Diagnosing suspension problems

An article written by Jerry Hastings which appears on http://www.helium.com/, http://www.diggs.com/, http://www.del.ico.us.com/ & www.hastprotrucks.com/forum

Realizing that most people will likely be confused by the content of this article, what's real and what's not are two completely different things. First, I'll make an attempt to define the words "vehicle suspension", then I'll go through some of the particulars associated with how to diagnose suspension problems.

There are many different designs or versions of a particular design relating to suspensions that require more specific discussion and I (and I hope readers will) realize that fact. The following is a more or less generalized summary.

Vehicular suspensions are generally the components that your vehicle weight sets on, excluding wheel bearings, hubs and wheels (they are sort of in a class or classes by themselves). Such things as springs and spring hangers, struts, A-frames, kingpins and steering knuckles (or spindles & kingpins on straight front axles) and axles (where applicable) make up a vehicle's suspension.

Components such as ball joints, steering knuckles (or spindles & kingpins)and straight front axles play a dual role in that they are one of the links between the steering and the suspension. They pivot or allow pivoting making them part of the steering and support the vehicles weight making them part of the suspension.

Steering knuckles or spindles with kingpins and straight axles play a different part in steering in that wheel alignment angles are manufactured into these components along with the fact previously noted that they pivot or allow pivoting to turn the front wheels. Plus the wheel bearings, hubs and wheels are attached to these components making yet another link (or links). The additional unadjustable wheel alignment angles provided by these components, enhance steering quality and performance.

Rear axles on rear driven vehicles sort of fall into the category of suspensions but their role is unique in the scheme of things. Rear axles on front wheel drive vehicles can be considered suspension components but they also provide the link between wheel bearings, hubs and wheels.

When you really want to define the term "suspension", axles of all sorts really do not fit in the category completely, but are more in a class by themselves and generally shops and literature recognizes them that way.
Items like tie rods and tie rod ends, idler arms, pitman arms, control arms and other components all the way up to the steering wheel, fall under the classification of steering components exclusively and should not be confused with suspension components.

However, for the sake of those that need a little insight on how to check for wear in steering components, I will add these suggestions. Slack in these steering components can best be found by leaving the vehicle weight on the wheels and observing each component while a helper turns the steering wheel slowly back and forth only the amount necessary to cause some movement. Normally slack in steering components can be felt as slack at the steering wheel. If that is the case, turning the steering wheel back an forth only as far as the amount slack present will help locate the source of that slack.

Ball joints and kingpins usually wear to some extent especially if the wrong type of grease is used or the frequency of grease jobs are not adequate enough. Slack results from this wear. A normal cheap real grease is better than a high dollar synthetic grease for these and all suspension and steering components. The only place synthetic grease should be used is in the wheel bearings. I know, the advertisements says this or that but advertisements are sometimes far from reality.

Two people are required for a lot of suspension diagnosis techniques, especially in the absence of specialized equipment. Most of the following require two people. One to provide movement of the part in question and the other to watch the part for any signs of slack.

Upper ball joints are the easier of the two to check for slack. Simply jack the weight off the wheels while a friend observes the movement in the ball joints (other than pivoting movement). Lower ball joints may require a pry bar placed under the wheel or through holes in the wheel while the vehicle is jacked up, and prying upward or inward while observing the lower ball joint for the same type of movement.

While large differences in an A-frame or straight front axle and a strut type front suspension exists, many of these suggestions will also apply to strut types. The front spring and strut are an assembly and therefore must be diagnosed as such. Check for abnormal slack in much the same way as used on ball joints.

Straight front axles with kingpins must be checked in two directions for slack. Jack the vehicle up securely (sometimes a large vehicle weighing many times as much as a small car-heavy duty jack stands are recommended), then push hard sideways on the top of each tire while observing for any abnormal movement in the kingpin area. Next place a long prybar under the tire and pry upward while observing for any abnormal movement between the axle eye and the spindle
(up and down movement).

Excessive slack observed while pushing on the top of the tire is a result of kingpin and bushing wear. Excessive slack while prying up on the tire is a result of bearing or shim wear (bearing between the axle and spindle on the bottom side of the axle and shims between the axle and spindle on the upper side of the axle-the kingpin is through both).

If the vehicle sets lower than it used to or leans to one side, spring fatigue may well be the problem. However, care should be exercised to eliminate frame damage (many cars and light trucks have unibodies-not frames per se). Did some sort of trauma happen to the vehicle or is there door and/or window sealing problems? This could also signal frame or unibody damage.

Unusual tire wear, especially on the front, may be a sign of suspension problems but cannot be depended on exclusively. For instance, wear on the inside of the tires is a sign of excessive ball joint or kingpin wear and resulting slack BUT may be from several other wheel alignment problems instead.

Tire dipping can be a contributing factor of shock problems BUT may also be tire and wheel imbalance or out of roundness. Shimmy in the front is usually from a bent wheel, out of round tire (dipping as a result), extreme tire/wheel imbalance or other out of round causing problems.

Although shocks are lumped into the suspension category, they really are not part of a suspension. They are just another link from the body or frame to the axle or suspension and who's function is to control bounce and/or sway. Problems with shocks are usually self evident. Excessive leaning during turns, excessive vehicle bouncing, clunking noises and more are signals that the shocks need replaced.

Perhaps one of the most ignored areas of a vehicle's suspension is the rear spring eye bushing and pin or the pin hole in the spring hanger as well as loose hanger to frame bolts. Wear and slack in one or more of those areas can cause a myriad of handling or wheel alignment issues. Normally any slack will be back and forth movement at the tire. Check for these problems by chocking the front tires securely, then unlock the brakes and put the transmission in neutral. Next pry forward and rearward at the tire with a pry bar or something (a port-a-power comes in handy on larger vehicles), and observe for any movement in these areas.

The allowable amount of slack in a particular component depends on the exact component. Generally speaking, there must not be very much or no slack observable in any suspension component because movement promotes additional wear and could be a potentially dangerous situation waiting for time to present itself.

There are way too many suspension problem diagnosis techniques and fixes to include them all in depth in a single article. Volumes of repair manuals and books are written on these subjects, Anyone interested in vehicle suspensions should certainly read up on the subject well, before attempting any repair themselves.

An example of one of these books is my ebook for medium and heavy trucks. Many of the topics discussed can be applied to regular cars and trucks too. A repair manual, especially about the vehicle being dealt with, should round off the information aspect of vehicle maintenance. Repair manuals normally do not include a real technician's input and sense of direction, however.

Remember, suspension repair and diagnosis must be done while the vehicle is kept secured from falling and also remember spring tension can be deadly. Most suspension repair is an area for a professional or at least a well versed and informed do it yourself person.

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