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Discussion Starter #1
On the 65 I put the 620's I had (for ever) which were for my 67 convertible build. Anyone remember Canadian Mustang? These are far too stiff and sit way high, even though they are 1 inch drop. And I know cutting these down isn't going to solve the super stiffness. Stock GT's are 291 and NPD has the 480's as well. I'm building this to handle well, but not in a kidney-bleed sort of way. The wife (who's car this is) likes the low stance of the original collapsed standard suspension, and definitely not the waterbed road feel it had. So looking for opinions on the 480's if anyone has them, and of course the GT's. I have just completed the suspension swap in the front. Still working on the back. Have not tightened the lower control arm bolts (stock Moog) or done the alignment yet. I sit on the front fender and it barely dips and I am not as skinny as I was in my sig pic, lol.

Car Details:
1965 Coupe, 302 with aluminum intake and stock heads, AC, Manual Steering, Disc, Arning drop, 1 inch front sway bar, Automatic (C4 now, but will probably be AOD/4R70W by spring). Upper A-arms are the SPC units with the thicker strut.
 

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You still might have to let it sit for a while and drive it some to see the final ride height. I have the 620s. I would be reluctant to go with shorter springs on a street car bc of risking tire scrub on speed bumps or dipping driveways while turning. Somebody put coil spring spacers on the worn-out stock springs on the Emberglo car I bought and it was really close to rubbing even on level ground when turning with a 195/70/14 tire. But the 480s sound nice as I've gotten older. Man, I hate to say that...
 

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Discussion Starter #3
Right now they are the 1 inch shorter springs, and then the Arning drop and I still have a solid 4 1/2 inches above the 205/70R14's on it. And it also seems the SPC uppers have a rub problem on the inside of the tire in a turn. I think this will actually get worse as the springs settle as the arm will move up the side wall which will narrow that gap even more. Might have to take some meat off the end for clearance or go to a larger rim to get around that. I placed the upper ball joint in the most outboard position, so no more room to be had there.
 

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Right now they are the 1 inch shorter springs, and then the Arning drop and I still have a solid 4 1/2 inches above the 205/70R14's on it. And it also seems the SPC uppers have a rub problem on the inside of the tire in a turn. I think this will actually get worse as the springs settle as the arm will move up the side wall which will narrow that gap even more. Might have to take some meat off the end for clearance or go to a larger rim to get around that. I placed the upper ball joint in the most outboard position, so no more room to be had there.
Just because they say they're 1" lowering springs doesn't mean they're actually going to be 1" lower than what you had on there previously. If the previous springs you had on the car were the originals from the factory or have been on there for 20+ years they're going to sag considerably and are going to sit much lower than the new ones you replace them with. Oftentimes people get new 1" lowering springs and they sit considerably higher because of this and the new ones are a much thicker gauge coil than the stock ones you're likely replacing. Since you already have the 620's, I'd try using them and see if they work out for you, cut off 1/4 of a coil at a time with a cutoff wheel until you get the ride height you want. I mean might as well since you've already got them right? Second, what shocks are you using? Imo, shocks are more indicative of comfort and whether you're going to have a jarring ride as opposed to the springs. Lots of people have the 620's or something stiff like them but will go with a nice, quality shock like a Bilstein or similar so it's not jarring. If your shocks are old, worn or cheap that's probably where the jarring part is coming from and it's going to be even worse with a stiffer spring.
 

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The 67+ springs are taller than 65-66 springs. So yea, wrong springs. You could cut them down and end up with 1000lb springs.

I have some NPD 480's for a 65-66 never used sitting in a corner as I went SoT coilover.
 

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Discussion Starter #6
Yeah, I knew I was going to be screwed if I had to cut them. Makes sense about the years difference. The 67 has a rake to the upper A-arm so for the same basic height it would have to be longer.
PMed you about the 480s.
 

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Yeah, I knew I was going to be screwed if I had to cut them. Makes sense about the years difference. The 67 has a rake to the upper A-arm so for the same basic height it would have to be longer.
PMed you about the 480s.
You didn't PM me. You started a conversation.:rolleyes: And I responded.
 

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I have the .620" springs on the front and, yes, they ARE stiff but to my liking. My '65 GT didn't have a BAD ride though so the "GT" springs might be up your alley. You can also try using a "lighter" spring and moving the lower spring saddle out 1" on the upper control arm.
 

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The 67+ springs are taller than 65-66 springs. So yea, wrong springs. You could cut them down and end up with 1000lb springs.

I have some NPD 480's for a 65-66 never used sitting in a corner as I went SoT coilover.
Part of that also depends on the manufacturer and the initial spring rating. Some manufacturers make coil springs that are essentially a universal fit for 1965-1970 mustangs and do so at a certain spring rating and then you cut them to the ride height you'd like. I'm thinking your "67" coil springs with a half coil cut off would probably be right about where you want to be in terms of ride height and they're not going to go from 620's to 1000lb springs with a half coil cut off. I have 600lb springs and cut off 1/2 of a coil and it's neither jarring nor uncomfortable. As stated before, a good deal of that is going to also depend on the shocks you use but a decent shock and a cut 620lb coil spring isn't going to be an issue.
 

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Discussion Starter #10
Ordered the 480's from NPD. Idea here is survival in highway 40 driving. I think that's a nice compromise on stiffness and getting the desired ride height. The 620's are already too stiff for the wife. She wants to enjoy the ride. I want it to be sure footed, especially in a nose dive brake check with a sudden lane change topper. The 620's will go back to their original purpose for my convertible. Everything in the suspension and brakes are new now. Just wrapping that up. The only original parts of the braking system are the pedal and a couple of hard lines. Valving on a shock will not make a spring any softer. In fact you should use the softest spring you can to keep the tire on the road and use the right shock to stiffen the attack while maintaining a good release characteristic. That's straight from Chassis Engineering by Adams. Not building a race car here so good cost compromise is the other direction, stiff spring and a mild shock. A little wheel hop on a rough road is acceptable here. They don't normally set up cones at the entrance of the Dairy Queen either. ;)
 

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Discussion Starter #12
Understood. Seen it both ways, ad diameter in a scholary article on the subject and inch pound in almost all of the catalogs. Just sticking with the parlance as the catalogs almost universally list it as and inch pound rate. That's why I just use the number by itself.
 

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Came about when TMC was selling their blue "contour coils" (whatever the hell that meant) back 25 years ago.....
they called them 620's. They were 620#/in originally.

ex-Global West GM
1991-1995
 

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If you start to use roller bearing spring perches or a lower control arm with a bearing that's going to effect things. With my all bearing suspension the 290 # GT springs were entirely too soft. For some reason I thought they were 480# so I went to the .620" spring which I was avoiding. I cut a half coil off at first but in hindsight maybe I should have left it as it settled about 3/4". Anyway I was surprised to see that ride quality wasn't too bad at all. Firm for sure but not harsh. Very much like today's cars. I wouldn't want to run this spring on a rubber bushing suspension though, that's my taste.
 

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Valving on a shock will not make a spring any softer. In fact you should use the softest spring you can to keep the tire on the road and use the right shock to stiffen the attack while maintaining a good release characteristic. That's straight from Chassis Engineering by Adams.
What shocks are you running? 600lb coil springs with half a coil cut off and Bilstein sport valved shocks here... plenty comfortable and no jarring or rough ride in the slightest.
 

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Discussion Starter #17
Nah. Completely interchangeable, lol. 67-70 620 on left, 65/66 480in/lb on right. Did not even need the spring compressor for reinstall. Not back on the ground yet. Have to bleed the brakes again. Also swapping out the rear springs tomorrow.

737197
 
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