Hendon Publishing - Article Archive Details

Print Article Rate Comment Reprint Information

Shot Show Workshop Schedule

 

The alignment specs published by all auto manufacturers have a wide range of acceptable adjustments. This is due to normal production tolerances and the different driving habits of retail and police drivers. Additionally, some settings may vary slightly on the police models due to the differences in tires and suspensions on the police models, but keep in mind that the four-door sedans used by the police are sold in much greater quantities to retail customers. Retail drivers typically do not drive over 100 mph (with 400 pounds in the trunk), expecting stable and responsive handling at these speeds and load conditions. The typical retail driver in the Impala, and especially the Charger, may be younger than the typical retail driver for the Crown Victoria, but the point is the same. The typical traffic officer has very different performance and handling expectations than most retail buyers. The California Highway Patrol found that the fully loaded Ford CVPI had better high-speed stability with camber, caster and toe settings different than the nominal (middle) factory alignment adjustments. The CHP went with minimal to nominal negative camber; nominal to maximum toe, i.e., a slight toe-in; and the absolute maximum positive caster, all within the factory range. And instead of setting the right side caster different from the left side, to account for the crown in the road, both sides were set the same. CHP Experience The California Highway Patrol (CHP) fleet exceeds 4,300 vehicles, with about half of that figure as marked patrol vehicles. Officers put about 95 million miles a year on their vehicles. Over the years, the CHP has done extensive testing, research, and development to determine which vehicles will best serve the needs of the CHP. This development mentality also includes tweaking adjustments inside the normal range of factory settings for the powertrain and chassis. Soon after their 2005 Ford CVPIs went into service, CHP Fleet Operations Section received complaints of unstable handling at high speeds. At speeds above 70 mph, the steering would feel “light” or “loose” and the cruisers felt “squirrelly” at high speeds, giving feeling to the driver that the car would oversteer during high-speed turning maneuvers. This was odd because the problem did not surface with earlier model Ford CVPIs, which use the same platform and suspension as models going back to 2003. It was quickly determined that the problem did not manifest itself on a newly delivered car, but it did crop up after car was outfitted and placed into service. Part of preparing the car for service includes mounting about 200 pounds of police equipment in the trunk, not including the gear added by the officer. Both the CHP and Ford looked into the problem extensively. Ford engineers went to Sacramento to get a first-hand look at the concern. By trial and error, and with Ford’s approval, the CHP found that setting the toe near the minimum factory setting (almost the most negative toe, i.e., almost maximum toe-out) seemed to cure the problem. CHP Fleet Operations issued Technical Service Bulletin #05-12 on July 21, 2005, to all commands revising front-end alignment settings on their 2005 and 2006 Ford CVPIs. Toe-in, Toe-out Toe is adjusted individually for each front wheel by lengthening or shortening the tie-rod ends on each side. While proper toe sittings are critical, the recommended settings allow tolerances to compensate for normal suspension component wear and allow for the compression of the suspension arm bushings when the vehicle is at speed. Toe used to be measured in terms of inches. The distance between the front of the front tires was simplistically compared to the distance between the rear of the front tires. Toe-in was where the distance between the fronts of the tire was less than the rears of the tire. Today, the actual angle of each tire is measured. A positive (+) reading is toe-in, while a negative reading (-) is toe-out. The technician can also “finesse” the vehicle’s handling characteristics by varying toe settings within the specified limits. An increase in toe-in (decrease in front tire traction while cornering) will result in reduced oversteer, while an increase in toe-out (increase in front tire traction while cornering) will reduce understeer. Adjustment of the tie-rods also centers the steering wheel. One of the indicators that toe might be out of specification is when the steering wheel is canted off-center while the vehicle is driving down a flat and level roadway surface. After the steering wheel is centered and left and right toe settings have been made the adjustments must be within the combined or total toe range, which is the settings of both sides added together. For example, the toe settings on a late-model Ford CVPI call for each side to be set at the nominal (preferred) setting of -0.19 degrees (toe-out) with an allowable tolerance of +/- 0.07 degrees. The revised settings called for the combined toe, the total of both sides added together the adjusted, is to be -0.37 degrees with a tolerance +/- 0.13 degrees. VAPS Often in police work, things aren’t always what they appear to be. This is also true in automotive troubleshooting. After months of testing, Ford engineers discovered that the revised alignment settings only served to mask the real problem. A computer glitch within the PCM caused the variable assist power steering (VAPS) to go in to “default mode.” When the PCM went into default mode, the PCM gave unneeded full power-steering boost at high speeds, making the car feel unstable. VAPS is a sophisticated power steering system designed to deliver full steering boost when needed, i.e., during slow-speed operation and parking maneuvers. At about 20 mph, as speed increases, the need for steering boost decreases, the VAPS will reduce steering boost by 20% to 25%. By 80 mph, the steering pressures are reduced to about 50% giving more feedback to road conditions and allowing the driver better control. A sharp turn of the steering wheel, however, will restore full boost to assist the driver in an emergency turning maneuver. If there is any glitch in the system, the VAPS system will switch into a default mode, providing full steering boost at all times until the system is repaired. This is similar to the feel of early power steering systems, which felt “numb” at road speeds. This particular VAPS problem was intermittent, making it extremely difficult to track down. It was determined that driving the car at a speed of 2 mph for at least 3 seconds would place the VAPS into default mode. In CHP service, this wouldn’t be difficult to achieve, such as leaving a parking stall and exiting the CHP parking lot or creeping along in slow traffic. However, if the vehicle did not travel for 3 or more seconds at 2 mph, such as moderate to rapid initial acceleration, the VAPS problem would not occur. Adding to the confusion, the system would reset itself every time the engine was shut off and restarted. Sometimes the problem was there, and sometimes not. Ford determined that the real problem was an issue in the powertrain control module (PCM) controlling the VAPS. In December 2005, Ford came out with Technical Service Bulletin #05-26-13, instructing dealers to reprogram the PCM to the latest calibration, which eliminated unwanted VAPS activation. In January 2006, the California Highway Patrol Fleet Operations Section released Technical Service Bulletin #06-12, advising all commands to have the PCM recalibrated on all the 2005 and 2006 Crown Victorias. This operation can be performed with a handheld scan tool, which means that a Ford technician can come out to a CHP facility and reprogram the PCM in the field. And yes, this program is covered under Ford’s three-year / 36,000-mile warranty. So what of the revised alignment settings with max toe-out? Reflashing the PCM per Ford’s TSB #05-26-13 cured the problem, and the CHP opted to stick with the original slight toe-in specs. Future alignments will also revert to the previous CHP recommendations. For more information, contact the CHP Fleet Operations Section at (916) 376-3500. John Bellah is the technical editor of Police Fleet Manager and a corporal with the California State University, Long Beach Police. He can be reached at jbellah@csulb.edu.

Published in Law and Order, Jan 2007

Rating : Not Yet Rated


Comments

Comment on This Article

No Comments


Related Products

SHOT ShowTrade Shows
 

Article Images

Click to enlarge images.

 
Events and Tradeshows: LAOPFMTRPSIT
Latest News: LAOPFMTRPSIT
 
Close ...