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Frame/Suspension/Brake... Talk & Q&A All things... Frame/Suspension/Brake

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  #1  
Old 09-23-2020, 03:58 PM
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DozerII DozerII is offline
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Default HELP with spring rates

So just when you think you are done things that don't seem quite right start to nag the brain. On the 28 Dodge I am running a Mustang II cross member with tubular control arms, rack and pinion and air bags. Because of that huge heavy 440 I am using 2800lb 7.5"dia bags at approx 45psi if I go to the smaller 2600lb bags I will have to run 65psi or higher along with a real harsh ride. The 2800lb bags are a real tight fit and in places there is only 1/8 inch clearance and on a full turn either way the caliper just touches the bag

I'm seriously considering changing to a set of Mustang II coils, it will involve a bunch of cutting and grinding and welding, but in the end they won't leave me stranded on the side of the road. The springs are available in 25lb rate increments from 250lb to 450lb I have no idea where to start? The motor is set back a long ways as the rad is centered on the crossmember. I'ts been suggested to start with a 375lb rate the supplier has free exchanges but it would be about $40. each way in shipping!

I would really like some advice from all of you that have gone before me.
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  #2  
Old 09-23-2020, 05:32 PM
bob w bob w is offline
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In the Mustang II the engine sits just about centered over the crossmember. In your car and in most hot rods the engine is well behind the crossmember. When I first used Pinto crossmembers I would look for the lightest oem spring which was in a 4 cylinder car with no accessories. The heaviest was in a V8 station wagon with air. I've always used the lightest spring with small block Chevy engines. Sometimes one coil would have to be cut to get a lower ride height. That increases the spring rate.

I put a Fatman MII in my Anglia. It arrived with 450 lb springs and had no suspension at all. For the last 20 years it has had the lightest springs I could find.

And in conclusion...I suggest a pretty light spring rate to start.
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  #3  
Old 09-23-2020, 07:41 PM
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Quote:
Originally Posted by DozerII View Post
So just when you think you are done things that don't seem quite right start to nag the brain. On the 28 Dodge I am running a Mustang II cross member with tubular control arms, rack and pinion and air bags. Because of that huge heavy 440 I am using 2800lb 7.5"dia bags at approx 45psi if I go to the smaller 2600lb bags I will have to run 65psi or higher along with a real harsh ride. The 2800lb bags are a real tight fit and in places there is only 1/8 inch clearance and on a full turn either way the caliper just touches the bag

I'm seriously considering changing to a set of Mustang II coils, it will involve a bunch of cutting and grinding and welding, but in the end they won't leave me stranded on the side of the road. The springs are available in 25lb rate increments from 250lb to 450lb I have no idea where to start? The motor is set back a long ways as the rad is centered on the crossmember. I'ts been suggested to start with a 375lb rate the supplier has free exchanges but it would be about $40. each way in shipping!

I would really like some advice from all of you that have gone before me.
Air bags are really tough. If it is just touching it, and there is no motion, like just a little kiss, it will likely last forever. That said, if you were to put a little barrier between the part of the caliper that is touching and the air bag, it would either block the caliper from making contact, or at worst, it would transfer the contact point over a greater area. (Think pushing against something with the palm of your hand, rather than poking it with a finger.) The way I envision it from what you say above, it doesn't sound like a huge concern. To me...

Another possibility is to put a stop on the steering so the caliper can't get to the air bag. That would be even better. And easier and cheaper. All you would lose is a little turning radius.
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  #4  
Old 09-24-2020, 05:22 AM
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Quote:
Originally Posted by bob w View Post
In the Mustang II the engine sits just about centered over the crossmember. In your car and in most hot rods the engine is well behind the crossmember. When I first used Pinto crossmembers I would look for the lightest oem spring which was in a 4 cylinder car with no accessories. The heaviest was in a V8 station wagon with air. I've always used the lightest spring with small block Chevy engines. Sometimes one coil would have to be cut to get a lower ride height. That increases the spring rate.

I put a Fatman MII in my Anglia. It arrived with 450 lb springs and had no suspension at all. For the last 20 years it has had the lightest springs I could find.

And in conclusion...I suggest a pretty light spring rate to start.
Thank You for the great information Bob

Quote:
Originally Posted by Skip View Post
Air bags are really tough. If it is just touching it, and there is no motion, like just a little kiss, it will likely last forever. That said, if you were to put a little barrier between the part of the caliper that is touching and the air bag, it would either block the caliper from making contact, or at worst, it would transfer the contact point over a greater area. (Think pushing against something with the palm of your hand, rather than poking it with a finger.) The way I envision it from what you say above, it doesn't sound like a huge concern. To me...

Another possibility is to put a stop on the steering so the caliper can't get to the air bag. That would be even better. And easier and cheaper. All you would lose is a little turning radius.
You are correct Skip, the caliper touching the bag is an easy fix, it's the other close areas that are bugging me. Maybe I'm over thinking this, but the thought of a blown bag in the middle of no where worries me.

Decisions, decisions.
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  #5  
Old 09-24-2020, 07:03 AM
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  #6  
Old 09-24-2020, 01:10 PM
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Dozer, if it's only the kiss at the extreme steering angles, don't worry about it. How often do you hear your power-steering belt squealing when you turn? Almost never, because you usually don't have to make that tight of a turn, and you are not an amateur driver, so there won't be much contact, ever.
I vote with Skip.
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  #7  
Old 09-24-2020, 08:06 PM
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I run right at 60 lbs 40 on the front, 40 lbs in the back of my Olds with a SBC for the most part it's not bad at all. It is right at the limit of comfort though. Any higher and the bumps get noticeable.

EDIT: But I do have about 10" of padding on my seat.
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  #8  
Old 09-25-2020, 05:14 AM
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Quote:
Originally Posted by MercuryMac View Post
Dozer, if it's only the kiss at the extreme steering angles, don't worry about it. How often do you hear your power-steering belt squealing when you turn? Almost never, because you usually don't have to make that tight of a turn, and you are not an amateur driver, so there won't be much contact, ever.
I vote with Skip.
Thanks Mac, still working this out in my head.

Quote:
Originally Posted by Sam_Fear View Post
I run right at 60 lbs 40 on the front, 40 lbs in the back of my Olds with a SBC for the most part it's not bad at all. It is right at the limit of comfort though. Any higher and the bumps get noticeable.

EDIT: But I do have about 10" of padding on my seat.

Thanks Sam, My Essex was the same but I only had 3 inches of padding in the seat.
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  #9  
Old 09-25-2020, 12:01 PM
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Quote:
Originally Posted by DozerII View Post
Thanks Mac, still working this out in my head.




Thanks Sam, My Essex was the same but I only had 3 inches of padding in the seat.
The older I get the less padding I have in my seat, too.
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  #10  
Old 09-25-2020, 02:12 PM
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Overheard my wife and daughter talking and the wife says, "why is it the men loose their butt's and the women's grow when we get older"
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