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How Much Flex Is Too Much

Nigel Mulvey

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I've been driving my new 240 around for a few days now and have noticed an awful lot of clunking and creaking. I've just bought the Z Therapy video and I'll get round to changing the bushings over one day - that should sort out the clunking.

I'm a bit concerned about the creaking though, while it seems to be coming from the interior decorative paneling which does not have all of its plastic rivets in place surely the cause of it is the body flexing. How much 'flexing' should a 240 do before I should worry?

I'm not driving like a maniac, quite the opposite since I wrote off the 260 last weekend. I'm driving it like a Volvo with a fish sticker in the rear window.

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If doors start popping open or the hood won't stay latched. :rolleyes:

Just kidding. In reality all unibody cars have some amount of flex in the chassis. Some just have more than others. If someone did a torsional rigidity test of the Z cars, especially the early ones, they would probably flex more than a new passenger car, even a Hyandai. In the 70's no one was worried about crash testing and safety like they are today with the crumple zones etc.

One of the biggest reasons the early cars flex a bit more than they should is because they were built using what today is thought of as very thin sheetmetal for the basic chassis. That coupled with the fact that all the panels are spot welded together instead of being seam welded contributes to the chassis flexing.

One trick a lot of racers have used is to strip the chassis down and seam weld key areas of the unibody.

If you are missing rivets on the interior panels it is just magnifying what little flex there is. If you go under your car and find panel seams that are starting to separate then it's time to start worrying, until then, "enjoy the ride".

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The flip side of the 'interior panels' discussion is if they are all new and tight in an older car, you can get quite a bit of squeaking. I stripped the interior of mine and cleaned and refinished everything and used all new rivets and when I was done, I had a little choir going inside. Much of it has abated now, (500 miles later) thanks to a few well-placed felt 'cabinet bumpers', a little wax paper in a couple places, and general breaking-in.

As far as the oroginal question goes, I do not currently own a 240, so I can not testify to the rigidity of the chassis. I don't want to start a war, but I SUSPECT, based on thicker metal used and general improvements to the 'comfort' zones as the Z progressed, the '77 is a bit stiffer than the 240. With that said, my car (very un-rusty and no seams popping) creakes considerably. At speed, it is hard to notice, but driving over curb entrances slowly while parking and whatnot, it is really noticeable--especially while navigating them diagonally. Front and rear strut braces (just the cheap MSA ones) solved 75% of it though. The car is ALOT quieter.

The other thing the strut braces improved was hard cornering. With out them, you would pitch the car into a corner or even a hard sweeper, and the rear end was really unpredictable and you felt the rear of the chassis flex and you get the sort of 'wheel hop' as the wheels load and unload unevenly as the frame twists. With the bars, the car is really predictable. You get an even scrub. It seems the car slides out easier (could be I am just driving it harder) with the bars, but it does it evenly and you know exactly when it is going to happen. The rear end drifts as a unit. Throttle pressure is all that is needed to control it. Make sense? I am not a racer and don't know all the technical terms, but this is how it appears to me in the driver's seat.


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