Engine vibration on GMC 1987 P/U

[mars bar]

Hello all you mechanics out there, I have a 1987 GMC P/U with a 4.3 V6. I started to get a vibration at 30klms (sorry Canadian) I stopped on the side of the road and press the gas pedal a bit and still feel vibs. so that rules out tires ,driveshaft and transmission,rear end. Whats left... one clue, my clutch fan was not turning freely when the engine was cold? Or could it be the harmonic balancer as quoted by a friend? Any help would be most appreciated. Mars Bar

 

[IMPATIENT 1]

Re: Engine vibration on GMC 1987 P/U

could be the balancer elastic gave up and split, flywheel could've thrown its weight. the 4.3 motors back then were externally balanced, the newer 1's have a counterbalance shaft above the cam.
i'd pull off the drive belt, see it it goes away, if it does, look at those things driven by the belt. if it doesn't, check the balancer to see if rubber has split.

be carefull not to overheat the motor with the belt off, the water pumps not do anything without a belt.

 

[mars bar]

Re: Engine vibration on GMC 1987 P/U

First of all "How did you get that donkey into the boat hahaha. But the clutch fan being snug at cold start isn't an option? It's an old truck but a good one 500,000+ on original engine. I'll try your advice thanks.

 

[IMPATIENT 1]

Re: Engine vibration on GMC 1987 P/U

lol, its just the way i feel sometimes, a *** in a boat

if its the fan clutch, it'll go away when you pull the belt off. is this truck a standard or automatic?

 

[IMPATIENT 1]

Re: Engine vibration on GMC 1987 P/U

you 100% sure its not misfiring as well? a miss on a 4.3l will make em shake and bake

 

[chiefalen]

Re: Engine vibration on GMC 1987 P/U

A little advice, open the hood you look at the motor, have someone else start it and rev it a bit.

The motor jump like a mount broke??

Upper mount lower mount maybe, rubber gets old and brittle sometime the mount goes.

You'll see it if a mount went the whole motor will twist and jump.

 

[mars bar]

Re: Engine vibration on GMC 1987 P/U

Lots of good advice, I know it's related to the motor so I'll start with the easiest, The fan belt removal. But I'll still check it all. Thanks again for the advice. Oh, it's an automatic tranny. No truck, no fishing! : (

 

[Bob_VT]

Re: Engine vibration on GMC 1987 P/U

With a vibration I would look for a misfire too. How old are the plugs?

 

[Splat]

Re: Engine vibration on GMC 1987 P/U

A little advice, open the hood you look at the motor, have someone else start it and rev it a bit.

The motor jump like a mount broke??

Upper mount lower mount maybe, rubber gets old and brittle sometime the mount goes.

You'll see it if a mount went the whole motor will twist and jump.

Yea they"ll jump allright, when I was in high school my buddy said his engine was shaking, so I popped the hood and grabbed a hold of the throttle linkage and revved it good, the engine spun around and pinned my hand between the block and the firewall. Even tho it was just for a second, it hurt like hell.I thought I broke my hand for about 20 minutes after that. It puffed up and turned all kinds of pretty colors.

I pay more attention now.....

BIll

 

[slasmith1]

Re: Engine vibration on GMC 1987 P/U

sounds very much like a bad motor mount

 

[chiefalen]

Re: Engine vibration on GMC 1987 P/U

I keep my face and hands away and have someone else give it gas saw this a lot older car the tranny mount can also go.

Then when i know it's safe i put my hands and face in.

Saw a guy open a hood and stuck his face in the radiator cap went, that was not pretty.

And saw other guys not so lucky missing fingers from fans.

Just say be careful till you know it's safe to put your only set of body parts in a running motor.

Oh no loose cloths saw a guy get sucked into a motor cause his tie got caught on the fan. No one in the car to shut it off.

 

[projecthog]

Re: Engine vibration on GMC 1987 P/U

lol, its just the way i feel sometimes, a *** in a boat

if its the fan clutch, it'll go away when you pull the belt off. is this truck a standard or automatic?

LOL, looks more like a Bass boat then an Aass boat to me.
PH.

 

[mars bar]

Re: Engine vibration on GMC 1987 P/U

Ok, the motor mounts are good, Sprayed some de-greaser on the shaft of the clutch fan and started to free it up to the point where it spins abit. After this mornings hang-over I'm taking it for a ride. Thanks again guys (gals) calm waters to all.

 

[jay_merrill]

Re: Engine vibration on GMC 1987 P/U

How do you know the motor mounts are good? I have a 4.3 litre in my Astro and had the same problem. I had the motor mounts and the tranny mount changed and the vibration disaappeared entirely.

 

[chiefalen]

Re: Engine vibration on GMC 1987 P/U

Not a 4.3 but i was going hell bent down the road in my Trans Am and hit a bump and the transmission mount went.

Took me a day with my then girlfriend now wife sitting in the car and me tracing down the stikin motor shakin.

And you would swear, why would the motor jump when the transmission mount went?

But he says it ain't that, could be alot of other things. I gotta believe him.

You know spraying it ain't gonna fix nothing for long.

Good luck fair winds at ya back.

 

[mla2ofus]

Re: Engine vibration on GMC 1987 P/U

Check to be sure the bell housing bolts are all tight. If it gets loose, it will put the flex plate between torque converter and crankshaft in a bind causing a vibration. If run too long like that it will break the flex plate.
Mike