BATHO
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| posted on 9/5/09 at 10:25 AM |
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SELF CENTRING, with LOWER TRUNNIONS
Hi,
can anybody help, i need more self centring action from a triumph spitfire set up. I know that more castor helps this but does it work in the
same way with lower trunnions? or would this make the steering to heavy and stop the trunnions from working! It's currently set at
CASTOR 3.0 degrees
FRONT NEG CAMBER 0.5 degrees
TOE IN 3mm
195/50/15
FRONT 15 psi
REAR 20 PSI
REAR NEG CAMBER 2.5 degrees
Any help and advise would be great as this is one of my seven failures at sva, i have till september to rectify, clock's ticking!!!
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Dusty
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| posted on 9/5/09 at 11:38 AM |
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I still have an old GT6 manual. This gives shimming the brackets that attach the inboard ends of the wishbones as the method of adjusting castor and
camber. The manual allows 3.5 +/- 1 degree so 4.5 is permissible. The outboard lower wishbone joint is bolt together sandwiching the trunion and lower
shocker mount. If these bolts are slackened while the castor is adjusted, the car then lowered onto its wheels and the bolts re-tightened the trunion
will take up a better angle. I seem to remember the advice to lubricate the trunions at least monthly with oil not grease as they were a common and
dramatic failure point.
15psi seems low for the front. You should get more self centering with 20+ psi or even 30 for the test.
[Edited on 9/5/09 by Dusty]
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BATHO
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| posted on 9/5/09 at 12:14 PM |
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I've been playing about with the tyre pressures and i got a response when i raised the rear to 45 and lowered the front to 15. which to me
indicates that i need to reduce the castor! what do think?
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britishtrident
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| posted on 9/5/09 at 03:33 PM |
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Raising the rear tyre pressures will have no effect on self centering --- 45 psi is really dangerously too high on what I presume is a fairly light
front engined vehicle with wide tyres.
Camber has an effect on self centering because if you set more more negative camber you will increase the king pin inclination which gives natural
true self centering.
Reducing the front tyre pressures will increase the self-aligning torque generated by the tyres increasing self-centering.
The amount of caster used by manufacturers is generally higher on lighter vehicles the setting for the Spitfire IV was 4 degrees + or - 1 degree
Also are the threads on the bottom Triumph upright in good condition ? they suffer badly form corrosion if not regaularly oiled (nb oil not grease)
-- also check you have them fitted to the correct sides.
Also check the damper pad isn't over adjusted ---- it must be set to allow the steering rack to move freely at both the centre positio AND at
full lock.
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BATHO
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| posted on 10/5/09 at 11:20 AM |
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Thanks for your reply, some interesting points there. As for the 45psi i was just experimenting i intend to sort it out properly. The camber setting
in the haynes manual for the triumph spitfire it says 2-4 degrees positive but this just don't seem right or look right on the car. The
trunnions and uprights are new items and are filled with ep90 oil and everything seems free and easy to move. So i am unsure on what to do next?
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