Hello everyone,

i just mounted a new rear sway bar (stock style from OPGI) on my 71 cutlass S and the sway bar touches the pumpkin. Is this normal? Lower control arms are boxed and i shimmed out the space between the sway bar and the control arms.

thanks for any ideas

 

Early A body rear sway bars had little bow to them, enough for the 8.2" 10 bolt rear. Later GM replacement bars for 64-72 years had more bow to clear the bigger pumpkins of the 12 bolt Chevy rear, etc. It would be best for the bar not to touch the differential.

 

It's fine to add a little bow to the bar if you have the capability to bend it. Just be sure to use the correct shim stack where the bar mates to the LCAs, as bending the bar will pull the ends inward.

 

I would leave it installed and swing by a muffler/suspension shop, have them heat it and tweak it a little. As Joe mentioned, if you don't have a torch, I wouldn't bother attempting it, either way you try to bend it unheated and or unmounted, it will want to pull .

 

 

And not to mention if its heat treated spring steel , it will take a heluva lot of purse-wading to bend it unheated... near impossible . Just be careful not to bend it too much after heat. Depending on what material ,be it 4130, 4140 chromoly. I would hit it with a file of spark test it to see how hard it is before the attempt .

 

https://www.opgi.com/cutlass/1971/chassis-suspension/suspension-components/ADDC939/

this is the bar i have, OPGI says 64 - 72? My rear end is a 8.5 and seems to be stock.. i also thougt about bending it a bit more (acetylen torch is around), but i don't understand why this is like that. May its because it is 1" diameter instead of 7/8"? The Item obly has good reviews at OPGI. Maybe a monday's product..

 

If you heat it, you will destroy the spring temper in that area. It would be better to get an OEM bar that already has enough bow in it.#394926

 

I'm very sure the sway bar is not heat treated, just mild steel. The torsional stiffness of a mild steel bar is unaffected by heat. Frankly, I'm sure you could bend this without heat. I would not bend it on the car, as this will put a side load on the LCAs and could damage them. Bend it off the car, fit it to the LCAs and shim as needed.

 

Picture of the mounted sway bar? Shims don't always have to be placed equally on the LCA ends. Some factory cars had more on one side than the other. That might move the center of the bar to a location that gives clearance...

EDIT: What did you use for shims? The link for that bar on OPGI doesn't show anything except washers and LCA spacers.

 

I agree with Joe if its just mild steel . Although, 1" dia will be a bugger to bend without a bit of heat haha , If your arm strongin' on it with a pipe, well... eyeee maybe. If its mild steel , which it could very well be from OPGI, then I agree, heat won't affect the mild steel if needed to help it move to where you want it go.
The best way to know what material it is , would be to hit it lightly with a disk grinder to spark test it.
You could also use a file initially to see if it has any hardness at all.

 

How far off is it? Snap a good pic of the interference and of the pumpkin.
Is there any up/down play with the 4 mount bolts loose? If so loosen all 4 bar bolts. Pull down on the center of the bar and hold or shim with wood between bar and center of pumpkin then re-tighten and remove wood. See if that gains you any room. You don't need a ton. You may get more room by switching to a slightly smaller bolt and slightly enlarging the through holes on the bar? Also, noninvasive removal of material in other key spots of the bar or the pumpkin could make the difference too. Little here little there etc...Then there's the idea of trading it in for an OEM.

 

The factory ones are mild steel. There is no reason to heat treat it. Frankly, I'd bend this by propping it up on either side of the center and driving the car over the middle.

 

The rear sway bar I purchased from Summit and installed last summer was 1.125- 4140 spring steel. I wouldn't have wanted to tweak it , can be done thou . Its about 45hrc
The description below is from the summit site .Summit Racing® Sway Bars SUM-720209

We know how body roll, understeer, and sloppy handling can ruin a drive (or cost you a race)--that's why we offer you these affordable Summit® sway bars. They're made from solid 4140 chromoly spring steel for strong suspension support.

 

OPGI lists the ADDC939 as premium steel . Sounds as thou you probably did get a monday or Friday afternoon product . They must not have hit it with the re-strike form to fully form it properly . A second hit takes the spring back out from the first form .
Also, if they list mild steel sway bars as premium steel, I myself, would send it back to them .
Jus' sayin

Eric

 

Ok, ill take a picture when im back in the garage. Maybe i have to say that the body is off at the moment, so theres no weight on the chassis. Im in the progress of assembling the chassis back together after sandblasting and painting the frame.

maybe better to mount/shim/adjust the rear sway bar with the full weight of the car with wheels on the ground?

just sending it back to OPGI isnt that easy.. im in Austria 😁

thanks to all who try to help me, in this forum the answers coming so fast, this shows me the enthusiasm of the people here!

 

[QUOTE=71OldscutlassS;1145629]Ok, ill take a picture when im back in the garage. Maybe i have to say that the body is off at the moment, so theres no weight on the chassis. Im in the progress of assembling the chassis back together after sandblasting and painting the frame.

maybe better to mount/shim/adjust the rear sway bar with the full weight of the car with wheels on the ground?
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This information may have been helpful to the other posters that weighed in on your issue. I have never performed a body off resto , so I really can't comment . I would think, in any case, the rear sway bar shouldn't hit the rear differential loaded with weight or not. I could be wrong.
I'm sure other's will comment on this updated info.

Eric

 

I'm curious to see the picture. My sway bar hits the pumpkin too. I have 2 shims on each side. It should be a perfect fit but isn't. It's a 7/8" bar. I also had the LCA's boxed and new bushings installed. The sway bar was installed with the rear of the car supported by jackstands under the axle tube.

 

here you can see the sway bar touching the pumpkin

 

You may be able to rotate the bar on the two mounting points, possibly slightly slot one hole on each control arm, to get a little clearance.

 

I tried this.. i loosened all 4 bolts and pushed it down.. didnt worked..

 

Use smaller diameter bolts in the two rear locations?

 

Kenneth, that won't give the 1/4" to 1/2" of clearance that typically goes with these bars.

 

Good call on posting some pics Allan !
I agree with all others on slotting the holes . It would be quick if you have a dremel and a carbide burr to extend the hole into a slot. Arm strongin' on round file would also work .
The forward holes need to be slotted downwards, the rear holes need to be slotted upwards . That should work without having to bend the bar .

Eric

 

But the original question still remains - WHY won't the bar mount without hitting the pumpkin. Something is wrong, but what??? Shouldn't need to modify the bar to have it work right.

 

As you guys all know ,
These bars get stamped . Hand transfer . This was probably a first or second off in which the press shut height was not set properly . It is very difficult and near impossible to form premium spring steels afterwards, it will continue to spring back for the little amount it needs to go to hit the fixture, no matter how many times you hit it afterwards. I'n other words you need to pre-form so you don't get too much distortion , then re-strike form in order to fit the fixture properly +/- tolerance . This bar appears to be way out of bending tolerance, must have got mixed up and went through to shipping by the looks of things.
That's my .02 on this bar .

Eric

 

I don't buy it. My bar came from a donor car that was factory installed and it has the same problem.

 

I wasn't sellin' anything haha. Either way, it can be made to work with a bit of effort. Run to Rund mentioned in the beginning of this thread ....

"Early A body rear sway bars had little bow to them, enough for the 8.2" 10 bolt rear. Later GM replacement bars for 64-72 years had more bow to clear the bigger pumpkins of the 12 bolt Chevy rear, etc."

^^^^^^This sounds like the problem.^^^^^^^^

 

Ok, just for comparision, i watched some videos of some olds 442's of VanguardMotorSales (they always show the car on the lift) and it seem like its normal for these kind of sway bars (the stock style) to touch the pumpkin or to be very close to it.

maybe it really is normal like that 🤔

 

I guess most guys just drive around with the bar on the pumpkin

 

I just did a quick search for Vanguard and this 1970 442 is what they have under current inventory. Note Sway bar position



But this 1968 is really close....



AS is this 68 (with a never issued W27 cover)



And this 1969



1971 fits like it should...



And 1972 with lots of clearance

 

What's the tolerance on the mounting holes on the LCAs and the distance from the LCA mounting holes on the rear axle to the CL of the axle? Probably tighter than the bend of the sway bar, but both of these contribute to the gap between the sway bar and pumpkin (or lack thereof).

I think you have that backwards, the forward holes would need to be slotted upwards and the rear holes downwards to increase the gap between the bar and pumpkin.

 

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I would slot the sway bar holes myself. That would make life easier without pulling the LCA's off the car. Now, If the poster wanted to slot the LCA's instead, then yes, I would have it backwards.

 

The rear sway bar adds stiffness to the suspension during cornering by twisting as the lower control arms move. The more clearance in the mounting holes, the more slop that must be taken up before the bar is effective. Yeah, clamping the bar by tightening the bolts helps, but friction alone will not transfer the loads completely. The harder you corner, the higher the loads on the mounting bolts and the more sensitive the bar is to slop in the bolt holes. This is not the best solution.

 

Slotting the holes on the sway bar 3/8" both ways wouldn't hurt anything. If your turning left, the movement would shift to the slotted side ,no ?, turn right, again the movement would shift to the slotted side, no, ? I can't see the bar moving myself. Now if you want to corner at 60 MPH then, you should add some lock washers haha.

 

1. DON'T use a torch to bend it.
2. DON'T slot the control arm holes.
3. DON'T use smaller bolts.
DO bend it using the suggestion by Joe P. You only need to tweak it a very small amount and re-shim. You may also be able to "tweak" it with a hydraulic press. Be sure to put it on a flat surface, resting on the ends, upside down and measure the distance in the center to the floor with a tape measure or framing square. You can easily measure the change.
If the bar is in fact 4140 (hRC) heat treated steel. A torch would soften the bar in the spot you heated and reduce the effectiveness.......as Run to Rund tried to point out.

To add some theory here.......... 4140 is an SAE steel classification. Its heated to 1550-1600 F and quenched in a tank of oil down to about 100 F and then air cooled to room temperature. It is then tempered back to hRC 45 by heating it in a "large oven" at 650-700 F for a period of 1 hour per inch after a 45 minute to 1 hour initial "soak" to bring the bar to the oven temp. It is then air cooled to room temp.
NOW, if the bars are dropped into the quench oil bottom first, the cooling on the bottom will tend to straighten out the bar in the middle. If it was dropped in the quench oil top down, the bar could cool the top side of the bar and produce more bend. The ideal way would be to have a suitable quench tank (6-7 feet deep) to drop it in lengthwise. I suspect the bars are "batch quenched".....on a rack, some stacked up and some stacked down in a shallower tank.
........Just my two cents worth

 

Aye, I assumed you were referring to the holes in the LCAs, not the sway bar. There's a lot more material that would need to be removed by slotting the sway bar holes instead of the LCA holes. But yeah, providing an opportunity for the sway bar to slip on the LCAs by slotting the holes and relying on sheer friction / clamping force to prevent this is not something I'd want to take a chance on.

What is the downside of just allowing the sway bar to contact the pumpkin? Seems we are over thinking this (unless it is preventing the holes in the sway bar from lining up w/ the holes in the LCAs).

FYI, I've swapped my LCAs with the SSM (South Side Machine) lift bars, which provides a lower mounting point on the axle for the LCAs. However, the holes in the SSM LCAs for the sway bar are located such that it keeps it up near the pumpkin so that ground clearance is not compromised.

 

Sorry, but this is not correct. Do not confuse a material's stiffness with strength. The spring rate of the bar is a function of a property called modulus of elasticity (also called Young's Modulus), which is a measurement of the relative stiffness of a material. ALL steels have a modulus of about 3 x 10^7 PSI. This is NOT effected by any heat treat. High strength steels have the same modulus as mild steel. Heat treating (or lack thereof) affects STRENGTH, not STIFFNESS. Springs are typically heat treated not to increase stiffness (since it can't) but to increase strength so that the coils don't yield at full compression. The sway bar doesn't have enough deflection to yield even with mild steel, which is why I seriously doubt the factory bar is heat treated. I'll also add that if it IS heat treated, you aren't going to drill the holes out very easily.

Sorry, no. This is a classic case of "eyeball engineering". Lock washers will NOT hold this. Opening the holes means that the bar will shift on the LCA without twisting, which means that it is LESS effective as a sway bar. Eventually you will fatigue and fail the mounting bolts. This is a baaaad idea.

 

Sorry, no. This is a classic case of "eyeball engineering". Lock washers will NOT hold this. Opening the holes means that the bar will shift on the LCA without twisting, which means that it is LESS effective as a sway bar. Eventually you will fatigue and fail the mounting bolts. This is a baaaad idea.[/QUOTE]

I have seen so much over engineering over the years, that, "eyeball engineering" can work in some cases. This being a case IMO.
1) The poster has boxed LCA's.
2) slotting that bar 3/8" using the 1/2-13 bolts supplied for installation.
3) The aftermarket bar hole diameter is likely pierced to 7/8 already. Giving .1875 clearance per side as it is... +/-
4) His lower LCA's are boxed , so no worries of pulling the control arm/s in due to over tightening.
5) The 1/2-13 bolts can be torqued/arm strong tightened ( to the nut/bolt grade supplied ) more than enough, that bar won't move with the rate of speed his car could corner at. Even put sideways on wet pavement IMO.
However,
I may be "under engineering/thinking" this, so I will back out of this thread at this point.
All the best to the poster if he so decides to rework/tweak his sway bar for a better fit.

Eric

 

Go to a Detroit Speed set up.