Pulsing vibration at around 55-65 mph

[GMC Guy]

as title says...i can't figure it out. i have gone through everything on my truck,
driveshaft balanced with new u-joints, new wheel bearings and brakes all around, all new bushings on the front end. what's weird is that it's like a pulsing vibration when i'm going around 55-65 mph give or take 5 mph... no vibration on braking or accelerating either. my only idea is to have the tires rotated and re-balanced. otherwise i'm

you guys have any suggestions?

[3r!c84]

get the wheels balanced

[PRattenbury]

My first guess would have been drive shaft. Maybe get the truck on stands in the back, start the truck, put it in gear, and just let it idle while you watch to see if there's any runout. Maybe you have a bad pinion flange or something.

[GMC Guy]

Originally Posted by PRattenbury

My first guess would have been drive shaft. Maybe get the truck on stands in the back, start the truck, put it in gear, and just let it idle while you watch to see if there's any runout. Maybe you have a bad pinion flange or something.

runout from the rearend? what exactly should i look for?

[nbpro]

I have seen tires do this. The steel belt be worn out. Maybe somewhere to start looking.Torque Converter exhaust mounts allso

[GMC Guy]

Originally Posted by nbpro

I have seen tires do this. The steel belt be worn out. Maybe somewhere to start looking.Torque Converter exhaust mounts allso

really? the tires are only a couple years old with like 85% tread. 275/60/15 bfg radial t/a's

[PRattenbury]

You could certainly have a defective tire with a bad belt causing a vibration. But typically a bad belt like that can also be felt at low speed. If you jack up the back wheels, start it up and put it in gear to let the drive line work while you watch, it may become obvious what the problem is if you look at the wheels, if you have a center bearing in the drive shaft check it out, and if all else fails, be ABSOLUTELY SURE the vehicle is stable and safe on the stands. Tape a piece of chalk to a screwdriver and go to the rear of the driveshaft. Slowly bring the chalk closer to the driveshaft till it touches. Do the same at the middle and forward end of the shaft. If the driveline is straight the chalk will leave a continuous line on the shaft. If the driveline has runout in it, the chalk will touch the shaft in one spot, but not leave a continuous line. Whatever you do, though, please, BE SAFE.

[GMC Guy]

i guess i'll start with having the wheels re-balanced lol

[white82]

Originally Posted by GMC Guy

really? the tires are only a couple years old with like 85% tread. 275/60/15 bfg radial t/a's

if they sit at any point for long time.. the tire can create flat spots.. thats why u see people putting there classics on jack stands in the winter..

[nbpro]

Yeah. My nephew's truck did this. Truck had been sitting for some time. Got flat spots in the tires. Also, I did a search on the net. Torque converter came up quite a bit.

[nbpro]

well keep us posted bro

[GMC Guy]

i will, i need my truck to get back and forth to school everyday, which is about a 20 min commute on the freeway. so this problem needs to be fixed asap

[irishman999]

Im locking in unbalanced tire, possibly a separated tire.

[Keith Seymore]

Usually if it's a "pulsing vibration" (what we call a "boom/beat") then there are two root causes that are combining, like a driveline disturbance combining with engine firing frequency.

What transmission do you have? Does it still do it if you pull the trans down from OD into Drive (for example), or from 3 into 2? That could provide clues.

Similarly, it could be a tire disturbance (imbalance, out of round) combining with driveline or a rear axle problem.

I think if you can find one potential root cause and fix it then it will take care of the "pulsing" effect.

Lastly, rear axle companion flange runout is when the flange (the part the driveshaft goes into) is not spinning true. If that is the case it whips the driveshaft like a jump rope, causing a vibration. You won't be able to check that for sure without a special (Kent-Moore) tool, other than using Rattenbury's techniques above.

In any case, I don't think it's a durability issue - just an annoyance.

K

[GMC Guy]

thanks for the help guys

i'm running a th350, and i think i will try dropping into 2nd and seeing if i get the same effects. but i'm definitely going to start with balancing the tires and go from there (keep my fingers crossed)

[chrismoore701]

Originally Posted by Keith Seymore

Usually if it's a "pulsing vibration" (what we call a "boom/beat") then there are two root causes that are combining, like a driveline disturbance combining with engine firing frequency.

What transmission do you have? Does it still do it if you pull the trans down from OD into Drive (for example), or from 3 into 2? That could provide clues.

Similarly, it could be a tire disturbance (imbalance, out of round) combining with driveline or a rear axle problem.

I think if you can find one potential root cause and fix it then it will take care of the "pulsing" effect.

Lastly, rear axle companion flange runout is when the flange (the part the driveshaft goes into) is not spinning true. If that is the case it whips the driveshaft like a jump rope, causing a vibration. You won't be able to check that for sure without a special (Kent-Moore) tool, other than using Rattenbury's techniques above.

In any case, I don't think it's a durability issue - just an annoyance.

K

How do you go about fixing the issue with the flange runout? I had this problem 20 years ago, and still have it. Did a frame off restoration and re-installed the axle. New tires and rims. Problem still there, so I believe it is in the axle. I have small front seal leak as well. replaced the seal and it still leaks. Making me think the rearend is the issue.

[54Caddy]

could also have a tire seperation problem. my junk pepboys tires are all seperated will never buy tires from them again.

[Adams74Chevy]

Originally Posted by 54Caddy

could also have a tire seperation problem. my junk pepboys tires are all seperated will never buy tires from them again.

My dad had trouble with the Pirelli(sp?) Scorpions on the front of his 87 V20 the looked ok but as he put it "it felt like someone put square wheels on the front." So it's not just "junk" tires all the time.

[nbpro]

Originally Posted by 54Caddy

could also have a tire seperation problem. my junk pepboys tires are all seperated will never buy tires from them again.

We don't have Pepboys down here, but when I lived in IL, I had the same issue. Bought a brand new set for my wife's car. In about 3 months they were falling apart. But it's usually the one's they have on sale. You know, buy 3 get the 4th free... something to that nature.

[54Caddy]

these tires are junk. My grandpad had a set on his truck that did the same thing and my set is doing the same as well as the set i already replaced on my brothers truck. Also if you were to take your tires to get balanced take it some where were they have a nice hunter balancing machine that has the road force variation on it. This will tell you if the tires have flat spots and it will let them know if they need to measure the rim runout if they do not balance properly to get down to the issue. We had this machine at school and i have the access to one at work and they work great just dont take it to a shop where they are to lazy to do the full job on the wheels.

[Cue-Ball]

I would also bet good money it's the tires. You may have a bulging sidewall or separating belt. Generally pretty easy to see and feel if you jack up the car and spin the tires (or just let them spin with the vehicle in gear). Could also be a bent wheel.

If you can't find anything wrong with the tires or wheels, there's another possibility: pinion angle. If the angles of your trans/rear are off, you can get a bad vibration. Google pinion angle vibration and you should get a lot of info.

It could also be driveshaft critical speed, but that's usually only a factor for guys that are running 5 or 6-speed transmissions with real low (numerically high) rear end gears.

But definitely check the tires over very carefully first. That's almost certainly your issue.

[GMC Guy]

thanks for the suggestions, i just had the tires rotated and balanced today. so i'm keeping my fingers crossed that when i hit the highway tomorrow that solved the problem. as far as the tires go, has anyone ever had problems with radial t/a tires?

[Cue-Ball]

Originally Posted by GMC Guy

thanks for the suggestions, i just had the tires rotated and balanced today. so i'm keeping my fingers crossed that when i hit the highway tomorrow that solved the problem.

Do yourself a favor: spin the tires and look at them with your own two eyes and feel them with your own two hands. It's possible to balance a tire that has a separating belt, a bulging sidewall, cupping problems, etc.

My wife's car was having vibration issues at highway speeds. I figured that I threw a wheel weight and had the tires balanced. The problem was still there. Went back and had the tire shop try again. Again, the problem was still there. Jacked up the car and spun the tires while watching and feeling the tread...there was an obvious bulge in the tire. It balanced just fine on their computerized machine, but it simply WAS NOT ROUND. No amount of balancing in the world is going to make a not-round tire roll smoothly. Had I just taken 15 minutes to look at the tires myself, I would have saved hours of time and three trips to the tire shop.

[Davidmichael]

I think it's your tire(s). There is one with a belt broken or breaking. I have one on one of my vehicles. I just keep driving it though cause it rarely sees the highway.

[mrnize]

From prior experience its a driveline issue maybe, pull it, rebuild it and call it done!