AOD causes vibration

the first thing to check is the balance factor of the flexplate you are using, compared to the crankshaft you are using. if you are using a post 81 5.0 crank, then you need a 50oz balance factor flexplate. if you are using the pre 81 crank, then you need a 28oz balance factor flexplate.

you can tell the difference as the balance weight on the 50ox flexplate is nearly twice as big.

it is possible that the converter is out of balance. if so you can have it rebalanced.

the 50oz balance crank is missing a couple of counterweights in the middle of the crank.

rbohm,
Did the balance factor change the same time that they went to a one piece rear seal? Just curious and hoping to help our friend across the pond figure out what he's got without dropping the oil pan.
Thanks,
Gene

to be honest i dont know, as i am not sure when ford went to the one piece rear main seal on the 5.0s. i can only tell you that they changed teh balance factor in 1981. one thing he can check is the balancer. if it is the 28oz balancer then he has the older crank. you can tell that by looking for a large cutout on the inner edge of the balancer. if it is there then he has the 50oz balancer. no cut out means he has the 28ox balancer.

mhjo,
I'll do my best to help relieve some of the confusion.
> Early 289 & 302 engines (until, I think, 1981) had a crankshaft imbalance factor of 28 ounces
> Later 302/5.0 engines (I believe 1981 & later) had a crankshaft imbalance factor of 50 ounces
> Each of these engine groups need to have
A. The correctly balanced/weighted vibration damper (also referred to as a harmonic balancer) fastened to the front of the crankshaft and your front crankshaft pulley bolts to it
B. The correctly balanced flex plate/fly wheel that bolts on to the rear of the crankshaft and your torque converter bolts on to it.
C. These parts need to match each other AND the crankshaft to provide proper crankshaft balance,
> If one or the other, or both, of these pieces is incorrect it will cause vibration issues much as you are describing. It will also cause serious damage to your engine in the long (or maybe short) run.
> When only one or the other of the parts is incorrect, the vibration is often less evident/noticeable and more difficult to track down.
> One difficult part of the issue is that the 50 ounce parts will "bolt on" to a 28 ounce engine and also the 28 ounce parts will "bolt on" to a 50 ounce engine.
> What many people who are unaware of the balance issue have done, is to install an AOD or T5 (from a later model car/engine) onto the back of an early engine, utilizing the flex plate/fly wheel from the late engine that likely came with the transmission. There are several other scenarios of mixing the wrong parts, but seeing that you have an AOD, we will not address those at this time. All (or at least, most) AOD transmissions that came with the 5.0 engine with a factory/OEM flex plate are for a 50 ounce imbalance, but I'm not sure about an AOD from a 351, (see next bullet)
> 351 engines don't fall into the same specifics and as long as you don't have a 351, we won't worry about it for now. If I recall correctly, all 351 engines have the same imbalance factor, I just don't remember if it is 28 or 50 ounce. The only thing that may or may not be pertinent here is that the flex plate and vibration damper from a 351 will physically "bolt on" to both early and late 289/302/5.0 engines.

What we need to do to help you, is determine what engine you have and ESPECIALLY what year it is. We really can't do this by identifying the "bolt on" damper or flex plate, as one or the other, or both of them may be wrong. We also don't want to try identifying from numbers on the heads or intake, as who knows what has been swapped in the last 45+ years. I believe there are some numbers stamped and/or cast into your engine block, I'm just not sure where or which ones will help us, except for the numbers/letters cast onto the block just above the starter. If you can see these (from under the car) please post them so that we can at least get a start on this. I am hoping that someone else will speak up to help with ways to make this identification, as my knowledge in this is a little lacking.
I realize that this all can sound confusing, but rest assured that the parts are available to make this right and are not terribly expensive, once we have all of the detective work done. Once we have the engine identified, we can work on identifying the vibration damper and flex plate and determine if they are right or wrong for your application.
Hope This Helps,
Gene

all 351s have the same 28ox balance factor.

check the flexplate carefully for any cracks, check the bolts for looseness, check the engine and trans mounts for condition. if needed check the converter for balance.

Check to make sure the exhaust is not hitting anywhere nor the tranny contacting any portion of the body or tranny crossmember other than at the mount.

If you have a 289 make sure the flexplate you are using is a 28.8oz imbalance unit. The harmonic balancer should be for the same imbalance also. You mentioned that it vibrates in park/neutral at around 1000 rpm. This means that it's not a driveshaft issue. How have you adjusted your throttle valve pressure? Also, have you ensured that the drain plug in the converter is sticking through its hole in the flexplate? Did you convert from manual trans? If so, make sure the pilot bushing has been removed from the back of the crankshaft. Have you tried running the engine without the belts to make sure it's not an accessory problem? I've had cooling fans do a similar vibration. Also, make sure the spark plug wires from cylinders 7 and 8 are not running next to each other and only cross at right angles to prevent spark jump. Last thing I can think of is if you know someone with a diagnostic occilliscope that can check cylinder balance to see if something is up there.