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Front Suspension Turret Alignment?


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Hello All,

Before I embark on stripping everything down on my modified Spitfire Mk3, I need to ask a question regarding the front turret location to the chassis.  It is many years since I bolted the turrets to the chassis, hence my query.  As we know there are tapped plates in the chassis to which the turret is bolted (4 off) and a single vertical bolt that holds it down at the inner point.  My question is, with all bolts slackened, is it possible to adjust the rotational angle and then tighten them to give more or less incline when viewed perpendicular to the chassis?  Or do the tapped plates dictate that there is little or no adjustment?  I ask because I have so much more visible caster on the N/S compared to the O/S on my car and I do not wish to have a huge stack of lower wishbone shims to correct this - if it is indeed possible to tweak the turret angle.  The car has been off the road during a very long development/build, everything is new and up-rated and I'd like to get it roughly correct before taking it to the MOT and subsequent all-four wheel alignment.  Anyone out there got a chassis and turret to hand to try this experiment?

Thanks in advance,

Chris

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Hello Pete.

Thanks for your response.  No., I am not talking about that optional shim between the chassis top and turret inner.  And I really do mean caster.  I am talking about turret rotation from the 12 0' clock vertical.  Our chassis is up-swept at front so as to give a built-in amount of caster.  That's why the lower wishbone brackets are different i.e. higher at the front, lower at the rear.  What I am asking is if the turrets have any scope to  increase/decrease that up-swept angle.  Do you see what I mean?  By the way, for any future replies, I have Canley upper wishbones and the Caterham lower ball joint, so stressing vertical link threads and trunnions is not an issue here.

Best Regards,

Chris

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12 hours ago, krissto2015 said:

That's why the lower wishbone brackets are different i.e. higher at the front, lower at the rear.  What I am asking is if the turrets have any scope to  increase/decrease that up-swept angle. 

No, Chris, they're at a fixed angle and not designed to be adjustable as they are - the top shim was to take up any gap left by manufacturing and so strengthen the fit, not to increase any angle. Because of the way the turrets bolt to the chassis - the four lower bolts, two at each side - you'd have to move the brackets and as they take up almost the entire side of the chassis rail there's very very little room to move them anywhere. Technically you could do it - remove the brackets, replace them with new brackets with the holes in different places as required, maybe at a different angle to the chassis rail, and with the rear bracket raised and the front lowered you might gain some change in the angle, but you'd need to really know what you're doing in terms of geometry and handling. No doubt someone, somewhere, has done it before, but it's beyond me!

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So, in conclusion, there is no way of rotating the turret in the plane of the wheel rotation.  This is due to the tight fit of the tapped plates within the chassis brackets, right?  So a turret will always go back in the same fixed position every time.  I will therefore not waste any time stripping my suspension and attempting it.  Lower shims seems the only option here, to get my caster equalised on each side. 

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Krissto,

You have "much more visible caster on the N/S compared to the O/S "?

Have you considered previous crash damage?    An impact may have left the front of the chassis rails distorted.    If you have a flat floor, then careful measurement and triangulation may reveal it.  They are given in the workshop manual and I enclose a copy here:

Reference photo wanted for frame outrigger repair. : Spitfire & GT6 Forum :  Triumph Experience Car Forums : The Triumph Experience

Spitfire Chassis Dimensions

If distortion is present, then a bodyshop with a pulling frame may be able to correct it.

JOhn

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6 minutes ago, JohnD said:

Have you considered previous crash damage?

Hello John,

No way is there any crash damage.  The car has been in the family since I was a mere 8 year old and it has never hit anything!  I suspect that maybe the lower wishbones have bent slightly over the years.  Or perhaps the turrets were never equal when made in 1969.  Since everything else on the car is either new or bespoke, I might buy a new pair of lower wishbones and beef them up while at it.  I'll be hillclimbing it next year (I hope)...

Chris

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Just to clear up any confusion, I have circled in red the view of the turret when looking in from the side.  It can be seen that it is angled somewhere between 12 and 1 o'clock.  It is this angle that we conclude cannot be adjusted even if the bolts are slackened and an attempt made to rotate.  Do we all agree?

image.png.5bb9b87405c470432adff0425c933e1d.png

 

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You are absolutely right about the fixity of the castor, set by the engle to the turret on the chassis rail.   But even kerbing a wheel at speed could bend a rail!  Don't reject a potential solution just because 'it can't be possible'!    Get the plumbline and measuring tape out!

Do you know how to check a chassis' straingtness?      Chassis on axle stands, level above a level floor.    Plumbline from equivalent points each side and make marks on the floor.  Draw  diagonals between them and plot the centre line - does it pass through all the diagonal crosses?  Then the chassis si straight.   Then measure the height of each point - they should match side to side, if not it's twisted.

Goodluck!

John

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2 hours ago, krissto2015 said:

  Lower shims seems the only option here, to get my caster equalised on each side. 

Just a thought - do you have a matched pair of turrets? Later Spitfire versions were lower, only by 1/2 an inch or thereabouts, but if a PO has replaced one with an incorrect version it may cause a visible difference? I think this was done so as to lower the engine and gain bonnet clearance so it may not affect the suspension at all, but it's a thought. 

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My late Father bought the car in 1972, when it was only 3 years old.  The car has been in the family ever since, so they are the same turrets, never changed.  The chassis is the same too, albeit completely refurbished by myself i.e. blast cleaned, 2K painted, internally waxoyled etc.  There is no sign of any damage to the front of the chassis.  I appreciate John's comments that I should check it with plumb lines but that is not easy on a car that is 99.9% fully built... 

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