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front struts
with the ball joint and tie rod end removed it is really easy to compress the front shock. Is this typical and is there a way to measure this to ensure it is within specs?
------------------ Rob Fix '78 SC Targa |
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12-09-2000, 12:03 PM
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I believe it should take at least a bit of muscle to compress the strut. It should, even under load, compress slowly. If it compresses easily AND quickly, then its probably collapsed and needs replacement.
Nick. ------------------ __________ Nick Shumaker 1982 911SC Coupe |
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12-09-2000, 12:17 PM
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The more critical function is the rebound stroke of the shock insert, and typically twice as much force is required to pull the rod back out as to push it in. In use, the springs of any car resist the major force causing upward movement of the strut and axle, the shock insert damping some on the upward stroke, but the major and most important function of the shock is to damp the downward motion and prevent oscillation of the axle.
The 'compression' testing by humans is very subjective, and the only accurate tests are done on a very specialized test jig that can measure, record and vary compression and rebound stroke forces, and plot the result on a graph. What brand of strut insert are you dealing with, and are they OEM or replacements? ------------------ Warren Hall 1973 911S Targa |
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12-09-2000, 01:17 PM
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A "shock dyno" is what Warren speaks of. Pretty cool machine really. You fixture the damper in question into the machine (looks a bit like an Instron tensile tester) and it then strokes the damper at various speeds (defined by the operator) and records the damping forces in both directions. You can get all kinds of plots, but the most oft used are the "football" curves which overlay all the curves (force vs. displacement - shown as a football shaped loop) from the different speeds, and the simple force vs velocity curves.
It really is a tool only used when developing the valve code for the dampers. Another sign that a damper has gone south (at least with gas charged dampers) is that once compressed it won't self return to the extended position. Anyway, probably more info than you care about. Chris B 78 SC |
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12-09-2000, 05:57 PM
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thank you gentlemen. and let me say there is no such thing as more info than what I want to deal with. I will respond shortly with the brand, I'm in Seattle right now, but the downward motion is at least as fast as the upwards push, I'll expand further on sunday when I get back to Bellingham, thanks for the input.
------------------ Rob Fix '78 SC Targa |
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12-09-2000, 07:27 PM
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