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Old 07-14-2009, 05:27 PM
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adding weight to the trunk

Has anyone ever heard of adding weight to the trunk of a car to stop it from bouncing???? Over the 4th of July weekend I got a chance to drive one of my dream cars that got me into street rodding a 40 chevy coupe. It looked great but drove like crap. I asked the guy who built it who has a 38 plymouth coupe why it drove like that and he said it needed some added weight. I have a 47 ford and I went home and added it and away went the bounce. My car has a 75 camaro rear end along with the same leafs and shocks. I changed the shocks about 6 months ago. The car is not road ready but just by driving it around our yard it bounced like a car with no coil springs, but with the weight in the trunk it did ok. Is this a good idea??? I can hide the steel bars when I upholster the trunk. By the way the guy built all 3 cars. He said his doesnt bounce as it is heavier. Give me your thoughts.

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Old 07-14-2009, 09:30 PM
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ride heigth?

Is you car set at ride height and are the shock mounting brackets at the right height to match a stock donor length at ride height?
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Old 07-14-2009, 10:52 PM
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While adding weight can certainly make your car ride smoother if it is too stiff, it is a band-aid to the real problem. I would recommend altering the spring rates and the dampening to get the car to ride the way you want it.

Andy
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Old 07-14-2009, 10:55 PM
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Quote:
Originally Posted by impalalover60
Has anyone ever heard of adding weight to the trunk of a car to stop it from bouncing????
Whether or not the added weight stopped the "bouncing", this is not the cure.

There's a lack of rebound damping by the sounds of it, this can be addressed by properly damped shocks or adjustable shocks. If the spring and/or shock mounting locations have changed, this will alter the rates the wheels "see".

IIRC, 2nd. gen F-bodies rear leaf springs were rated at around 130 in/lb. I would check to see that there is sufficient arch still in the leaf spring so the spring can perform properly. If there isn't enough arch it could be because the spring rate is too low or the springs are worn out. Trans Am w/WS6 will have the stiffest OEM rates followed by the Z-28's F41 deal. The aftermarket has this app well covered, so OEM springs really aren't even needed.

The bushings all need to be tight as well.
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Old 07-20-2009, 02:55 PM
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Ok if this was before coilovers came into play what type of shock would you rodders use. I mean the type of shock that I could get at autozone. For what specific year of car to make these fat fendered cars not bounce in the rear.
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Old 07-20-2009, 03:11 PM
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Quote:
Originally Posted by impalalover60
Ok if this was before coilovers came into play what type of shock would you rodders use. I mean the type of shock that I could get at autozone. For what specific year of car to make these fat fendered cars not bounce in the rear.
actually what you need to do is to weigh the car in the finished condition and then we can make an educated guess as to what we need in the way of spring rate and shock valving..the unfortunate thing about auto zone shocks is that no one has a clue as to how they are valved...best off is to bite it and get some pro shocks that are adjustable and revalvable..or similar..Just an FYI when we set up a race car we take a whole box of springs and shocks with us to the
track and change them as needed to get the car right..

Sam
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Old 07-20-2009, 04:22 PM
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I'm with Sam. You at least need to know what your car weighs and what the front to rear bias is then you can go from there. Most people tend to overspring. I like to go with less than what the parts houses say. Seems like they always say you need more than what you really need. If they tell me I need a 130's on the rear of my drag car for what it weighs, I'll order 110's and it usually works out better than the 130's did. I feel I don't have many sets but there's 3 sets hanging around here. Shocks are cheaper and easier to sort out imo. Softer shocks usually give you a better ride but I usually start at least with a 50/50 and as long as they are not really stiff, they usually work well on a light weight street car.
There's lots of info on the net about suspensions and shocks so do some studying. Also, a lot of people think shocks helps support the car but they don't. That's the job of the springs and shocks control what the spring does. They 'dampen' the action of the springs. You mentioned in your first post about the car riding and bouncing like it didn't have coil springs. Without springs, it'll 'hit' ya like a hammer but springs without shocks will just go up and down and top out and bottom out because there's no shocks to control them....
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Old 07-20-2009, 10:37 PM
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Quote:
Originally Posted by impalalover60
Ok if this was before coilovers came into play what type of shock would you rodders use. I mean the type of shock that I could get at autozone. For what specific year of car to make these fat fendered cars not bounce in the rear.
If you have a shock that came with a kit for example, and you can cross reference the number on the shock to an application, half the battle is over. At that point typically you can choose between a low cost oil shock (Monroe Matic), low pressure gas (KYB GR2) or high pressure gas (KYB Gas-a-Just or any other shock that has a leash on it to keep it from expanding). Typically the oil shocks are the cheapest and the softest dampening and the cost and stiffness generally go up from there.

If you are trying to find a shock by dimension and mounting type, I used to just go through the NAPA or TRW catalog that lists all the shocks by extended/collapsed length and mount type. When you found one that would work, cross reference to an application and go from there as I described above.

Don't put shocks designed for front suspension on the rear, they tend to be too stiff, and don't use shocks for a truck application in the rear, they tend to be too stiff also. If you find a shock that is the right dimension, oil or low pressure gas and are for a vehicle similar in axle weight and shock mounting position to what you are building, you might get lucky and find one that works. Otherwise, buy a single adjustable, or if you really like to spend money, a double adjustable shock, set it to full soft and go start tuning!

If all this seems like a lot of trouble to go through for a shock, consider the alternative of having a car that rides terrible and doesn't get driven because it beats you to death.

Andy
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