View Full Version : Harmonic vibration at 2800 rpm...where to start looking?
I have a vibration that starts at 2800 rpm...it is one of those nice rythmic ones :) what should be my process of elimination?
TheJDMan
10-04-2014, 04:42 PM
Can you provide more detail.
Oops...
I deleted your post...
Sorry.
Can you restate what you said?
Andrew
dirty rick
10-05-2014, 05:31 AM
Start by removing all accy belts from motor.
Around 2800 the car gets a harmonic rythmic vibration. I have 700r4 tranny. I jacked the rear up and put it on jackstands. Put the car in gear and brought the rpm up to 2800 and the vibration was present. I then put the car in neutral and did the same thing and the vibration was still there when i hit 2800.
I was thinking pinion angle or driveshaft issue...but since it did it in neutral I am thinking flywheel out of balance or something with the tranny or torque convertor.
andrewb70
10-05-2014, 06:03 PM
Around 2800 the car gets a harmonic rythmic vibration. I have 700r4 tranny. I jacked the rear up and put it on jackstands. Put the car in gear and brought the rpm up to 2800 and the vibration was present. I then put the car in neutral and did the same thing and the vibration was still there when i hit 2800.
I was thinking pinion angle or driveshaft issue...but since it did it in neutral I am thinking flywheel out of balance or something with the tranny or torque convertor.
What engine do you have?
Andrew
dontlifttoshift
10-05-2014, 06:06 PM
Vibrations are either rpm related or vehicle speed related. It sounds like you already confirmed rpm. I am not a fan of the jackstand trick.
Manually put the car in second gear and run the engine to 2800 and then past it, Does the vibration get worse with more rpm? Then shift but maintain speed, did the vibration go away? change pitch?
After that we need more info. Is this a new car? New engine? Did this problem just show up after many trouble free miles? I agree with the accessory belt idea, it is a good place to start. If it is rhythmic, like someone is turning the volume knob up and down, look hard at exhaust mounting and routing.
Engine is a 383 and was balanced assembled and dynoed by a well known race engine builder in the area.
When I am in any gear and I hit the 2800 the vibration starts and remains constant or gets a little worse as the rpms increase..if my speed remains the same or even increases as soon as i go up a gear , vibration instantly goes away and car runs smooth as silk unti I hit 2800. I have not had it up to 2800 in OD yet I need to find a long straight stretch to do that cause I will be over 100mph..
This will sound odd..but the vibration is worse on certain roads that I travel.
andrewb70
10-06-2014, 07:40 AM
Saying that it is a 383 doesn't mean much. Is it an early two piece rear main engine or the later one piece? The early engines were internally balanced while the later engines were externally balanced.
Have you contacted your "well known race engine" builder?
Andrew
Saying that it is a 383 doesn't mean much. Is it an early two piece rear main engine or the later one piece? The early engines were internally balanced while the later engines were externally balanced.
Have you contacted your "well known race engine" builder?
Andrew
I have not contacted my "well known race engine builder" yet no.
TheJDMan
10-06-2014, 03:57 PM
The problem does not appear to be in the drive line since you get the vibration in neutral. I'm guessing it also vibrates in park. Did your engine builder install the engine in the car? If so you need to take it back to him. If not, based on the info you have provided, you may have installed an incorrect harmonic balancer or flexplate or torque converter. A 383 SBC stroker can be either internally or externally balanced depending on what crankshaft was used in the build. You must use the correct balancer and flexplate or you will get vibration. The engine builder should have balanced the engine with the correct balancer and flexplate but if he used a complete pre-balanced rotating assembly he may not have. You also need to take a look at the torque converter and make sure it is correct and/or correctly attached to the flexplate.
You need to!
that is helpful...thanks.
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