Engine Vibration

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digithead

Well-known member
Joined
Jan 24, 2016
Messages
264
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Location
UPSTATE NY
My Car
1973 Mustang 351C-4V 4BBL 4 SPEED CONVERTIBLE White
Hi all. I have a engine vibration that I cant pinpoint. I did read a lot of posts here but nothing that totally matched mine.

I have a 73 Convertible, 351C V8, with Edelbrock 650CFM carb and Weiand Intake for 4BRL to 2V heads. 4 Speed Manual.

Car starts well, idles well.Never bucks or backfires. Strickly a vibration complaint. You can feel it pronounced in steering wheel, and a bit through pedals and shift. It never goes away. It varies with certain RPMS, but never gone. So I started with basics. I pulled all plugs they all looked good. Since I had each one out I checked compression on each. They were 155/185/175/165/150/165/165/165. I put in all new plugs albeit old ones looked a NICE color. No real change. It has aftermarket Pertronix ignition no points. New coil. New plug wires. Pulled distributor cap and checked it and rotor. Looked nice but cleaned some very minor black. Ran car with distributor slightly loose and varied timing. No change in vibration, idle speed just went up and down of course. Idles smooth . When you drive it, accelerates fine, no hesitation, no pops or farts. Just steady vibration in steering wheel. If I get it going about 30-60 and toss in neutral and let out clutch and just do a high speed cost, wheel feels pretty good. Barely and vibration, car tracks nice and straight. So its not alignment or suspension. The vibration goes directly with engine RPM only. So its been run quite awhile since rebuild and not blown up. I pushed it hard a few times no explosions or parts exiting hood area. Where do I go from here to find source of such steady vibration. Literally like something simply out of balance. TIA!

 
Does it go away with the Clutch in (Throw Out Bearing)? I have a Baja Bug that did that vibration but went away with the clutch in and needed a throw out bearing replaced. Once fixed was back to nice and smooth.

 
Last edited by a moderator:
Does it go away with the Clutch in (Throw Out Bearing)? I have a Baja Bug that did that vibration but went away with the clutch in and needed a throw out bearing replaced. Once fixed was back to nice and smooth.
I will double check that tomorrow, but I am pretty sure it was no.

 
Has it vibrated since it was rebuilt? I suspect the harmonic damper ring has shifted, or either the flywheel or pressure plate are out of balance.

The variance between low and high compression readings is a little more than it should be, but it should still fire OK at 150 psi. Was the engine warmed up, but not hot, when you took the readings?

 
Has it vibrated since it was rebuilt? I suspect the harmonic damper ring has shifted, or either the flywheel or pressure plate are out of balance.

The variance between low and high compression readings is a little more than it should be, but it should still fire OK at 150 psi. Was the engine warmed up, but not hot, when you took the readings?
I agree with the balancer or flywheel balance choices. Not quite sure how you verify that though. Probably just replace the balancer with a new one since that is the easiest and cheapest route to try.

Of course the smarty pants in me says the lowest cost and best guarantee to stop engine vibration is to turn the car off!

kcmash

 
Tossing in my fishing line...

On my 73 when my driver side mount spit out a rubber insulator the

engine height dropped just enough to let the header rest on the

steering gear felt like the steering wheel was connected to the engine.

Paul

 
.

if nothing is touching the body, yank the engine and have it balanced.

 
From the description, its an issue under load at speed. Drive shaft out of balance or U-joints going south can cause that. But you say its readily apparent in the steering wheel which generally points to front suspension or engine. Vibration in the seat typically indicates rear drive train components. If it were the harmonic balancer, that would create engine vibration while running sitting in the driveway.

When you disengage the clutch it runs smoother....transmission internally may have something bent / failing but then again you say you're cruising at speed, but with no load so the transmission is turning, just not in gear. Flywheel out of balance would do it/ or something warped in clutch disc / pressure plate.

If you can find someone with a dyno see about getting the car strapped in and observing the drive train under load to see if any vibration (bellhousing, transmission, etc) is evident. Using a long bar to touch the various components while running may narrow it down. A long bar can also serve as a stethoscope on each component.

Just some thoughts.

 
It could be the damper but, it idles smoothly. What does it do if you are stopped, in neutral, and you rev it up? Does the vibration happen the same way as when you are driving the car?

Chuck

 
It could be the damper but, it idles smoothly. What does it do if you are stopped, in neutral, and you rev it up? Does the vibration happen the same way as when you are driving the car?

Chuck
Yes. Absolutely. Parked in garage not moving it vibrates.

 
It could be the damper but, it idles smoothly. What does it do if you are stopped, in neutral, and you rev it up? Does the vibration happen the same way as when you are driving the car?

Chuck
Yes. Absolutely. Parked in garage not moving it vibrates.
So it's basically not when your in gear. I have a similar problem where I feel it in the steering wheel. Mine gets progressively worse from 1300 to 1800 rpm's then smooths out. I didn't get a chance to play with it much(went to body and paint) but it was suggested that I remove all belts and see if that makes any difference as my balancer was ok. It didn't so I was gonna try and slide the tranny back to separate the converter from fly wheel. One thing that I noticed when I last started it to take it to paint was it didn't seem to be as bad. I only added air cleaner so I was wondering if the vac. to the distributor changed something. It will be a few months before I can play with mine again.

 
I'd check your motor and tranny mounts (easy to do) to see if the rubber isolation pads are still good. Are the headers or anything else hitting the frame?

 
I'm with everyone else, damper, mounts, headers, or flywheel. Let us know what you find. Chuck

 
Thank you. Lots of things to check. I unexpectedly to trip to ER in ambulance with chest pains so I have been out of commission this week. Hopefully next week I can get back out there and check the stuff you are telling me. Thanks for all your input.

 
Does it have a Center Force clutch? The most frustrating vibration issue I ever chased was from the weights of a CF clutch moving around. The car would have different symptoms as the weights would shift to different positions. Eventually the weights got stuck way off center and made the car shake too much to drive.

Most people love these clutches but a few of us don't.

 
I would start by making sure everything is tight. Mounts to engine and frame, bellhousing to block, clutch to flywheel, trans to bellhousing. Then I would make sure nothing from the engine, drivetrain or exhaust is touching any body, suspension or steering component.

 
Well we all seem to be on the same page here and someone mentioned flywheel, on an automatic if it is one it does not use a flywheel but a flexplate and after 40+ years could be cracked and that will cause the vibration and you will never see it till the trans comes off the back of the block. If its a manual car like was already said could be numerous things, Pressure Plate might be warped, flywheel weight, Throw Out Bearing, Input Shaft Bearing, all sorts of little goodies to play with and give you headaches.

 
Well we all seem to be on the same page here and someone mentioned flywheel, on an automatic if it is one it does not use a flywheel but a flexplate and after 40+ years could be cracked and that will cause the vibration and you will never see it till the trans comes off the back of the block. If its a manual car like was already said could be numerous things, Pressure Plate might be warped, flywheel weight, Throw Out Bearing, Input Shaft Bearing, all sorts of little goodies to play with and give you headaches.
Thanks all. YEs its a 4 speed manual tranny.

 
Well we all seem to be on the same page here and someone mentioned flywheel, on an automatic if it is one it does not use a flywheel but a flexplate and after 40+ years could be cracked and that will cause the vibration and you will never see it till the trans comes off the back of the block. If its a manual car like was already said could be numerous things, Pressure Plate might be warped, flywheel weight, Throw Out Bearing, Input Shaft Bearing, all sorts of little goodies to play with and give you headaches.
Thanks all. YEs its a 4 speed manual tranny.
I too had a bad vibration on my original 85K miles engine, thought it could be any one of the above issues. I took the car to someone I know who is a former well known drag racer and an expert Ford engine builder. The verdict, worn out main bearings. He was right, the bearings were just a few miles shy of failing.

I had the engine rebuilt and balanced as a complete unit (engine and clutch)!!! Runs as smooth as silk. I do use a Center Force 2 clutch and have had no issues with weights sticking. Something to keep in mind though.

Geoff.

 
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