Vibration when accelerating in high gear stops when...

LarryT · June 30, 2018

Hi I have a 1997 Sierra k1500 that sometimes vibrates only when moderately accelerating (not enough to downshift) and when I let off the accelerator and press it again, the vibration is gone.

I have read that u joints cold be the problem, so brought it into the local GM shop and they told me that the overdrive gear is going out (it's an automatic) and I need a new transmission.

This doesn't seem logical to me. It has 138,000 miles on it and had been serviced and shifts fine.

Should I get another opinion? or just get rid of it?

TIA,

Larry

no HD · June 30, 2018

Hey Larry, When I read the title to your post my first impression was probably the lock up in the torque converter causing the shutter or as the folks at the shop advised, the overdrive clutch pack. Either of them have been known to cause the symptoms you are experiencing. You could try a transmission service and the additive of your choice (and cross your fingers) and see what happens.

As far as keeping the truck, if it's worth a transmission, I would keep it! There is something about driving a 20+ year old pickup. The older I get, the more I like old stuff.

LarryT · July 1, 2018

Hi Buddy

Thanks for the response. I might just give that a try. I am actually not sure when the transmission was last serviced.

Regards,

Larry

TW97C1500 · July 9, 2018

I hope you check back in on this. How bad is the vibration? I bought a 97 a few weeks ago and I've noticed a slight vibration or something if I'm on the interstate and cruising at 60 and up. My first thought is a wheel bearing starting to go bad. I had a front go out on a 98 C2500 I had years ago, and this feels similar but not as severe, and it goes away. That bad bearing shook the whole truck and you knew something was wrong. This I'm feeling now seems like it is the whole truck but is what I would call noticeable to the driver, not a screaming problem. My Grand Cherokee had a rear axle bearing go bad and it was noise that I noticed, not vibration. But, it had only begun to spall off flakes and hadn't cratered big pits like my 98 truck did.

Reading your post made me think that maybe it does start when the it's under slight acceleration, going up an incline or something. (The truck had not been driven much the last few years by the older guy who owned it. The brakes were bad, a ball joint was bad, and the wheels were out of balance, so I'm not sure what else I might be feeling now that I've fixed that stuff and started driving it on the highway.)

LarryT · July 11, 2018

Well after driving it for around 400 miles last week and paying close attention, I found that the vibration only happens in high gear and only when I am going 55 mph (~1,500 rpm). This seems to be the optimal gearing/speed for the truck. i.e. it seems to get the best gas mileage etc. But, when accelerating on an incline I can almost always get it to vibrate. If I give it enough gas to downshift, there is no vibration.

I am now thinking it is not the transmission, but possibly an engine vibration caused by the stress of accelerating in high gear without a downshift. I cannot get it to happen in 3rd, and I think that is because 3rd is easier on the engine.

As to what is wrong? Not sure. Possibly an engine mount? I'm not a mechanic, so I really have no idea.

Larry

Supreme Pizza · July 11, 2018

I would climb under the rig with a pry bar and a flashlight, and check all the rubber mounts. Cross member, motor mounts, etc. Also check your shocks, shock bushings, and all of the front end control arm (A-Arm) bushings.Grab the drive shaft and move it up and down vigorously - is there any play? Make sure your bell housing bolts are tight. Grab the mechanical engine cooling fan, and check to see if there is any play by moving the blades toward the front and rear of the vehicle.

EDL · July 11, 2018

1 hour ago, LarryT said:

Well after driving it for around 400 miles last week and paying close attention, I found that the vibration only happens in high gear and only when I am going 55 mph (~1,500 rpm). This seems to be the optimal gearing/speed for the truck. i.e. it seems to get the best gas mileage etc. But, when accelerating on an incline I can almost always get it to vibrate. If I give it enough gas to downshift, there is no vibration.

I am now thinking it is not the transmission, but possibly an engine vibration caused by the stress of accelerating in high gear without a downshift. I cannot get it to happen in 3rd, and I think that is because 3rd is easier on the engine.

As to what is wrong? Not sure. Possibly an engine mount? I'm not a mechanic, so I really have no idea.

Larry

If the engine is running at 1500 RPM and you're adding throttle to go up the hill without it downshifting, it sounds like the engine is lugging and causing the vibration. That's a pretty low RPM for doing grunt work.

Supreme Pizza · July 11, 2018

That's true. It could be a low rpm misfire. Putting it in "tow mode" to raise the RPM's might be a good diagnostic test.

SarahsGMC · July 11, 2018

My moms 97 Silverado does the same thing on incline or under load and its the torque convertor

TW97C1500 · July 22, 2018

On 7/11/2018 at 1:57 PM, SarahsGMC said:

My moms 97 Silverado does the same thing on incline or under load and its the torque convertor

Sarah, what is it about the torque converter? Is it coming loose, i.e. bolts backing out, or do you mean something is wrong inside it so that it has to be replaced?

The more I've driven mine the last few weeks, the more severe the shaking is getting and it comes on at a lower speed now. The first time on the interstate, it had a large shake begin at 67-68 mph. Had the rear wheels balanced and then it was smooth until 72, where a small shake began. The fronts checked out and didn't need any more weights. I've had it at interstate speed 10 or 12 times since. Now the shake begins at 62-63 mph and is more than just an "annoying shimmy". You don't want to keep going with it doing it. I'm tired of driving 60. That's not my style.

The shake feels like the whole vehicle, not like it's just from the front end. I couldn't feel any play in the u-joints and I was rocking the whole truck. I replaced a bad ball joint already and didn't notice looseness in the others, but I was just yanking the wheel by hand, not doing the "pry with a long bar" method to feel for play.

SarahsGMC · July 23, 2018

loose bolts or a cracked/broken flywheel can cause it, best bet is to drop the trans and investigate before you grenade it

did they by chance check the wheel bearings when they had it up doing the alignments?

TW97C1500 · July 25, 2018

Yesterday on the interstate I accelerated from 60 and by 64 the shaking had started and was beyond "annoying". I was exiting so I put it in Neutral. The shaking stayed as the RPM dropped to idle speed, 5-600. I revved up slowly and went all the way to 4000 and the shaking stayed. Well, it lessened a little as the speed dropped.

That seems to me to rule out the torque converter. I want to get a transmission and rebuild it to have for the inevitable failure anyway, so if I can find one I will probably switch out the original anyway.

TW97C1500 · July 27, 2018

Well, I'll continue to hijack this thread, but in my defense, one thing I forgot to mention about my shaking that is related, but opposite the OP, is that the shaking I would get would greatly lessen when I accelerated, but come back stronger when I let off, because I was at a higher speed I assume.

That being said, I got a chance today to get in the garage and scrounged a long piece of pipe to do the "pry the wheel up with a long bar" method of checking the ball joints. The lower right is bad. 5 or 6 weeks ago when I first got the truck, the upper right was really bad. Just yanking and lifting the wheel by hand was enough to see the movement in it. When I put in the new one, both wheels were tight by the hand method. Also, this time I found the Pitman arm joint is bad (wobbly). That didn't show up either previously.

The story is that the older man I got it from only drove it a couple thousand miles a year for the 4 years he had it, and he got it from an older guy who didn't drive it for the last couple of years and only a few thousand a year for a few years prior. It seems that when vehicles that sit like that, once you start driving them again, there's an avalanche of failures. I don't remember how far I drove it, 50 miles, no more than 80, and almost all on city streets, before I greased the front end trying to head off trouble from dry joints. I saw that lower right ball joint had a split open boot, so I was expecting it to go bad at some point. I planned on greasing it frequently until I noticed movement, and hoped that would be in the Fall with cooler weather.

TW97C1500 · August 8, 2018

That lower ball joint was murder. Here's a hint, allow plenty of time, remove the cotter pin from the stud and back off the nut a little, then spray with penetrating oil like PB Blaster and let it sit at least an hour. Also get a loan-a-tool pickle fork in case the "beat on the knuckle with a hammer" method doesn't work.

After that hell on earth job, I still had a shake. In the couple of weeks since I had them balanced, one of the rears had separated. Another of those things that go wrong with a vehicle that has barely been driven for years. And I still have a little annoying shake begin about 70, not horrible, but I don't want to put up with it for a long trip. 5 or 6 miles until I hit the city limits is OK, but I still don't want to go anywhere else.