Standard rear differential gear ratio question
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Transmission & Drivetrain
Forum Description: If it's between the engine and wheels, it goes here
URL: https://theamcforum.com/forum/forum_posts.asp?TID=28391
Printed Date: Apr/16/2024 at 4:27am
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Topic: Standard rear differential gear ratio question
Posted By: Rambler Mexicano
Subject: Standard rear differential gear ratio question
Date Posted: Apr/10/2011 at 5:16pm
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Hi, I have some questions regarding the AMX, Javelin, Rebel and the Matador. What is the STANDARD gear ratio for the rear differential in all these lines? I know that within Group 19 parts you had the option of five different gear ratios: 3.73:1, 3.91:1, 4.10:1, 4.44:1, 5.00:1, at least in the 1968-1974 Javelins and AMXs, I don't know if they were available in the Rebel Machine, Hornet SC/360 or any other line. Is the standard ratio the same for all units regardless if they are six cylinder cars or V8 cars? If not, what's the standard ratio for the sixes and what's the standard ratio for the V8s? What ratios were available as optional equipment (excluding the Group 19 ones) in these four lines? Thanks in advance. ------------- Mauricio Jordán Cuando no se es una empresa famosa se deben hacer mejores automóviles. - Vehículos Automotores Mexicanos S. A. de C. V. |
Replies:
Posted By: poormansMACHINE
Date Posted: Apr/10/2011 at 5:26pm
| 2.87 with a factory option 3.15 was usually the common with V-8 car. |
Posted By: Rambler Mexicano
Date Posted: Apr/10/2011 at 5:55pm
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Thanks Ron, I just found this. http://www.amx-perience.com/1971JavAMX.htm Specs for the 1971 Javelin AMX, It came standard with the 2.87:1 gear ratio with the 360 cubic inch V8 regardless of carburetor and exhausts, and had the 3.15:1 and the 3.54:1 gear ratios as optional equipment. Also, the same car with the 401 V8 already had the 3.15:1 as standard equipment even though the 2.87:1 was still available as optional equipment as was the 3.54:1 gear ratio. Thanks again. ------------- Mauricio Jordán Cuando no se es una empresa famosa se deben hacer mejores automóviles. - Vehículos Automotores Mexicanos S. A. de C. V. |
Posted By: ramblinrev
Date Posted: Apr/10/2011 at 8:04pm
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Often there was a difference between a manual transmission car and an automatic equipped car. '70 AMX with Go-Package, for example: 3.15 with automatic, 3.54 with 4-speed. ------------- 74 Hornet Hatchback X twins (since 1977) 62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981) |
Posted By: billd
Date Posted: Apr/11/2011 at 7:53am
Yes - my 70 (390 auto) is stamped with the code for 2.87 yet the gears are actually 3.15 The invoice that the original owner got said "gear ratio" on it, and it cost about 10 bucks. -------------  http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
poormansMACHINE wrote:Posted By: Rambler Mexicano
Date Posted: Apr/11/2011 at 12:04pm
Thanks Rev, I actually saw that now also engine and transmission combination are vital to the gear ratio but also the shift control configuration. The 401 1971 AMX with automatic transmission on the column has a gear ratio of 3.15:1 while the same car with the same engine and transmission with floor shift has the 2.87:1 ratio. I'll keep on investigating. ------------- Mauricio Jordán Cuando no se es una empresa famosa se deben hacer mejores automóviles. - Vehículos Automotores Mexicanos S. A. de C. V. |
Posted By: farna
Date Posted: Apr/12/2011 at 11:46am
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Six cylinder cars most often used 3.08 gears in the Javelin, 3.15 in the bigger cars -- auto and manual trannys (from the 71 TSM). The Hornet and Gremlin used a bit taller gearing -- 2.73 was most common. Hornets with manual used a 3.08, Gremlins 2.73 with auto or manual. Without AC both used a 2.37 with auto trans. Note that Mexican built cars (VAM cars) most likely have a bit lower gearing due to the high elevation in the vicinity of Mexico City. ------------- Frank Swygert |
Posted By: 70bigbadorange
Date Posted: Jan/10/2013 at 10:13pm
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guys, thanks for all the info on diffs. I have a 70 Javelin. don't know about stamps or stickers but I'm putting in a lock right so I got mine apart enough to count the ring gear and pinion teeth and I got a 3.15. wish I had the 3.54 but I guess this will do for now. Mine also came with the 904 3 speed auto trans (i believe)... years ago I put the 727 in it. now I would like to upgrade to a 4spd auto. does anyone have advise for me on that???????? does anyone know the best way to go if I want to put a 4sp auto in it.
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Posted By: FuzzFace2
Date Posted: Jan/11/2013 at 8:18am
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I am hoping my 70 Javelin has 3.54 gears too and should because it is a 390/4sp car but will not know till I drop the cover for oil change and count the teeth.
As for the 4 sp auto you may want to do a search or make your own post for it.
In short AMC only had 1 and it was used in later Jeeps.
Could use any og the GM atuo 4sp but need adapter to use them.
Lastly Gear Venders OD unit bolts on the back of your auto trany (727?) and turns it into a 6sp with OD.
Dave ---- ------------- TSM = Technical Service Manual 75 Gremlin X v8 for sale 70 Javelin 360/auto drag car 70 Javelin 360/T5 Street car |
Posted By: sidewinder
Date Posted: Jan/11/2013 at 8:52am
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About a year or so ago I discovered my 70 AMX with auto transmission and go-pac had 2.87 gears. With the go-pac it should have had 3.15 gears. I assume that the original owner opted fore the 2.87 for better highway driving ( calif. car) I bought a set of new NOS 3.15 gears from a forum member here and changed the gears. Not really a tremendous difference but a noticeable one. Also had to change the speedo gear...... Chuck Page ------------- Chuck Page ,AKA Sidewinder 1968 "BLACK CHERRY" Javelin Previous owner of 2013 Heritage Cup winner 1970 BBO AMX |
Posted By: WCKAMX390
Date Posted: Jan/11/2013 at 11:09am
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Best gear for street use is 3:54 or 3:73. 3:91 works , but you lose some of your 4th gear hiway driveabilty ------------- 1970AMX, 390ci, 4spd, RamAir, 3.54posi 2002WS6TransAm, ls-1, 6spd, T-tops, 22,000mi, ALLfactorystock 2012DodgeChallenger"Yellow Jacket"SRT8, 6spd, 392Hemi, 1of1000made, 1st owner2receive YJ in Calif |
Posted By: FuzzFace2
Date Posted: Jan/11/2013 at 1:44pm
You have to look at the whole package, trany gears & rear gear, power out put & weight of car.
I think a 2.95 first, .68 over drive and hoping 3.54 rear in my 360 power Javelin will be a good driver.
Dave ---- ------------- TSM = Technical Service Manual 75 Gremlin X v8 for sale 70 Javelin 360/auto drag car 70 Javelin 360/T5 Street car |
Posted By: Plan B
Date Posted: Jan/11/2013 at 7:26pm
| Just to share I am going with a new set of 3.73 that should be at my door any day now. I will be using a 700r4 reverse manual valve body.Here are the trans ratios 700r4 3.06 1.62 1.00 0.70 2.29 Running 2800 stall. My 68 AMX 390 was running 3.15s? I think |
Posted By: farna
Date Posted: Jan/11/2013 at 8:49pm
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You have to understand that the engine needs to turn around 2000 rpm to be producing enough power to pull an overdrive gear effectively at cruising speed. 3.23-3.91 gears are needed, depending on tire size and what your average high speed cruise speed will be. Even with 3.55 gears, a 26" diameter tire (215/65R15 in my case), and a 0.70 OD (typical, but varies from 0.83-0.65, with the bigger number being "less" OD... subtract from 100, that's the percent OD, 0.70 = 30% OD) my car is traveling 62.3 mph @ 2000 rpm. Cruising at 55 mph it's only turning 1766 rpm. I've got a good torque cam that "comes in" at 1800 rpm, but 55 mph works the motor a bit. Dropping to 3rd gear brings engine rpm up to 2523, which is more like it, but the 4.0L computer starts to richen the fuel mixture right at 2500 rpm. So I cruise at 60 in OD, and usually don't travel at 55 at all -- it's either around 50 or it's up to 60. Best for economy! It's geared about right to cruise in the 70-75 rpm range (2250-2410 rpm). That's turning fast enough to produce good power to not fast enough for the computer to start throwing a bit more gas in the mix. I'd gain 5 mph in cruise speed at 2410 rpm with 3.31 gears, 3 mph with a 1" taller tire (27" diameter -- 215/70R15). I'm going to change to 70 series tires when I need new tires. There's a lot more to selecting gears for an OD trans than just reducing rpm! Another thing to consider -- a "lumpy" cam is going to want more than 2000 rpm to be in the torque band of the engine, so you will need more gear. Your lowest cruising speed in OD should be no less than the lowest rpm in the rpm range of the cam, and you really need to be a couple hundred rpm over that. The Isky 280-HL has a "lopey" idle and an rpm range of 2500-6500. I would want to cruise at 70 mph in the 2600-2700 range. That would require a 4.11 rear axle, which would give 2600 rpm with the 26" tires and 0.70 OD. Less OD might be the way to go, but you're kind of limited there. Oh, one thing about the GV OD.... They correctly state that you can get six forward gears from it. It's just not practical. 1+OD is only 100-200 rpm from 2nd, 2+OD only 100-200 rpm from 3rd. Not enough difference to warrant shifting gears, not in a street car anyway. It MIGHT be useful in a heavy tow vehicle, but even that is "iffy". AMC did it with the Twin-Stick, which split-shifts an OD unit to achieve five forward gears. OD isn't used with 1st, just 2nd and 3rd. There is a big "jump" between 2nd and 3rd gear in the three speed trans to make this practical. If you lock OD out (or just remove the fuse to disable it) and shift it will feel like using a four speed and skipping 3rd gear (1-2-4 shift). ------------- Frank Swygert |
Posted By: amx39068
Date Posted: Jan/12/2013 at 8:16am
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My favorite combo for a 343, 360, 390 or a 401 is the 3:15 rear gear with the wide ratio 2.64 first gear 4 spd that was in 67 and earlier cars with a T-10. You end up with the equivalent of a 3.73 rear gear in 1st (when comparing ratios against the more common 2.23 first gear 4 spd) but still maintain lower RPMs on the freeway with 1000 RPM per 25 MPH on stock diameter tires in 4th gear with the 3:15 rear end gear. Our speed limits outside of the major Phoenix area are 75 MPH which can be somewhat annoyingly buzzy even with 3.54 gears. I would imagine it would be downright unpleasant with 3.73 gears and even awful with 3.91s at those speeds. I once had 4:10 gears in 68 AMX that I used to drive to work from time to time when I lived in the Boston area in the late 80s and really hated driving that car on the freeway even at just 65 MPH. ------------- Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development 
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Posted By: amcenthusiast
Date Posted: Jul/08/2013 at 11:37pm
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Just found this article about 727 automatic conversion to OD; http://www.hemmings.com/mus/stories/2006/07/01/hmn_feature15. - http://www.hemmings.com/mus/stories/2006/07/01/hmn_feature15.html |
Posted By: farna
Date Posted: Jul/09/2013 at 7:06am
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I think they are just stating that you can swap the entire A-518 in. That won't work for an AMC because the bell bolt pattern is different from Chrysler. Many people don't know that, just assume that since the rest of the trans is the same as Chrysler so is the bolt pattern. The article does state that the OD unit is in the tailshaft housing, so it may be possible to rebuild a 727 with the A-518 output shaft and tailshaft housing to add OD to an AMC 727. The statement about "other internal changes" (between the 727 and A-518/46RH) and that they say you can't use the 727 converter makes me think that's NOT what the article writer did though. Still might be possible, you'd have to tear both apart and see. If that will work the 727 converter could be used.
------------- Frank Swygert |
Posted By: uncljohn
Date Posted: Jul/09/2013 at 7:35am
I agree with DAN, I got rid of the 3.54:1 final drive on my Donohue some time shortly after I got the car. Growling down the freeway at 75 mph became incredibly boring. It did cause a problem in heavy stop and go city traffic though as 1st gear was rather tall and you had to slip the clutch a lot when driving in those conditions and I went through a couple of clutches. No complaints though, replacing a clutch was a small price to pay to not put up with the growling at 75mph. However I lost the 4 speed on a trip to Sacramento and replaced it with a World Class 5 speed in the late 80's which gave me a wide ratio 4 speed plus a highway gathering overdrive and it was the best dang thing since sliced bread with the 3.15 rear axle. The question asked about whether 6 cylinder rear axles were the same ratio as V8's and the answer is no they are not. Close maybe but no cigar. ------------- 70 390 5spd Donohue 74 Hornet In restoration 76 Hornet, 5.7L Mercury Marine Power 80 Fuel Injected I6 Spirit 74 232 I-6, 4bbl, 270HL Isky Cam |
Posted By: uncljohn
Date Posted: Jul/09/2013 at 7:44am
One thing you cannot do for sure is use a lock up torque converter on a non-lock up transmission and visa versa. So if what you want to do is build a overdrive transmission from an A-518 to work on an AMC V8 and do so by using an AMC V8 torque converter, it CANNOT be done using a NON-lock up torque converter. If it can be done and I don't know, you are going to have to start with a lock up torque converter transmission that was used in the late stages of AMC life. OR Say the heck with it and use a 700R4 ------------- 70 390 5spd Donohue 74 Hornet In restoration 76 Hornet, 5.7L Mercury Marine Power 80 Fuel Injected I6 Spirit 74 232 I-6, 4bbl, 270HL Isky Cam |
Posted By: carnuck
Date Posted: Jul/09/2013 at 6:31pm
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If the trans is new enough ('80 up in FSJs for sure) the passages for the lockup are there, but they chose to make them non-lockup due to issues with clutches in the converters and fluid (Dex II) not cooling/lubing enough. You need a lockup trans for parts (can be Mopar) to do the conversion (valve body, input shaft and clutch drums, etc) , but the rear of a 518 case is different from a 727 so that swap is not easily doable. AW4 from an XJ or MJ (more than 1/2 of Comanches are 2wd, like the one I'm selling for parts) is a direct bolt up and stronger than the 42RE used in most Grand Cherokees with 4.0L except early '93. ------------- Got an Eagle? http://forums.amceaglesden.com" rel="nofollow - http://forums.amceaglesden.com |
Posted By: Rambler Man 69
Date Posted: Apr/11/2024 at 2:24pm
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Ok, so if the common rear gear ratio for the smaller cars is 3.08 with a six cylinder, then would that include the Rambler "American" body style or would that be considered a larger car? I would think it would be the smaller cars. Fyi... mine was an automatic from the factory. ------------- It's their car, they can do what they want with it. |
Posted By: farna
Date Posted: Apr/11/2024 at 5:05pm
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American is considered "small car". Rear axle ratios varied with engine and transmission though. Early small Americans (58-63) used 4.10 axles with flat-head six and overdrive, for example. ------------- Frank Swygert |