Idler Pulleys

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I generally take pretty good care of my Jeep, but once in a while I screw up.  There was a little squeak when the Jeep first started that I had been putting off diagnosing.  I figured there was no coolant leaking (water pump), the alternator was working (according to the gauges), the A/C was working fine, and the power steering/power brakes pump never squealed when steering or braking, and I had the belt replaced last year, so everything must be OK...

Sooner or later whatever it was would make itself more clearly known and I would deal with it then.  Words to live by.  More like Famous Last WordsOne day I was on the trail.   It was getting near sundown.  There was between 8 and 10 inches of snow on the ground and though the trail had not been impossible, there had been some rough going that kept us happily occupied for most of the day.

Now it was getting colder and dark and we were heading out for the road and a ride home, perhaps punctuated by a stop for dinner and talk of the days events.  Along the way, my good friend Jim stopped and came over to me and asked if I was the one "chirping".  "Chirping"?  I figured he meant the squeaking sound so I got out and without the benefit of the stereo to cover it, there was a definite chirping sound coming from under the hood.

I opened the hood to check it out.  We mistakenly concluded that the A/C clutch was giving out.  I figured that was a bummer but it would not spoil our day.  We didn't need the A/C, and the belt would keep on working even if the A/C clutch didn't.  So I got back in the Jeep and continued on the way out.

A little ways down the trail I began to smell the unmistakable odor of burning drive belt.  I have burned up a few on the lawnmower, so I knew the smell pretty well.  I shut off the Jeep and took another look under the hood.  Give the man a cigar!  The drive belt was smoking and frayed.  No problem, I have a spare!  And then I saw the reason:  A bearing on one of the idler pulleys had given up the ghost.  No more squeaking, no more chirping, and no more idler pulley.  It was canted at a sick angle and seized.

You can read the whole sad story in the trail report but suffice to say we did not effect a trail repair that day.  We just didn't have the parts needed to get it done.   And the trail just happened to have a couple more steep hills that were tough enough without a dead Jeep strapped on the back, so the Jeep spent the night in the woods and I strained my marital bonds by returning the next day with all the parts I would need to do the repair in the woods. 

I looked up the parts I knew were bad or missing (bolt, belt, idler pulley) and included extra parts to repair associated components in the event that I broke them trying to do the work.  We had trouble trying to loosen the tensioner on the other idler pulley and I expected to have to break the bolts to get it undone.  It would have been no better had we fixed the broken pulley only to break the other one trying to install the drive belt!

Here is the parts list that I filled, though some of the dealers I called did not have all the parts...

PULLEY, Idler 4792 112
BUSHING, Idler Pulley, Belt Tensioner Pulley 3300 2201
SCREW AND WASHER, M10x1.5x40 6504 239
SPACER, Belt Tensioner, Pulley 6503 230
BOLT, Hex Flange Head, M10x1.50x50 3420 2029
PULLEY, Idler, Tensioning 4792 112

BUSHING, Idler Pulley, Belt Tensioner Pulley

3300 2201
COLLAR, Tensioner Adjustment

5301 0149

BOLT, Adjusting Bracket 6503 198
BELT, Accessory Drive, With Air Conditioning 5301 0150

Pulley Parts - Click to Enlarge

I later learned that I could have replaced just the bearings in the idler pulley with one of these parts:

FAG: 6203 RS

SKS: 6203 2RSJEM

(I have not confirmed these numbers but they are probably correct.  As soon as I do, I will update this section.)



I was just as happy to get factory parts for it made the installation that much easier.  I wasn't in a position to be running back and forth between the dealer to trade in parts that didn't fit.  The Jeep was over 100 miles away and accessible only in a decent 4-wheel drive vehicle.  I had to get all the right parts first try, and get it done before it got dark.  We got to the Jeep with an hour of daylight left...

The repair was easy.  I simply installed the passenger side idler pulley with M10x1.50x50 bolt.  The correct one is 40mm long but the dealer didn't have it, and mine was on the trail in 8 inches of powdery snow, so I put a few washers in to space it off the necessary depth.

Idler Pulley

Then I took out the breaker bar that I brought along just for the occasion, and loosened the bolt that holds the center of the lower driver's side tensioner pulley tight against the mounting plate.  It had been unwilling to come loose the night before with only a short ratchet.  Both bolts were 15mm hex heads.

Label, Belt Path

Once the tensioner pulley was loose from it's mounting, I removed it completely and replaced it too, being careful not to lose the bolt, spacer washer (also not available from the dealer), and the retainer and adjuster bolts in the process.

Tensioner Idler Pulley

After what I went through the night before, I decided that an ounce of prevention was worth a pound of cure.  That tensioner pulley was exactly the same as the one that failed, exactly the same age, and closer to the ground.   It probably was on the way out too.  No sense tempting fate.

With both pulleys in place, I put on a new drive belt, then did up the tensioner pulley until the belt didn't squeak when the A/C compressor came on.

Accessory Belt

Apparently there is a specified tension that is measured with a special tool.  I don't have the tool but I have common sense.  It failed me once (my common sense that is...) so I guess I will just have to cross my fingers on the belt tension...

I put the removed pulley in my spares box, cleaned up around where we were working, and started the Jeep.  We checked the belt for run-out and found that I had placed it one groove too deep on the alternator pulley so I shut the engine down and adjusted it.  After that it ran nice and quiet.  We hit the trail.

I learned a lesson about preventative maintenance.  Check the squeak!

Idler PulleyAccessory BeltIdler PulleyTensioning Bolt



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