Feature September 1, 2013 by
Jim Anderton, Technical Editor
Rubber Bushing Blues
Tracking down chassis noise is surprisingly frustrating. Ever notice how, from the driver’s seat, the sound seems to be coming from the opposite corner of the vehicle? There are dozens of possible sources for noise, with just one thing in...
Tracking down chassis noise is surprisingly frustrating. Ever notice how, from the driver’s seat, the sound seems to be coming from the opposite corner of the vehicle? There are dozens of possible sources for noise, with just one thing in common: the time and cost of tracking them down and eliminating them is rarely worth it on an out-of-warranty car or light truck…with one possible exception: leaf spring shackles and bushings.
Thanks to the SUV craze, there are a surprising number of vehicles on Canadian roads using buggy springs out back and the bushings, hangars and spring isolators take a beating over years of salt and neglect. When was the last time you took apart a stack of leaf springs to replace the isolators? Me neither. As a result, by the time the machine comes in for service about chassis noise it has already progressed to seriously bad news for the tech.
I had a recent experience with a leaf sprung vehicle (the name of the manufacturer will remain hidden, so you can guess which one) which confirmed everything I’ve complained about in these pages about manufacturer indifference to the repair industry. It started with a rusted rear shackle, corroded to the point of a real risk of failure. This safety item was a must do and the leaf spring to shackle bolt came off with just a touch of the gun and no heat needed. A good start. The upper, however, was a different story. The bolt was inserted at the factory from the frame side, and with the box in place it was impossible to drive it back. A fat trailer wiring harness sat about 5 mm from the assembly making the “blue tip wrench” inadvisable.
Why would the OEM design this mess to make it so difficult to service? Because the chassis is assembled as a roller first, with the body drop near the end of the line. With no box and new fasteners, it’s easy. Not for us, however. What to do? I ended up rigging a sheet metal flame shield and working quickly with a big tip blew off the bolt head. This naturally set the rubber on fire which always adds aroma to the dirt and falling rust. The rest was, as they say, in the manuals, “assembly is the reverse of disassembly.”
That’s when it hit me…there’s a reason why I’ve been struggling with torch-driven bushing replacement: too small a cutting tip. It’s fine work in a closed space, so it’s natural to want to use the smallest tip you can to avoid nasty accidents. Oxy-acetylene cutting, however, requires the metal to be white hot before adding the oxygen blast, and a big bolt head with an integral washer is a pretty good heat sink. Lots of heat soaks into the bushing before you’re ready to squeeze the lever. With a big tip, however, the bolt was ready for the cut almost immediately and with minimal burning rubber because the amount of time the flame was on the bolt was minimal. It made the other side much easier to “re and re.”
It’s counter-intuitive: use a big tip to do a delicate job, but if you’re in a similar situation, give it a try. Just watch for flammables in the area, keep that fire extinguisher handy and kids, don’t try this at home.