I have 2WD '78 F250 with a remanned 351m. This donor 351m was in a 4x4 but I dont know if it was a manual or auto. I have read that there are different harmonic balancers not only between the 400 and 351m but between the 351m auto & manual. Can anyone confirm this? My problem is I am trying to figure out where my vibration is coming from - in park if I rev between 1500 & 2000 I get pretty decent vibration in the steering wheel. I can also hear an off-Kilter rotation in the engine when driving 45 - 50 MPH. If I step on it the uneven sound goes away but is noticeable and slight cruise / throttle. I am not sure where to start to look. I thought the transmission would be eliminated since the vibration in park or neutral at 1500 rpm but am I wrong? I did check to make sure the torque converter bolts were all snug and they are. Thanks in advance for the help. The attached pic is from the balancer off my 400 and is bigger in size that the one currently on the 351m. The # on it is D7TE-BA then the letter E in a small square box.

 

There are differences in the dampers but there is no difference in the amount of external balance weight(28oz). Torque converters can cause vibration issues. Also it might be a good idea to take off the belts and start the engine just to eliminate the accessories, fan etc. for a test.

 

Any signs of the outer ring moving?

How does the rubber look?

Is the outer ring straight and true to the hub?

 

I was checking mine on a 400 gifted me and found this picture years ago, it did not have the added notes but it fit my two HBs. It shows the width, but as already said, same 28oz counterweights on hub.

Your's is like the one that was OEM in my father in law's '77 F-250 4 speed 400. 10.4 pounds.

I seen that the 9 pound one (middle of picture) that was on my 400 was somewhere said to be for an automatic, but I know mine was from a 400 with 4 speed in a F-350 wrecker.

Oddly, I found that the 7.3 pound one (top of picture) on my 351M that is OEM was said in one source to be for a 351M manual, but my '77 has always been an automatic. It was 9 years old when I bought it, but it had just 35,xxx miles then so I'm confident that it's stock.

My main reason for saving and noting was to gain / retain weights and thickness information as I was gonna put the 400 in my '77 in place of my 351M someday. I was wanting to be sure about the HB I would use. In my case, I feel confident that either one will be just fine. I read that the differences in total weight of the HB relate to damping the "power pulses" spinning the crankshaft, that 400s jerk the crank harder in rotation due to the longer stroke, so they tend to have heavier HBs. Maybe so as with each 360 degree crank revolution, there are 4 "power pulses". Automatics dampen "power pulses" in the torque converter, so they use lighter HBs ... but manuals pass these "power pulses" on through the drive train ... as I understand it.

I don't recall mention of or seeing a little E in a box stamp.

 

Was the engine balanced ? Does it idle ok ? Does it seem down on power ?

 

@mark a. @tbear853 I do believe the engine was balanced. It was built by a reputable builder I have used before however the balancing is not reflected on my invoice. It seems to idle ok but fluctuates slightly. Power seems ok. I have a new correct balancer on the way and will be installing it tomorrow. I know that when I first went to install the trans I didn't have the torque converter n all the way. i started to tighten it down and realized something was off so I didn't completely tighten it but I did some. What would I have bent when doing this? Could I have ruined the flexplate? They are inexpensive and napa has one in stock here.

 

To shake like you're describing the assembly probably has to be out of balance 200 grams or so at one end or the other. The damper isn't going to do that but a 300 6 cylinder flexplate instead of a 28oz one for a V8 sure will.

 

Thanks @DaveMcLain - Well i am at that moment where I feel a need to throw money and parts but I don't want to replace things for nothing. I already have a balancer on the way and might order a flexplate but where else should I be looking. I am having a hard time accepting the shaking on a newly built engine and really want to find / fix it before something worse happens.

 

Just check and see if there is a weight on the flexplate. It'll be a few inches long and you can see it if you take off the inspection cover and then bar the engine over by hand. A 6 cylinder one is identical except that it doesn't have the weight attached.

 

What do the spark plugs look like ?

 

I'd check distributor, plugs, wires and do a compression check for the vibration being described.