Looking for an angry fix for Jeep's mysterious howl

  • Article by: PAUL BRAND , Star Tribune
  • Updated: August 5, 2011 - 4:08 PM
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enonormanAug. 5, 11 8:47 PM

2002 F-150 with the 4.6-liter engine....... Before you start adding refrigerant I would check the function of the cooling fan. If it is an electric fan, it should be on high speed when ever the AC is on. If it has a fan clutch make sure it is engaged when the under hood temp. is high. If the system cools normally at road speed, the increased air flow allows for proper condenser operation. The fan is only needed at idle. If the refrigerant is low, the cycle time will be short at both idle and road speed. If you have access to a factory shop manual you can predict the cycle time using a chart which will plot ambient temperature on one axis and cycle time on the other. With temp and high humidity that we have had recently, the compressor should be on almost constantly. You didn't mention any prior service, but if it were improperly serviced, and to much oil has been added, this will also cause low efficiency of the condenser.

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hobie2Aug. 6, 11 6:00 PM

Jeep differential noise - it is NOT normal to be louder after a bearing change. Especially when it increases with speed, because the gears are round and don't wear on one half to allow the out of round noise that gets louder with speed, but bearings and misaligned shafts do..... The noise in worn differential gears is very different than the sound from worn or damaged bearings (lower pitched than bearings or or mis-alignments) and worn gears can be checked by listening during accelerating, decelerating, and coasting/matching. If you lose the sound in one of the three it is not worn gears - especially with new bearings. ( caution - If you don't lose the sound, it does NOT mean that it is definitely gears)... And in jeeps, the drive shafts HAVE to be put back on with the alignment marks exactly where they were before, and shaft balance rechecked - or they will cause the bearings to make noise, the faster the louder... If the mechanic dropped the bearing, or hit the bearings with a hammer to get them in, the bearings easily get a spot on the rolling element that makes the noise - a howling noise, again, the faster the louder. Dry bearings also make noise.... A caution - gear-sourced sound can mimic bearing sound if the source comes from lash or misalignment because the gearshaft vibrates - when you replace bearings you need to check gear lash and shim for lash at minimum spacing.... You will be able to tell if it was an installation error when it breaks because 90% of the time on gear and gearbox work errors, there will be a double failure ring from the added loading due to not aligning the gears and shafts. That said - not sure, but I think Jeep recommends replacing the differential gearbox as a unit and not trying to rebuild, for those reasons. FWIW.

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hobie2Aug. 6, 11 6:04 PM

AC - side note - most of the R134 units will not cool when overfilled by even a few pounds(or under filled, obviously) so use a gauge - on the LOW side connector.

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