Before we had sealed for life bearings, ball joints, universal joints and kingpins we had to grease our nipples. This would force out the old grease and crud allowing new grease in to lubricate them. Neglect causes the old grease to solidify contaminated with water and road dirt leading to corrosion. Remember the old Morris Minor with its sore paw due to kingpin failure? When the grease solidifies new grease cannot push out the old grease.
Most nipples fit a standard grease gun. Keeping gentle pressure on the gun activate the lever until the old grease is forced out and you see new grease coming out of the joints.
If you cannot get any grease in the nipple may be clogged with crud and will need to be cleaned. Clean around the nipple with WD40 and small paint brush and a cloth. Using the correct size spanner remove the nipple carefully. Using a pin prod the little ball bearing that is used to seal nipple. If this will not move then it will need to be soaked in WD40 or petrol.
If this fails you will need to replace it.
While the nipple is out look into the hole and check to see if the grease is still sticky – hopefully it is. If it is solid try easing some out with a pin and squirting in WD40 to try to soften it and hopefully it will move when you re-grease it after putting back in the nipple.
If this does not work you may have to dismantle the joint and clean or replace it if corroded.
Make sure you use the correct type of grease when refitting and/or greasing. When the grease oozes out of the joint do not wipe it off as it will act as a dirt-guard and leave a blob on the nipple as well. If the joint is a sealed type add a few gentle pumps so as not to blow the rubber seal out. In most cases LM2 lithium grease is used but always check your manual. In some cases, as in my Vitesse, gear oil is used to lubricate the kingpins/trunnions.
Tip: When doing my trunnions I put the front of my car up on axel stands, hand-break on and the back wheels chocked. As I grease each nipple I rotate the steering wheel backwards and forwards to help ease the gear oil into place, this may have to be done a few times. When done I smear grease around the joint to keep dirt out and the oil in.
Remember to grease your nipples at least twice a year.