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Alvis 12/50 - a shock to the wallet
Thu, Feb 28 2013 03:29
| alvis, dampers, shock absorbers, vintage and classic shock absorbers
Over the years I've owned many vintage and post-vintage cars - Rileys, Alvises, British Salmsons and Amilcars and without exception they have all had Andre Hartford friction shock absorbers, or dampers as some people prefer to call them.
From an early age I realised that to hold my own in the pub bragging stakes I would have to be able to claim to be able to adjust them; this is easily done by turning the nut on the shock absorber. "Just tightened them up by a turn old boy and now I can get round Woodcote at…blah, blah"
But firstly, how do they work?
By adjusting the nut you can adjust the friction to get the desired driving "experience".
One thing I had never realised was that these discs should be lubricated…and I don't think I'm alone in that.
Now assuming that the damper doesn't suffer from stiction (defined as the inability to move, because something has stuck - as I grow older I am beginning to experience that…) then a 9 kilo weight as represented by the 18 half-kilo packs of flour balanced on the offside front wing should be sufficient.
Sadly the Alvis was suffering from a lot more than stiction…
Without going into too much detail about my weight let's just say that I had to jump on the nearside shock absorber to get it moving and even then...
So please do lubricate your friction Hartford shock absorbers.
So, assuming you've taken them apart and applied a little grease or 140 grade oil to both the discs and the mounts and reassembled them you'll need to know how to adjust them
Adjusting the Hartfords
If you want to lay claim to some speedy driving such as circuits or just fast touring then the answer used to be to do them up as tight as possible.
On the other hand if you're doing trials then you want as much movement as possible so that when your bouncer bounces, his or her weight actually does something to the car rather than their vertebrae so you slacken them right off.
But science does come into it and there are several pet methods.
Method 1 - push down on the wing and if it bounces back then the dampers need tightening up. If the wing drops off, please don't blame me.
Method 2 - tighten the shock absorbers right up, jack the chassis up and slacken off the shock absorber until the axle just starts to drop. Apparently this is the way the works MG K3s were set up.
Method 3 - as suggested on a VSCC forum. Take the shock absorber off the car, clamp one end of the bracket and from the other end hang a four gallon tin of water. Tighten the nut up until the arm just holds the water. With one UK pint weighing 20 ounces then this would be equivalent to (4 gallons * 8 pints * 20 ounces)/16 = 40 lbs
Method 4 - which sounds a lot easier and more scientific is to get a spring balance of the sort that ensures that you're not going to pay exorbitant amounts to some airline or other. Take the damper off the car, clamp one arm of the shock absorber, attach the spring balance to the other arm and adjust the nut to give between 19 lbs and 25 lbs on the balance.
The actual amount depends on the car and my well-thumbed Alvis manual (The Vintage Alvis Manual by Micky Radford…and most of the contents will apply to other vintage cars as well)
Adjustments are as follows.
Weight of car, using Silentbloc bushes <20 cwt = 16 lbs, 20 - 25 cwt = 19 lbs and 25 - 30 cwt = 23 lbs.
Method 1 - push down on the wing and if it bounces back then the dampers need tightening up. If the wing drops off, please don't blame me.
Method 2 - tighten the shock absorbers right up, jack the chassis up and slacken off the shock absorber until the axle just starts to drop. Apparently this is the way the works MG K3s were set up.
Method 3 - as suggested on a VSCC forum. Take the shock absorber off the car, clamp one end of the bracket and from the other end hang a four gallon tin of water. Tighten the nut up until the arm just holds the water. With one UK pint weighing 20 ounces then this would be equivalent to (4 gallons * 8 pints * 20 ounces)/16 = 40 lbs
Method 4 - which sounds a lot easier and more scientific is to get a spring balance of the sort that ensures that you're not going to pay exorbitant amounts to some airline or other. Take the damper off the car, clamp one arm of the shock absorber, attach the spring balance to the other arm and adjust the nut to give between 19 lbs and 25 lbs on the balance.
The actual amount depends on the car and my well-thumbed Alvis manual (The Vintage Alvis Manual by Micky Radford…and most of the contents will apply to other vintage cars as well)
Adjustments are as follows.
Weight of car, using Silentbloc bushes <20 cwt = 16 lbs, 20 - 25 cwt = 19 lbs and 25 - 30 cwt = 23 lbs.
Annual Maintenance
1. First the Hartfords must have been correctly greased up.
Vintage and Classic Shock Absorbers Ltd who are rebuilding mine are fitting new wooden discs for obvious reasons…
They pressure treat the wooden discs with 140 grade oil before reassembling them.
Michael Brown, the son of Graham who runs the company also had to cut out the old Silentblocs, heat up and reshape one of the arms where there had been too much contact with an immoveable object, replace the centre bushes and all at a very reasonable price. They can always be found at the September Beaulieu Autojumble.
2. Having just collected the rebuilt shock absorbers (February 28, 2013) from Vintage and Classic Shock Absorbers, Michael Brown is suggesting an initial setting of around 30 to 40 lbs because "the roads are better"; Michael has presumably not been to Brighton's Marine Parade for a while...
3. Michael also suggests slackening them off and then splashing thick oil all over them before readjusting them. But do wipe off any excess oil as otherwise it will collect grit which won't do your shock absorber discs any good at all.
I'm pretty certain that if a previous owner had followed this advice then the discs wouldn't have split; mind you some of the centre bushes were either missing or shot-to-pieces, two of the mounting bolts could not be shifted and both the shock absorbers were mounted upside down!
Hopefully this may go part way to curing the dreaded wheel shimmy on the Alvis.
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