An interesting and informative video from Eaton Detroit Springs

[Stanglover]

Adding a stiffer sway bar is not necessarily better. First of all, unfortunately, we look at sway bars by their diameter but that's not the only important aspect. Also important is the material, which defines how stiff it is, and the distance from the center of the cross-bar to the attachment point in your springs, which defines the leverage.

After figuring out the above then you have to think that the stiffer the sway bar is, the more lateral force the rear axle will be seeing, which could lead to more oversteer. The way it works is that the more the sway bar limits the roll of an axis, the more that axis "gets" the total lateral force of the car compared to the other axle. Therefore, it is critical to balance the roll between the front and rear to keep all under control.

Tony, I get what you're saying. A 3/4" bar might be better, but  ADDCO don't offer that option. Unfortunately the one they currently offer for our cars is wrong. On mine, I have the 1 1/8" up front which does seem to balance the car out ok. Like most, I'm not an engineer,  so we guess, for the want of a better word, at what will work. As for material the bars are made of, well we have to trust the manufacturer did his homework. they don't stipulate the grade of steel they use. I don't overdrive my car, but it will handle curves without scaring the sh*t out on me. However, I appreciate your input. Thanks.

 

[tony-muscle]

Tony, I get what you're saying. A 3/4" bar might be better, but  ADDCO don't offer that option. Unfortunately the one they currently offer for our cars is wrong. On mine, I have the 1 1/8" up front which does seem to balance the car out ok. Like most, I'm not an engineer,  so we guess, for the want of a better word, at what will work. As for material the bars are made of, well we have to trust the manufacturer did his homework. they don't stipulate the grade of steel they use. I don't overdrive my car, but it will handle curves without scaring the sh*t out on me. However, I appreciate your input. Thanks.

Geoff, I posted this not so much related to your setup but more as a general information. I recently started reading more and more about suspension setups and just recently understood this issue. A few weeks ago I would have thought that stiffer was better, but now I understand the physics behind why that's not necessarily true. I don't think that the difference between 3/4 and 7/8 would be enough to worry about it. There are many other subtle issues such as chassis stiffness, stiffness of bushings and attachment points. Technically speaking you could reduce the effectiveness of the sway bar by using rubber bushings instead of polyurethane, which would be equivalent to reducing the diameter. Also, the less stiff a chassis is (as not having cross-braces and/or subframe connectors), the less effective a sway bar is, and the more difficult would be to balance the car front/rear.

 

[Stanglover]

Geoff, I posted this not so much related to your setup but more as a general information. I recently started reading more and more about suspension setups and just recently understood this issue. A few weeks ago I would have thought that stiffer was better, but now I understand the physics behind why that's not necessarily true. I don't think that the difference between 3/4 and 7/8 would be enough to worry about it. There are many other subtle issues such as chassis stiffness, stiffness of bushings and attachment points. Technically speaking you could reduce the effectiveness of the sway bar by using rubber bushings instead of polyurethane, which would be equivalent to reducing the diameter. Also, the less stiff a chassis is (as not having cross-braces and/or subframe connectors), the less effective a sway bar is, and the more difficult would be to balance the car front/rear.

 Tony, I see what you're talking about now. Yes good information and little things like bushings can and do make a huge difference. That is explained in one of the Eaton video's. For me, it was about reducing some of the body roll without spending a fortune and basically rebuilding the entire chassis as one would need to do for a race car of some sort. Unfortunately, there really is not too much offered and even less information as to the best approach to improve handling for a street car. All the so called performance parts manufacturers really want to do, is sell product, so they'll say just about anything, right or wrong to make that sale. As we know, the Addco rear bar is far from correct,  so what was it made for and why did they think it was okay for the 71-73 Mustangs?

As for the 1/2" factory bar, it may as well have not been there as far as I'm concerned, the car rolled like a pig in mud going around corners.

By the way, my last nights reply may have been slightly influenced by the last bottle of beer! Didn't mean it to be offensive.

 

[tony-muscle]

By the way, my last nights reply may have been slightly influenced by the last bottle of beer! Didn't mean it to be offensive.

Not at all. Never took it offensive, I was more making sure that you didn't think I was criticizing your choice of sway bar. All good my friend!

There is so much to learn in regards to suspension and cars in general. Plus, we can have all these theories, but at the end of the day what matters is what works for each of us.

 

[Stanglover]

I forgot to mention that after a nice little drive yesterday, I re-torqued the U bolt nuts after about 50-60 miles of letting the axle and springs "settle in". I was surprised how much more I had to crank on the nuts to get 45 ft/lbs or actually, I go a little over as I think my wrench is on the low side. 

Topped up the gas tank so job done, almost time to put her to bed for winter.

 

[Stanglover]

Not at all. Never took it offensive, I was more making sure that you didn't think I was criticizing your choice of sway bar. All good my friend!

There is so much to learn in regards to suspension and cars in general. Plus, we can have all these theories, but at the end of the day what matters is what works for each of us.

Well said Tony and yeah glad you were not offended. That is the last thing I want to do to anybody.

 

[Stanglover]

Although the car is tucked away for winter, I did finally get some information from ADDCO in a live chat session (they never returned my emails) and they confirm that moving forward for the 71-73 Mustangs, the revised rear anti-sway bar design, thanks to Jpaz, will be available from 2/14/21. It actually reads "all 990's currently in stock and that are produced going forward are this revised design". That's a bit vague to me so I'll bet on the February date. I also suggested that they update their listing to reflect the "Revised design" and that has been forwarded to whom ever deals with that.

On rear leaf springs, I have not had any real success in finding out for sure, who make the GAT's, but on one chat forum, it seems AFCO make them. Looking on their website, I was unable to find any reference to GAT's. Also, as there are many steel types to make leaf springs, ASI 5160 is the preferred material. 1095 was mentioned as well, but it seems some are made from 4140, which, while tough is not nearly as durable. My suspicion is the cheap leaf springs are 4140 and possibly GAT's seeing how mine have bent out of shape. Now, to be fair, they were over de-arched when I had the altered and that may have contributed to the deformation. None the less, It pays to do proper research. Cheap is not necessarily the cheapest way in the end. Ask me how I know! For a few bucks more, buy Eaton D.S. springs and know you're getting best quality 5160 steel. By the way, probably your old factory springs can be rebuilt, so another alternative.

A call to Eaton is a good idea, they are very helpful. 1-313-963-7047. Sign up for the Monday 1 minute video as well. They're fun and informative. Geeze, now I sound like I'm doing a advert for them........... and not getting paid.

 

[Tegemus]

I can confirm the February release date for the revised 990 rear sway bar. I spoke with Addco on Nov. 27th. Despite their website talking about "all 990s currently in stock", they admitted they actually have none in stock. New bars will be available after Feb. 14, 2021. I also suggested, like Stanglover, that they update their website description of the bar to indicate its unavailability. Not holding my breath for them to do that.

 

[Stanglover]

Going back over this one more time, I found a picture of the old Grab-A-Track spring just before the swap to the Eatons. Now, as I've said before, I did have these de-arched, but the guy who did it, went way passed what I'd asked for. However, they did not look like this beforehand when I installed them. This is after running them for most of the year. The reverse bending is obvious. I seriously doubt these are made from anywhere near the grade of 5160 steel. Was it just me that got a set of weak springs?

 

[kcmash]

So I am glad I watched this.  I went back to check the torque on the u bolts on mine and found them all loose.

upon finding a missing nut I remembered that the u-bolt kit I bought years ago was missing one of the 8 nuts.  I grabbed a spare I had, torqued them all to 65 and found a significant improvement in rear suspension quality.

kcmash

 

[Stanglover]

So I am glad I watched this.  I went back to check the torque on the u bolts on mine and found them all loose.

upon finding a missing nut I remembered that the u-bolt kit I bought years ago was missing one of the 8 nuts.  I grabbed a spare I had, torqued them all to 65 and found a significant improvement in rear suspension quality.

kcmash

Kc, I so glad this thread has helped you. I guess it would make a huge difference after driving around with the back axle about ready to fall out..... well, maybe not quite that bad, but at least loose enough to notice. You mentioned 65 ft/lbs, that is a bit above the spec for a 7/16" fine thread bolt. 45 is the recommended torque. I went to 50 ft/lbs as I think my torque wrench is on the light side. 

 

[kcmash]

Kc, I so glad this thread has helped you. I guess it would make a huge difference after driving around with the back axle about ready to fall out..... well, maybe not quite that bad, but at least loose enough to notice. You mentioned 65 ft/lbs, that is a bit above the spec for a 7/16" fine thread bolt. 45 is the recommended torque. I went to 50 ft/lbs as I think my torque wrench is on the light side. 

I googled the torque for a 9 inch Mustang U-bolt.  I see the 65-66rs saying 30 ft lbs, but for the 9 inch I see a lot of 65 to 75 ft lbs.  

I guess we will see if they break while driving.

Yep I am feeling pretty stupid this year.  I have been off the road for over 20 years.  With confined space there were times I put parts on the car so they would not get damaged, or to get them out of my way.  So the advice I have for everyone is this.  After restoration, have a nice long sunny Saturday where you buy the food and some drinks. Invite a gear head friend or 2 over and put the car up in the air.  Go front to back checking every torque on every part of the suspension and drivetrain just to make sure.

kcmash

 

[Stanglover]

In this 1 minute video, it states to use manufacturers U bolt nut specs, or use Eaton's

As long as you didn't use an impact wrench, as I've seen done before, you should be ok with 65 ft/lbs. That's not a huge amount. I take it you saw the video that say to torque the U bolt nuts with the car sitting on the ground, not up in the air.

 

[kcmash]

Well,  I did torque in the air, but I thought that made no sense.

When in the air and supported bu the rear axle housing, you should have the same up force load on the u-bolts as you do when sitting on the ground.  The angle is slightly different but the force is the same.

So being an engineer I am having a tough time thinking about having a bolt under it’s designed tensile load for the application while I am torquing the bolts.  So anyway, I did use a torque wrench, torqued with the car supported by the rear axle, then supported it by the frame, letting the axle hang on the springs and double checked the  torque.

kcmash

 

[Stanglover]

Well,  I did torque in the air, but I thought that made no sense.

When in the air and supported bu the rear axle housing, you should have the same up force load on the u-bolts as you do when sitting on the ground.  The angle is slightly different but the force is the same.

So being an engineer I am having a tough time thinking about having a bolt under it’s designed tensile load for the application while I am torquing the bolts.  So anyway, I did use a torque wrench, torqued with the car supported by the rear axle, then supported it by the frame, letting the axle hang on the springs and double checked the  torque.

kcmash

 I would have to think Eaton suggest torqueing the U bolt nuts with all the weight on the axle and springs is because the spring arch may change a bit at the point where the spring plates touch. I'm with you, I wouldn't have thought it would make any difference either, I have in the past torqued the U bolt nut with the axle hanging without any (noticeable) problems. It might be worth a phone call and ask why.

 

[Stanglover]

How To Interpret Ford Part Numbers - EATON Detroit Spring

The above link may be of interest to some newer members. Most will already know this about the Ford numbering system. Print it off for future reference.