Rear Shock Absorbers.

[Mike Costigan]

John Sutton's views on shock absorbers:

https://www.youtube.com/watch?v=eesEiGQng7U

[JonE]

Thanks Mike. John's film seems to suggest the brass going against the steel on the front but its a bit generic and ambiguous. I've always set up my front as Platts diagram with no brass discs....
Surely the drag of the disc - "ferodo" or beech, depends on the user's tightening of the fine thread on the central axis.

ARE people using brass on front to good effect? Or are people completely happy with damping as per Platts? What about feelings on non-beech material?

[cwchrisp]

Could I please check again whether the pins should be really tight within the rubbers or allowing movement as implied by the youtube video?

If the rubber is squashed as hard as possible, then hardly any movement but nipped up as per Woodrow allows some movement.

Also, rubber as supplied with fibre washers either side forces the arm fork apart too much, hence the shortening of the rubber.

Any thoughts please?

Cheers

[Tony Griffiths]

Surely these are dampers - not "shock absorbers". Shock absorption is done by the tyre material, air in the tyre, flex in the wheels, the leaf springs and of course, on an Austin seven, by the chassis flexing. In a sense, I suppose the dampers do some "shock absorbing" by the rise in temperature of the friction disc - but surely their main function is to dampen oscillations of the springs?

[cwchrisp]

As oscillation dampers, the amount of damping is controlled by the coil spring compression on the friction plates and moving brass discs.

That would indicate that the spring pin and the link pin should be allowed some movement within the rubber bushes, albeit not loose, to allow for movement at the other end of the arm?
That would preclude forcing the excess rubber being squashed almost flat against the link and no fibre washers being included, so that the pins are ceased solid within the bushes?

[David Stepney]

The arms don't move that much. The rubber bushes should be tight against both the link and the pin. Its the deflection of the rubber that gives the movement.

[cwchrisp]

Thank you David for that explanation, much appreciated.

My original setup had original beachwood discs (one cut) with faint logo stamped onto surface and lignum vitae forward bush with 1/4 W bolts as link pins. The bolts had worn a thread in the link bushes so was glad to replace them with pegged pins!

No way could I get fibre washers and supplied bushes into the arm fork without some fettling and get spring washer,nuts and locking half nut to fit onto the link pin!

Seems to be stable when driven over bumps and I have a great place to test it on the Campbell Straight at a welknown motor and aircraft museum !

[Dennis Nicholas]

July 38 the link bushes were made with flanged ends so the fibre washers were not required.  + link bolts increased in length.  The nuts are tightened to achieve 1 1/8 inch distance across the rubber flanges.

At least one supplier I have spoken to was not aware of this.

[cwchrisp]

Thank you, Dennis, for that insight into later development of the rear dampers. I guess the squash of the rubber bushes had the effect of making a flange between the rubber and the arm fork pre-1938?

Big improvement in handling, especially on corners where the road surface is rutted!
I can confidently cruise at 30mph, keeping up with traffic, without a dread that the car would leap into the unknown .

So, for the trip to Morton, new links, ferodo discs, coil springs, rubber bushes (cut to length to give squash but allow fibre washers, bores opened out for tight fit on bushes), new link pins, nuts and spring washers. Brass discs allowed to move as per Austin design.

The coil spring tension was obtained by tightening the fine threaded nuts and lock nuts, with no excess thread showing. I couldn't obtain 12 ft/lbs on the nuts without the spring being fully compressed.

Thank you all for your time explaining .

[John Cornforth]

Hi

It's a long time since I refurbished a rear damper, but I seem to remember that unlike the front, the rears are not designed to be adjustable. By that, I mean that the coil spring BU27 is tensioned by cup washers and spring washer plus nut/locknut which are tightened hard down onto the unthreaded "shoulder" of the mushroom-headed bolt BU24. I don't remember them having an especially fine thread, just BSF. One assumes that the pre-set amount of spring compression (not quite coil-bound) gave the correct damping action, at least when everything was new and of original design.

I have always checked both front and rear dampers with a pull on the end of the arm via a spring balance. A pull of 15 to 20 lb to get the arm moving seems to be about right.

At the link end of the arm, the bushes are gripped tight so there is no turning by the bolt shanks inside the rubber. I assume it's best to tighten the nuts with the suspension in the normal position, i.e. weight on the wheels. With suspension motion, the bush will then "squirm" back and forth over a fairly small range of angle.