QuestionQUESTION: I have a 1970 Mustang that starts and runs, but when it reaches High RPMS is shakes bad. What do you think the problem is? Thanks
Mike
ANSWER: There are a very large number of things to check. If it vibrates when the car is standing still, in neutral or park, it could be a bad flex plate or flywheel (cracked, or loose bolts), a bad front harmonic balancer, bad motor mounts, a problem in the converter or clutch (you didn't mention what transmission it has), or it could be the engine has some internal problem. Check to make sure the engine is firing on all cylinders (you don't say whether it is a 6 or an 8, but check all of them). If the car has to be moving to get the shaking, it could be anything that rotates when it is moving (tires, wheels, driveline etc.)
Give me more information and maybe I can help narrow it down a bit.
Dick
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QUESTION: It's Automatic and it has a 351 cleveland in it. It's when I start to pick up speed it vibrates really bad so I may only drive it for short distances at a low speed if that. Thanks
Mike
AnswerOK, that narrows down the list a lot since it only vibrates when you are moving.
(I assume that from what you just said, but just to double check, if you shift to Park and rev the engine to around 2000 RPM, it should roar, but not shake your teeth out). 2000 RPM is just above what you would call "fast idle", not really racing the engine.
We'll go with the assumption that it only vibrates when you are moving:
#1 thing to check is for an incorrect, bent or loose wheel or a bad tire. The way to do that is to jack up each wheel and spin it while you watch the wheel. Also, shake the wheels to make sure they are on tight, and check the lug bolts to make sure they are all in place and tight. Watch the wheel for a bump on the tire, or any wobbling of the wheel or tire. They should run smooth and without any up/down or side to side motion. I think that is by far the most likely cause of your problem. Also, pay attention to the noise each wheel makes as it goes around - if you hear any grinding noise or other racket, have your wheel bearings inspected for condition and adjustment.
#2: It is remotely possible that there is a problem in your driveline (driveshaft bent, coming loose at either end), so if the wheel examination doesn't find it, jack up the whole rear end of the car (use safety stands!) and start the engine, and let the car idle in drive. The rear wheels will start spinning - and then look under the car at the driveshaft - if it is shaking or whipping around like a jumprope, drive the car (SLOWLY) to a driveline service outfit - they will fix it for you. Don't ignore a driveshaft problem - if it comes down it can cause a serious accident, and also will leave you stranded.
Let me know what you find out, please.
Dick
