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Coil over conversion advice

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DMack View Drop Down
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    Posted: Oct/09/2019 at 5:35pm
Hey All,

I am looking to do a front coil over conversion on my 73' Javelin.  I have received a ton of valuable information from Forum member "Mopar_guy" (many thanks again!)....But I'm looking for someone who has put either (Ride-tech or QA1) coil overs on and has utilized the factory upper control arm and upper shock mount.  I am curious what part numbers(either Ride-Tech or QA1) were used for the actual "shock" component.   I have the part number for the (tapered) spring, but I'm curious what shock worked in conjunction with the spring?  Looking to lower the factory stance by 1"-2" up front.  The rear will have to have the springs de-arched to get the lowered (dead level) look i'm going for.  

There's a ton of knowledge in here, I figure i cant be the only guy who has wanted to do this.  

Thanks again everyone.

**All, I've updated this posting with part numbers and pictures of the final product.  Check out page 5 if you need more info**

Dave


Edited by DMack - Dec/02/2020 at 1:43pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Oct/09/2019 at 7:11pm
What ever you do to lower the front... don't use springs or coilovers to lower the OEM suspension.

Use lowering plates or redesign with proper geometry. AMC did well with proper geometry with the stock height, once out of spec, the arms will be off on angles with camber on up swing, even after alignment.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Oct/09/2019 at 8:09pm
An inch or so is not going to whack out the geometry enough to worry about. I ran 6 cylinder springs in mine for years and it aligned just fine.

"Hemilina" My 1973, 5.7 Hemi powered Javelin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2019 at 7:04am
An inch is typically considered the most you should lower with springs, though many have lowered twice that much or more. Lowering too much does mess up steering geometry, but if just cruising around it doesn't mess it up so bad that tires are worn or steering is off too much. It DOES affect ride as it's a lot harder (or you're bottoming out a lot!). For handling performance you really don't want to drop it much with the springs!
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Jmerican Quote  Post ReplyReply Direct Link To This Post Posted: Oct/12/2019 at 9:46pm
Lowering much without geometry compensation will have a negative affect on roll center geometry and will require more spring to keep the same roll rate. Plus being lower, one has less travel, and hence need more rate to prevent acting on the bump stops. On the stops or near them, you better have some stiff shocks to control the high rate. And on. 

In addition to bump steer type or related issues. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2019 at 12:47am
don't forget these are unibodies, monocoque designs where sheet metal constructs are taking loads. no AMC shock mount is able to support the car's weight on any corner. the front inner fender, spring tower, and the connection up to the firewall are designed for the vertical load. the shock mounts are not. (many folk who put air shocks in the rear of and AMC experience a punched-through upper shock mount.)

up front the only chassis member designed and able to support the weight is that upper spring socket. the AMC front suspension design is very clever and technically sweet -- the static load is directly over the "king pin" (virtual) and wheel upward impulses directed straight up into the socket. the upper arm is under nearly zero load oif any kind and mostly keeps the knuckle vertical. the lower arm of course deals with all of the horizontal forces (parallel to the road), bumping curbs, braking, cornering, etc.

the AMC spring-over-knuckle has the best features of a McPherson strut without the dynamic geometry changes. camber in turns can be (but isn't :-) precisely controlled. the downside for AMC was, it's really tall! it really hurt styling choices early on.

a GM system transfers the static load to the lower control arm, so the lower arm is very stiff and heavy (high unsprung weight), and the upper end of the spring can be tied into the frame since it's so low. this allows for a lot more flexibility in styling the car. it has the terrible feature of a radically changing "leverage" over the spring, in turns. it is LOUSY handling by design. AMCs is flatly superior.

the common Ford spring in the upper arm isn't bad but has some dynamic (roll) spring-leverage changes.

AMCs system is very nice. i think product-engineering-wise, the older Nash type trunnions were more labor intensive (63 Classic...). the AMX type trunnion is a no-brainer -- it's very nice to work with! it has a bit of mass though (not that it would matter in Ramblerdom).

i would imagine that late 60's AMC suspensions have less unsprung mass than GM, for sure, and likely Ford. the early Americans have good geometry, but bizarre and terrible construction details.  but those are extremely light weight! and AMC fixed all that crap starting with the 64 Americans.

AMC suspension design is good, not junk at all. certainly late model stuff is superior -- it has 50 years of experience and now, computer design and simulation. but Ford, GM crap from the 70's and 80's is in no way "superior". the mustang 2 stuff is mainly easy to bolt on. it doesn't automatically work better.

as always, modifications depend entirely on what you expect to do, and get out of it. i'm no purist, and it's your car, do what's the most enjoyable! i'm no stranger to heavy mods for fun and the challenge of it.



Edited by tomj - Oct/13/2019 at 12:53am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jmerican Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2019 at 11:50am
Well put, as usual Tomj. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2019 at 1:56pm
All he's trying to do is replace the stock springs and shocks with a coilover setup just like the CF conversion but without the control arms and the high price tag. He's going to keep his stock control arms and the springs will sit in the stock spring pockets. The shock is still a shock and will hook to the stock shock bracket with no extra load on it. The load is carried the same way as it was designed.

There was a guy who use to make a conversion as I'm describing. (don't remember his name) I called him years ago to get one but he quit making them since the sales fell off. I got tired of guessing what springs to use and wanted the adjustability that a coilover will give you in both ride height and rebound. Lowering the ride height an inch or two is not going to kill the geometry. What happened to all the cars that were driven thousands of miles when the original springs sagged out? They kept driving them! Most restored cars now a days aren't driven a few hundred miles a year so it's a non issue.

"Hemilina" My 1973, 5.7 Hemi powered Javelin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jmerican Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2019 at 2:26pm
I get it. Those coil over conversions are nice. I saw on one that fed the loads into the chassis very nicely. I’ve seen other unibody cars converted with varying degrees of success and failure. One thing mentioned on another post was about low profile tires and ride quality. I mentioned that modern cars that run those have massive compliance in their bushings. Often strategic compliance. Kinematic engineering. 
Take a Porsche 911 or 924/44/68. Torsion bar rear, where the bar is effectively isolated by bushings, as is the very rigid crossmember. The loads from the spring into the chassis are very well isolated and well distributed into the chassis. The shock is separate, and fed into the unibody in another mount. People circumvent all that with a simple and effective coilover. It solves a few things, but my point is that all the spring and shock loads AND vibration now pass through a weak body point and with a small rigid spherical or shock bushing. Sometimes the unibody will break, depending on spring and shock rates used. Mostly for track use so vibration takes a back seat (literally).

Tom’s points, to me, are well put. 

And I stand by my comments in geometry. Particularly when I say that when roll centers are altered for the worse, your need for excessively high spring rates kills compliance and ride. 

As for worn out hoopties and cars driven a couple hundred miles, and it being a non issue. Ok. Sure. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2019 at 3:43pm
Well, I can say this for sure, since I put the Fatman IFS in my car, it rides and handles light years ahead of the stock front suspension - and that's with 17' wheels on it. A friend of mine that has a '14 Challenger says my Javelin rides as nice as his car so take it for what it's worth. You guys sit here and argue how great the stock suspension is but when you put a low profile tire on it, the rides goes out the window. I sure don't have that problem and I have poly A arm bushings. My tires sure wear better than they ever did with the stock suspension too. I'm sure we can argue this all day but al I know is that I'm glad I got rid of it almost 12k miles ago now. Big smile

"Hemilina" My 1973, 5.7 Hemi powered Javelin
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