Setting-up the suspension

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Hal Mercier
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Setting-up the suspension

Post by Hal Mercier »

I decided to check the shock mounting points to see if they had been correctly set when the car was built as it seemed I recalled it had an odd 'stance'.

Pity this wasn't done when we built it for racing, it might not have been quite so prone to spinning.....but that was mainly oil on the rear left tyre.

I'd asked Tim Duffee if the early cars came with the shock mounts fitted, and it seems that not only were they not fitted, the holes weren't pre-drilled either, and as Tim said "a lot of people got it wrong".

Now this should, of course, be done on a proper jig, or a giant engineering table.

Lacking one, I used the smooth concrete floor of the barn, which measures as totally horizontal and flat.

I used two equal length supports under the rear cross member, which was checked for horizontality. I had two more identical supports under the front end of the sill beams. This is where it could get confusing, as if the sills aren't exactly on level, on the same plane end to end and side to side and diagonally, you need to forget anything on the body as a datum point, and use just the cross member and support the front of the car in the middle, between the ends of the wishbones.

Once it's supported on these three points, measure from the table or floor to establish the correct heights for the tops of the front shock supports, and the same at the back.

In Dolores' case, front left support was about 13mm too high on the shell, and the rear left was 6mm too high, so the left side of the car was 'drooping' and unequally at that.

Pointless messing about with spring platform height if this hasn't been done properly first.

I remember when I first got this car in 1980, the rear end was way too low, to the point it used to eat Rotoflexes due to the massive deflection in the driveshafts.

Dolores on old shock mounts, showing negative camber at the rear, in 1983. I'm unclear as to how this is even possible, given the suspension design, the trailing arm should surely hold the wheel in its original setting, as it's dictated by the cross member and arm pickup points.

Image

I made new rear shock supports, the originals were very weedy looking and corroded. I used the existing holes for the rear supports.....assuming they were pre-drilled by Davrian!

On the question of camber at the front, I assume the way to alter it is to raise or lower the central wishbone pivot points? By lowering them ie spacing the pickup point from the shell, negative camber should be produced.

Nugget, have you noticed this on your car? You do seem to have a lot of negative on the front....judging by this photo at Combe...

Image

...compared with this car, cornering at Llandow...

Image
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graham
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Re: Setting-up the suspension

Post by graham »

Regarding question above, about negative camber on the front.
Other than modifying the central pivot points as mentioned above, you can also do the following:

I'm not trying to teach "grannie to suck eggs", as I'm sure a lot of people already know the tried and trusted method, but thought I'd just mention it here for any newbies.

Negative camber is usually easily created as soon as you fit shorter springs, but you usually end up with too much, and need to square the angle up a bit to reduce or remove it.
The stub axle can be modified and shimmed to do this.
1. At the boss at the end of the stub axle, where the vertical bolt passes through it and the wishbone.
2. File down the top of the boss.
3. Whatever is removed from the top....shim the same amount at the bottom.

Or just file and shim opposite side if trying to remove positive camber.

Cheers
Graham
Heathrow Area Centre Organsiser (The Imp Club)
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Nugget
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Re: Setting-up the suspension

Post by Nugget »

Yep, I'm definitely running a lot of -ve camber, and I was going to do the mod over the winter, having said that I did this mod on my old Imp (first car) 20 odd years ago after lowering it on Montes, and if my memory serves me right it didn't correct it much, I'll do it anyway to eliminate as much as possible.

Incidentally, although my Dav has too much -ve it did handle bloody well on track, but then again I didn't manage to get it on the limit so I don't know what the characteristics are at the point of the car loosing grip.

Interesting reading about setting the heights Hal, mine has developed a bit of Near Side to Off Side tilt, it was a bit of a punt went I built the car for the initial settings of the coil overs basically I made sure the drive shafts were horizontal on the rear then leveled the front to the rear and made sure the spring heights were correct right to left, this resulted in horizontal front wishbones and reasonable ground clearance (fortunately just enough to get it on the brake rollers)

I'm going to have a look to see why they car has dropped on the drivers side this weekend, I have a sneaking suspicion that it may be that as it hasn't had an adult passenger (weight) in the passenger side for any significant amount of time since build, that it may be that the drivers side has bedded in more than the passengers side, any more thoughts on this? I know my Ginetta dropped a fair bit after the first few drives.
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Hal Mercier
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Re: Setting-up the suspension

Post by Hal Mercier »

Graham,

Thanks for that, actually I'd not heard about the file/shim idea!

Fitting shorter springs will indeed have an effect on camber, but for a given spring length, the camber can be altered easily by lowering the central pivots for more negative.

Nuggett, That sounds very odd, frankly....almost as if you have stiction in the shocks, worse on the right side, so the springs aren't returning to fully extended. Either that or there's a problem with the springs themselves....can you remove them from the shocks to verify the free lengths...and compare to the other side?

I've removed the rear shock support brackets as the tops are at entirely the wrong angle, which does the AVO shocks no good at all.....tending to put the shaft into flex.

This is, I think, because when they were made up, I thought the shock ends would fit further back on the arms....
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Nugget
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Re: Setting-up the suspension

Post by Nugget »

I checked mine today, distances from the rear cross member to the floor are within 5mm, the discrepancy appears to be with the rear body (clam) which makes the car look lower on the drivers side, it's very hard to tell as the R/H has the cut out for the exhaust and has a very different sweep up to the rear lower corner compared to the L/H
robfromsomerset
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Re: Setting-up the suspension

Post by robfromsomerset »

 Buy Hillman Imps: Tuning, Overhaul, Servicing by Tim Millington (ISBN: 9781870519410
Millington was ex comps dept at roots/crysler/talbot/Peugeot. ..and it's a good reference for mild/road car tuning and covers the stub axle mods in detail. Davrian axles don't have a box here so are easier to shim.

Tyre manufactures will recommend max camber settings...too much will reduce the grip under braking. Due to the swing axle system camber is increased significantly under compression, exagerating this effect. My old imp was compromised at >3° -ve static, though may have less anti-dive dialled in compared to a Davrian.
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Hal Mercier
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Re: Setting-up the suspension

Post by Hal Mercier »

Rob, do you mean negative camber is increased under braking?
The way Nugget's car seems to be running on the inner edges of the tyres,already, that would not help!

I remember at one point for some reason Dolores was running a lot of negative at the front, but it turned out to be because there was massive toe-out....I don't recall how this happened, but with toe-out, this suspension system develops a lot of negative.
It was so bad I started to hear tyre squeal on certain road surfaces while moving in a straight line! When I looked at the tyres, they were down to the steel bands on the inner part of the tread.
Last edited by Hal Mercier on Sat Nov 29, 2014 9:24 pm, edited 1 time in total.
robfromsomerset
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Re: Setting-up the suspension

Post by robfromsomerset »

Yes the camber becomes more negative under heavy braking
davrian6140
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Re: Setting-up the suspension

Post by davrian6140 »

Hal, I run 1/2 degree neg and 1/32 toe in on the front, but the swinging
arms are made by tim duffee and very easy to change settings.
Dave
Dave Cooper
davrian6140

Mk6a DAV 373H
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Hal Mercier
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Re: Setting-up the suspension

Post by Hal Mercier »

Hi Dave,

I had a look at the pix of your build on Photobucket...very impressive job. Lots of attention to detail.

Which electric waterpump did you use?

I have Tim D suspension arms on the Mk 7 but Imp on the Mk 4.
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