What does the grease do?
Grease is oil held in place by a thickener. The thickener, usually a metallic soap or a synthetic filler, keeps the oil from moving away from the point where it is needed. Most of the grease's working properties come from its base oil, so two greases with the same thickener can behave differently.
Grease does two jobs in a rod end. It lubricates the sliding surfaces, so the metal surfaces do not touch. It also fills the space around the ball, which keeps out some dirt and water while the grease is in place. Once the grease has been pushed out or washed away, the second job stops as well as the first.
Consistency is graded by an NLGI number. The maker names the grade for the joint, and you should use that grade, not one chosen only by price. The temperature range must cover the service temperature of the joint. Where the temperature is high, a greaseable rod end with a high-temperature grease is usually the route, because a PTFE liner has its own upper limit (Q1-04).
How does the grease get to the sliding surface?
Through the lubrication network. Greased rod ends usually have lube holes and grooves, plus a fitting, so grease can pass from the outside to the ball and race. Relubrication can be done through the housing or through the pin, depending on the design. On medium and large sizes, transverse grooves are cut into the race blank, so the grease reaches more of the sliding surface. The ball must also be fed, not only the outside of the race.
This is why a blocked or badly placed fitting is a common cause of greasing that does nothing. The grease goes in and stops at the first obstruction, and the sliding surface gets none.
How often should a rod end be greased?
There is no single figure. The interval depends on four things, and each one shortens it when it rises:
- Movement. More cycles and more angle mean more wear and more grease consumed.
- Load. A high load squeezes the film out faster.
- Temperature. Heat thins the grease and speeds oxidation.
- Exposure. Dirt and water remove grease and bring in abrasive particles.
The interval must reflect these conditions, and no fixed number fits every joint. A greaseable rod end is a good choice only if it is really serviced regularly. An interval that is never kept is the same as a joint that was never greased.
For a new installation, set the first interval conservatively, check the joint at the first service, and adjust it from what you find. Record what you see at each service, including the state of the grease and any play, so the next interval is based on the joint's own history.
How do you grease the joint properly?
Clean the fitting first, so that dirt is not pushed into the joint. Use a hand gun where you can, because it gives you more control over how much grease goes in than a pressure gun does.
Pump slowly and, where it is safe, move the joint through its angle while you pump, so the grease reaches the whole sliding surface and not only one side. Stop when fresh grease appears at the joint, or when the joint feels free. Wipe the fitting and the area round it clean afterwards, so the next dirt is not drawn in.
After any washdown, regrease. Water or detergent can strip the grease, leaving the rod end under-lubricated for much of its life. If the washdown is routine and the regrease cannot be done every time, a correctly rated PTFE-lined rod end is the more reliable choice. The choice itself is covered in Q1-04.
Which loads change the grease routine?
Reversing loads help a greased joint, because each reversal draws grease back into the loaded area instead of squeezing it out. Without reversal, a grease-lubricated bearing tends to gall unless lubrication is very frequent. With a load in one direction, the grease is squeezed out of the loaded zone quickly. NHBB's advice for that case is a dry film, with PTFE worth investigating.
So a greaseable rod end under a one-way heavy load needs either a dry-film or PTFE construction, or a much shorter interval. Choose the route when you design the joint, not after the rod end has galled.
What about the greased joint and the maintenance-free one?
The choice between a greased joint and a PTFE-lined one turns on access, washdown, load, dirt and temperature, and it is set out in Q1-04. Once a greased construction has been chosen, the rules in this article apply: reachable fitting, approved grease, an interval set by the conditions, and a regrease after every wash.
How does a vehicle change when and where you grease a rod end?
The grease rules hold, but the vehicle changes what "exposure" means in the list above. Water crossings and pressure washing strip grease from the joint, and the next drive pulls in dust while the joint is under-lubricated. So the routine is tied to events, not to the calendar: regrease after a wash or a deep crossing, and set the interval from hours of rough running as well as time, then correct it from what you find at each inspection.
Two layout points are specific to vehicles. First, the grease fitting sticks out of the housing or the pin, and on a link that tilts through a long travel it can be the first thing to touch the bracket. Check that it clears at both ends of the travel, and if it does not, turn the housing or use a different fitting position before the angle margin is lost (Q1-06). Second, links under the car or behind a panel are hard to reach, and a fitting that cannot be reached is a joint that does not get greased; decide before the build whether it can be serviced in place.
A locating link that takes braking, traction and cornering loads sees the load reverse, and that helps draw grease back into the loaded zone. A pivot that mainly carries the vehicle's weight, or a link loaded one way such as some towing or winching arrangements, does not get that help and needs the dry-film or PTFE route, or a shorter interval. Service intervals for steering and suspension links are set by the vehicle's designer or the builder, not by this article. See off-road rod ends for the application.