Cotter Pin 101 (Front Suspension Tech)


   The front suspension on the spridget was from the Austin A30/A35 and while its design may have been common back in the 1950's when it was designed, this isn't really the case these days. One result being that the factory manuals pretty much assumed that the mechanics at the dealer would know how to remove a cotter without too much difficulty. This of course in turn leads to frustrated home mechanics who have little to no idea how to remove them. This type of cotter while uncommon in automotive use, is a lot more common on english bicycles manufactured as early as the 1940's and as late as the 1970's. on bicycles the cotters were used to lock the crank arms to the bottom bracket. Consequently, the best advice out there for removing and refitting these cotter pins is found in books on bicycle repair, and the best website is These cotter pins are made of a soft steel. While one end of it is threaded and when installed always has a nut tightened down on it, this is really more to prevent vibration from rattling it free. Never tighten the nut down on the cotter pin before the pin has been properly installed. The best way to install a cotter is with a cotter press. Enthusiasts of british bicycles have begun manufacturing such devices.

   Unfortunately it appears that these tools wont fit around the lower a arm to get to the cotter. It may be possible to use one with the swivel axle removed and the kingpin lying flat against the a-arm but I haven't tried this.

   The second best way to remove these pins is with a hammer. Of course you may already have thought of that since all three of my repair manuals recommend this method. What is not so often recommended is the following trick. Please do this only after the kingpin and a-arm have been removed from the car as a unit. Soak the cotter in penetrating oil such as liquid wrench or PB-Blast. Find a good solid pipe or bench vice and support the kingpin from the other side of the cotter. Remove the nut and the lock washer. then thread the nut back on the cotter until it is flush with the end of the cotter. Then with a good size hammer, hit the cotter with a good hard blow squarely on the nut. If it doesn't come out in three blows of a hammer, its time to drill.

   When drilling be sure to use a smaller drill bit than the cotter because the cotter has a flat tapered side and if the bit is too large you will hit the hardened fulcrum pin and find that you aren't going anywhere. Next use a center punch to remove the remains.

   When installing always use antiseez and wiggle the kingpin around the fulcrum as you install the cotter to make sure that the fulcrum and kingpin are aligned properly. You can tap the cotter in but don't use too much force because you may cause headaches for yourself later on. A press of some sort would be ideal. You may be able to improvise with a C-clamp and a small 3/8" drive socket. Once the cotter is in, put on the lockwasher and nut and tighten down the nut but don't overdo it. See for more details.

┬ęSeth Jones 6/13/2011