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Bob uk
Unregistered guest
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Posted on Friday, 29 August, 2014 - 06:31:   Edit PostDelete PostView Post/Check IP

There is an endless discussion to be had as to exactly what shock absorbers actually are

3 arguments

The whole suspension including subframes and subframe mountings.

Only the dampers

Or the first one excluding the dampers which is the one I subscribe to.

RR to save academic arguments call them shock/dampers.

Anvil effect.
The mass of the subframes and suspension members absorb shocks.

Rubber also absorbs shocks and has hysteresis

Steel springs also have hysteresis. Multi leaf springs have friction damping from between the leaves.

First dampers were friction discs usually leather. These had high static friction and lower dynamic friction. Which meant they lock on smooth surfaces and gave a jiggly ride. On rough surfaces they would have to be manually tightened. They would often overheat. These were used till 1925 when the hydraulic damper appeared.

The first hydraulic dampers appear in 1906 but not adopted until 1925 when the much cheaper friction damper could no longer cope with much faster speeds.

The first type is a rotary vane or paddle that moves through oil. In the vane is two valves compression and rebound. These are still in use and Honda used them on GP race bikes.

Next came the lever arm. Inside is either two pistons or one double ended piston. These pass oil from one piston to the other through valves.

Main disadvantage is heat dissipation, sometimes the lever arm is also the upper wishbone as on the MGB. Lever arms are considered inferior to telescopic dampers. However they are not that far behind telescopic and can be easily tuned by changing oil viscosity and valve settings.

IMO changing from lever to telescopic is not worth the time or money.

Also a weird one from Armstrong two telescopic dampers in a casing worked by an arm. The advantage being that the compression can be completely different from rebound using very simple valving.

Telescopic dampers used to be twin tube the outer tube used as a reservoir because as the damper rod goes into the damper the volume of the rod displaces oil.Above the oil in the outer tube was an air gap. This sort of damper when worked hard would cavitate and fad. The piston had simple holes and rebound was the same as compression. These lasted until 1960s and we're replaced ny the mono tube.

The mono tube has in the bottom a piston with nitrogen behind it. The piston floats. Above the piston is oil. The other piston is fixed to the damper rod. As the rod volume takes up room the floating piston moves down. The mono tube will work up side down where as most twin tubes won't.

There are many variations on the theme and many types of valves. One type of telescopic damper has groves in the tube wall in the centre position of the damper with allows oil to easily go round the piston so that on smooth roads the car has very little damping. When a big bump happens the piston moves down into where the grooves stop and full damping. It's called the comfort zone.

On race stuff they us damper with adjustable valves. The range is not large so a close to choice has to be made.

Setting dampers.
To set lever arms. Clamp in vice and hang a weight on the end and time the 90 degree movement. The weight is unimportant too much weight will make it move to fast to time. Then when setting the valving a test will show if the improvement sought has happened.

Telescopes need a jig which simply has an arm to hang weights on taking in to account the lever ratio.

(Message approved by david_gore)
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Jan Forrest
Grand Master
Username: got_one

Post Number: 637
Registered: 1-2008
Posted on Friday, 29 August, 2014 - 21:22:   Edit PostDelete PostView Post/Check IP

As you say, Bob; What most of us call 'shock absorbers' are nothing of the sort. Just about every other component of the suspension system, including the tyres, will absorb its share of shocks/thumps coming up from the road surface. The dampers (if fitted ... Have you seen a 60's Yank tank wallowing down the road?) are there to damp out the oscillations in the springing while allowing the tyres to get back in contact with the ground and do what they're supposed to do - push the vehicle and/or steer in the general direction you wish to go.
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Bob uk
Unregistered guest
Posted From:
Posted on Saturday, 30 August, 2014 - 08:22:   Edit PostDelete PostView Post/Check IP

We forgot the seat springs and padding which is maybe a damper. Then it's flesh and bone of one's butt.

I quite like the lever arm because they are easy to repair and reset. The rotary vane type can be designed to out perform a monotone tele. Honda proved that but unfortunately the bikers saw it as old fashioned and a step back.

Incidently the comfort zone grooves in a mono tele. Mean that the ride height must be correct because the grooves only extend a small amount. If the piston is to low then the comfort zone will upset the rebound action and feel like weak dampers.

Comfort zone dampers are fitted to lots of modern cars made in the last 30 years. So all the pub mechanics who lower cars because everybody thinks lower cars handle better are wrong. Also if one needs a modern car to go round corner faster then maybe one is driving too fast. In Dorset 1 young driver is killed each week going too fast round blind bends. 52 sets of family campaigning for safer toads. Which are safe but dangerous at 60 plus. It's pointless saying anything to them because they can't accept that driving fast down Dorset lanes is deadly. Rant over.

Lawrence of Arabia got killed in Dorset riding to fast.
Good film with Peter o'toole.

Mono tube because of the floating piston on nitrogen is sealed and dangerous to take apart. The nitrogen pressure is below 500 psi. And can discharge by drilling as in the manual.

The top is induction welded on.

If my dampers went I would have a go at rebuilding them. How I am not entirely sure.

Motor bike Telescopic forks are infinitely tweakable.

The nitrogen could be air at 100 psi through a Schrader valve and compensate else where say by thicker oil shim the valves. The varieties are endless.

Only problem is putting the damper back together after hack sawing the top off.

The pistons rods are high grade and quality steel. I saw them off old dampers and make other stuff out of them. I made a nifty flower pot hanger for my bathroom out of two damper rods.

(Message approved by david_gore)

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