shakes on the road

[umrthrower]

I have a 1994 Chevy 1500, 5.7L, automatic, with 125,000 miles. As I go down the road and get to speeds between 60 and 75 the truck shakes pretty hard. If I let off the gas pedal just a hair or get on the gas a little it stops, but if I keep it at a constant speed it will shake. It was doing this before I put on new tires. I thought new tires would help since the old ones were about bald. I also thought it could be bad gas, and put in a fuel system cleaner on my last fill up. These things didn't help any and I'm running out of ideas. If anyone has some ideas of what it could be I'd appreciate the feedback. Thanks.

[Moostang]

How long has it been happening.. any changes made to the truck?

My other only thought it something it out of balance.. drive shaft maybe? Just throwing that out there cause I know if can happen to mustangs, but normally it is when the shaft it taken off and replaced.
Also I wonder if it could be something like a loose motor mount?
Ok.. rambling... need to get back to work

[mrjohnwayne]

I'd check the ujoints

[umrthrower]

It's been happening for the last 900-1000 miles. The only changes I've made were new tires but it started a week before I put new ones on. Wouldn't think it would be a motor mount. Could be a drive shaft, but if it was wouldn't it shake at all speeds, not just at a certain range of speed. I know its not the suspension or tires. Thanks.

[mrjohnwayne]

Originally Posted by umrthrower

Could be a drive shaft, but if it was wouldn't it shake at all speeds, not just at a certain range of speed.

Not all the time. Higher revolutions tend to want to throw it out of balance.

[umrthrower]

Originally Posted by mrjohnwayne

Not all the time. Higher revolutions tend to want to throw it out of balance.

This happens when I'm in overdrive at 2000 rpm. If it shakes I'll put it in drive and it won't do it, approx. 3000 rpm. Just feathering the pedal will make it stop.

[umrthrower]

While I'm on here is there a governor on a 1994 C1500 5.7L TBI auto.? If there is can I remove it? Once I peg the needle, (I'm guessing 90-95 mph) it downshifts and hits the rev limiter. My buddy has the same truck I do except its an extended cab and his doesn't do this. I know this has nothing to do with my truck shaking. Just wondering.

[mrjohnwayne]

There should not be one. If I remember they did not put govenors on till 96.

[75K30]

mrjohnwayne is right on the money! (he usually is,,,pat on the back)
The problem is at least one u-joint, maybe more.
When was the last time you lubed them. If you are like most, you are not sure, that's alright, it happens. A dry u-joint will cause all kinds of troubles that will lead into the eventual failure. Get under there and check it out.
Will bet a nice cold beer this is the trouble........

[Sneakysportsman]

Some 93's have it, More 94's had it depending on state destination at time of ECM installation all 95 and up have it. I can chip it out for $75 wit no other mods. It is also possible that you may just might have a planetary gear or torque converter in the trans going bad. Because when you pull it down into Drive you unlock the torque converter. If you change the engine rpm the drive shaft does not change speeds only the components in the trans. You could also have bad plug or Throttle position sensor that is not delivering the right amount of fuel or combustion causing the motor to shake or vibrate. I have this trouble with this motor in the picture on the right all because it is still way to rich. I simply give it more gas and change the rpms wether it downshifts or just accelerates. Vibrations are sometimes hard to figure, don't give up some has the right answer.