control arm bushings -----what is really happening on a-arm movement

[micbrody]

Ok; If you read my recent posts, I am replacing control arm bushings on a 1981 Fiat 2000. Maybe I am overthinking this, but I really want to understand how the actual bushing works.

The manual states that car should be weighed down when finally torquing bolts; or else the rubber will shear. I get that.......but what exactly is moving to cause the shearing.

The bushings have an inner metal sleeve. The salient question is : When bolts are fully tightened to specs under load of car, what is or isn't moving when a-arm rotates because of bump in road?

When I removed lower pivot bolt, it slid easily out of old bushing. But when trying to push pivot rod into new bushing, it seemed like the inner sleeve was too small; I could not get it to go through; it got so tight that when I rotated pivot bar, the inner sleeve was stuck to pivot bar; and the outer part of inner sleeve rotated in rubber. I thought this was wrong. But then I started to think about what happens when one tightens the bolts when car is fully laden with weight. I conceptualize that the rubber is compressed against inner sleeve. But if inner sleeve is loose relative to pivot bar, what's the point of tightening? Wouldn't the pivot arm just rotate in the inside of the inner sleeve? The sleeve wouldn't rotate if cupped washers also compress the inner sleeve, thus fixing it relative to pivot shaft. Which brings the argument in full circle: I don't think the inner sleeve should move relative to pivot bolt when tightened; instead the deflection is solely accomplished by the elastic properties of the actual rubber; and if tightened before laden weight applied, the rubber will be forced into too much rotational direction, shearing it. In fact (I think and hope), if bolt not tightened (no compression of rubber), but inner sleeve very tight to pivot rod, the sleeve will rotate within the rubber; so when re-attaching arm, and rotating a-arm, no rubber will be sheared (presently, without tightening bolt, my inner sleeve is fixed to pivot rod, and sleeve seems to rotate against rubber without causing any apparent damage)

Ok , sounds great in my mind........but now let me talk about upper control rod bushings:
My upper pivot bolts easily slid out of old bushings. Upon inspection of old bushings, there was a fair amount of play between pivot rod and inside sleeve of bushing. Also, the inside part of sleeve closest to shock tower is flared out. Based on how the bushing had play, the flaring matched up with the deflection of the play between the pivot and inside sleeve. Sounds like I need new bushings. So I slid new bushing onto pivot rod; slides easily with very tiny amount of wiggle play. What I can't conceptualize is how tightening the cupped washer and bolt will "tighten" up the inner sleeve to the pivot rod? Seems like this tiny amount of play between inner sleeve and pivot rod will result eventually in the same flaring and looseness as old bushings? And when tightening, is bushing suppose to be pressed against shock tower? If so, which part of bushing? the rubber only; or both the rubber and metal sleeve? My brain hurts

[v6spider]

Sounds like your old bushings weren't torqued correctly.. That would cause them to wear in the manner your describing I think. You may have to replace the lower pivot rod and upper control arm pivot bolts. sometimes those become worn. Hence the play..

When properly torqued the sleeves will become stationary with the bolts on the upper control arms and the studs. Also the cupped washers force the rubber into the joint making it tight. This is by design to help minimise flexing of each of the joints. The rubber acts as a lubricant to a point. So if you torque the joints without setting the car on the ground the rubber will be torn because it was twisted past its shear point. One thing you have to make sure of is that the bushing shells are centered on the upper control arm. Or it will not line up right. Other than that follow the book's advice about torquing etc.. And it will work out fine..

Cheers!
Rob