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Rear axle position

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1968 AMX-R View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1968 AMX-R Quote  Post ReplyReply Direct Link To This Post Topic: Rear axle position
    Posted: Oct/08/2015 at 7:09pm
The whole rear axle assembly in my 68 amx 390 4spd doesn't not sit directly in the middle of the rear wheel openings ... It sits just a little bit towards the front of the car ... It is evenly forward on each side ... The original owner who I bought the car from, said he has never moved the axle forward ... Does anyone know if this was something done from the factory or what it might be? Thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1970390amx Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2015 at 9:33pm
To me it looks like all amx and javelins have the issue you describe. My guess would be that as the leaf spring flattens out the tire moves back and needs more room at the rear of the wheel well.
1970 390 4speed Bittersweet shadow mask AMX
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2015 at 11:25pm
If you take a close look at the leaf spring you will find that the forward section of the spring is both shorter and thicker. That portion of the spring acts more like a traction bar or something some times called a slapper bar and serves to help keep the axle from rotating under hard acceleration. The portion of the spring from the axle back to the spring shackle is linger and thinner and is the part that actually gives you the spring action or the ride that the car has. Thus the spring serves as a couple functions. 1. as a traction bar, 2. as a locator for the axle itself, 3. as a cushioning device the ride control. A leaf spring is not as simple as it looks, it is designed to perform multiple functions.
Keep in mind, looking at a 1970 (for example)a 45 year old car, you are looking at something that may have been sold with a 10,000 mile warranty and with the expectations that in normal use it would travel about 12,000 miles a year and become a derelict inside of a decade and be driven in a multitude of environments including doses of heavy salt which causes and aggravates rusting.
Depending on what component you are looking at it might be surprising that anything at all still exists.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Oct/09/2015 at 10:12am
I agree with 70390AMX. My Javelin has that same appearance, and I thought the exact thing too, when loaded the axle moves toward the rear a bit, because the shackles at the rear and the single locating bolt in the front. Put a couple adults in the car, a couple hundred pounds of stuff in the trunk and take a look at it then.
70 Javelin SST, second owner, purchased 1972
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXFSTBK390 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/09/2015 at 1:01pm
My '68 AMX wheels are perfectly centered in the wheel wells. The car has the original leaf springs and 151,000 miles on the chassis. Do the torque links help keep the axle centered in the wheel well?

Edited by AMXFSTBK390 - Oct/09/2015 at 1:12pm
Questions are powerful tools...what's in your toolbox?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mmaher94087 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/09/2015 at 6:39pm
Are the bolts that hold the spring leaves together and locate the spring on the axle perch intact? I had an AMX that had the heads of the bolts sheared off and the rearend slid back and forth on the springs until I replaced the broken bolts.
Mike
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Post Options Post Options   Thanks (0) Thanks(0)   Quote THE MENACE Quote  Post ReplyReply Direct Link To This Post Posted: Oct/09/2015 at 6:55pm
The rear wheels on my 70 AMX sit 1/2" forward in the wheel openings.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave Z Quote  Post ReplyReply Direct Link To This Post Posted: Oct/09/2015 at 7:45pm
Originally posted by 1968 AMX-R 1968 AMX-R wrote:

The whole rear axle assembly in my 68 amx 390 4spd doesn't not sit directly in the middle of the rear wheel openings ... It sits just a little bit towards the front of the car ... It is evenly forward on each side ... The original owner who I bought the car from, said he has never moved the axle forward ... Does anyone know if this was something done from the factory or what it might be? Thanks

What you are seeing is normal and is caused by the arch of the spring. As the spring gets loaded it loses it's arch and the wheel moves towards the rear of the car. So the wheel has to be located forward with no load to allow the wheel to move towards the rear without hitting the wheel opening when loaded.

Dave Z
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2015 at 4:19am
As stated earlier, the forward or leading section of the spring being both shorter and thicker acts as a traction bar and has less flex that the trailing section and is used to position the axle in relation to the front mounting point and as the spring deflects from what ever it's nominal position is he axle will swing in an arc in relation to the front mounting bolt. The rear shackle allows the spring to flatten out when the car is loaded or the spring is deflected due to road conditions.
The axle is located on the spring with a pin that goes through the spring and is part of the mounting assembly. And if this is damaged due to rust for example, the axle will indeed move on the spring and generally causes the car to "crab" when going down the road as the axle then would be no longer square to the car.
So the exact location of the axle is due to the position of it in relation to the front mounting, the amount of flex in the spring when loaded thus where in the "Arc" of movement it will be in and also in part as the mounting position is determined by the "rubber" sleeve which is part of the mounting hardware. Why rubber? it flexes so it gives some wiggle room in assembly, is quiet and does not transmit some movement or "jiggle" to the car. It replaces metal used before rubber became commonly used and saves the use of a grease fitting commonly found on springs used at least into the 1930's.
Your TSM has a section which may have different names depending on the year of the manual, the 1980 TSM it us called Body Components and gives dimensions of multiple portions of the car. The 1970 TSM calls it Bodies-Panels-Subassemblies. The dimensions are in inches and no tolerances are given. This is the section that would be used to restore the vehicle after major damage would have been caused due to an accident.
As the car ages the deflection of the spring may change due either to corrosion or use and it may have been replaced for a variety of reasons with an aftermarket spring. The aftermarket spring may approximate the OEM specifications.
I have a TRW Spring manual obtained from a NAPA store when they replaced the manuals that would have sat on the front counter with a computer which stored the data and provided a look up means. The TRW Spring application chart shows only 5 spring numbers to be used by AMC automobiles for the front coil spring for the years 1970 to end of production in 1988 for ALL 2 wheel drive models with the exception of the PACER. One of the 5 springs would be called out depending on the weight of the car and it's accessories for all models. Thus a spring might be the light duty spring for an Ambassador and the same spring, the heavy duty spring for the Gremlin. The spring specifics would call out where it was needed and the dimensions said it would fit either application.
So yes, the axle might be in slightly different apparent positions depending on a number of factors that may have taken place in the 40+ years since the car was manufactured. Including but not limited to manufacturing tolerances in the first place.
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1968 AMX-R Quote  Post ReplyReply Direct Link To This Post Posted: Oct/12/2015 at 5:11pm
Thanks for your input guys
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