Rotoflex Mk3 GT6 Swing Spring Conversion

[Stratton Jimmer]

Noting that my 77 Sixfire with its swing spring suspension handles a lot better than the early Mk3 GT6, I wonder if anyone has any thoughts or ideas about a swing spring conversion of the latter. It no longer has the rotoflexes as I fitted Classic Driving Developments CV drive shafts. That also cleared the way to change the tall shock absorbers mounted under the wheel arch to diagonal ones mounted to the chassis extensions.

So, has anyone done such a conversion and if so what might be involved? Thanks in anticipation, Jimmer.

[JohnD]

First, "diagonal" dampers suffer from the geometrical disadvantage that their damping effect gets lesser and lesser as they go into bump.   They should be mounted as vertical as possible and if possible in a way that doesn't change from drop to bump.  Hence the universal use of coil-overs for competition cars.

And, Rotoflex donuts were there only to absorb plunge as the suspension moved.  If your CV mod allows that then there is no reason not to fit a swing spring.   But then the swing-spring was invented to alleviate the shortcoming of the swing axle suspension, namely, tuck-under/jack-up, caused by the solid halfshaft.   So fitting it to a car that has plunging halfshafts and a wishbone to locate the wheel is pointless.

JOhn  

[Stratton Jimmer]

Thanks John. I really appreciate your insights.

[Works Spitfires]

We did all this to one of our GT6's twenty years ago. 

Aluminium vertical links, CV conversion, Konis fitted to the 'normal' none rotoflex upper chassis mounts, and as an experiment a swing spring (in conjunction with the larger dimeter anti roll bar). 

Not a scientific test by any means, but I think it handles really well (and I've driven many GT6's!).

I thought I had a picture of the back end before we put the body back on, but I can't find it at the moment, so just a picture of the car

[Ian Foster]

On 11/05/2024 at 13:43, Stratton Jimmer said:

Noting that my 77 Sixfire with its swing spring suspension handles a lot better than the early Mk3 GT6

I'm quite surprised that you say this. In what way do you consider it better and what spec/condition is the early car?

Back in the 80's my friend had a late Mk3 and I found that the rear end 'squirmed' on bumpy roads as the track changed due to the swing axle geometry.

I have had my GT6 Mk2 since 1977 and have now converted it to CV axles with Koni dampers on improved chassis mounts. I have uprated the original spring by adding an additional leaf and now find the handling very neutral, compliant and predicable.

Ian

 

[Pete Lewis]

bunny hops at the back and rear steer is all down to incorrect rear toe settings 

you dont need any silly laser stuff just some common sense and tape measure will work if you 

follow the specifications in the WSM 

and have  look   at  

 

[Stratton Jimmer]

On 13/05/2024 at 08:51, Ian Foster said:

Koni dampers on improved chassis mounts

How are the chassis mounts improved? My 6 being a very early Mk3 should be almost identical to yours. If anything, my rear end is a little on the high side so I don't think an extra spring leaf would help in any way. My Sixfire handles beautifully and corners superbly while the 6 always seems to be wanting to tuck up when trying to corner quickly. I will check the toe in as per Pete's instructions and see what I find.

[Ian Foster]

When I restored my GT6 Mk2 in 2010/11, the Jones Bowler CV conversion was very much the catalyst, as the wheel arch damper mount was the cause of much corrosion in the tub and I didn’t want to replace it like for like.

We actually designed and fabricated a bracket that not only extended out the top damper mounting point to place the damper in a more vertical position, but also corrected the fore and aft alignment that the standard extension brackets not achieve. This is designed to work with Koni 80-1717 adjustable dampers (292mm open/216mm closed). Drawing attached as posted previously and also a photo. Note we actually welded the bracket onto the chassis in the end, but it could be bolted on.

I am very happy with this mod and that the damper loads are transmitted into the chassis as Triumph originally intended.

Ian

GT6-Damper Bracket.pdfGT6-Damper Bracket.pdf 

[Stratton Jimmer]

Thanks Ian, that all makes eminent sense. Seeing this, I suspect that my shock absorbers are angled too far from the vertical. Time to have a rethink!

[Steve P]

I had the same issue with polybushes on the front of my Vitesse getting chewed by the angle of the shock, I have converted the bottom to spherical bearings, doesn`t seem to affect the ride.

Steve