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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Suspension - Brakes - Steering> This is the wrong size shock, correct?
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Topic Review (Newest First)
03-09-2013 06:08 PM
jaw22w I have a fiberglass 27T that looks a lot like yours. I am running coilovers on the rear. My current rear springs are 150#. The car rides just a very little stiff. I would think our rear weights are about the same. I think that 125 to 140# springs should be perfect. My car looks like this.
Just guessing, but looking at the length of your shock versus the length of your spring, the shock is bottomed out at ride height.
Does the shock go through the middle of the spring?
All the above questions are good questions. With some answers, we could get you straightened out.
03-09-2013 11:36 AM
aosborn jetskibob1, the approximate spring rate you need can be calculated with a bit more information from you. You don't need to go get the car scaled, but I do need to know...

Spring free height=13"
Spring installed height= (exact height, don't guess)
Spring wire diameter= (measured with calipers to the nearest .001)
Spring coil diameter= (the diameter of the spring center to center)
Space between the spring seats at the desired ride height=
Distance between the shock mounts at the desired ride height=

When this information is known I can calculate what the rate is of the spring you currently have, and then knowing the installed height it can easily be determined what the current load is on the spring. Knowing the unsprung weight can be helpful, but with a light car and a live axle, I just assume it is really heavy in relation to the rest of the car and adjust accordingly. Since we also know that the spring you have is WAY too stiff, that gives us a starting point to adjust from.

Let me know if you have questions.


03-08-2013 07:31 PM
46streetrod Call afco 1812-897-0900ext 56236 They will tell you all the info you need to get for the proper shock. they custom build shocks for everything.
02-17-2013 08:55 PM
OneMoreTime Actually what is needed is the weight of the car at the rear axle..From that the correct shock valving and spring rate can be estimated..A light car like that will never ride like a mercedes but can be made better..Get the weight and then call the tech line at pro shock to see of they can set you up..

02-17-2013 08:54 PM
sedanbob An easy way to get close on your weight per axle, is to go to your local truck scales and park with each axle on a separate section of the scale. Once you have the weight (of your rear axle in this case), you can talk to the spring folks about which to use. You should also be armed with your suspension travel measurements. A softer spring may be appropriate, but too soft and you might be bottoming out.
02-17-2013 08:45 PM
Pantaz As long as the shock doesn't top-out/bottom-out, then the length is acceptable. The damping characteristics are independent of the shock body length and/or diameter.

The majority of your problem is too stiff springs. The rule-of-thumb I use is to have the suspension compress 1/3 of total travel at operating weight.

At minimum, you need to know the vehicle's weight (front and rear) before you can find proper springs. You'll do better if you take the time to figure out the actual unsprung weight (wheels, tires, axles, etc.)
02-17-2013 08:10 PM
jetskibob1 Shock...compressed is 9.25" extended 14.125"

Spring...The spring is 13" when out of car. When installed, the spring compresses, to about 12-12.5"

It's in a fiberglass 27 raodster. Here is the car...

02-17-2013 07:55 PM
shock/ spring

need more info. you need to know the shock's installed height. what is the free lenght of the spring (uninstalled) lenght of spring installed and what kind of vehicle is it in?
02-17-2013 07:34 PM
This is the wrong size shock, correct?

Because my car is light in the back, the spring even when installed isn't compressed much more than in this photo, if at all.

My car is the roughest riding vehicle I've ever been in... Since this shock is basically the same size as the spring, do you think this is why my car feels as if there is no suspension in the rear at all?

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