Guest DRK Posted January 28, 2003 Share Posted January 28, 2003 I broke my front diff mount Sunday night a week ago, and just this past weekend got around to fabbing up a replacement. My car is a 78, and there was a large goofy looking weight bolted to the bottom of the front differential crossmember. Does anybody know what this is for? It is two large steel plates approximately 3x6 and about 3/8" thick. Then there are also some smaller ones stacked on the end. Thanks, Danny Quote Link to comment Share on other sites More sharing options...
JoeinCA Posted January 28, 2003 Share Posted January 28, 2003 I havent put mine back in yet (i'm not driving the car) I think it is there to improve weight distribution and stabilize the diferential. Joe. Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 28, 2003 Share Posted January 28, 2003 This comes up about once a year or so. The weight is called a mass damper - it's basically a band-aid fix for a noise/vibration problem that was discovered after cars started rolling off the assembly line. At this point, it's too late to make major changes. Some of the crossmembers were apparently resonating at some speed, and making objectionable noises. Adding weight to it forces it to resonate at a different frequency (presumably one that was not a problem for the diff), and the problem goes away. Common practice in the auto industry, even today. This is usually only done for noise/harshness issues, so if you don't notice funny noises, I wouldn't worry too much about replacing it. Mine fell off some time back in the eighties, and I've never been able to tell the difference. Quote Link to comment Share on other sites More sharing options...
Guest silverbullet Posted January 28, 2003 Share Posted January 28, 2003 I have a "77" with one of these things on it now I finally know what it is. Quote Link to comment Share on other sites More sharing options...
Guest DRK Posted January 28, 2003 Share Posted January 28, 2003 Wow! I have only driven the car maybe 10 minutes since I redid the diff mount and removed the weight, but I did notice a resonance/vibration sound coming from the back. I figured it was just the way I decided to mount the the front of the diff. I may have to experiment with putting it back on to see if the noise goes away. Thanks, Danny Quote Link to comment Share on other sites More sharing options...
JoeinCA Posted January 28, 2003 Share Posted January 28, 2003 Doh, i hate only being 1/4 right....(aka wrong). lol Joe. Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 28, 2003 Share Posted January 28, 2003 i dont think its the weight (or absence of) thats causing that vibration, did you remember to put the driveshaft back in the exact same way it was taken out?? ive found that to cause vibration, first thing i did when i went for diff work was toss the weights, but i did remember to mark the alignment of bolts on pinion flange, and number the bolts clockwise. Quote Link to comment Share on other sites More sharing options...
Guest DRK Posted January 30, 2003 Share Posted January 30, 2003 Nope. I did not mark the driveshaft. I guess it could be 180 out. It is not like a vibration though, more like a shield buzzing at a high frequency or something. The starter broke the other night though, so I have not had a chance to drive it. Danny Quote Link to comment Share on other sites More sharing options...
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