97 Chevy Tahoe jerking at 50 MPH or 70 MPH

Hi guys I have a 1997 Chevy Tahoe 4x4 5.7L four door with over 200,000 miles on it, (second engine (don't ask, LOL) has 100,000 of those miles on it). Recently my wife was driving on the freeway coming back from a long road trip and the car started jerking when at speed. I tested it when she got home and noticed it also jerks when going over a freeway overpass or a slight incline on the freeway. When driving around town on city streets at 45 mph or under everything is fine. The engine revs up fine when just sitting at a red light and I put it in neutral.

Any ideas? Other questions I need to answer for you to diagnose?

does it only do it under load, or at steady speed? more imfo neede please

thank you for helping

I guess it does it under a bit of acceleration, for example lets say you are on the freeway in the slow lane going 65 MPH and you decide to pass the car in front of you, so you accelerate to 75 MPH to switch to the middle lane, when the speedo reaches 70ish the car will jerk until you reach 75 then settle back in to a nice smooth ride

same happens from 45 mph to 55 when you are driving on city streets you accelerate to change lanes and as the car hits 50 mph it jerks for a few seconds then settles in to a nice smooth ride as you cruise at 55 mph

no jerking on deceleration

so 10 mph = fine => 20 mph = fine => 30 mph = fine => 40 mph = fine => 50 mph = fine => 55 mph = jerking => 60 mph = fine, etc...

what rpm is the motor at, and does it kick passing gear in before it does it,or after it does it, have you checked motor mounts recently, and how long has it been going on

rpm is around 3,000 not sure about the gear its in, it's been going on for about a week or two

is it kicking into passing gear, or loading the motor?

if its not kicking into passing gear you might need to get some shop help,or you may have a broke motor mount if it is im not sure but im sure someone on here can help

I have to be honest, this sounds like your drive shaft may be out of balance or your u-joints being weak, etc. Unfortunately, you would more than likely need to take it to a dealer or other shop that can check the true balance on the drive shaft. I had a similar issue on a 2002 Duramax Dually and as it turned out, while hauling a load of pumpkins that year, I hit a tractor trailer tread in the road that somehow got kicked up into the drive shaft wrapping around it bending the drive shaft which in turn actually cracking the rear housing on the transfer case.

If it were tuning or fueling issues, with a symptom like that, I doubt it would continue to climb in speed.

thoughts?

hey gregski, is it constant.....like if your going at a steedy speed of 70 does it do it or only under acceleration.......sorry to ask so many questions but im triin to help

oaleystormakleyguyh1 said:

... have you checked motor mounts recently...

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First of all thank you very much for reading and providing ideas and advice. Second of all I know you mention more things to try/check than the motor mounts, but I must address this motor mount recommendation.

I am almost 40 years old and have been driving cars since 16. I had my first car(s) at 15 that I would tinker with... counting my wife's cars, my friends cars, my parents cars and my own cars I have worked on quite a number of cars of different makes and models, my 68' Mustang being the oldest and my moms 2010 Civic the newest, I have yet to come across a broken motor mount that would cause any driveability problems. If I ever came across a broken motor mount it was because we were removing the motor to paint the engine bay or to rebuild the motor, and we didn't even know it was broken to begin with. Maybe I'm just lucky that's all, but I doubt my problem is due to a busted motor mount, it's not like the engine is anchored by just one mount, and one going out is not enough to cause a problem in my semi amateur opinion, LOL, (keep your humor in your replies, we can't let the cars have us turn on ourselves)

clkelley said:

I have to be honest, this sounds like your drive shaft may be out of balance or your u-joints being weak, etc...

Click to expand...

I thought the same thing, but then my co worker Mike, said if it was the drive shaft or U joint than if you think about it, it would happen all of the time it's not like the drive shaft won't wobble at 45 but wobble at 55 then stop wobbling at 60 and once again wobble at 75

U-joints in my opinion are either happy or they are not, good way to stress test them is do a hard donut or two to the left go to a court and turn the wheel all the way to the left and go in circle a few times with the window rolled down, and the STEREO OFF all you women out there (and we just lost the last girl reading this thread, LOL, just kidding people just kidding) then do the same thing to the right, this is also a brilliant test for the front wheel bearing but I digress

thank you for your input, I am still scratching my head on this one, I DON'T want it to be the transmission, it is an automatic and a four wheel drive, pronounced EXPENSIVE

MISFIRE

Remember what your grandfather told your father to check and replace first?

Remember what your father told you to check and replace first?

That's right SPARK PLUGS, well it goes a little deeper than that, but this is so IMPORTANT I am taking the time to share it with you.

The problem ended up being a misfire.

So I replaced the spark plugs with AC Delco brand. AC Delco for those of you who don't know is or was the OEM supplier for GM. Anyway I did a complete tune up, plugs, wires, distributor cap and rotor. $150 dollar repair that I gladly spent and about 3 hours under the hood. I took my time and made sure I did not screw up the firing order when replacing the wires, very important.

Now she runs like a bat out of hell, and the wife will have to wait that much longer before I replace it with that Honda Pilot I promised her years ago, LOL, thanks once again for reading and lending a helping hand.

Im surprised you didnt get a CEL. Glad you found the problem and fixed it!

Motor mounts on my brothers Cavalier Wagon are toast, at least the one on the passenger rear motor mount, transmission mount are both bad, knocks like crazy when at idle in gear. Peace out...