Engine Vibration - The 1947 - Present Chevrolet & GMC Truck Message Board Network

fb1411 · 12-14-2013, 01:38 AM

I have a 70 C-20 350 when the RPM's are between 1200 and 1500 the engine shake and can be felt in the cab and seen in the steering wheel. I have check the fallowing.
spark to all cylinders at these RPM's
disconnected from trans
removed all moving parts from front of engine including harmonic balancer
shaking always the same

any ideas

stepsider · 12-14-2013, 02:05 AM

stick or auto ? Many be in tranny. flywheel, pressure plate or internal problem with torque converter. check the bolts to those items.

**SIXTY9** · 12-14-2013, 05:42 AM

Did you check the flex plate or flywheel?

BluTrukker · 12-14-2013, 07:07 AM

Try unhooking one plug wire at a time to determine which cylinder is not firing or misfiring, assuming the issue is just one cylinder. Pull the valve covers and roll the engine over slowly to verify that all of your valvetrain is operating correctly too.

71K20chevy · 12-14-2013, 08:24 AM

Make sure if you try the spark plug method that you wear thick welding gloves or something, 40,000 volts doesn't feel good. Don't ask how I know...

Andy4639 · 12-14-2013, 09:17 AM

I would check the engine mounts first.
Have U ever seen the chains tieing down a motor? There is a reason for it. The V-8 is a great motor but it has a problem of viberation when running!
Why all this about spark plugs when U haven't said anything about it running bad?

hamjet · 12-14-2013, 10:01 AM

Also something to think about, the exhaust might be resonating a harmonic back pressure at that RPM. I use to drag race many years ago and when I removed the exhaust from the headers I got what seemed like a vibration at a certain RPM.

chewychevy67 · 12-14-2013, 10:13 AM

I had a 454 with a vibration problem once. For over a year I tried to figure it out. The engine ran well gut at 2000 rpm and up it would vibrate. Finally I chsnged tne engine balancer and that was the problem. It had moved on the rubber just enough to untrue the balance. It was hard to time properly as well due to this.

stepsider · 12-14-2013, 11:37 AM

Clutch Fan ??, usually Vibs in steering wheel means front rims,tires,balance, Ect.

Wrenchbender Ret · 12-14-2013, 04:14 PM

Its probably a mismatch of parts. You may have a harmonic balancer or flywheel from a small block 400. Or the truck has a 400 engine in it with the balancer &/or flywheel from a 350.

BluTrukker · 12-16-2013, 07:56 AM

Quote:

Originally Posted by Andy4639

I would check the engine mounts first.
Have U ever seen the chains tieing down a motor? There is a reason for it. The V-8 is a great motor but it has a problem of viberation when running!
Why all this about spark plugs when U haven't said anything about it running bad?

This is a quick and easy way to determine if a cylinder is misfiring and causing the vibration. If it is, when you pull 7 of the plug wires one at at a time, it will run worse. The eighth one there will be no change. That will be the one with the issue. If this doesn't produce any results, than you are able to look elsewhere for the vibration.

67 chevelle · 12-16-2013, 08:37 AM

Quote:

Originally Posted by Andy4639

I would check the engine mounts first.
Have U ever seen the chains tieing down a motor? There is a reason for it. The V-8 is a great motor but it has a problem of viberation when running!
Why all this about spark plugs when U haven't said anything about it running bad?

Agree , chevy did not "fix" their fireing order mistake untill the ls engines came out

12-14-2013, 01:38 AM	#1
fb1411 Registered User Join Date: Jun 2013 Location: Lancaster CA Posts: 15	Engine Vibration I have a 70 C-20 350 when the RPM's are between 1200 and 1500 the engine shake and can be felt in the cab and seen in the steering wheel. I have check the fallowing. spark to all cylinders at these RPM's disconnected from trans removed all moving parts from front of engine including harmonic balancer shaking always the same any ideas

12-14-2013, 02:05 AM	#2
stepsider Registered User Join Date: Nov 2013 Location: Roseville, CA Posts: 207	Re: Engine Vibration stick or auto ? Many be in tranny. flywheel, pressure plate or internal problem with torque converter. check the bolts to those items.

12-14-2013, 05:42 AM	#3
SIXTY9 Senior Member Join Date: Jan 2013 Location: North Charleston SC Posts: 503	Re: Engine Vibration Did you check the flex plate or flywheel?

12-14-2013, 07:07 AM	#4
BluTrukker BOHICA Join Date: Mar 2008 Location: Stewartville, MN Posts: 440	Re: Engine Vibration Try unhooking one plug wire at a time to determine which cylinder is not firing or misfiring, assuming the issue is just one cylinder. Pull the valve covers and roll the engine over slowly to verify that all of your valvetrain is operating correctly too. __________________ Trying to save someone from their own stupidity is like teaching a pig to dance. It is a waste of your time, and it annoys the pig!

12-14-2013, 08:24 AM	#5
71K20chevy Registered User Join Date: Jul 2012 Location: Ft Wayne Indiana Posts: 1,204	Re: Engine Vibration Make sure if you try the spark plug method that you wear thick welding gloves or something, 40,000 volts doesn't feel good. Don't ask how I know... __________________ 71 K20 64 GMC mud truck

12-14-2013, 09:17 AM	#6
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Engine Vibration I would check the engine mounts first. Have U ever seen the chains tieing down a motor? There is a reason for it. The V-8 is a great motor but it has a problem of viberation when running! Why all this about spark plugs when U haven't said anything about it running bad? __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

12-14-2013, 10:01 AM	#7
hamjet Registered User Join Date: Apr 2013 Location: South Westerlo, New York Posts: 1,325	Re: Engine Vibration Also something to think about, the exhaust might be resonating a harmonic back pressure at that RPM. I use to drag race many years ago and when I removed the exhaust from the headers I got what seemed like a vibration at a certain RPM. __________________ Thanks, Joe.. 1969 C/10, 348 C.I., 3X2 bbl. V8, 2004r , LWB.

12-14-2013, 10:13 AM	#8
chewychevy67 Registered User Join Date: Jan 2010 Location: Here Posts: 5,438	Re: Engine Vibration I had a 454 with a vibration problem once. For over a year I tried to figure it out. The engine ran well gut at 2000 rpm and up it would vibrate. Finally I chsnged tne engine balancer and that was the problem. It had moved on the rubber just enough to untrue the balance. It was hard to time properly as well due to this.

12-14-2013, 11:37 AM	#9
stepsider Registered User Join Date: Nov 2013 Location: Roseville, CA Posts: 207	Re: Engine Vibration Clutch Fan ??, usually Vibs in steering wheel means front rims,tires,balance, Ect.

12-14-2013, 04:14 PM	#10
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,204	Re: Engine Vibration Its probably a mismatch of parts. You may have a harmonic balancer or flywheel from a small block 400. Or the truck has a 400 engine in it with the balancer &/or flywheel from a 350.



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