Cutting Coil Springs?

[64impala]

What is the acceptable limit on cutting springs. I bought new heavy duty springs for my 64 impala and to get the correct ride height, i cut 2 1/2 coils. Im thinkin that i will need to buy new springs with the current height i have now, or can i just run with what i have? Thanks

[Mr. Anderson]

2.5 coils is a lot...the most I ever went was 2. With front coils (at least on my A-bodies) the ends of the coils sit in a certain spot in the frame and control arm, so they really don't like to have half a coil cut. I'm not sure on B-bodies.

The suspension wont like 2.5 coils either because there's a lot of travel gone, and if you are still running stock shocks, then thats a lot of their intended travel that is gone to, so there's a lot less compression than you had before. You'll never be able to align it properly either.

I ran my Olds around for a couple years on some heavily cut coils. By the time I could afford to air bag the car my bumpstops were completely flattened, the bushings and balljoints just about shot, and I went through a pair of used tires every 6 weeks. That was near-daily driving though...

[64impala]

2.5 coils is a lot...the most I ever went was 2. With front coils (at least on my A-bodies) the ends of the coils sit in a certain spot in the frame and control arm, so they really don't like to have half a coil cut. I'm not sure on B-bodies.

The suspension wont like 2.5 coils either because there's a lot of travel gone, and if you are still running stock shocks, then thats a lot of their intended travel that is gone to, so there's a lot less compression than you had before. You'll never be able to align it properly either.

I ran my Olds around for a couple years on some heavily cut coils. By the time I could afford to air bag the car my bumpstops were completely flattened, the bushings and balljoints just about shot, and I went through a pair of used tires every 6 weeks. That was near-daily driving though...

I cut the rear springs, which are new from classic industries. Also they are for heavy duty application so i would think thay are stiffer. I would never cut any more than 1 coil in the front. Thanks for the reply! Anyone else please chime in!

[dontlifttoshift]

When you cut a coil spring the rate increases. Picture it like this, your coil spring is a torsion bar, longer torsion bars of the same diameter are softer in rate than shorter ones. When you cut coils you have shortened the torsion bar and raised the rate. Your heavy duty springs which probably already had too much rate are are now stiffer.

i found this calculator with a quick search. http://www.pontiacracing.net/js_coil_spring_rate.htm Plug your numbers in and compare the rates of your cut and uncut spring rate......report back, I'm curious.

Donny

[monteboy84]

In terms of the spring's performance, there shouldn't be any issue with cutting too much, just the rate change that dontlift mentioned, beyond that if your ride height is where you want it you should be all set.

-matt

[Mr. Anderson]

Ah, would have helped if you mentioned rear springs. No problem there...

[David Pozzi]

Most factory or HD factory springs are pretty soft to start with. A GM HD coil is usually only 25 lbs stiffer, but there were some Corvette coils that were twice as stiff. When you lower a car you need to be stiffer to keep the car from bottming out, so up to double stock rates works for most "Tuner" suspensions. You want the front to match the increase if it's a big increase.
If you shorten the coil by 25%, the rate goes up 25%.
David

[64impala]

Thanks guys for all the info! Much appretiated

[64impala]

when you cut a coil spring the rate increases. Picture it like this, your coil spring is a torsion bar, longer torsion bars of the same diameter are softer in rate than shorter ones. When you cut coils you have shortened the torsion bar and raised the rate. Your heavy duty springs which probably already had too much rate are are now stiffer.

I found this calculator with a quick search. http://www.pontiacracing.net/js_coil_spring_rate.htm plug your numbers in and compare the rates of your cut and uncut spring rate......report back, i'm curious.

Donny


will do. Thanks for the link

[dontlifttoshift]

If you shorten the coil by 25%, the rate goes up 25%.
David

I had never heard that. I realize that its not exact but pretty close I assume? That's good information to know. Thanks

[MonzaRacer]

Another trick is looking in say a NAPA coil spring book in back it will give you spring rates, heights, diameters, etc. Determine just what needs t ochange to get you where you need to go, I have found that if you wish to lift and stiffen an Abody rear spring the appropriate amount and not ride bad and still handle ok look for a cargo coil for 69 Pontiac Catalina/Executive (this is an example only).
Now, I have had a friend run same spring who wanted the load capacity, but not the height, so we bought a second set(I was working at a Sears and we had a set for a 69 Pontiac FS instock and they turned out to be perfect for my 70 Monte Carlo!) bead blasted them. measured my springs in height got some 1/2" all thread and channel iron and compressed the springs lower ( we figured out what he wanted by putting cylinder heads in trunk till it sat ok for him) measured, then compressed the springs same amount. Now clean all the parts then put in a cold oven, yeah dont let mom or wife find you do this, especially if they have sensitive nose, and turn oven on to 200, and let get hot till thermostat cycles off, then go to 400-450 degrees, and wait till it cycles off, thne let sit for 12 hrs, then turn down to 200 (or lowest setting), let cool till it actually cycles back on and off at 200, then turn off and let cool over night.
This will "re set " the ride height of the springs, BUT warning, it may also make them lower than what you want so be sure you actually leave them a little high. and be ready for it to NOT work properly every time.
I have had as many good sets as bad sets so if the price of a set of stock springs and a lot of electricity or gas is an ok chance for you , good luck.
this trick is called "heat setting" the springs nad was used by a lot of round track guys to shove 3/4 ton truck springs in older cars and not have the car weight jacked and getting "teched" out of race. Spring changes were ok, modifying the frames to shove them in wasnt.
also it looked pretty bad and didnt handle as well as the CG was off.

[64impala]

Another trick is looking in say a NAPA coil spring book in back it will give you spring rates, heights, diameters, etc. Determine just what needs t ochange to get you where you need to go, I have found that if you wish to lift and stiffen an Abody rear spring the appropriate amount and not ride bad and still handle ok look for a cargo coil for 69 Pontiac Catalina/Executive (this is an example only).
Now, I have had a friend run same spring who wanted the load capacity, but not the height, so we bought a second set(I was working at a Sears and we had a set for a 69 Pontiac FS instock and they turned out to be perfect for my 70 Monte Carlo!) bead blasted them. measured my springs in height got some 1/2" all thread and channel iron and compressed the springs lower ( we figured out what he wanted by putting cylinder heads in trunk till it sat ok for him) measured, then compressed the springs same amount. Now clean all the parts then put in a cold oven, yeah dont let mom or wife find you do this, especially if they have sensitive nose, and turn oven on to 200, and let get hot till thermostat cycles off, then go to 400-450 degrees, and wait till it cycles off, thne let sit for 12 hrs, then turn down to 200 (or lowest setting), let cool till it actually cycles back on and off at 200, then turn off and let cool over night.
This will "re set " the ride height of the springs, BUT warning, it may also make them lower than what you want so be sure you actually leave them a little high. and be ready for it to NOT work properly every time.
I have had as many good sets as bad sets so if the price of a set of stock springs and a lot of electricity or gas is an ok chance for you , good luck.
this trick is called "heat setting" the springs nad was used by a lot of round track guys to shove 3/4 ton truck springs in older cars and not have the car weight jacked and getting "teched" out of race. Spring changes were ok, modifying the frames to shove them in wasnt.
also it looked pretty bad and didnt handle as well as the CG was off.

Thanks for the info! Great!