New member here. I have a 1988 W150 360 that has a bad engine vibration at about 2300-2400 rpm. A little history about the truck: the truck originally had a 318 with TBI that was seized when i bought it. I had a 360 from an 86 W250 laying around that i swapped in and converted it to a carburetor and also installed an HEI distributor with new plugs and wires, and removed all the emissions equipment. I know that the 318's are internally balanced and the 360's are external. The 360 originally had a 4spd behind it and this new truck has a 727 so i installed a B&M weighted flexplate from summit when i put the engine in. I used the same torque converter that was behind the 318 (no weights on it) and i did not notice a vibration. A few months later, i had the tranny rebuilt and a new torque converter was installed that did not have weights. I then started noticing a vibration at any engine speed and found that the inspection cover on the tranny was slightly bent inwards when I installed it and the torque converter bolts were rubbing on it slightly in one spot and i fixed that. After that i only noticed the vibration when i was on the freeway, so i had the tires balanced and put new ujoints in the rear driveshaft. The vibration was still there, but i found that it would do it in park or neutral at 2300 rpm, but is smooth at all other rpm. I started looking at the engine and found that the harmonic balancer was bad (the rubber ring was cracked and squeezing out the sides) so i installed a new weighted one from summit, but the vibration is still present at 2300-2400 rpm. Has anyone had this problem?

 

How are the engine/trans mounts?

 

Can you notice the vibration in neutral when you rev it or only in drive?

 

I put in new engine mounts with the engine and the trans mount is good. The vibration can be felt when I rev it in park and also when I'm driving at about 50-60mph

 

What kind of shape is the harmonic balancer in? Have you hooked a timing light to it since the vibration started and if you have, is the light steady or jumping around.

 

The harmonic balancer is brand new I replaced it less than a month ago. Timing is set at 12°BTDC and purrs like a kitten at all rpm except 2300

 

Is it misfiring?

 

It doesnt feel like its misfiring and it has good power but I will check the plugs/wires and do a compression test later today

 

Was the problem there before the balancer swap?

 

Yes. I replaced the balancer because the rubber dampener ring was falling apart