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Old 02-13-2021, 05:52 PM   #1
KivPanther
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Default Question for 5-speed owners

Iíve noticed that there isnít but about 500 RPM or so difference between 4th and 5th gear on my truck, and Iím typically up around 3500+ RPM at 65-70 mph on the highway in 5th. Is this typical or might there be something odd about my transmission?
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Old 02-13-2021, 08:58 PM   #2
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5th is overdrive. May be quite a while until the next time I take the D21 on the highway, so can't say what my RPMs are at 70.



Have the gears in your differential(s) been changed?
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Old 02-13-2021, 09:23 PM   #3
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Thats the same with mine. I cant recall off hand what my gearing is, but my rpms are around there at that speed.
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Old 02-13-2021, 09:27 PM   #4
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As far as I know the differentials are bone stock and haven’t been tampered with. Mine is a V6 for reference. I’m trying to chase down why I’m getting about 13 mpg and wondered if that was a normal rev range.

After some further looking it seems like that’s normal for the 5-speed V6. I must have something else going on.
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Old 02-14-2021, 01:05 AM   #5
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What axle ratio do you have?



I have 4.11s in my truck. I turn 2700RPM ish at 70. I get about 18MPG with 31x10.5s and a TBI VG33 with long tubes. My truck was rated at 20MPG on the highway when stock on 235/75/15s and a VG30. I could get as high as 25MPG at 70 on a flat highway.
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Old 02-14-2021, 04:09 AM   #6
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Going from narrow OEM-type highway to mud/snow tires dropped my highway MPG by at least 1.
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Old 02-14-2021, 04:32 AM   #7
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Ok, remember back in the 80s-90s when the speed limit was 55-60 mph. RPMs were right around 3k to 3100 rpm at 60. So 3500 at 70 is normal.
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Old 02-14-2021, 05:21 AM   #8
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I'm not running weird tires or anything. Just Goodyear Wranglers in 235/75r15. Rear axle is an HG43.


I'm fairly certain my fuel issues lie elsewhere in the engine or exhaust, but I wanted to make sure that was normal.
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Old 02-14-2021, 06:40 AM   #9
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Check for vacuum or exhaust leaks.

My 97 HB was in "Open Loop" due to an exhaust leak. I pulled the midpipe off the exhaust manifold collector and there are two crush washers that were split and should have been solid circular. Changed them out and drove my truck to close the monitors. I was only getting 130 mi. with a full tank driving between 55-60 mph and shift points were every 15 mph. Disgraceful. All good now.

Mine is a 4 cyl. 2-wheel drive; 5-spd. with a MagnaFlow Cat Back exhaust system. I can pull 23.5 mpg, if I go easy on the pedal while driving.
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Old 02-14-2021, 07:01 AM   #10
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Just from a numerical standpoint, 4th gear is 1:1 and 5th is 0.86:1, or a 14% difference. 3,500 RPM x 1.14 = 3,990 RPM, so a 500 RPM difference seems right to me. 3500 RPM at 70 MPH doesn’t seem abnormal to me.
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