Re: [AMC-list] HMX back on the road!- Marc Montoni

[Allison Stevens <alliups@xxxxxxxxx>]

Short answer I don’t know. Can’t find the specs I thought I had seen before. 
What I can say is spring rate and ride height should match intended use and 
power level. Without getting into roll center height and stuff that is beyond my 
current knowledge level it is smart to illustrate a few basics:
 
Stock AMX rear spring specs for the uprated “Ralley tuned” version is 110 lbs. 
per inch. The stock rear roll-bar imparts 85 lbs. per inch .  Front specs are 
hazy but the max front spring pressure listed, that I know about, was 350 lbs 
per inch-my guess was the ’79 with optional suspension rate was 325 lbs. to 350 
approximately. Coupled to the AMX bar that goes up to an additional 325 lbs. per 
sq. inch. When the wheel rate is calculated the total factors in at about 490 
lbs. per sq inch when cornering.
 
 Dropping the spring an inch changes the requirement and thus I’d increase the 
spring 25 % or roughly 422 lbs per inch which would result in a net wheel height 
( center of wheel- presumably hub height and approximately mid-spring ) of 165 
lbs wheel rate.  That would work coupled with a light intake, headers and small 
starter. Goes without saying to also locate the bar with urethane bushes and top 
grade fasteners ( if they are bigger than stock- even better )
 
At the rear with less arch to achieve 1 inch drop probably want to go about 15 
to 20 percent, maybe only 10 percent based upon leaf dynamics. So 125 lbs per 
inch would be my guess.
 
Contacting the spring maker of choice ( not a vendor ) and stating your goals 
will result in the best result

Regarding the Mitchell bar pak. I got mine directly from Tony Zamisch's Defender 
Javelin including his better attachment blocks. Will have to experiment because 
for a shorter wheel base AMX with torque links the rear bar may be too stiff 
without backing off on the rear spring spec.

Interesting that the '79 AMX uses, instead of links, staggered rear shocks.


Message: 5
Date: Tue, 12 Apr 2011 21:46:00 -0400
From: Marc Montoni <Freedom@xxxxxxxx>
To: amc-list@xxxxxxxxxxxxxxxxx
Subject: Re: [AMC-list] HMX back on the road!
Message-ID: <20110413014948.2009B984036@xxxxxxxxxxxxxxxxxxxx>
Content-Type: text/plain; charset="us-ascii"


Steve Avery <stoverstevens@xxxxxxxxx> said:

>Don't know about part numbers but gather settings changed between factory
>bias ply cars vs. later  ones radial ones. The '79 AMX and later Spirit GT
>definitely handle better and with better feel than my '70 AMX even though it
>has better than factory alignment and camber specs done to complement the
>wheels/ tires and offset, wider rims and tires, all new bushes and
>reinforced suspension arms.


Yes,  there is no doubt the Spirit AMX and GT handled much better than the  
AMX.  Unusual that this is true even though the early AMX body was  stiffer than 
the Spirit body.

Not having any money to do any real  major engineering, AMC diddled with details 
until they got things very  "right".  The major suspension components were 
mostly the same -- ball  joints, bushings, control arms, etc.  The 79 AMX sway 
bars were a huge  -- and fairly cheap -- improvement.  The rear isoclamp 
assembly, another  big (and relatively cheap) improvement, was a Ford-designed 
unit that  was similar to the pieces developed for the Muskrat.


>In addition, the factory GT or SAMX ( Spirit AMX ) have a factory rear roll
>bar and a much fatter front bar than my '70. 


Yep.   I often wondered why AMC didn't develop those mondo fat sway bars for  
the original AMX.  The benefits to handling were already well-known by  the 
mid-60's.  One of the pieces I always look for when in junkyards are  the 
super-huge front and rear sway bars AMC put on the Ambassador (and  later 
Matador).  I have them on my 71 Ambassador (they were original  equipment on 
that car), my two 69 Ambassadors's, and my 77 Matador.  You  would be amazed at 
the difference.  I used to go looking for twisty  back roads to run my 71 on, it 
was such a joy to drive.  Instant  steering response, easy to 'drift', easy to 
throw into oversteer if you  wanted to, etc.


>There are changes that can improve upon the factory offering. Ride height
>about an inch lower and front/rear spring specs more in line with what the
>B.F. Goodrich  Spirit AMX's used along with using poly supported stock bars,
>or better, a set from Larry Mitchell plus a set of KYB's or Koni's, new
>suspension bushes, new isolators for the rear spring leafs as well as the
>perches, a better steering box or the box built by a performance house, etc.
>really ties it all together. The ride height change really needs to
>accompany the spring change to make a real noticeable difference.


I've  been wondering if Mitchell's bar set has seen any redevelopment since  
Mitchell's heyday back in the 80's.  Some of his sway bar kits way back  then 
were Firebird parts.

Otherwise, I agree on all of the  above.  Individual components with more modern 
technology / materials  (better bushings, etc) makes the old stuff we drive work 
one heck of a  lot better.

BTW, Steve, do you have the suspension specs for the BFG Spirit AMX's?
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