Yukon 5.38 Gears



The Mod:

Change the stock 4.10 gears to 5.38 gears.

What it does:

After changing the tires from 32" to 35" there were some issues I noticed:

  1. The first time I drove it I noticed it needed a little more gas to get going. Over time I noticed that it felt more like the gears had a very slight binding/I had to drive up a very small hump when starting - no real binding/bump - just felt that way.
  2. On very slight hills and in 2WD or 4High in Drive the transmission canít hold and it rolls back.
  3. In 2WD or 4High and going 20mph or less thereís almost no difference between D, 2nd, and 1st (no difference in engine braking, torque).
  4. On the freeway it kicks out of OD going over simple/small overpasses.
  5. On the freeway going up a steeper hill it kicks down to 2nd to keep up.
  6. Going down some steep dirt hills in 4Low had to use brakes.
  7. Acceleration from stop not great.
  8. Crawling on rocks in 4Low and 1st not much worse than stock.
  9. MPG: 32s (14.6K miles): 16.1, 35s (2.2K miles): 15.1

After switching to the Yukon 5.38 gears:

  1. Starting feels great. No extra gas needed.
  2. Transmission holds on small hills.
  3. Thereís noticeable engine braking and torque in 2nd and a lot in 1st. 4High is nicer on the trail with the engine braking.
  4. Doesn't kick out of OD on simple/small overpasses and small hills. Doesn't seem to struggle at all on these types of hills.
  5. On larger hills kicks down to 3rd and holds with no struggling going up the hill.
  6. On the same hills additional braking is not needed. On most hills no braking is needed at all.
  7. Acceleration from a stop is great - no issues.
  8. Crawling on rocks in 4Low and 1st better than stock.
  9. Breaking in gears (500 miles): 16.8, My normal driving (8.7K miles): 15.0


No photos of the Gears and Master Install Kits as they were purchased and installed at Absolute Offroad.

I broke in the gears by driving 15 miles then stopped for 6 or more hours and repeated until I hit 500 miles. I was driving on straight roads, so at times I kicked it into 4 High to add some heat/stress to the front gears.

Draining the oil from the rear:

Stuff from the drain plug magnet - very fine metal and grease:

I dug around in the sludge and found these two small (metal?) grains - smaller than sand (actually they may have even been in the rag before I used it :S)

Draining the oil from the front - a lot clearer as it didn't get nearly as much stress. The drain plug look about the same as the rear:

Stuff from the front drain plug magnet - no pieces that I could feel, just some shiny "flakes":

3,000 miles after the oil change the rear looked pretty clean (the front was even cleaner):

See Riddler Differential Covers for information on the gear oil quantity and type.

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Last modified: February 23, 2013 05:14:17 PM