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mechanical engineers please help!
#197636
01/18/09 11:01 PM
01/18/09 11:01 PM
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Joined: Feb 2007
Posts: 5,080
organ
maximum entropy
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OP
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Joined: Feb 2007
Posts: 5,080
organ
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it seems to me that lowering blocks would reduce axle windup, by virtue of the center of rotation being further from the spring, and also from the forward vector of the axle having more leverage to flatten the spring as it moves forward. what do you guys think?
for what is the good life if not doing things thoughtfully?
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Re: mechanical engineers please help!
[Re: maximum entropy]
#197642
01/19/09 12:36 AM
01/19/09 12:36 AM
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Joined: Aug 2003
Posts: 4,384
Madison Wi
NTOLERANCE
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Joined: Aug 2003
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Madison Wi
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TO put it in perspective, think of a 4WD truck with really big lift blocks in the back. Say like 8 or 10 inch blocks. Without a control device on the rear, those axles will move ALOT.
Seen people driving on the road, with a lifted truck and big blocks, and I can actually watch the spring wrap. Especially if its a stick truck.
I used to care but....... things have changed
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Re: mechanical engineers please help!
[Re: NTOLERANCE]
#197644
01/19/09 02:55 AM
01/19/09 02:55 AM
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Joined: Feb 2007
Posts: 5,080
organ
maximum entropy
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organ
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lowering block and axle above the spring. also the traction input has additional leverage on the system. my guess is it cancels out the rotational moment. i'm seriously considering mounting a camera under my car and documenting the shenanegans. thanks for your input.
for what is the good life if not doing things thoughtfully?
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Re: mechanical engineers please help!
[Re: maximum entropy]
#197646
01/19/09 03:35 AM
01/19/09 03:35 AM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
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Canton, Ohio
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Quote:
it seems to me that lowering blocks would reduce axle windup, by virtue of the center of rotation being further from the spring, and also from the forward vector of the axle having more leverage to flatten the spring as it moves forward. what do you guys think?
I think your Dead wrong 
Under power the axel is going to try to wrap up on the spring. And it doesnt care if its mounted above or below the spring.
Adding any additional space between the axel and spring by a spacer block will only increase wrap up leverage. Says me and science. mike  
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Re: mechanical engineers please help!
[Re: Sport440]
#197647
01/19/09 06:38 AM
01/19/09 06:38 AM
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Joined: Apr 2007
Posts: 871
WA 98043
thecarfarmer
super stock
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super stock
Joined: Apr 2007
Posts: 871
WA 98043
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 Not a mechanical engineer, but a mechanical designer... what I get for dropping out! Here's a thought experiment: Imagine you have your park brake on real tight. Your car's on a lift. You grab that rear wheel and try to turn it - you go grab a socket, breaker bar, and six foot 'cheater' pipe; try to turn that wheel with a lug nut (let's pretend you don't twist that lug off!) You know that you'd feel that leaf spring move around, right? Of course, with that much bar, you could probably knock the car off the lift, too... pretend it's welded on. Now, imagine you had a foot of spacer between the spring and the axle; doesn't it make sense how the rotational forces applied to the axle would tend to grab that long block and twist the spring? Hope this helps. -bill
Seduce the attractive, and charm the rest.
******
489 C.I.D., roller cam, aftermarket heads, tunnel ram, stock '54 Dodge rear axle assembly: which of these doesn't belong?
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Re: mechanical engineers please help!
[Re: Thumperdart]
#197652
01/19/09 02:48 PM
01/19/09 02:48 PM
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Joined: Oct 2003
Posts: 11,688
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,688
W. Kentucky
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Quote:
Calvert has no issues w/using em eighter. 
I have 3/4" billet blocks on my Dart. When I called Calvert, Travis recommended that I not do it  . He suggested changing the rear (Mono leaf)segment of the spring.
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Re: mechanical engineers please help!
[Re: Thumperdart]
#197653
01/19/09 02:53 PM
01/19/09 02:53 PM
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Joined: Feb 2007
Posts: 970
Backwater, PA
bwdst6
Bob George Racing #1 Fan
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Bob George Racing #1 Fan
Joined: Feb 2007
Posts: 970
Backwater, PA
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I am a Mechanical Engineer and my feeling is that lowering blocks won't improve axle wrap. The overall stiffness needs to be increased. Which is why getting the axle closer to the front of the leaf works. Ever notice how Mopar's didn't have the same wheel hop problem back in the day compared to other makes? But obviously if traction bars are used that changes things.
This post is available in double vision where drunk.
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Re: mechanical engineers please help!
[Re: maximum entropy]
#197658
01/19/09 04:00 PM
01/19/09 04:00 PM
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Joined: Mar 2007
Posts: 3,291
West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,291
West Coast, USA
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The forces at work are significant and strong enough to crush something as seemingly stout as the spring perches. Some of the guys on here where talking about it on another thread. Now I'm going to have to take mine back apart and re-enforce them...
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: mechanical engineers please help!
[Re: BADDART]
#197659
01/19/09 04:09 PM
01/19/09 04:09 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
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Posts: 52,972
Romeo MI
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If your springs are strong enough to keep from defecting and you have good shocks you probably wouldnt see any difference. But with a 4-link the farther you go from the axle centerline to the rear heim joints the easier it is to pull the front wheels(greater leverage) even with the IC at the same distance and height 
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Re: mechanical engineers please help!
[Re: BADDART]
#197663
01/19/09 11:59 PM
01/19/09 11:59 PM
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Joined: Jan 2005
Posts: 3,635
Oakland, MI
dizuster
master
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master
Joined: Jan 2005
Posts: 3,635
Oakland, MI
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Ok non-engineers get a pass, but you engineers need to study a little more! Many people got this right, but nobody got it for the right reason.
First of all... Lets talk basics.
Torque= Force x Distance
So if you have 500 ft-lbs of torque. That is equal to
500lbs x 1 ft
OR
1 lb x 500ft
You can easily see that with a given input torque (from the axle) the force to counteract that force gets LOWER as the length gets longer.
Practical example:
You have a tight lugnut you need to get off. It is applying a torque to stay tight. You have to counter act this torque with a wrench and a force. We all know as the wrench gets longer, the force gets smaller.
Torque=Force x Distance.
Ok now for the specific example, Maximum E. almost got it right in the begining, he was on the right track.
You can see from my example above that the longer distance would have less force on the spring (less wheel hop). So many of you are thinking, then why when I add 2" of lowering blocks does the wheel hop get worse (Just as mentioned by the old guy above who probably hasn't read this far because he only cares what he knows, not why it works)
What you need to think about though is the distance from the application of the torque center, to the point the force is being applied. In this case, the critical area for high force is near the front eye of the spring. That's because the spring is at it's weakest point with only one leaf section there.
So if you think about the geometry, the spring is in an arc. As you space the axle upwards, the axle center actually gets closer to that front eye of the spring! Think about if you were to measure from the eye of the spring straight rearward, it's a shorter distance then if you measure on the angle downward. This means as you space the axle upwards, the distance gets shorter.
Torque=force x distance.
The torque is the same no matter where you put the axle. So if you space it upwards and the distance is shorter, the Force is actually increased.
So yes, the forces on the spring get worse with the lowering blocks, but it's not because the distance get's longer, it's because it gets shorter.
Hope that's not too confusing, if anyone wants a picture (Free Body Diagram) just ask and I'll draw one up and post it...
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Re: mechanical engineers please help!
[Re: dizuster]
#197664
01/20/09 12:40 AM
01/20/09 12:40 AM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Quote:
Ok non-engineers get a pass, but you engineers need to study a little more! Many people got this right, but nobody got it for the right reason.
First of all... Lets talk basics.
Torque= Force x Distance
So if you have 500 ft-lbs of torque. That is equal to
500lbs x 1 ft
OR
1 lb x 500ft
You can easily see that with a given input torque (from the axle) the force to counteract that force gets LOWER as the length gets longer.
Practical example:
You have a tight lugnut you need to get off. It is applying a torque to stay tight. You have to counter act this torque with a wrench and a force. We all know as the wrench gets longer, the force gets smaller.
Torque=Force x Distance.
Everything above as Stated is Correct IMO
Everything below as stated is mostly incorrect.IMO 
I will give my arguements on this tommorow And its all good, I look forward to sparring with you dizuster, you know your stuff. mike
What you need to think about though is the distance from the application of the torque center, to the point the force is being applied. In this case, the critical area for high force is near the front eye of the spring. That's because the spring is at it's weakest point with only one leaf section there.
So if you think about the geometry, the spring is in an arc. As you space the axle upwards, the axle center actually gets closer to that front eye of the spring! Think about if you were to measure from the eye of the spring straight rearward, it's a shorter distance then if you measure on the angle downward. This means as you space the axle upwards, the distance gets shorter.
Torque=force x distance.
The torque is the same no matter where you put the axle. So if you space it upwards and the distance is shorter, the Force is actually increased.
So yes, the forces on the spring get worse with the lowering blocks, but it's not because the distance get's longer, it's because it gets shorter.
Hope that's not too confusing, if anyone wants a picture (Free Body Diagram) just ask and I'll draw one up and post it...
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Re: mechanical engineers please help!
[Re: dizuster]
#197665
01/20/09 01:44 AM
01/20/09 01:44 AM
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Joined: Jan 2003
Posts: 1,278
Mission BC
10sec440
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,278
Mission BC
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Quote:
Ok non-engineers get a pass, but you engineers need to study a little more! Many people got this right, but nobody got it for the right reason.
First of all... Lets talk basics.
Torque= Force x Distance
So if you have 500 ft-lbs of torque. That is equal to
500lbs x 1 ft
OR
1 lb x 500ft
You can easily see that with a given input torque (from the axle) the force to counteract that force gets LOWER as the length gets longer.
Practical example:
You have a tight lugnut you need to get off. It is applying a torque to stay tight. You have to counter act this torque with a wrench and a force. We all know as the wrench gets longer, the force gets smaller.
Torque=Force x Distance.
Ok now for the specific example, Maximum E. almost got it right in the begining, he was on the right track.
You can see from my example above that the longer distance would have less force on the spring (less wheel hop). So many of you are thinking, then why when I add 2" of lowering blocks does the wheel hop get worse (Just as mentioned by the old guy above who probably hasn't read this far because he only cares what he knows, not why it works)
What you need to think about though is the distance from the application of the torque center, to the point the force is being applied. In this case, the critical area for high force is near the front eye of the spring. That's because the spring is at it's weakest point with only one leaf section there.
So if you think about the geometry, the spring is in an arc. As you space the axle upwards, the axle center actually gets closer to that front eye of the spring! Think about if you were to measure from the eye of the spring straight rearward, it's a shorter distance then if you measure on the angle downward. This means as you space the axle upwards, the distance gets shorter.
Torque=force x distance.
The torque is the same no matter where you put the axle. So if you space it upwards and the distance is shorter, the Force is actually increased.
So yes, the forces on the spring get worse with the lowering blocks, but it's not because the distance get's longer, it's because it gets shorter.
Hope that's not too confusing, if anyone wants a picture (Free Body Diagram) just ask and I'll draw one up and post it...
I'm no engineer but I have enough experience in auto repair that I think I can comment...I don't agree with this:
"So yes, the forces on the spring get worse with the lowering blocks, but it's not because the distance get's longer, it's because it gets shorter."
I agree that the distance between the axle center and the spring eye get shorter, but it's the force that the axle perch exerts on the center of the spring that causes the windup,not the spring against the eye. Spacing that perch farther from the spring will make it more prone to rotate IMO. Can a car be built with a 2"lowering blocks and be strong enough that it will hold together and run 8's? Sounds like it.Is it optimal? I don't think so. 
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Re: mechanical engineers please help!
[Re: 10sec440]
#197666
01/20/09 03:08 AM
01/20/09 03:08 AM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Remember TWO forces are happening here. One is rotational force from the diff housing to the springs. The other is the diff housing pushing the car (via the spring) forward...... in a linear motion. As I see it one force will counter act the other to some degree.How much one force will counter the other I am not sure.The stiffness of the spring, weight of the car and traction may have some effect. This may explain the differing experiences stated here. I would imagine a longer lowering block would lessen the rotational force on the spring pad at least.Particularly when the diff housing would be more likely to 'run over' the spring mount! Some times it is just easier to try it and see what happens. 
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Re: mechanical engineers please help!
[Re: bwdst6]
#197669
01/20/09 07:31 PM
01/20/09 07:31 PM
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Joined: Jan 2005
Posts: 3,635
Oakland, MI
dizuster
master
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master
Joined: Jan 2005
Posts: 3,635
Oakland, MI
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Quote:
And there's no need for a free body diagram, it's a Mechanical Vibrations problem, not a Statics problem where everything is assumed to be rigid.
True but the load path applied is still calculated in a similar fashion. If you can come up with a simply explained vibrations solution on a forum like this feel free...
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