather generous and I am of a mind to offset rear axle (Dolomite) to the nearside by moving spring platforms and using a spacer on the offside. together with reducing the width of the tunnel. Another possibility would be to move seat forward as the 50" distance cockpit length is more than adequate for my leg length. What do you think ? (I also have a Cabrio but think the RHS Roadster is the most delightful piece of steel fabrication I have seen since the Forth Bridge !)

  • #2
    A couple of points about your ideas.
    Firstly, if you offset the axle, you will need to consider offsetting the engine. UJ's are not designed to be out of line and you will get unwanted vibrations from the prop shaft.
    The tunnel is overly wide and this can be narrowed but remember the axle will move from side to side under cornering etc. This is just the flex in the system when using cart springs. You will need to add lateral control such as a panhard rod or watts linkage to reduce this. If not then the prop and the diff nose will make contact with the tunnel. You could also consider lowering the tunnel but again, make sure no contact from diff /axle and prop when the axle is at full deflection. If you have the rear bump stops still intact than this will help.
    Mk2 SWB Marina Roadster with a 1800 Fiat Twin Cam engine and 5 speed Abarth gearbox built in 1987
    - I have no idea what I am talking about........ but my advice is always free! -

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    • #3
      As I posted in the 'larger driver' thread about legroom, the shape of roadsters mean it is actually possible to not have seats as such, which gives more legroom and more width (and headroom with hood up) as well. I am 6 foot 5 so I did it for legroom, but this gives more width too. I made a single plywood backboard which spanned the whole width of the car with cutouts to clear the trans tunnel.It sits at a reasonable angle on the rear bulkhead, and pulls forward to get in the 'boot' area. Then I upholstered the board to make a kind of 'bench' seat, and made rectangular cushions which simply sat on the floor to fit between the tunnel and the outside chassis rail. To a casual observer, it looked like two seats joined at the back. Yes it sounds nuts, but with high density foam it actually worked really well and was comfortable. I had this arrangement for several years, later converting my roadster to LWB.
      Last edited by TVRFan; 24-03-23, 12:41 AM. Reason: fix typos

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      • #4
        Offsetting the engine or the axle - UJ will cope perfectly well as long as the two drivelines are parallel - in other words a UJ is fine with an X degrees angle as long as the other UJ has a negative X degrees angle

        My roadster has the engine and gearbox moved 75 mm towards passengers side to make the drivers pedal area larger

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        • #5
          Originally posted by duncan View Post
          Offsetting the engine or the axle - UJ will cope perfectly well as long as the two drivelines are parallel - in other words a UJ is fine with an X degrees angle as long as the other UJ has a negative X degrees angle

          My roadster has the engine and gearbox moved 75 mm towards passengers side to make the drivers pedal area larger
          Watch this video so you understand what is being discussed here. https://www.youtube.com/watch?v=Idk3BVDVHq4
          In the case of the Marina based roadsters, with a live rear axle, you only really have control of the UJ angles in a single plane. As the rear axle moves up and down and side to side and the diff nose also moves up and down during acceleration and deacceleration (leaf spring wind up) you introduce constant changes in UJ angle. Panhard rods, watts linkages and anti tramp bars are often deployed to remove this. Cars with fixed diffs are so much easier to set up...
          Early marinas suffered due to design issues in this area. The result was to introduce a 3 degree angle on the diff nose by adding wedges underneath the axle spring platforms. Eventually the later cars had the platforms welded on at an angle removing the need for the wedge.
          Mk2 SWB Marina Roadster with a 1800 Fiat Twin Cam engine and 5 speed Abarth gearbox built in 1987
          - I have no idea what I am talking about........ but my advice is always free! -

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          • #6
            I would be very concerned about the effect on steering behaviour if you start moving the rear axle off centre. You need to read up on Ackermann angle. In simple terms, with the wheels pointing straight forward, a line drawn from the centre of the rear axle should pass through the steering arm ball joints and the steering swivel axis. That is so that in a corner each inner front wheel turns out more and so follows the rolling radius for that wheel. Moving the rear axle away from this geometry is bound to introduce errors. Link below. Peter.

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            • #7
              Originally posted by jon_cox View Post

              Watch this video so you understand what is being discussed here. https://www.youtube.com/watch?v=Idk3BVDVHq4
              In the case of the Marina based roadsters, with a live rear axle, you only really have control of the UJ angles in a single plane. As the rear axle moves up and down and side to side and the diff nose also moves up and down during acceleration and deacceleration (leaf spring wind up) you introduce constant changes in UJ angle. Panhard rods, watts linkages and anti tramp bars are often deployed to remove this. Cars with fixed diffs are so much easier to set up...
              Early marinas suffered due to design issues in this area. The result was to introduce a 3 degree angle on the diff nose by adding wedges underneath the axle spring platforms. Eventually the later cars had the platforms welded on at an angle removing the need for the wedge.
              Nope all balls
              The axle can move sideways a small amount - a very small amount - and that does not significantly change the angles
              When I got my kit it did have a Panhard rod - the first thing I threw away - it was an abortion!
              Way back when almost all cars had live axles and they all used two UJ's
              If you know what you are doing there should be no problem

              If I was putting a lot of power through that marina axle I could worry a little
              But I would worry a lot more about the poor marina axle than about the tiny changes in the UJ angles

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              • #8
                Thank you all for that. I am happy with prop shaft mechanics, as the guy in the video shows the most important is to keep yokes parallel. (A million years ago I helped build glider launching winches, if you got it wrong the varying paying on speed went up the wire and gave the pilot a very unpleasant ride!) I did mention that as well as offsetting the axle I would add a spacer to the off side which keeps everything symmetrical, I would think braking a bit 'iffy with unequal tracks? This will limit the offset to 30mm.
                I will have to go for seat squabs but would have thought moving forward better to make use of the thinning of the prop shaft tunnel ahead of the diff? I am a little shorter in the leg than most I have found! The 3degree nose down sounds vital and as I am fabricating pads for a Dolomite axle it can be easily incorporated.

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