The 1947 - Present Chevrolet & GMC Truck Message Board Network

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The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)

- The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=4)

- - Pulsing vibration at around 55-65 mph (https://67-72chevytrucks.com/vboard/showthread.php?t=423626)

Sick5

12-15-2012 07:53 PM

Re: Pulsing vibration at around 55-65 mph

So... did you find out what it was...?
this is all good info for me since im having same issue but mine doesnt go away till the speed drop. And i dont mean letting off the gas. Thats one of the reason why im thinking it may be my tires

GMC Guy

12-15-2012 09:32 PM

Re: Pulsing vibration at around 55-65 mph

well i haven't done anything yet to really resolve the issue. since buying a 97 K2500 over a year and a half ago, the old truck has been parked in the garage relieved of daily driving service. it's just waiting for a complete build with a larger budget and more time.

but the problem has to be either a bad tire(s), out of round wheels (they're old aluminum wheels), or the fact that i have wheel spacers on the rear. all of which will be getting replaced with my choice of wheels and tires anyway. total build up, new rubber, new wheels, and the correct backspacing has to make the vibrations go away, right....? :smoke:

Redline

06-27-2013 09:36 PM

Re: Pulsing vibration at around 55-65 mph

Any updates on this issue. I have a 74, k20 350 , 350 trans with same problem. New tires, new ujoints, new drive shaft. Had the back cover off of the rearend no obvious wear patterns. PO did replace 203 with a 205. After replacing extremely loud exhaust with a stock exhaust I noticed it does it also when I press the gas pedal all the way to the floor. It appears the heavy vibration( imbalance) is when the engine is under load. This morning I was in 3 gear and started feeling it at about 55, I down shifted to 2nd and imbalance speed up. This confirms it is not in the tires. Any help is appreciated, even WAG's

Thanks Mike
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y5mgisi

06-27-2013 10:20 PM

Re: Pulsing vibration at around 55-65 mph

Subscribed. I HATE vibrations...

Keith Seymore

06-28-2013 08:27 AM

Re: Pulsing vibration at around 55-65 mph

Quote:

Originally Posted by Redline (Post 6146000)

Quote:

Originally Posted by y5mgisi (Post 6146072)

Subscribed. I HATE vibrations...

Please refer to the flow charts at the end of this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=522180

This is the thought process used to fix any vibration.

It's all about separating the potential root causes (so that you know what you don't have to worry about - so you can focus on what you do have to worry about).

K

y5mgisi

06-28-2013 07:23 PM

Re: Pulsing vibration at around 55-65 mph

Thanks for that Keith!

Redline

06-28-2013 07:34 PM

Re: Pulsing vibration at around 55-65 mph

Thank you for the chart I will start working down the list tomorrow morning. I have been messing with the truck a little today and did confirm if I am in 3 gear running around 45 I can not feel anything as soon as I get over 50 I do. As soon as I drop down in to 2 gear at 45 or and the RPM's are high the vibration is much much worse. Basically anytime the RPMs are over 2500 or I have the throttle wide open is when I feel the vibration.

Mike

Redline

06-29-2013 05:21 PM

Re: Pulsing vibration at around 55-65 mph

After working on the truck a few hours this afternnon I have ruled out tires, rear end and drive shaft. While the truck is in park I can rev the engine to about 25k. The vibration is clear and present!

Now.... what next. I did replace the fan clutch (bearing was worn out). Vibration still there.... torque converter? flywheel? pressure plate? harmonic balancer? Any ideas on how to rule these out?

I did check all the ground, timing, vac leaks no problems found there.

Is there another tread out there I should be on since I have eliminated that the truck does not have to be in motion?

Thanks again for everybodys help

Mike

Redline

06-30-2013 07:49 PM

Re: Pulsing vibration at around 55-65 mph

Replaced harmonic balancer. Not it.....
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motornut

07-01-2013 09:51 AM

Re: Pulsing vibration at around 55-65 mph

I had a blade throw off a burbs block took out the brake lines ,but caused a heck of a vibration
check it for cracks?

wildjoe330

07-12-2017 03:58 PM

Re: Pulsing vibration at around 55-65 mph

Do all of these trucks with the vibration problem have the NP 203 Transfer Case???
All Dodge, Ford, Chevrolet, have these put into them. And I have seen a dodge online
with the same. Does the NP203 have need for a new bearing on the front of the output
Shaft???

riz	07-12-2017 09:50 PM

Re: Pulsing vibration at around 55-65 mph

Check your transfer case bolts for tightness and also could be a front axle seal that is bad that allowed gunk to to get in and wear a groove into the axle shaft...I know these from my experiences.

RIZ
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DANTIP

06-15-2020 04:44 PM

Re: Pulsing vibration at around 55-65 mph

I had a vibration in a 3/4-ton '72 that would come on around 55 and was gone by 63 or so. I had several "Experts" try to fix the problem including rebalancing the driveshaft, etc.

Later, I found a super nice Dana 60 rear and had it serviced and installed in my truck. The vibration was somewhere in the corporate rear. Pinion bearing maybe?? I don't know, but it's gone and I'm happy!!

Good luck!

chrismoore701

06-16-2020 07:32 AM

Re: Pulsing vibration at around 55-65 mph

Quote:

Originally Posted by Keith Seymore (Post 4215758)

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.

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