[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
On 30 Sep 2003 at 13:12, Neil Verdon wrote: > what i think is happening here is a common unrealised problem on our cars > the body to rear subframe mounts have collapsed ! > > does your car droop in the rear generally ie if you lowered the front end of > the car would it then sit level? > > where the shock absorbers fit there is a tower going up to the body this is > the point i mean take a look the body may have even rusted in this area and > settled down to the subframe! At least in this case, he's asking about an IRS car. On these, the rear of the engine is suspended from the body of the car. While settling of the subframe mounts may have happened, it would just lower the body and the front of the transmission; the rear of the engine, being attached directly to the body would just lower along with it. It's position relative to the body wouldn't change. Neil, I'm glad you brought this up again. We had a conversation about rear subframe rubber mounts a month or so ago. I believe that you and I disagreed about how much body sag they could be responsible for. While I still don't think they can shrink enough to do much, I had a couple of long, 8 hour, drives right after that to think about it. I realized that one of the reasons that my 69 was noisy and shaky was that the rubber mounts have probably shrunk enough to make that mounting loose. Here's the problem as I see it: The subframe is mounted to the body in a number of places by what amount to thick (~1cm) rubber washers. The mount points of the subframe are captured between a pair of these washers and then a large bolt, with a washer under it's head, is passed thru that sandwich and into the body. Originally this bolt tightened to a stop that left the washers slightly compressed. With the subframe captured between the 2 compressed rubber washers, the effective spring constant was pretty high, making this connection resilient, but quite stiff. Today, however, the 2 washers have shrunk a bit, so they may no longer be under any compression. This completely removes any stiffness from that joint, and it may even be loose. In addition, the rubber parts are probably harder now, so that, if the joint is loose, the parts may "rattle around" against rather harsh stops. So, as I see it, a 1 cm rubber mount that shrinks by 2mm may only cause about 2- 3mm of body sag, but that 2mm of compression set could completely remove all preload from the mounts, making them MUCH looser than they were originally. Let me know what you think of this. I suspect that I'll want to see if I can replace any more of the bushings in my sun belt 69 with ones from some of my scrapped out, rust belt cars. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org