Engine/Transmission (1994 - 1998) Engine Shake?

[MMcCallie]

Bought new tires today because the shops were all telling me that's what was causing my truck's horrible vibration. True, there was little tread left and the tires couldn't hold a balance for a single day, so it needed to be done anyhow.



The vibration is not in the steering wheel. The whole truck shakes, sometimes violently like riding a jack hammer. Really, it can be that bad, so bad, that I have to drastically drop speed. It is usually worst between the speeds of 60-75 mph. Can be felt at lower speeds more subtly. I've had several people ride with me and everyone can feel it. All of them have ridden in the truck before it did this and can tell the difference.



The vibration is a very fast shaking, seems to be coming from the rear, almost a shimmy. Doesn't do it predictably, sometimes rides smooth as glass. No clunking or other noises along with it, just the noise of the whole vehicle rattling when it happens. Gonna crawl under and check out my shocks to see if anything is visibly wrong with them.



Here's where things get more confusing. I installed a Vernier throttle cable this weekend and dialed in my idle and handle throttle perfectly. Had the idle purring quiet and slow like a kitten, barely needing to twist the knob to bring up the idle and use it as a cruise control. My new throttle cable has a return spring built into it but someone hooked up the engine mounted throttle return spring down low on the block. Truck felt way under powered, throttle was hard to depress.



It started surging today so I checked things out, disconnecting the throttle return spring. The truck immediately had WAY more power than it ever has. At least 50 hp more. Like a rocket, unbelievable! Hardly made 31 psi boost this morning, upper 30s immediately after.



Downside is that the idle wasn't returning down low so I disconnected the Vernier cable. Idle is no longer hanging up around 2 grand when stopped like it was, but even after setting the idle as low as it will go, the RPMs will not drop. I estimate the idle to be around 900 RPMs. Should be able to idle so low it won't stay running, like it was last weekend when i set it all up.



So now my idle is not dropping all the way, I have way more power, and there is still this total vehicular shake randomly occuring at interstate speeds. I was thinking it could be the 4KGSK, or something to do with the governor lever arm. Hoping nothing broke off in the pump. Going to change the fuel filter, but what else could cause the engine to shake the truck so harshly and not retun idle?



Any Ideas?

Thanks,

Matt

 

[JFaughn]

It seems like you post goes both ways , the shacking is in rear , then you put it all on the eng .
For the drive train , put up on jack stands , test while in truck , to make sure that you can make the shack happen with out the truck falling off jack stands , then start at wheels , look for uneven spinning , bent rim , axial ect , then under truck , drive shafts , flex plate cracking , vibration dampener .
Then cracking injectors one at a time to see if they all affect the running of truck at same time .
All this with the throttle locked at what ever RPM it takes for the shake to happen during the testing .

 

[tony597fitter]

Is this on the Excursion?

How are your pinion angles? When I had my Lifted Jeep the thing would have bad vibes at 60-65mph. I found the pinion angles were out, so I intalled some new shims and the vibes went away.

Also, check the driveshaft especially the front and the carrier bearing.

 

[MMcCallie]

Took it to Laser Bob today and we checked things out. The long lower throttle linkage arm was loose, causing my idle set screw adjustments to have no effect. Made perfect sense when he showed and explained it to me.

Bob drove it and he too thinks the quivering vibration is in the rear. He found all of my driveline to be perfect, as had i. He suspects something in the rear axle or a bent wheel. I told him one of my new tires on my old wheels required over 8 ounces to get to zero and he said that is way too much.

I need to pull the rear differential cover and look for debris as i somewhat suspect that the factory limited slip that barely works now, has worn, leaving debris in the axle that may have gotten into wheel bearings. Perhaps the clutches have heated and warped? I've driven the same roads at the same and different speeds and cannot consistently make the vibration occur. Driven well over 80 mph smooth as glass so i am still baffled.

-Forgot to mention, as soon as Bob took off from a stop on the highway in my truck, he totally noticed the major increase in power my truck has. He was quite pleased with how hard the engine now pulls. His guess was that the linkage must have been misadjusted this whole time.

 

[MAngelotti]

Just wondering if you replaced the drums and shoes when you put the tires on? I recently did my brakes and got an awful shake like your talking about. It was the new drums, I returned them for new and now the shake is gone.

 

[MMcCallie]

Disk brakes all around. Rotors have tons of metal left on them and feel pretty darn smooth. Pads still have a lot of material left too. Brakes do squeek a bit and started doing so not long before the vibration started. The shake seems to be lessening, which makes me nervous, not knowing what has been causing it. Maybe it is my turbo, which is being replaced this week. I doubt it but i'll soon find out.