[NEW INTERIORS]

A lot of work and money for a very little gain...(if any)
I would put the money into the motor... Or something else..

[Nuck Chorris]

would stiffening the rear bushings reduce deflection in turns? I've got rubber now, would moving to aluminum or poly be a good idea?

[1971BB427]

Yes, poly bushings will definitely stop deflection. Aluminum will also, but it will transfer too much road noise to the body, and you'll get tired of that quickly!
I put poly bushings in my front control arms, body bushings, and rear spring bushings, and it really stiffened the suspension up on my '71 Camaro. I also added HD swaybars front and rear, lowering springs all around, and Lakewood ladder bars in the rear. It handles like a slot car after that.

[aosborn]

Originally Posted by Nuck Chorris

would stiffening the rear bushings reduce deflection in turns? I've got rubber now, would moving to aluminum or poly be a good idea?

The beauty of rubber bushings in a leaf spring set-up is that they do distort and deflect. When you go over a one wheel bump or when you are cornering and have body roll, the rubber bushings allow the rear suspension to twist slightly and not bind. If you replace the rubber bushings with polyurethane or aluminum or delrin or any other stiff material you have compromised the ability of the axle to "twist" in one wheel bumps. Stiff bushings are not a problem when both wheels hit a bump at the same time (speed bump for example) or if the car is used mainly for drag racing, but for the street, keep good rubber bushings in there.

If you want to get rid of that flexing feeling while cornering, but still want compliance in the rear suspension, then install a panhard bar as I described in an earlier posting. It will help also if your tires rub while cornering.

Regards,

Andy

[kso]

There will be no binding action w/ stiff bushings. In the event of body roll or hitting a bump w/ one wheel etc., leaf springs simply twist. It's part of what they are made to do, and the reason why a leaf-spring car doesn't need much rear sway bar...the leafs are already (by design) providing roll resistance by twisting. (In fact you might save the weight/cost of having to use a rr bar by using stiffer bushings, depending on your setup.)

Binding is what happens when you have two conflicting types of suspension links working against each other...which you may or may-not end up with here, depending on who's advice you are going with...

The downside of stiff bushings is increased transfer of vibration and spike loads into the mounts which may become more prone to cracking, and of-course noise...for that reason I would hold the line at plastic and not go any stiffer.

[1971BB427]

There is no binding with poly or aluminum bushings in your springs. As mentioned above, a leaf spring can twist in it's length, just from design. If you rely on the rubber bushing to allow flexing instead of the spring's length, then your rubber bushings will also cause sloppy handling, and eventual wear. A poly bushing removes the play but gives you more positive feel for the road.
Car makers use rubber for one reason, it deadens noise transfer to the car. It does so at the cost of handling.
Swaybars and leaf springs do not fight each other, they compliment each other. Almost every performance car ever made that has leaf springs, also has swaybars. If you want positive handling, you can't do much better than multileaf springs with a swaybar front and rear.

[NEW INTERIORS]

I never seen where these cars are bad handing cars like they are..Unless you have the tail end way up in the air..

[1971BB427]

Originally Posted by NEW INTERIORS

I never seen where these cars are bad handing cars like they are..

I have, but only when things are not like they were when new. Worn out parts, or the wrong wheel/tire combo will cause poor handling, but if all is stock and in good shape they handle well. They all had front swaybars, and most performance versions of the Firebird had a rear swaybar too.

[NEW INTERIORS]

Originally Posted by 1971BB427

I have, but only when things are not like they were when new. Worn out parts, or the wrong wheel/tire combo will cause poor handling, but if all is stock and in good shape they handle well. They all had front swaybars, and most performance versions of the Firebird had a rear swaybar too.

That's what I'm getting at... I just can't see doing this make that much difference in the handleing... Just a waste of time if you ask me... I'm sorry if someone doesn't like my say on this.. Just don't see it being a plus..

[aosborn]

Originally Posted by 1971BB427

As mentioned above, a leaf spring can twist in it's length, just from design. If you rely on the rubber bushing to allow flexing instead of the spring's length, then your rubber bushings will also cause sloppy handling, and eventual wear. A poly bushing removes the play but gives you more positive feel for the road.
Car makers use rubber for one reason, it deadens noise transfer to the car. It does so at the cost of handling.
Swaybars and leaf springs do not fight each other, they compliment each other. Almost every performance car ever made that has leaf springs, also has swaybars. If you want positive handling, you can't do much better than multileaf springs with a swaybar front and rear.

First off, I appreciate your opinion and my goal is not to start an argument. I just want to put out some more food for thought...

I would be interested to know where you got the information that a leaf spring can twist longitudinally within its length. If it does, the amount would be so small as to be insignificant. Especially since the center of its length is solidly mounted to the axle housing (except for some factory axle mounts that have a rubber pad). The majority of the rotation of the leaf springs are due to the fact that they are arched. In a one wheel bump the wheel moves up as the arch flattens out and the small amount of rotation is taken up in the bushings. Herb Adams in his book Chassis Engineering points out that since leaf springs are so stiff as to not need a lateral locating device such as a panhard bar (for a race car), he also states that you should never put poly bushings in the front spring eye of a leaf spring "as they will bind up and prevent the body from rolling in relation to the axle". To further illustrate the motion of leaf springs, some Hotchkiss suspension systems even mount the front of the leafs closer together than the rears to cause the rear axle to steer the car toward understeer in order to make it more stable and predictable to drive.

The great thing about rubber bushings, other than noise isolation and low cost, is the fact that they can repeatedly distort and then return to their original shape. Poly will do that also to a very small degree, but they won't be able to do that near as long as rubber.

As to anti-roll bars causing bind, they most certainly do. With an anti-roll bar you are tying one side of the suspension to the other with a very stiff spring. In the relatively small amount of suspension travel in most street cars it really isn't an issue (and as you pointed out it can be used to your advantage) but if you go too big (or stiff if you like) you can bind up your suspension so much it will hardly move. Almost like a solid axle. Look for photos on the web of cars that have too stiff of anti-roll bars, in a corner you can actully lift the inside tire off the ground! That is also why off-road guys who drive their vehicles on the street have quick disconnects on their anti-roll bars, it frees up the suspension when they are off-road so it can rotate to the limits of their axle locating linkage.

Good discussion...

[lakeroadster]

Originally Posted by aosborn

If you want to get rid of that flexing feeling while cornering, but still want compliance in the rear suspension, then install a panhard bar as I described in an earlier posting. It will help also if your tires rub while cornering.

Regards,

Andy

Do have personal experience doing this? Can you show us a working example of a leaf spring suspension with a panhard bar?

[MARTINSR]

If I can toss out there, I don't know the exact issues with the Firebird, with the springs being as flat as they are and with new bushings and such I can't imagine the need to a "locator" of any kind unless some VERY serious racing was being done. At the new Goodguys autocross track, you bet your butt there are plenty of leaf spring cars out there with some serious rear axle locators like watts and panhard setups. But with any "normal" hot rod I don't see it honestly. But we all have different images and expectations so ok.

I ran a panhard bar in my truck with leaf springs not for the handling but because I had so little space between the tires and the bed running a 67 Camaro 12 bolt with 8" wide Americans I had about 3/8th inch room on both the inside from the tire hitting the bed side and the outside with the tire hitting the fender. That being said, with the large arch of the stock springs (with lowerblocks too) and the worn out original bushings. I was running, I wanted the rear end to not move at all. So I wasn't using it for handleing, I was using it to correct a poor design of something else I had done, namely too narrow a rear end for the truck! Now, honestly, I don't remember if I drove it around and then added the panhard to stop it, and it worked. I honestly don't remember how well it worked from without it if I even knew or if I put the panhard from the start of the build, I don't remember. But that was my intentions at the very least, was to limit it's movement as much as I could. I don't have any photos of it in the truck but in the link below I have a few photos showing how I had it mocked up out in my wrecking yard behind my house.

1930u Panhard bar geometry?


Brian

[gow589]

Like I mentioned earlier, how much suspension travel is a big key to how good or bad a panhard can be. In the MGB I put one on, I cannot get a finger between the tire and fender. Without a panhard minor movement in the suspension with side loads would make contact with the fender.

The movement with the panhard rod from arcing is so minimal it has not only made zero contact with about a 1/4" clearance and has in fact kept it located and kept it from contacting.

Binding is ZERO issue with this car. It is common on these sorts of cars and makes it a blast on curvy roads. It has allowed me to autocross without screwing up the fenders.

BUT....I still say success is largely dependent on suspension travel. More suspension travel = more arcing. Admittedly suspension travel on an MGB is less then on many other cars.

[1971BB427]

The twisting of leaf springs is not rocket science. One of the reasons (beyond greater spring rate) for multi leaf springs sets is to eliminate spring twist. A greater arc in a spring will also eliminate spring twist somewhat, and that also is a reason for greater spring arc beyond just giving it more travel. Stack enough spring leafs and make them greater length leafs, and you will almost totally eliminate spring twist, but use a single leaf like some 70's F body cars had, and spring twist will be very noticeable.
Rubber bushings eliminate spring twist by allowing the bushing to do the work, rather than the spring. I've read what Herb Adams has written, and he's extremely knowledgeable on suspension, but I still disagree on use of poly bushings in the front eye, as I think it's just making the rubber bushing do the work, instead of the rest of the suspension.
The reason track/street cars use a disconnect on their anti roll systems is because they use such heavy systems that they wont work well on the street. Swaybars designed specifically for street use do not bind so much as to lift the rear wheel when cornering. A swaybar's whole design is based on binding, but the material used, and diameter will dictate how much it binds, and that's why they work well if sized correctly.

[MARTINSR]

Now again, just throwing something out there I don't understand. Wouldn't more arch have more sideways movement? I would think the straight spring of a 69 F body would have less sideways movement than a large arched spring because that large arch can "swing" side to side at the bottom of the arch like a pendulum. Even if the spring is a mono leaf as I think it is on that 69 Firebird, wouldn't it being flat make all the difference as far as side movement of the rear axle?

I personally am not a fan of poly bushings because I like the cushy ride and lack of noise of the rubber. On my Gran Sport I have poly on one side of the sway bar links for instance so I get a little bit of stiff without making it totally stiff with the poly at both ends.

Brian