My car is very loud on bumpy streets. What do I look for?
Thanks everyone. First off..I changed everything. All bushings and parts. I used poly bushing in the upper control arms but it was making the noises before that. The steering link is pretty close to the exhaust pipes but I dont see any damage on the pipes. I reckon there would be. Has disc brakes already and holding the brakes improve it. And no sway bar installed.
Could you expand on that torsion bar comment? My build sheet says I have 891 and 890 bars. My car has the 5.3L motor. I have a hard time understanding torsion bars. They say stiffer bars give harsher ride..but isnt that what you need to absord potholes and things? A soft torsion bar would just bounce the car around and bottom things out no?
Also in the spring my tires were very low on air and the ride was much more quiet. It got louder after I filled to specs. That might be a clue no?
If holding the brakes improves it, look for loose brake parts and check the wheel bearings- ie, think about parts that won't be able to move around as much if there's pressure on the brakes to hold them in place.
The noises likely got worse when you aired up the tires because with more air in the tires the sidewalls will be stiffer, so they're absorbing less of those bumps and transmitting more to the suspension.
As for the torsion bars, 890/891 bars are .85" in diameter, which is stock for a 318 car with no A/C. The have a wheel rate of only 100 lb/in. Think about that for a second. You have about 5" of total suspension travel or so. Heck let's call it 6" for even numbers. If your ride height is adjusted so the control arm has equal travel in both directions, that means 3". Which means that 300 lbs of added force will bottom out your suspension. Now think about a 3,500 lb car traveling down the road at 40 mph and hitting a pothole. Think that's more than 300 lbs of additional force? Yeah of course it is. And that assumes you have equal travel, if the car is lowered a little from factory height, which is probably is unless you specifically set the factory height, that means it'll take less than 300 lbs of force to bottom your suspension. These cars bottomed the suspension even with the factory bars at the factory ride height, the bump stops are designed to be progressive because of that, to take the harshness out of bottoming the suspension all the time.
The torsion bars from the factory were small because these cars came with bias ply tires, which have very little grip and therefore don't transmit a lot of cornering force to the suspension. And because shock technology wasn't great, and the demand in the 70's was for cars that rode really soft- some of it was just marketing. Fast forward to now and you have radial tires, which transmit more cornering forces. You have better shock technology available to deal with higher wheel rates, and we know better than to want a car that rides like you're floating on a marshmallow because it'll float and flop all over the road, just like these cars do from the factory.
So how big do you want the torsion bars to be? It's a trade off, just like EVERYTHING with suspension. If the bars are too stiff, the suspension will move very little and all of that force will be transmitted to the car- it'll rattle your teeth out and won't keep the tires on the road, which is the whole point of suspension. If they're too soft, the suspension will bottom out all the time, which will create a crappy ride because of all the suspension components crashing together and unpredictable handling too. What you want is suspension that is stiff enough not to bottom out all the time, but still soft enough that it absorbs as much of the road forces as possible. Ideally, the softest suspension that doesn't bottom out frequently is what you want.
In my opinion, there's no point running bars that are smaller than 1" on anything that sees frequent street use. That size bar has about a 200 lb/in rate depending on the manufacturer, which is double the factory rate. That also means running better shocks, because if you do that the ride won't be harsh. Shocks have to matched to the wheel rate, if you run KYB's with 1" or larger bars the ride will be harsh, because KYB's are lousy shocks for larger bars.
Now, does any of the torsion bar stuff have ANYTHING to do with what's making noise on your car right now? No idea. It does sound like you're bottoming out, but that's just from what you're saying. Pictures of your suspension would help, so would a video or sound clip of the noise. And you need to put the thing up on jackstands and look for loose or broken parts at the very least. Lower control arm bushings are easy to damage on install, and the rubber quality of the re-popped bushings now has gone down considerably, so just because there was a recent rebuild doesn't mean you can assume any of those parts are good.
