I remember very well working in a variety of shops and even service stations in the old, old days when a customer would come in when it was raining and have a rag or sock wrapped around a wiper blade because it fell off the arm when he used the wipers during a downpour. As ridiculous as it seems, it happened -- and it still happens. Wipers usually come in pairs on a vehicle, although there have been vehicles with three wipers. The fact is that on any front-facing windshield when you replace one wiper, you should at least thoroughly inspect the other one and attempt to determine its age and serviceability. If its age is unknown or if it looks as old as the one you’re replacing and you’re replacing that one because it has a problem of not cleaning the windshield correctly, or is partially torn away from its mount, it would behoove you to recommend that both wipers be replaced.

It’s extremely common today to find wipers on the right and left side of the vehicle that are different lengths. Therefore, the old days of two-pack or twin-pack wiper blades are long gone. Also, when you replace wipers, if you’re using any type of premium product with anti-streak improved design, improved cleaning and anti-wind-lift, you should really put them on in pairs, as you want both wipers to operate with the same level of efficiency.

Wipers are seldom inspected thoroughly in some shops. At times, technicians don’t take the time to do it, nor do they take the time to spray some water on the windshield and turn the wipers on to see how cleanly they work or how well they clean. It’s a sure bet that if one side needs replacement the other side is not far behind, unless it was previously replaced as a single item. Furthermore, with the growing popularity of SUVs on the road today, don’t forget to get a good look at the rear wiper blade, as well.  Often, those blades have been damaged by automatic car washes.  And sometimes, the front blades get attention while the rubber isa literally hanging off on the rear blade.

Other items that may carry a heavy recommendation for replacement in pairs are headlights, if anything but the same type of bulb is installed. If you buy a premium type of bulb with a different light intensity, output or shade of output, it is extremely irritating to everyone but you if you don’t have a pair of headlights operating at the same amount of brightness. We all remember the “blue” headlight issue of a few years back and how irritating they were. Recently, a Honda Fit, which isn’t too bad of a job to put a headlight in, came in and the customer requested that a single headlight be installed because only one had burned out. In addition, he had heard of a new type of headlight that was brighter and would give better visibility in fog so that is what he wanted. The fact is, however, that if this new headlight had been installed, the vehicle would have appeared as a Cyclops or almost a Cyclops-and-a-half because of the difference in the intensity of light coming from each headlight. Would he have noticed it when driving it? No. Would he have noticed it if the car was being driven behind him or coming toward him? Yes. The shop actually refused to install a headlight that differed from the one that had previously been installed unless it and another matching headlight were installed as a pair. The customer didn’t seem to understand and settled for the installation of the same type of headlight that was there from the factory.

Brakes, shocks, struts, springs and many other parts that operate on left front-right front or front and rear are balanced and operate in unison or partnership with each other. Putting only one shock or strut on a vehicle is outright foolish, particularly if the other unit is anything but brand new, as there will be a definite difference in damping which could, depending upon the specific vehicle, lend itself to some handling issues. Various regulatory agencies and consumer groups say that nothing should be replaced unless it’s absolutely necessary. This may be true, but the fact is that if you have mechanical components that operate in unison or in partnership with other parts, having only one side serviced can be a bit foolhardy. Regulatory agencies may say you sold a part that wasn’t absolutely necessary. Yes, this is true, but common sense tells you that if you have something like a leaky wheel cylinder on one side of the vehicle and you replace only that side, odds are that the other side will soon leak and have the same issue the vehicle initially came in with.

It is my understanding that you can have a “It’s-my-shop’s-policy” type of procedure and this will assist you in eliminating any issues as to why you recommend things be done in pairs.** The strange thing is that if you have a vehicle with a left front brake hanging up because of a caliper-slide issue you would fix the left-front brake and replace the left-front friction. You would normally also put new pads on the right front. Pads do not come per wheel. They come per axle, being front-to-rear. There are never any problems with installing things that way.

I recently was in a shop where there was a customer who needed a new heater hose on his vehicle. It was a considerably older vehicle and the hose had failed because of age and deterioration. The shop quoted an amount for replacement of the bad hose as well as for the other heater hoses on the vehicle. A careful visual inspection had revealed that every hose on the cooling system was ready to fail, so they quoted the job as it should be done in order to keep the vehicle running and prevent an almost immediate comeback. The customer was extremely irritated because he understood that only one hose was physically leaking. The fact is that if only the one hose was replaced the pressure in the system would then find the next-weakest point. In this case, the customer refused to have anything but the leaky hose replaced and the shop’s only option was to return the vehicle to an immediate-driving condition by refilling the cooling system and firing the customer. They refused to replace the one hose. They chose not to do anything unless they did the job correctly.

This article could easily have been titled “Common Sense In Automotive Repair” rather than “Replacing Parts In Pairs.” Your experience, your skill, your knowledge and a high degree of common sense should be the driving factor. Your shop and your reputation are on the line for every repair that leaves your door. Do parts replacement in pairs when you know it’s right. Don’t buy into the “I can’t afford it” or “I’m going to sell the car tomorrow” mentality or story that you constantly hear.

** Editor's note: Ron is correct in noting that some regulatory agencies support “shop policy” recommendations for replacing related items together or in pairs, especially where safety is concerned.

However, the key to regulatory compliance requires that such policies are clearly communicated, and they are applied evenly, to all work orders, NOT on a case-by-case basis.

Additionally, industry standards support replacing many items together or in pairs. Motorist Assurance Program (MAP) Uniform Inspection and Communication Standards (UICS) state that if replacement of a part is ‘required’ (on one side of the vehicle), you may ‘suggest’ replacement of the other component, for one or more of the following reasons:  Improved performance or preventive maintenance; Part is close to the end of its useful life.