Hey everybody,

I've a question for the vibration guru's out there. I just had my 1978 f150 4x4 ford 400 engine rebuilt and replaced. It was balanced from fan to flywheel and all new parts installed by a very reputable shop here in town. The problem is a vibration that begins at around 2500 rpm's (slightly noticeable) and get worse until about 3000 rpm's (where it seems to level off, but still vibrates). I've taken it to my mechanic who installed the engine and he went over it with a fine toothed comb (drove it on the highway and the streets, accelerating/decelerating, different gears, clutch in/out and no matter what, it always vibrates at 2500+ rpm). He even disconnected the accesories and nothing changed. He also checked the driveshafts and the u-joints didn't have play. He was stumped at what it might be as the engine only has 550 miles and about 18 hours since install. I'm taking it to the engine shop tomorrow to see if they may know what may be causing the vibration. The strange thing is that the old engine I had did almost the exact same thing, but NOTHING was used from the old engine. Any suggestions? the engine has the edelbrock power package, w/ manifold and 600 carb, victory water pump, new p/s pump and alternator, new motor mounts (anchor). The only vacuum connections I have are: carb to dist, carb to PCV, carb to vacuum gauge. I have the edelbrock 1" carb spacer and heat spacer under the carb. It has a NP435. Please help me...I'm desperate as I can't drive this thing with it vibrating. Thanks a bunch everone.

Chris
78 f150, 400, NP435, NP205, D44 (4.56 open), Ford 9" (4.56-LSD), 32" BFG's

 

Well, it seems like if you had the same vibe before and didn't reuse anything of the old engine, it's not the engine. Does it vibrate when you're in neutral and not moving @ 2500? If so, does stepping on the clutch change anything? Did you use your old clutch? Was the pressure plate balanced with the rest of the assembly?

 

I have the same problem. Mine however is between 1200 and 1800. It did it before and after the rebuild. Frustrating. If you find anything out let me know.

Chad

 

I would have to say it's in the flywheel pressure plate area. the 400 has a counter weight on the flywheel and sometimes the pressure plate has some balance added to it ..

 

That may be true, but I have a C6 auto.

Chad

 

I had the same problem with vibration.I would suggest you replace your harmonic balancer.If your motor has ran at high rpm's, It is possible the outer hub has moved on the rubber. I replaced mine with a Fluid Damper and it is smooth. Well worth the money,$250.00 I built two blocks before I figured it out. Hope this will help you,,,And save you some headaches&Cash.

 

I had the harmonic balancer balanced with the crank and rotating assembly. Shouldn't this have taken care of this? I did use this before and after the rebuild. I might have to get one. Now, shouldn't this be balanced with the crank, or does the fluid damper adjust on its own?

Chad

 

 

I know this is an old post but did you ever find a solution to your problem?