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#758563 - 01/21/10 11:20 PM needed!! rear sway bar up grade  
Joined: Aug 2007
Posts: 278
red/white04 Offline
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red/white04  Offline
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millington, michigan
this summer i upgraded the front sway bar on the monte to a 36mm one off a 90 trans-am. all i can say is WOW! i love it, i'd like to upgrade the rear sway bar. i'm not looking for top of the line but i want one that utilizes stock location. also i am running and 8.5 rear. the stock 7.5 sway bar dont' really clear the pumkin. do they make one that works for the 8.5(grand national?) or would it be better to get the relocation brakets for the lower control arm? its lowered with base eibachs and i have edelbrock adjustable upppers

#758576 - 01/21/10 11:54 PM Re: needed!! rear sway bar up grade [Re: red/white04]  
Joined: May 2002
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MAP Offline
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MAP  Offline
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Yuma, AZ
Hi Red/White,

The amount of drop needed to clear the differential ought to be minimal, since GN's and 442's use the same control arms and the 8.5" rear. If it's outside of the range permissible by the normal loose fit between the CA holes and the fasteners, then I'm guessing that some judicious grinding to elongate vertically the front or rear pair of CA holes might be all that's needed.

About relocation brackets, these usually require a major correction for sway bar mounting points. With a 2" drop, I had to weld-in a block into the top of each LCA to receive relocated rear holes for the sway bar.

Best,
MAP

Last edited by MAP; 01/21/10 11:56 PM.
#758729 - 01/22/10 01:15 PM Re: needed!! rear sway bar up grade [Re: MAP]  
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84 ZZ4 Offline
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84 ZZ4  Offline
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San Antonio, TX
Check out some of the options SC&C has:

http://www.scandc.com/hellwigswaybars.htm

They also have several by Spohn:
Here is one of them...

http://www.scandc.com/spohnarms.htm

And remember, I am GOOD at spending YOUR money.... poke

#758845 - 01/22/10 07:34 PM Re: needed!! rear sway bar up grade [Re: 84 ZZ4]  
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MAP Offline
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MAP  Offline
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Yuma, AZ
Hi 84,

I like it, I like it. I like it especially because you can adjust the effective rear bar rate over a range of nearly 2:1 if I'm eyeballing that bottom picture correctly (the effective bar rate goes as the inverse square of the side swing arm length.)

Best,
MAP

#758861 - 01/22/10 09:01 PM Re: needed!! rear sway bar up grade [Re: MAP]  
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red/white04 Offline
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red/white04  Offline
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millington, michigan
i was looking for something of oem fit in the original location just alittle meatyier and something that would clear the 8.5 housing. i have the 7.5 sway bar on it as we speak..i don't really like the fact that it rubs on the pig.

#758881 - 01/22/10 09:53 PM Re: needed!! rear sway bar up grade [Re: red/white04]  
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MAP Offline
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MAP  Offline
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Yuma, AZ
Hi Red/White,

OK then - OEM but, "a little meatier." "Meat" in sway bars is determined by bar diameter and is very sensitive to even small changes in such. What do you have now? Please measure along the transverse section of the sway bar with a caliper or a micrometer or something of similar accuracy. Take the average of at least four readings along this section of the bar, and if you believe the bar has a significant paint layer on it, then scuff through it to reach the base metal for your measurements.

BTW if the result of all this points toward the purchase of a new bar, then I'd still consider the SC&C adjustable rear bar because the price difference might be surprisingly small.

Best,
MAP

Last edited by MAP; 01/22/10 10:08 PM.
#758941 - 01/23/10 01:18 AM Re: needed!! rear sway bar up grade [Re: MAP]  
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red/white04 Offline
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millington, michigan
um..i don't know about you but 150 to 400 is not a "surprisingly small" span in price. thats more then double. I believe its the factory 3/4 bar, but its been a while since i have been under the car. i figured a 1 inch or 1 1/8 would be more then enough considering i went from a factory SS sway bar(front) to one that is a shade under 1.5 inches.

#758954 - 01/23/10 02:08 AM Re: needed!! rear sway bar up grade [Re: red/white04]  
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84supersport Offline
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Louisville, KY
Sway bars are funny. Its not just about how thick they are. Its aso about how they are made and what they are made of. Thats how the hollow bar you have is stiffer than the factory soild bar. I'm sure MAP could shed some light on the subject. So bigger is better does not necessarily work here. You need to shop wisely first.


84 Monte SS stolen September 2012. 077 DFE Jefferson County KY plate. $2500 reward. Vortec headed 350ci, th350, 3:73 limited slip cast aluminum cover, Autometer gauges, Pro-Stick, 2.5" fiberglass hood.



Matt
#759108 - 01/23/10 04:59 PM Re: needed!! rear sway bar up grade [Re: 84supersport]  
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MAP Offline
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MAP  Offline
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Yuma, AZ
Hi Red/White,

I certainly agree that 150/400 isn't a small price difference! Were my numbers wrong? In any event Marcus will know the numbers for sure since I believe he sells both kinds.

The simplistic view is that your basic U-shaped sway bar introduces a roll stiffness that goes as the OD^4 minus ID^4 in the transverse section, and as the side swing-arm length ^-2. Many companies sell solid rear bars with phi=1", but none that I'm aware of sell phi=1-1/8". That's why I had to have Hellwig form a custom 1-1/8" bar for me some years ago (today the situation may be different.) I wanted 1-1/4", but 1-1/8" was as high as they could go with their fixturing. (1-1/8" is 60% stiffer in torsion than 1".)

I'm not a fan of lots of rear roll stiffness for a variety of reasons, including that a softer rear suspension maintains a better balance of traction between the two driven wheels over a bumpy surface. Now even a phi=1-1/8" bar doesn't make for a lot of roll stiffness - but if you think you need more to keep chassis handling more neutral, I'd next concentrate on raising the front roll center height. More height means less roll, and less roll means that the factory front suspension, which works horrifically in roll, is less coerced to do all the bad things it does that tend to worsen understeer. Less understeer from the front means less need for rear roll stiffness to maintain chassis balance, so voila. Marcus (Mark Savistke) can sell you the ball joints to make this happen if you're up to pulling some of the front end apart.

Best,
MAP

Last edited by MAP; 01/23/10 05:14 PM.
#759351 - 01/24/10 03:46 PM Re: needed!! rear sway bar up grade [Re: MAP]  
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Norm Peterson Offline
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Norm Peterson  Offline
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state of confusion
Rear bar diameter is going to be a function of whether the 36mm front bar is solid or tubular, and if tubular what the ID is. It will also be a function of the spring stiffnesses.

Starting from roughly OE stock, balancing just the swap to a 36 mm solid front bar wants just under a 27mm rear bar. If the front bar is tubular with wall thickness equal to 15% of OD (a common ratio, BTW), about 24 mm.

If, say, you swapped in Moog #5660 front springs, you'd then want the rear bar to be something a little over 27mm to balance a 36 solid front, but only about 25mm to balance a 36 tubular front.

Disclaimer:
Those numbers are for OE-style rear bars that attach to the LCAs. Consider them only approximate. They are intended to result in the same percentages of the lateral load to be transferred across the front axle as stock. It assumes stockish-height roll centers of about -1.4" front and +16.7" rear. There may also be a little sensitivity to the actual front weight distribution.


Norm


'08 GT coupe, 5M, suspension unstockish (mine)
'10 Legacy 2.5GT, 6M (hers)
'01 Maxima 20AE, 5M (spare, winter driver)

Gone but not forgotten dep't: '95 Mazda 626, V6/5M; '79 Chevy Malibu, 4M/5M; '87 Maxima, 5M; '72 Ford Pinto, 4M; '64 Dodge V8/3A . . .
#759391 - 01/24/10 05:51 PM Re: needed!! rear sway bar up grade [Re: Norm Peterson]  
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LSJM1 Offline
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Atlanta
I have a 34mm hollow front bar with a 23mm rear bar modified from a mid 90s 2dr blazer which is pretty close to the hellwig bar pic above.The balance is perfect but then again my car only weighs about 3200

#759392 - 01/24/10 05:54 PM Re: needed!! rear sway bar up grade [Re: LSJM1]  
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LSJM1 Offline
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LSJM1  Offline
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Atlanta
Never mind I see that hellwig bar is for the front mine clamps to the rear housing and goes to the frame like the pro touring bar

#759452 - 01/24/10 08:40 PM Re: needed!! rear sway bar up grade [Re: LSJM1]  
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Posts: 5,484
TPI Monte SS Offline
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TPI Monte SS  Offline
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North Jersey
LSJM1, do you have any pics of how you mounted the Blazer rear bar in your SS? Sounds like a great idea!


SSeeya,
Steve Ragusa - North Jersey
'88 SS - BudgetTourer - ZZ4-cammed 355 TPI, serpentine belt conversion, World Class 5-speed, 17" wheels, 12" front discs, Eibachs/Bilsteins, 1LE lower A-arms, tall lower balljoints, 34mm front swaybar, 3/4" straight rear bar, Celebrity headlights, and more. Sold on 2/28/11.

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