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Diff ratio - compare revs 3:15 v 3:54 |
Post Reply | Page 123 7> |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4741 |
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Posted: Mar/13/2019 at 12:19pm |
A 1:1 transmission high gear doesn't have to suck. It doesn't have to force a compromise axle ratio...if the lower gears in the transmission are a high enough (numerically) ratio. That is where AMC screwed up.
Most AMC manual and automatic transmissions have a 2.5:1 low gear and a 1:1 high gear. That sucks. The ratio spread simply is not wide enough to allow for one axle ratio that produces good low speed performance and good high speed performance. Most cars end up with a compromise gearing that doesn't make them truly good at anything. ...unless you bought Borg-Warner overdrive. Low gear is the same 2.5:1 but the high gear is now 0.7:1. You can run a high axle ratio for good low speed performance but drop into overdrive for high speeds. That 3.54 axle ratio becomes a 2.50 after the overdrive is engaged. It's absolutely perfect. AMC got smarter in later years too. Starting in about 1975 they switched to 3 speed manual transmissions with low gears around 3.2:1 and 4-speed transmissions with low gears around 4.2:1, all with 1:1 high gears. These transmissions got themselves off the line very well with axle ratios in the 2.5:1-3.08:1 range and produced excellent highway cruising. They got smarter on their automatic transmissions with the Eagle when they introduced the wide ratio lockup TC A998. A 2.7:1 first gear and a true 1:1 high gear. A 2.35:1-3.08:1 axle works perfectly with these. My Eagle gets itself off the line just as well with it's A998/2.35 as my Hornet does with it's A904/2.73. Wide ratio 3 and 4 speed transmissions are your friend. AMC engines have a broad torque curve that works well with wide ratios. |
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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vinny
Supporter of TheAMCForum Joined: Jan/05/2012 Location: Calgary Status: Offline Points: 2837 |
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I had a few GM vans with I think 3.54 and 700R4 or newer so not bad, couldn't fault them. With 1 to 1 in the Rambler I like the 3.15 as a compromise.
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Greyhounds_AMX
AMC Addicted Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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But you can have both if you run 3.54's with a T5.
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1968 AMX 390 w/T5
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16591 |
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Just me. In the old transmissions high gear is 1-1. (Unless you have OD). I have a 72 Gremlin with the 3.54s. Its noisy at high speeds. Way I see it...what do you want.
You want a highway criuser, get 2.56 or 2.87s. You want performance ...3.54s. Cant have both. Its a compromise. Stop complaining
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tomj
AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7522 |
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hey, i've got an online transmission axle tire calculator here if you wanna do what-ifs with axles and tires. basically it calculates MPH in each gear, in the blue columns to the right. sorry it's got too many digits. makes it look intimidating. |
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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
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amxdreamer
AMC Addicted Joined: Jul/30/2008 Location: Vancouver, BC Status: Offline Points: 8494 |
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I like the 3.31's that replaced the 2.87's that came in my car.
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Tony
Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
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amxron
AMC Nut Joined: Nov/18/2011 Status: Offline Points: 295 |
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About 90% of the V-8/auto cars built in the 70's had 2.87 gears.
Ron.
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AMXron
Fleet/Jeep Mgr. Orbit AMC/Jeep 50-1787 |
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19611 |
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Most of the Jeep places only carry 3.31 and lower gears. Looks like you can get 3.08 easy enough: Your other option is to drill the 7/16" holes in the carrier out to 3/8" and use the bolts that came with the 2.87 gears... or new grade 8 3/8" (fine thread, IIRC) bolts. I was thinking you should be able to find higher gears as my J-10 had 2.73 gears... but then I remembered it used Dana 44 axles, not AMC 20...
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Frank Swygert
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jjwbeach
AMC Apprentice Joined: Jun/26/2011 Location: Cocoa Beach, FL Status: Offline Points: 81 |
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Thank you for helping me too. Do you think I need to call a few Jeep aftermarket places and see if they carry something like the correct threading with highway ratio r&p options?
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1970 AMX BBG X-code 390, amc turbo 400 auto, model 20 3:54
1979 Spirit AMX H-code('71 amc blue), 401, A/C, amc turbo 400 auto, model 20 3:54 1970 BBO AMX 4 speed, A/C, Tilt, original needs restoring |
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jjwbeach
AMC Apprentice Joined: Jun/26/2011 Location: Cocoa Beach, FL Status: Offline Points: 81 |
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Yes, sure do, I purchased a 2.87 ring and pinion to change out my 3.54, and the threads on the 2.87 are 3/8th instead of 7/16ths, so I wanted to get a highway ratio and use the chunk I have...is my thinking correct there or am I needing some more info, as when I called around, no one has a highway gear with 7/16 threads for my chunk I have now...
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1970 AMX BBG X-code 390, amc turbo 400 auto, model 20 3:54
1979 Spirit AMX H-code('71 amc blue), 401, A/C, amc turbo 400 auto, model 20 3:54 1970 BBO AMX 4 speed, A/C, Tilt, original needs restoring |
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