some background:

purchased a 1966 coupe originally with a straight six but, as sold with nothing in it no eng/tranny. During the rebuild I discovered that some time in the 1970's the car underwent a major change. A whole host of upgrades including rear axel, all appropriate V8 hardwear, including 70's era disc brakes (which just barely work with some custom adapter hardwear). The fella I bought the car from also sold me a 289 (according to him) and a C4 transmission out of a 78 Ford Fairmont. I rebuilt the engine had the transmission gone through and replaced almost everything on the car.

Here's the deal, the engine was not a 289 it was in fact a 1971 302 orignally out of a Torino, so the harmonic balancer was wrong and I figured that it had been responsible for the wierd vibration i was getting (a pulsing recurring harmonic vibration at speeds in excess of 45 mph and a nasty vibration at idle). Replacing the balancer did not help so believe me we went through everything including buying a new block because the old one we'd rebuilt turned out to be crap it had really worn itself out(nearly eating through the main bearings and nasty scoring in the rods). The new block was a professional rebuild and I put in a 4bbl edelbrock(my holley blew out do to crap getting into it). the new engine was given a stock cam(rule out the RV cam theory) and just yesterday I completely rebuilt the rear end, brand new everything in that rear axel.

The thing is the engine still has the same vibration at speeds in excess of 45 mph. I'm at my wits end here so I took it into a shop and the dude drove it and he tells me that the vibration is in the COMPLETELY BRAND NEW ENGINE. Specifically he said it was a manifold vaccuum leak or a carb leak, all i can say is fat chance, no way in hell. I hope somebody has got some kind of theory on this.

In addition these are the only components used that are not new:

289 HP Heads
4bbl Intake Manifold
Oil pan

Also all components in the rear end were rebuilt and balanced (including the driveline). All components within the engine were balanced by the company that built the engine.

quote:

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Originally posted by Milkman385:
have been a long time customer of Mustangs Unlimited.

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Did Mustangs Unlimited restore your car? What is their role in this problem?
Or was that just to provide some background information?

If so much attention has been paid to the engine I would start to look at other components on the car, anything that rotates could cause a vibration.

Driveshaft (again)
Flywheel missing a weight or the wrong flywheel
brake drum or brake rotor
wheel or tire
bent axle

Not all C4's are the same. You may have a C4 that is supposed to be used with the 50 oz late model balancing.
I am no expert (understatement) but I had the same issue. I had a C4 that was supposed to have been from a early 70's 302. I put in a new engine, rebuilt 289, and had all kinds of vibration. I tried everything and finally out of desperation bought a C4 from a 66 from one of the members on this site. Put it in and vibration went away.

Don't run it long with this vibration or you will burn up the bearings on the new motor.

Firstly, the comment regarding mustangs unlimited was for background purposes and this post was originally on mustangsunlimited forum.

Now then, the fly wheel was sent in to the shop with the engine it is supposed to be properly balance and has a weight welded on it. This was brand new. The transmission as i have said is out of a 1978 ford Fairmont and is a C4 it was gone over but never with the engine. There is a chance that this could be the problem. However I am using the 70's style balancer and pulley on my 1972 engine(the new one).

I did the rebuild on the rear axel myself they did not appear bent at that time. Still it could be that the rims are bent, though I cannot tell, there is no noticable "wobble" in them while on the road. The rotor and drums were turned before being put on the car.

If you have a 50oz flywheel on a 28oz motor, you would NOT drive it, trust me on this, we're talking full on shaking, vibration isn't the word.

Could be the flywheel (custom balance, right?) may not be exact, could be the rims, tires, brake discs/drums, driveshaft, torque converter if it sat too long, etc...

I'm betting on wheels/tires/brakes, something in that area... could be front end parts that don't have slack in them until under severe strain (over 45+ mph) and heated, to give slack.

Thanks for your suggestions.

No, it has a bad recurring harmonic vibration at speeds in excess of 45 mph.

If the vibration goes away, it's in the engine. If it's still there, it's not.

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'70 Mustang Mach 1 351C 4V/FMX/3.25 Open
'70 Mustang Convertible 250 I6/3 speed/2.79 Open
'72 Mustang Sprint Hardtop 351C 4V/FMX/4.30 Trac Loc
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip

To me these are unrelated to the vibrations. The vacuum gauge reading sounds a little low to me should be about 20 if memory serves. This could be due to late timing, carb vacuum leak things like that right? I know my brand new carb is a 650 performer series. Also both manifolds I've had occurred simulatenously with the vibrations. The dumb dudes working on my car also now want to remove the transmission and torque converter and just hook the starter up and start the engine to see if the vibration is still in the engine.

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I'm an optimist, but I don't think it helps much
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Then never to have loved a tall"
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