mistergrumpy
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| posted on 21/12/08 at 04:14 PM |
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Self Centring (Sorry)
Got a bit of a sneaky first drive this morning and the sodding thing doesn't want to self centre  I took a wheel off and ran at it with a
grinder in rage and tried to pull the top wishbone brackets off before I realised that it wouldn't work without removing the sidepanels and
other stuff.
When I'd calmed down I had a look from the top with a plumb line and the top balljoint is about 17-20mm behind the bottom one. What gives?
Could anything else affect the centring? What about the top bones being a bit too tight in the brackets? They don't yet fall freely and will
stick and hold the front of the car down or up if you understand me. I'm confident that'll change once they wear and I've shown them
a bit of loving..with the hammer 
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BenB
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| posted on 21/12/08 at 04:18 PM |
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What PSI are your tyres at?
Pumping them up nice and high for SVA is an old trick but can work.....
The self-centering might improve a little as everything frees up a bit with use.
Otherwise the valve-springs-under-the-steering-rack-gaitors trick gives a bit of self-centering....
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David Jenkins
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| posted on 21/12/08 at 04:19 PM |
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Your castor angle should be fairly close to OK, so two things come to mind:
1. Steering joints stiff - I presume that they're brand new, so maybe they're just a bit tight.
2. Steering rack stiff - how easy is it to push the track rod in and out of the rack, with everything disconnected? Leave the steering shaft attached
when you try this.
If either of those are resisting the self-centering forces then it ain't going to happen!
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rusty nuts
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| posted on 21/12/08 at 04:23 PM |
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If you have Polybushes they may not get a lot looser mine didn't . In the end I stripped all of the suspension arms and skimmed about
0.030" off the outer end of all of my bushes. Some crush tubes are too short as supplied and no amount of use will ease the movement of the arms
. Did you use new ball joints and steering rack? I found my steering did get lighter after a few miles which also helped with self centering. Had to
drive about 60 miles to SVA which helped . IIRC 22mm seems to be what your looking for as regards top ball joint being behind lower joint. Have you
any adjustment in your wishbone mounting brackets ? IE the brackets wider than the wishbones?
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mistergrumpy
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| posted on 21/12/08 at 04:41 PM |
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Using new balljoints, Ebay steering rack which isn't too stiff and yes the bushes seem fractionally wider than the crush tube. There is no play
in the brackets, the bones are right up to the outsides due to an early mistake in buying Locost bones instead of Sierra bones.
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coozer
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| posted on 21/12/08 at 04:51 PM |
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Mine wouldn't self centre when I first built. For SVA I pumped the fronts up to 40psi and dialed in 2mm toe out. That gave it a little bit,
enough for the test.
Since then I've had MNR set the front and back suspension up correctly and it self centres real good now.
1972 V8 Jago
1980 Z750
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mistergrumpy
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| posted on 21/12/08 at 04:56 PM |
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I'm thinking that it's summat like the problem you had Coozer. Not set up properly and thus affecting it somehow. I just can't
understand it otherwise.
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maximill666
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| posted on 21/12/08 at 05:00 PM |
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quote:
Originally posted by mistergrumpy
Using new balljoints, Ebay steering rack which isn't too stiff and yes the bushes seem fractionally wider than the crush tube. There is no play
in the brackets, the bones are right up to the outsides due to an early mistake in buying Locost bones instead of Sierra bones.
When you say the rack isnt too stiff, does it move freely with only the slightest of pressure required to move it when the wheels are jacked up off
the ground, if you push one of the wheels/tyres to turn with one finger it should move nice & easy?
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mistergrumpy
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| posted on 21/12/08 at 05:03 PM |
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No the rack isn't that free to move. I'd have thought that a little too loose? Should I grease it some?
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maximill666
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| posted on 21/12/08 at 05:08 PM |
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Is it a sierra rack?
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mistergrumpy
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| posted on 21/12/08 at 05:11 PM |
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Nah MK.2 Escort
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maximill666
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| posted on 21/12/08 at 05:17 PM |
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Not sure about the escort rack, but I had a problem with mine self centering, all the geometry was set accurately but it still would not self centre,
in the end it turned out that the tensioner in the rack was adjusted up too tight. I had a nightmare of a time getting the slipper plug out to adjust
though.
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mistergrumpy
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| posted on 21/12/08 at 06:48 PM |
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I've just had a look at the rack. It'll turn easily enough with the steering wheel but with it jacked up, trying to move the rack with the
wheels is hard work and if I disconnect the rack and try to move the rod ends by hand it just won't budge.
I've opened the bolts at the pinion and there's a spring pressing down on a plastic drum that presses onto the rack. This is all bunged up
with tar like old grease so I'll give give it a bit of a clean see if this helps.
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maximill666
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| posted on 21/12/08 at 06:58 PM |
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The rack should be very free to move with only the slightest of resistance if you have disconnected the track rod ends & column.
The plastic drum & spring is what gives the resistance & stops the play in the rack.
[Edited on 21/12/08 by maximill666]
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MikeRJ
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| posted on 21/12/08 at 07:46 PM |
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Have you set the toe angle correctly? Do you have equal camber/castor on both sides of the car?
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3GEComponents
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| posted on 21/12/08 at 08:09 PM |
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Are you using offset mushroom inserts?
The big problem with the Sierra upright is that when you draw a line through the ball joint centres, it misses the the axle centre line, the offset
inserts re align these 3 points, they're not to give you any other type of adjustment, making self centring easier to acheive.
Regards
John
[Edited on 21/12/08 by 3GEComponents]
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mistergrumpy
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| posted on 21/12/08 at 11:03 PM |
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Hmm. No I'll admit that the wheels are set dead straight and upright by eye only, so no toe.
I have normal centricular(?) mushrooms. As I've read several times though, the offset mushrooms make absolutelt no effect to caster angle? It
maybe affects Kpi (though I don't know what this is).
I'm going to try cleaning and greasing the rack then introducing some toe to see if that works. If I'm honest I've written off the
affect of toe.
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mark chandler
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| posted on 22/12/08 at 12:17 AM |
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I had to back off the preload on my new rack to get it to self centre quickly, a quick dig about should sort things out if its full of gunge.
Use light grease, some people just use EP90 oil.
Regards Mark
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procomp
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| posted on 22/12/08 at 08:26 AM |
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Hi
You will need to free off all the bushing on the suspension also to get self centering to have a chance of working.
Remove the wishbones square the brackets up. Get the inner crush sleeves so they are a nice fit in the bracket. Then machine all the plastic bushes so
that when assembled they are 10-15 tho narrower than the inner sleeve. The wishbones should be able to move freely.
Cheers Matt
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mad-butcher
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| posted on 22/12/08 at 11:20 AM |
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not being funny, but when you say you took it out for a spin it wouldn't self centre, do you mean when you turned the corner the steering wheel
didn't come back as in a production car also when turning in a circle on full lock the turning circle didn't get any bigger without a
physical input from you, or did you mean it wouldn't go in a straight line and wanted to turn either left or right, as the two things are totaly
different, one is self centering the other is tracking, sorry if my question is offensive but I don't know your mechanical background,
Tony
[Edited on 22/12/08 by mad-butcher]
[Edited on 22/12/08 by mad-butcher]
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mistergrumpy
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| posted on 22/12/08 at 11:31 AM |
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Its alright mate all suggestions help. What I meant is that when I turned the corner and then let go of the steering wheel, the road wheels
wouldn't then bring themselves back straight again as they do on a production car.
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mad-butcher
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| posted on 22/12/08 at 11:40 AM |
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I think you'll find that is normal, mine needs a light input to get it back certainly no chance of using the palm of my hand as with a power
assisted jobbie, I was looking for the same as you untill it was explained to me that at the SVA they put it on full lock and expect the turning
circle to increase with no input by the driver. then it all became clear why people fit springs to the rack,
Tony
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mistergrumpy
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| posted on 22/12/08 at 11:47 AM |
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Ah right. I thought they just drove it around the corner and wanted the steering wheel to just come straight back into alignment. So they're
just looking for any degree of self centring rather than a proscribed amount. I think I'll still clean up the rack and get that old grease out
but that helps, thanks.
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mad-butcher
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| posted on 22/12/08 at 11:55 AM |
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This came from a u2u from jabbahutt when I asked him about self centering at his recent test at shrewsbury.
The spiral wrap came from car builder solutions, if you order it reasonably early in the day it should be with you by the next day.
Just the fronts were spiral wrapped.
For self centring he just drove it round the test centre at about 30mph and saw if the wheel triedd to straighten whilst turning.
mine was borderline but he went by the book which says shows signs of or something like that.
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maximill666
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| posted on 22/12/08 at 01:01 PM |
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I had my SVA at Chadderton in Manchester a couple of months ago. The examiner drove around the car park at about 20-30 mph and turned the wheel from
left to right, looking for a degree of self centering.
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