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I bought and drove my 71 Z car for one year, Last year could not drive it. Could not pass emissions. Pulled the engine (bad rings) last week to swap with other engine that I rebuilt two years ago. When I pulled the engine I noticed that frame section under the swaybar had rust damage. The guy that owned the car before me, had someone re-enforce the frame with 12" L shape metal plates and bolted it back together. Can a frame shop repair or weld these two sections with the metal plates. And could this cause the vibration I get when I accelerate over 40 mph, This didn't happen until a year ago, one month after I had the tranny serviced. Some times it rides smooth as glass if increase the speed to 70 mph but not all the time, If I reduce the speed slightly under 70 the vibration starts again. Any clues about vibration, I put bearing in and all U's on the drive and half shafts are new. What the verdict on the frame ????
 

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Sure, you can replace/repair the frame rails. Not too sure about using what you have already as it doesn't sound very good. Run a search on this forum and you'll find plenty of info about sources for parts.
As to the vibration, is seems unlikely that the frame would be a source of vibration (although I'm sure that frame flex would not dampen existing vibration). Its more likely that the vibration is related to the drivetrain. Perhaps a halfshaft out of balance or the driveshaft installed 90 degrees out of phase or perhaps even a wheel or tire out of balance. When were the tires last spin balanced? How accurately? The Z's are known to be sensitive to balance and the tires must be balanced as accurately as possible (within 1/4 oz would be great).
Dan
 

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Couple quick items for you.

Yes, it is possible for the weakened frame section to be affecting the ride, but if in fact those bolted on sections are structural and not cosmetic, then you might have something else to look at.

You CAN go to a Weld shop and have them weld just about anything as long as there is some good metal for them to weld to, however, if you're talking the cross member you might be better off finding one in a boneyard. If however you are talking the front to rear members, then the only way is to have the weld shop weld new structural metal into it.

I would suggest you check a couple other things out first, (although don't ignore that rust, get it fixed asap).

First off, are you sure the tires are balanced properly? That is, with the SPIN balancer and not the backyard mechanics bubble level. Also are they balanced to center axis? Up here in the Northwest, there is an outfit called Les Schwab, they do an awesome job of balancing not only for radial balance, but also for Axial balance, (i.e. inside edge versus outside edge). A poorly balanced tire ("that's close enough") may in fact exhibit the rattling shaking you are experiencing above 40mph. My wife's car was balanced to "almost perfect" but at 65 to 75 it would shake the steering wheel, not enough to loose control, but enough to make you slow down to avoid it. Yet there were times when you wouldn't notice it.

The other item is BELT SEPARATION. I had a set of Michelin tires on a 76 Mercury Capri II some years ago, that had a broken belt in each of the front tires. At 30 mph the whole car would shake and bounce, at 40 it would level off and be ok, and then it would pick up again at 55 or so, and drop off about 75. When I finally took it in to have the car serviced, the first thing they pointed out as needing to be done, was NEW tires. Mind you, there were times when you wouldn't notice it.

Lastly, check to make sure your front end is aligned, and also check to make sure that the front of the car has been aligned to the rear of the car. This is called dog-tracking. A car that's been hit, or had the rear-end completely worked on, or the front end, needs to make sure the front tires are in line and parallel to the rear tires. If they're not, you'll dog-track and in severe cases you'll have some of the shaking you wrote about.

FWIW
 

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Discussion Starter #4
Thanks All for the replies.
I will take this advise, One more thing, the vibration is not so much as shaking but a very loud, irritating vibration, Hopefully alignment or balancing.. Your thoughts
 

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Even without the shaking, could still be a problem with the tires, you might have a bad belt that is only starting to go bad. Wheel balancing is usually quick and easy, plus if you bought your tires from a reputable dealer, they'll usually check for free.

If the tire is going bad, have the dealer check that also. A cold tire or hot could cause the problem to be masked at times, and not show up till later. It isn't that hard to check them out and you'll have eliminated them as the source of the problem if they check out.
 
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