Replaced failed strutrod poly-bushing today - Took video of working suspension
Would this condition cause a noticeable ''clunk'' when going over a speed bump or small pot hole?
If so, my car does that and i suspect that the rubber bushings that i have in my strut rods are for an older '72 and down instead of a '73 and up.
What's the best way to check this?
BTW, my car is a '74 Dart Sport with the correct '73 and up front suspension and k-member. All of the suspension is rebuilt with new parts and factory style rubber bushings throughout. The only thing suspect are if the strut rod bushings are the correct ones.
I know that the strut rod bushings are tight when sitting on the tires with the weight on them. The car has about 1500 miles on it now since the rebuild, and the condition doesn't seem to be getting worse.
Other than that, the car drives fine and i may add, that i didn't order the parts or put that part of the front suspension together myself, so i don't know if the bushings are for the proper year and application.
I don't intend to hijack the thread, it's just a point of discussion that many might find interesting and relevant to their cars............
BTW, nice video footage!
It could be, if the rubber is worn out or too thin it could be allowing the strut rod washers to contact the K-frame under certain conditions. But a clunk in those situations could also be almost anything in the suspension or even parts of the steering. You'd definitely have to investigate further.
If the bushing is completely gone then the metal strutrod can knock/vibrate against the K-member. But the noise would be more constant during driving.
But a one should also inspect the ball joint in the UCA. This is a usually less loaded part that gets worked and possible play becomes noticable with larger suspension movements.
I've coated the fresh poly-bushings with ARP grey molycote grease. The shiny line between bushing and K-member is the grease.
I took notice when torquing the lock nuts if the LCA got pulled forward or not. Couldn't notice a difference so I suspect the bushings where the correct thickness.
I did make the fresh bushings 1mm thicker than the 'old', intact one that I removed.
Also decided to mount the large washers with the 'cup' side to the bushing now, thinking it would keep/grab/hold/ the bushing together a bit more. I know the washers are ment to be installed with the convex curve to the bushings to prevent the swivel-movements and cause bending/breakage of the strutrod-threads.
Ideally you'd want the LCA to be perpendicular to the frame and the LCA bushing all the way up against the shoulder on the LCA pin. You can pull a little tension on the LCA without causing binding, just enough to keep the LCA and bushings tight against the shoulder of the pin. Without angling the LCA or putting the bushing in a bind of course. With a non-adjustable strut rod though you pretty much just get what you get. The washer has to be tight to the bushing and the bushing to the K frame, you can pull a little more length out of the strut rod by tightening the strut rod nut further to compress the bushings, but obviously you don't want to overdo that.
i didn't say which performed better only that i have seen the hard plastic ones deformed or cracked and that they cannot provide any torsional resistance,or compression.Which performs better i can't say because i have never used the plastic ones but i think o.e. rubber are more durable.
The strut and sway bar bushings allow movement by compressing the rubber and the control arm bushings add some torsional resistance because they are vulcanized and fixed, that's the way the factory designed them.Tightening them on jack stands will indeed cause them to be permanently deformed when the suspension is loaded.
Ugh. First,
none of the bushings are "plastic". None of them. There are polyurethane bushings, polygraphite bushings, Delrin bushings, and of course the OE rubber bushings that I'm aware of. None of those are "plastic", and they all have different properties in regard to compressibility, durability, and elasticity. If you can't tell the difference between polyurethane and "plastic", you're probably not too well versed on their different properties either.
Second, I don't think you have a good idea of what torsional or compression forces are as they relate to the suspension. Because you don't want torsional resistance in
any of your suspension bushings, it's a
bad thing. Torsional resistance in the LCA bushings slows your suspensions response and keeps your suspension from moving freely. Same for the sway bars. And since polyurethane has higher a compression resistance than rubber by a long shot, I don't really understand at all what you're trying to say. The best case scenario at the sway bar bushings and the LCA bushings is the respective suspension parts moving without having the bushings resist or slow their movement. Now, harder bushings will transmit more suspension forces to the chassis and can add some harshness to the ride quality, but if your shocks and torsion bars are well matched that shouldn't be an issue. The softer the bushings are the more sluggish and vague the suspension response will be. And the rubber bushings are not more durable. They're more elastic, but they're softer, less resistance to cuts and tearing than the poly bushings are (just try and cut up a set of poly bushings!) That doesn't mean the poly bushings can't be damaged, but rubber bushings of the same shape would be damaged even faster. The strut rod bushings though are not the same shape, and you do have to consider the different properties of the different materials in those situations. Which I don't think is always done by the manufacturers, and why you get generic parts. Which is why I especially don't like the poly strut rod bushings that are out there, because they're generic for the whole A-body year range, which makes them the wrong size for at least half of the year range, if not everything.
And finally, no, the rubber bushings to not add any appreciable torsional resistance. When they work within their elastic range (which is what they're doing if installed properly) they have very little resistance at all. When they exceed their elastic range, they tear almost immediately. And since their elastic range is fairly small, you have to tighten everything with the bushing and suspension in the center of the available suspension travel, otherwise they'll tear. Not deform, tear. Ruining the bushing entirely. I added that they need to be centered in their range of travel because if you have a significantly lowered car and torsion bars that are too small, you could still ruin the OE bushings even if you tighten them at ride height, because ride height is at one end of the range of travel. And this wasn't something that the factory designed into the bushing. It's a side effect of the materials used, not an intended result. They did take advantage of the soft rubber bushings though, because all that movement at the bushings allowed the suspension tolerances to be fairly loose. So you could get away with things like fixed length strut rods to begin with. And the materials were just what was available and cost effective at the time, not necessarily what was best for performance.
