New Engine, New Drivetrain Vibrations

hot37shot · July 18, 2011

Just put in my new 383. The engine seems to run great. However when i put it in gear I can feel a vibration that gets worse as rpms increase. It does not do it in park/neutral. So it shouldnt be the engine. The truck didnt do it before the build so it has to be something I did during the rebuild.

where should i look? the vibration is not in the steering wheel and not when i brake. oh the trans is t350. thanks!

Shawn

cliobogger · July 18, 2011

first of all, truck looks great, id like a vid of it running/ taking off too, but thats neither here nor there.

not to insult your intelligence, but go back and make sure you tightened everything down 100% (bolts on the tranny cross-member, the x-fer case if its 4x4, everything).

secondly is it right under you or in back of you?

third, a vid of it running would help again, probably from the inside, if we could hear it, we could more easily help to identify what could be wrong.

hot37shot · July 18, 2011

The rebuild was for my '69 C10. At any rate, the vibration seems to be right under me in the drivers seat. Ill climb under it and double check all the driveline bolts. I was worried the torque converter was not seated all the way in the trans. Ill work on the video if it continues.

Thanks

hot37shot · August 1, 2011

Well i have tried everything. There is no loose mounts or cross members. Still vibrates with all the pulleys/belts removed. I have double checked the plugs and wires for a possible missfire. The vibration is present in PARK and in gear while driving down the road ( so it has to be an engine related vibration) .It is only present between 2500rpm and 3200 rpm. Every other rpm range is smooth, evan at 5000rpm! I have also messed with the timing and tried my old harmonic balancer. Now im leaning towards the flexplate, but I dont want to pull the trans. This vibration was not present before the rebuild. Any other info would be great!

specs: 1969 C10: 383 with scat rotating assembly externally balanced, isky 280 cam, dart heads, forged pistons about 10:1 comp, turbo 350 trans 3000 stall, 373 gears

THANKS , Shawn

thegeniusguy · August 6, 2011

Have you check the flywheel?

Duelin · August 6, 2011

If you haven't tried it yet move the torque converter a 1/3 of a turn and see if it get worse or better. Then move it another 1/3 and see if there is any difference. Factory flywheels and converters have a balance mark on them. They are marked with paint. You have to align those marks to make sure the set is in balance. I am not sure about you application.

hot37shot · August 10, 2011

Well the vibration is still there. I have checked all drivetrain bolts, ruled out ignition, new plugs( none foul), timed it, checked compression, ran it without the fan belts and pulleys attached, and put the old harmonic dampener back on. The vibration is present in gear and out. It starts at about 2800rpm and smooths out at 3200rpm. This thing shakes enough to vibrate the rearview mirror! Cant be good for the motor! Next ill check to see if the flexplate is installed correctly. Just not looking forward to dropping the trans!

Here are the specs: 383, scat rotating assembly external balanced, kb forged pistons, isky 280 cam, dart pro 1 heads, demon 650 carb, 10:1 compression, turbo 350 with 3000 stall, 373 12 bolt posi.

THANKS for the info !!

Shawn

thegeniusguy · August 10, 2011

the flexwheel and the harmonic balancer must match or you will have really bad vibrations...

exracer · August 19, 2011

if all rotating internals have been balance....you may need to change flexplate?......I bet that has some heavy weights welded on it used for a factory balancing job

jblakeney · August 24, 2011

Better pull the transmission and make sure the torque converter is all the way seated. Could be not seated all the way if, seeing as your questioning if it is....

But sounds like the flywheel. Did you put a new one in??????? Could have a crack or the weight could have hit and knocked a chunk off.

Jbo

hot37shot · August 28, 2011

Ya, i will be pulling the trans next week. I ordered a new flexplate just to rule that part out for sure. I remember when i put the engine in and bolted up the torque converter to the flexplate, one of the three bolts did not line up good and had to " jimmy" the two to get it through. So im wondering if something was bent or not seated all the way. The flexplate i used was new and came in the rotating kit from scat. So i will try a summit flexpate made for an externally balanced two pc seal.

Shawn

cliobogger · August 29, 2011

That SHOULD fix your problem. Never ever EVER jimmy a flexplate/tq converter...haha. If nothing else, it is a beautiful ride.

hot37shot · September 4, 2011

Well I figured it out! After dropping the trans out I found the flexplate was installed wrong. It was not backwards, but not installed on the correct holes. The scat crank did not have a dowel pin so my alignment was off. This is what I learned after hours searching... on an externally balanced engine, the weights on the flexplate must be aligned correctly with the weight on the harmonic balancer. If the crank does not have a dowel pin look for the hole that has no threads. That hole must align with the "extra hole" on the flexplate. Any ways, now I can start seating in those new rings!

Thanks everyone

Shawn