GT6 Roto Rear sping problems. Help!

[chrishawley]

HEEELPPP! Just fitted rear spring to to 1970 GT6.3 with standard roto. Outcome v.bad!

Even with 70kg static load in boot the geometry is all wrong: Road wheels are about 3 inches lower than they should be with about 15 - 20 degrees positive camber. Half shafts are pretty much sitting on the chassis - so way, way, out and not anything near the approx horizontal position the shafts should adopt in the usual static laden condition.

Tried two different GT6 leaf springs, one OE an one repro - no difference.

I don't see what I've done wrong - the rear suspension is entirely unmodded (although car was built up form 'box of bits'). I don't mind using spacer blocks to fine tune the suspension but at the moment but this is way beyond that.

I'd be really grateful for any advice or illumination or theories about how I can proceed.

Many thanks in advance

Chris

 

 

 

[Pete Lewis]

have you rolled the car after spring fitting, the suspension will not sit right if just dropped off the jack 

Pete

[NonMember]

Did you tighten all the suspension bolts while jacked up? If so you've probably locked it solid - you may have some incorrect trunnion bushes or sleeves.

[chrishawley]

Thanks,

I've acted on suggestions as above.

a) Checked for bound up bushes then set car on its wheels with everything still loose. No change. (bushes etc are all genuine Stanpart NOS)

b) Drive round the yard. No change

I'm fortunate to have a 4-post ramp with beam jack so I can look at the suspension behaviour directly. If I support the chassis on the beam and then start jacking one of the hubs the car is lifting off the beam long before the wheel reaches a neutral, approx zero camber, position.

I suppose there'd be nothing to loose by putting in a 1 inch spacer on the diff and see what happens?

Cheers

Chris

 

[Clive]

When fitting a new spring they seem to need a good "workout" to get them to settle. Needs a good load (100kg? ) In the boot, then a drive that involve several  hump-backed bridges so the suspension bottom out or near enough. 

A 1" spacer may work now, but need removing later. 

Remember incorrect tracking can cause the wheels to jack up significantly.

[Gully]

Something sounds wrong there. Have you measured the springs you've fitted eye to eye to check the length is correct? I think the correct dimensions are in the Triumph WSM. I ran a half inch lowering block when my new spring was first on the car, but removed it after around 5000 miles. I could have got away without it from the outset - had nowhere near the camber issue you are describing. 

Gully

[Pete Lewis]

there no spring length data in my wsm , just test loads etc.

question what caused the idea of a spring change , how was the stance before you swapped ??
Pete

[chrishawley]

Thanks. Had it to pieces again yesterday but no 'eureka' moment.

Picking up on  the last two posts together:

The car came to me completely disassembled ('box of bits') so I've no idea what 'before' might have been like. But it came with a Stanpart spring which I assumed was correct for vehicle. My other, new, spring is a repro from stock (Fitchetts orginally) which has the same dimensions, although stiffer.

I don't know of any data on free spring length although but know that I should be aiming for approx 3 degrees negative camber in the static laden condition. Spring rate should be approx 95 lb/inch at the wheel.

Reality check:Given the unknown prior history of the car I've assumed that the suspension config was common across Vitesse, GT6.2 and GT6.3 (except for the spring being 12 leaf on the Vit) so it's not the case of having mixed up parts. Correct?

I'll have another punt at it today and although further suggestions will be much appreciated. Perhaps some photos might help?

 

Cheers

C

 

[Clive]

These may help ID the spring

[chrishawley]

Thanks for the data. Confirms that I have GT6.3 springs as only these had 6 leaves. Will do some further measuring, I'm very open, still, to all suggestions.

Tried an experiment today: Using the original Stanpart spring I removed the top 3 leaves and then fitted it. With about 60kg of batteries in the boot this gives  a spring which is approximately flat, ride height now about an inch too low and positive camber of about 5 - 10 negative. Obviously this is not any kind of definitive solution as all I've really done is reduced the spring rate and load rate by quite a lot. But seems to suggest that the basic geometry is correct although I can't say I've got any final diagnosis.

More suggestions?

Cheers

Chris

 

[Pete Lewis]

has something odd been done with the uprights , drive shafts, wishbones  and such  , just out the box thoughts it may not be the spring as the base problem ??

Pete

[Colin Lindsay]

I was going to ask if the shafts are the correct length, but then it's roto? 

23 hours ago, chrishawley said:

 

I'll have another punt at it today and although further suggestions will be much appreciated. Perhaps some photos might help?

Cheers

C

 

Photos will certainly help; 6 leaf is GT6, as it's roto the halfshaft length won't be the factor and removing leaves will only weaken the spring and it may sit better but it will drive terribly.

Easiest solution is to try another spring, if you could lay your hands on one, to see what difference that makes before you start to change everything else to suit an incorrect spring.

[dougbgt6]

A picture would be good, You have a rotoflex GT6 mk3, however there are non-rotoflex GT6 mk3s, do you have got the right spring? Did you have to assemble it? 

Doug

[trigolf]

This is probably going to sound really daft - but as car was built from box of bits are the correct length dampers fitted to the correct location - i.e. to the inner wheel arch ?

Could the previous owner have possibly converted it to use the after market 'roto'  brackets, which attach to the chassis and use shorter dampers? Have the the dampers have been replaced with the 'correct' for Mk3  spec longer dampers ?

Gav

 

 

[chrishawley]

Thanks for all the suggestions. Plenty of things to check out which I duly did. Have a spare rear suspension so was able to make a visual comparison for bent wishbones etc but all seems ok. Spring is definitely original 6-leaf rotoflex version and arc height is approx correct at 4.5 inches. Shocks mount onto conversion brackets and are correct 'short'  ones for this.

But have had some partial progress, as follows:

a) Refitted spring with 3 top leaves missing. Put 60kg of batteries in boot, lowered car and left overnight.

b) Removed spring, reassembled with all leaves, refit. Jack car on vertical links (rather than chassis), lower to ground then 100kg of batteries in boot.

With this I have a static car with about the right at the back (maybe a tadge high), spring flat (ish) across the transverse and about 0 degrees camber.

So that's an improved situation. But what next? I wonder what happens when I take the 100kg out? Current idea is to leave it standing for a couple of days then take it for a spin round the yard with the weight still in. Or any other better idea!!?

 

Cheers

Chris