GT6 MK1 Suspension

[daveygravey]

Does anyone happen to know if the GT6 MK1 'Swing-axle' suspension can be converted to rotoflex. Presumably it needs the lower brackets welded to the chassis for the lower wishbones (available from canleys) but is it possible?

Thanks,

Dave

[JohnD]

Yes it can, you would need a complete set of uprights, radius arms, half shafts and an appropriate spring, etc.   These days, considereingbthe difficulty and cost of sourcing rotaflex donuts, you might do better to consider one of the CV jointed adaptations.

John

[daveygravey]

Thanks John, great to know - Yes CV conversion all the way, in fact I sourced my last one from Nick.

[Nick Jones]

13 minutes ago, daveygravey said:

but is it possible?

Yes.  But the devil is in the detail.  Chassis brackets as John says but you'll also need to move the radius arm brackets on the heelboard - or just add extra ones at the inner position.  Plus some fooling around with brake lines and flexi-hose attachment points.  Probably the biggest PITA is the handbrake cable run as the guides are on the tub on the roto cars.  With CVs you can keep the original run using the chassis guides, but it doesn't work well as the geometry is wrong and you get significant variation with suspension position.  The right solution is guides on the tub - which is hard unless you have the tub off the chassis and a pair of guides cut from a scrap roto tub.

Be warned...... CV conversion parts have got much harder to find.  I can do the UJ/CV adapters but not much else now.  Got lots of lower wishbones if you need any...... quite a few roto shafts too, but no vertical links or radius arms.

[zetecspit]

Nick has hit the nail on the head. The handbrake guides off a rotoflex car are almost impossible to source. But it is possible to make soem using those cut off a non-roto chassis but takes a bit on ingenuity.

I swerved that issue by using MGF rear discs/calipers, and getting the bowden cables shortened, with the cables entering the cabin horizontally through the heel board inline with the handbrake, a little above the transmission tunnel. Handbrake is very effective!

[SpitKseries]

If you choose to do this - so not use the standard lower arm. Make a new one with to connecting points to the frame. That way you can get rid of the radius arm 

[JohnD]

Good point from SpitK, but that demands high skill in fabrication     His look as if they have spherical joints on the inner ends - ?outer? - so you could adjust toe with these, but labourious.

I have fabricated wishbones (on MGF uprights) with Sphericals, but retained the reversed wishbone and turnbuckle raius arm, for adjustment and tuning.

This is the Mk2, made in heavier tube as the Mk1 failed after several racing years.

[SpitKseries]

Word, JohnD. 100% adjustable. As young mr Chapman once said: The more you can adjust, the more you will get it wrong :-)

[Nick Jones]

Well, if you are deviating from the original Triumph design.......

 

[JohnD]

57 minutes ago, SpitKseries said:

Word, JohnD. 100% adjustable. As young mr Chapman once said: The more you can adjust, the more you will get it wrong :-)

He also  said, just add lightnness.  I made Mk1 light, and it broke.

Mind you, that happened to Loti, a lot!

 

Nick, is that yours?    It could really do with an extension to carry the damper more vertical!

John

[Nick Jones]

Chris’s Spit.  It’s the standard damper in the standard position...... I do have extensions on the Vitesse which give a useful increase in damper rate.

FWIW, if it were me with the I’d either:

convert to Roto entirely as Triumph did it apart from a cv conversion

or, build up a pair of long Swing axles shafts with GT6 brakes (dodge the late Mk3 “self adjusters”) and assemble with a swing spring.  A mk 1 GT6 being sufficiently rare and high value to pay some regard to originality.....

[manana]

Hey guys, I’m just new to Sideways, love the technical nature of the Forum.

A few questions if I can. But first, much respect to all the lower wishbone set-ups here, very impressive.

1. I couldn’t find any dimensional data on your modifications. I’m specifically thinking of wishbone lengths, top and bottom if so equipped? (obviously in the interest of camber change)

2. Nick, your son’s set-up looks like a great in-between, that is, keeping the transverse leaf but eliminating the trailing/radius arm. If it’s on the road at this time has he had any issues with toe change on accel/decel-eration? I only wonder because of no cross bracing on the wishbone; truly I don’t know if it would be an issue, so thought I’d ask.

3. SpitKseries, looks like you’ve gone with double wishbones. Looking at your profile you write “IRS(crap)”; I’m guessing that was a previous iteration of your IRS? Any issues now, or elaboration?

Again, very nice stuff here, I’d really appreciate any reflections on the geometry you guys came up with. If it is published elsewhere, very sorry, but would appreciate some direction as to where.

I have gone through BiTurbo228’s stuff, also very cool, but perhaps too much frame work for me.

Thanks.

Steve

[Nick Jones]

On 8/21/2020 at 3:54 PM, manana said:

2. Nick, your son’s set-up looks like a great in-between, that is, keeping the transverse leaf but eliminating the trailing/radius arm. If it’s on the road at this time has he had any issues with toe change on accel/decel-eration? I only wonder because of no cross bracing on the wishbone; truly I don’t know if it would be an issue, so thought I’d ask.

It's on the road.  It's his only car.  No obvious issues with toe change power on / power off / braking.  Drives nicely and has very little camber/track changes so less wriggly on a bumpy road - and settles immediately to pretty much it's normal running height when lowered from the jack.  He did model a few pick-up points before we built it and probably still has the info.

[manana]

Thanks Nick, I figured he knew what he was doing.  

As background, I've got a '78 Spit with a Miata 1.6 and 5-speed, currently running a GT6 3.27 diff and I'm thinking about more power. Due to availability (lack of) of the R160 with 3.54 gears around here, plus the length of the unit (propshaft angle considerations), I'm looking at a shorter R200 fitment, which naturally leads to a complete new suspension.

At this point, I'd say that the thing I envision is most similar to the RoSpit double Wishbone set-up.  5  books later, I'm in the infancy of rear suspension design, and it looks like Chris used about the same wishbone mount locations that I am considering, so I'm happy about that.  As mentioned, I do like what BiTurbo228 did but leery of the cutting and welding and resultant strength (I may not be the welder he is).  Also Markus Bewley mounted his under the frame rails, which I will also consider when I start on the math.  Of course Jango's creation is a work of art, but again, a significant frame modification.

Any considerations / conclusions for mount points would be appreciated.

Thanks again.

Steve