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| Suspension bushing design http://delcohacking.net/forums/viewtopic.php?f=35&t=915 |
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| Author: | JT191 [ Thu May 13, 2010 4:16 pm ] |
| Post subject: | Suspension bushing design |
This sort of evolved sideways from the Front lower control arm assembly and attachment thread. viewtopic.php?f=35&t=879&p=5466#p5466 Good news: The front arm sleeves which hold the bushings do not appear to have a measurable taper. When a rubber bushing is cast into a steel sleeve and then pressed into the sleeve in the suspension arm, it usually distorts the inside diameter of the sleeve in the suspension arm. Bad news: After measuring the spacing and clearance between the arms and the mounting brackets attached to the car, the arms do not appear to be moving in a smooth arc. The arms are twisting sideways and out of normal alignment as they move through their range of motion. So the clearance between the arm and the mounting brackets is wider on one edge than on the other. The front upper brackets, which bolt to the side of the fender well, seem to be the most extreme problem, because they are no longer parallel, and the inside edges of the suspension arms are actually riding against the brackets. That's metal to metal contact! took a look at the spare upper arm and brackets and there are grooves worn into the bracket where the arm has ground against it. The new bushings will have a shoulder on both sides of the sleeves in the suspension arms. This shoulder will ride against the edge of the sleeve in the arm and the bracket (front upper arm and rear arm) or washer (front lower arm). The shoulder will prevent the arm from twisting or moving laterally. But the shoulder must be thick enough that it can do this job. It will take a little more thinking time to get the spacing right. This is really only going to be an issue with the front upper arm. And the brackets for the front upper arm bolt to the car. So there should be some flexibility there to get the brackets back to parallel and keep the metal of the arm from riding against the metal of the brackets. My concern with the front lower arm is the bolt spacing for the fulcrum attachment. I was not brave enough to remove the arms and the bolt hole positions could not be measured with the arms attached to the car. The spare lower arm assembly leaves some questions. The forward attachment is by a U bolt, with nuts on the back side of the lower cross member that are accessed from inside the engine compartment. The aft attachment is via bolts which thread into the lower cross member (weld nuts within the member). The semicircular recesses in the fulcrum have the same offset for both of these. But the ends of the forward U bolt do not match the measurement of the metal retainer for the aft bolts. The difference is about 1.25 mm. I can make the new fulcrum assembly with threaded holes and studs to hold the forward end onto the car. But, threaded studs become a problem if someone manages to break a stud off. I can make it with a bolt hole, which would resolve any broken fastener concern. But then installing and removing the fulcrum becomes a two person job. And if I make the offset and diameter of the bolt holes to match the U bolt spacing and the aft retainer spacing, the holes will be slotted, and possibly sloppy. I think I've resolved to take the front suspension apart and measure the attachment points on the car. I need the bolt hole spacing for both upper and lower front arms. Is there a preload on the stock springs? I am not interested in shooting springs across the room. |
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| Author: | JT191 [ Sat May 15, 2010 4:32 pm ] |
| Post subject: | Re: Suspension bushing design |
Here's something that occurred to me while comparing measurements: The lower suspension arm is wider when measured disassembled, than when measured on the car. The assembly, as mentioned before, involves pressing the bushings into the arm and onto the fulcrum. Then the bushings, and the arms they are pressed into, are drawn against the fulcrum when the nuts are tightened into place. it looks like it may be as much as 2.75 mm difference between the compressed and at uncompressed measurements. I wonder what that squeezing load does to the suspension arm movement. |
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