Ford installed a rear sway bar on the Boss 302 and Boss 429 Mustangs. The 1970 Mach 1 Mustangs also got the rear sway bar. Some of the 71-73 Mustangs had rear sway bars. And, believe it or not, some Mustangs IIs also had a rear sway bar.

Anyway, the rear sway bar on my Mach 1 is only 1/2". But even if it was larger, I can't imagine it causing any problems with the frame rails. Seems that rear pictures avoave bar would add a lot of weight and, on a Mustang, it would drag a lot.

 

Not a problem with the frame rail. They will usually cause oversteer on the early mustang. 67-70 big block mustang can benefit from a rear bar in combination with a 1-1/8" front bar. The big front bar reduces the big block body lean. But also cause understeer combined with the Big Block engine. You can make the mustang corner flat and neutral with big front and rear bars BUT a SB mustang with a 15/16"- 1" front bar and no rear bar will out corner it. A SB mustang with a big rear bar and locker works great in an autocross with tight 180 deg turns around cones if you know how to steer it. Leaf springs already act as a roll bar by resisting twisting from body lean in turns. Coil spring cars benefit greatly from rear bars due to the lack of twist resist that leafs have. A lot determines if a vehicle needs a rear bar. And thats where design engineers come in. Adding a 1" front bar to an early mustang is a great thing. Adding a rear bar to an early mustang for normal or fast corner driving is not a good thing for everyday driving.

 

Many (most) people who have put the rear bars on the early 65-70 Mustangs have endured them only for a short time before deciding to remove them.

 

Exactly my experience.

 

Cornering behavior of a car is the sum of many things and a rear sway bar is only a part of that sum. How much it influences the balance obviously depends on thickness and design (arm length, width).

I had one but not anymore. I got into a few "interesting" situations when I still had it. Although that maybe says more about my driving than about rear sway bars in general.......

 

I have a complete kit for one here I never installed after riding in a car that had one and thinking something was broken in the back of the car until we took it off...

 

Few Vintage Mustang owners have rear sway bars.
I never cared for them because I dont think our frame rails are strong enough.

Ford did. The 69-70 BOSS and 70 mach1 had a sway bar mounted to the rear rails, which was structurally identical to the 65 rail. The only modification was the addition of a backplate, into which the the bracket bolts attached. The 71-73 Mustang even more commonly had a rear sway bar, nearly identical to the 69-70.

As for whether you should, I had a 3/4" bar when I started running a 1" front bar. Years later, one of the brackets broke, and to stop the rattles until I could make a new bracket, I removed the bar. I liked the handling better without the rear bar, and never put it back in.

 

Ford did...The 71-73 Mustang even more commonly had a rear sway bar, nearly identical to the 69-70...

Yep. My '73 Sportsroof (non-Mach) 351CJ 4sp had the rear bar. The car had HD suspension, 3.50 traction lock, and was the best handling classic Mustang I have owned (unmodified). Better than my '68 GT. The rear bars were 1/2" IIRC.

 

One thing to keep in mind is that the stiffness of a sway bar is not linear with the diameter, but goes up with the diameter to the power 4. That means that a 3/4" bar is twice as stiff as a 5/8" bar and 5 times as stiff as a 1/2" bar, assuming that the design is otherwise identical.

 

good info to point out ! It is also worthy to add that the length of the arms is also a factor, some rear sway bars have short arms 8-10'' while i have seen arms at 15'' long. The longer arm will make the swaybar less effective or weaker. A thick bar with long arms will be similar to a thinner bar with shorter arms. This is where a bar that has multiple mounting holes at the end of the arm spaced 1'' apart. IDK why anyone would buy a non adjustable rear sway bar. The adjustability takes out a lot of factors of having a mis-matched bar

 

All of this talk about the addition of a rebar has me re-thinking my 1/2" bar installation 18-20 years ago. It's never caused me to experience any "interesting" situations, though. Once I get my garage re-construction. completed and my lift back in place I may remove it. Who knows, I might have to re-learn my "spirited" corner carving techniques.

 

“........ Who knows, I might have to re-learn my "spirited" corner carving techniques.

be sure to let your life insurance rep know you’ve removed the rear sway bar.

They usually will lower the policy premiums or raise your benefit once the sway bay is gone.



Z

 

I installed on on my I6 many years ago and the car decided to "corner carve" on the exit ramp. I can't remember if I sold it, gave it away o threw it in the trash. Snap oversteer is no fun.

 

The best bet on a 65-70 is to fix the front end so that it "works" and skip the rear bar.
(front end plows/pushes, fix that and don't introduce oversteer/loose via a bar in the rear to cover up the original issue)

ex-Global West GM
1991-1995

 

The best bet on a 65-70 is to fix the front end so that it "works" and skip the rear bar.
(front end plows/pushes, fix that and don't introduce oversteer/loose via a bar in the rear to cover up the original issue)

ex-Global West GM
1991-1995

Not wanting to go too far OT, but in the spirit of this thread, what should be done to the front end?

 

Few Vintage Mustang owners have rear sway bars.

Im curious if something like this would be of any benefit for someone who road races a Vintage Mustang?

The frame rails providing they are solid (no rust) can handle the SB's without issue but, those who raced these (track, such as myself) back in the 70's, 90% + chose not to run the rear SB because there was so much chassis twist that the Rear SB induced the rear wheel to lift so it was just easier and "safer" to muscle the car through the corners. Now with a full frame under the car...whole new ballgame... you bet +rear sway bar for the track!

On my street - weekend driver (I do like the take it on a mountain roads to lake arrowhead) I prefer it to have the rear sway bar, and I have run it (on select mountain roads, where the "environment was made safe to do so") up to 80 mph on the corners...... very stable/predictable... but I do have ti set up "loose" as well (it's an adjustable one)

Of course these are street tires not race tires either.... so you (track0 are dealing with alot more dynamic forces than on the street inducing alot more torsional chassis loading.

Hope this helps!

 

I had a rear bar on my 65 briefly several years ago and it indeed caused over steer. It sorta gave a false sense of improved handling. At medium speeds is felt like an improvement, but push the car a bit more and it became evident that it wouldn't be hard to put the car into a ditch tail lights first.

Also, I never liked how the rear bars mounted to the frame rails with squared U bolts and they started to leave a slight deformation to frame rails. Seems after being installed for a while the rails could get damaged.

There should be a disclaimer on the package of rear sway bars made for our cars. Not recommended.

 

The rear end of a vintage Mustang is as sensitive as a baby’s rear; no air shocks, no sway bars, and no rear disc brakes.
And once the rear end starts to swing out (too much), just counter-steer a tad, don’t lift your foot off the gas and stay off the brakes too.

Easy does it and baby’s happy.

Z