The pilot had been practising circuits and landings in light and variable wind conditions using the 170 degree grass strip. He made an approach for a practice short field landing with full flaps selected at an approach speed of 38 knots (stall speed in that configuration is 25 knots). The pilot said that as he approached the ground the rate of descent was high so he let the airspeed increase to 40 knots to initiate the flare. Rate of descent was still too high so he applied power. The aircraft landed in the three point attitude. The pilot described the landing as heavier than he would have liked. The aircraft did not bounce but ran straight and then started to sag on the right side. The right main gear diagonal brace had broken and the remainder of the structure gradually bent under the weight of the aircraft. The pilot steered the aircraft off the grass to the right and stopped. The broken diagonal brace was inspected and was found to have failed due to overload. The pilot advised that the main landing gear bungees were not the normal ones used on the Auster. They were in fact of a type that is fitted to the Piper Pawnee. The reason for this was that the correct ones for the Auster were not available at one stage so it was common practice to use the type fitted to the Pawnee. The effect was that the main landing gear was much stiffer. This was considered a possible factor in the failure of the diagonal brace. It was also determined that the pilot had not made any short field landings for some time. It was for that reason that he decided to practice a short field landing. This accident was not the subject of an on-scene investigation.