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Old 12-26-2008, 10:41 PM   #1
72skytop
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Driveline vibration

I have 71 Cheyenne big block 402 with a 400 trans. It has 182,000 miles on it and I have driven it with this vibration since I got it in 1991 with 130,000 miles. I keep thinking as I rebuild things, I will find the problem, but I don't. In fact, here lately it seems to be getting worse.

Here is what it does:

It is kind of a droning that comes in and out when it hits a certain speed and quits when you get it going fast enough. It starts to come in at about 40 mph and quits at about 52mph. Never feel it again after 60 mph at all. The main point I want to make in describing this is the fact that once it starts doing this at 40, it is like a droning that vibrates anything that might rattle about every two seconds. Then after another couple of seconds, it vibrates for another two seconds and continues this off and on vibration until you get it over 60 or slow down below 40mph.

I have replaced literally what I think is about everything on this rig. I have had the engine out twice for different reasons and had it balanced both times including the flywheel of course. The harmonic balancer was replaced with a new GM part. all the pulleys where sandblasted and repainted. When the trans was rebuilt, the torque convertor was replaced. It had a 3.08 posi rear in it and I found another rearend with a 4.10 posi and I switched the entire rear axles. Still makes the vibration. One thing did change when I changed the entire rear axle with one of a different ratio: The same sound and vibration, but came in at a different speed. With the 3.08 axle the drone came in at about 45 and left at 55mph. That should tell me something, but I don't know what. It has the original two piece drive shaft which has had all the u joints changed and I have had both shafts balanced TWICE. I also replaced the carrier bearing. I am wondering about the alignment of those shafts. I have just aligned them by eyeball and what I could do with a what appeared to be a straight yardstick. I have even removed and rotated each driveshaft 180 degees one at a time. I have service and overhaul manuals for it, but I can't find anything in there about a an alignment procedure.

Any ideas or suggestions would be greatly appreciated. I never thought I would see the day when I would not want to drive this truck, but it really not a pleasure to drive anymore, despite its good looks.

Thank you.
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Old 12-27-2008, 12:16 AM   #2
TR65
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Re: Driveline vibration

Hey skytop,

What you are hearing is called a beat frequency. Two vibrations are occuring at nearly the same frequency. They periodically amplify or cancel each other. I haven't worked on two piece drive shafts but the alignment could be the problem.

One thing to try. Put the rear axle on jack stands, level the front. Then see if the vibration occurs. It probably will. Then while it is vibrating, just touch the snout of the differential with a floor jack. If that stops it, the drive shaft is exciting a torsional vibration of the diff which is exciting the truck bed and thus everything else. That would be drive shaft alignment probably, assuming that the shaft is balanced correctly as you said.

It makes sense that a gear change would change the speed at which this occurs since it would require a certain drive shaft speed.

Let us know if you run the experiment how it turns out and we can go from there.

I ran into a similar problem with a friends Morris Minor custom built rod. We had to make a tuned passive damper attached to the axle to cure it. Yours being stock should be able to be fixed without that.

TR
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Old 12-27-2008, 12:37 AM   #3
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Re: Driveline vibration

skytop,

You might have to jack the truck by the fame and let the diff hang now that I think about it. The jack stands could interfere with the vibration.

Here is a graphic of the drivetrain vibration I mentioned above. In this case the vibration peaked every 1.6 seconds, 2 times the "beat frequency".

TR
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Old 12-27-2008, 05:20 AM   #4
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Re: Driveline vibration

good advise. Did you do a good once over on all of the bed and cab attach bolts. As well as the carrier bearing cross member. I am sure you did just throwing things out there.
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Old 12-27-2008, 09:40 AM   #5
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Re: Driveline vibration

I had a very similar problem before I tore my truck down for restification. Mine was RPM-related, as it seems yours is (since changing gear ratios affected the speed that you experience the vibration).

I found 2 broken exhaust valve springs - one on each cylinder head. I don't have my truck back together yet, so I'm not absolutely positive that the springs caused the vibration, but that's a likely candidate to me.

If you have a tach, see if you feel the vibration at the same RPM while in park/neutral.

HomerJ
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Old 12-27-2008, 10:38 AM   #6
bamabaxter
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Re: Driveline vibration

Just wondering if the truck is lowered.....could be the pinion angle if it isn't correct either. Mine was that and a bad balancer.
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Old 12-29-2008, 03:24 PM   #7
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Re: Driveline vibration

Deffinately drive shaft related, I have had shafts balanced, but some shops don't have the proper equipment to balance a shaft at the type of speeds it will see under the vehicle, so hunt out a "good driveline shop" and pay the $$$ to get it balanced correctly. or just buy a new shaft from Inland Empire

http://www.iedls.com/page4.html

That link is to the new 2 piece shafts, completely new and balanced, spendy but perfect IMO. A little wobble in the shaft will create that speed sensative vibration so this is why simply balancing a almost 40 year old shaft may not "fix" it?!

BTW, did you rotate and rebalnce tires, just to eliminate that as a variable?? If so then the shaft is the issue, replace it and I'll bet the issue goes away!
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Old 12-30-2008, 01:50 AM   #8
72skytop
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Re: Driveline vibration

Thank you for all the replies.

TR65: WoW. A graph and everything. You sure know what I am trying to describe. I will try your test this weekend and report back here what I come up with.

Meansting04: Good idea about those bolts. I replaced the cab supports, bushings, and bolts. Might be a good idea to retorque after driving it 25,000 miles since then. I'll double check the carrier crossmember bolts also.

bamabaxter: My truck is the stock height. Never been lowered.

HomerJ: I have tried the RPM test. No viberation. I had just recently adjusted the valves because the rocker arm nuts kept working loose, but that is another story. Hopefully that is fixed.

70rs/ss: I like your post. I went to check on price for these driveshafts, but could not find a listing. Do you have to call for a price?
You are right about my driveshaft balance shop...probably not the best place. Guys were just starting out and probably didn't have the most experience. There is a what I think a better shop up the road from me here. I probably just need to take it to them and see what they think. I have a few other local car guys I can check with before I go.

I still believe there is an adjustment procedure somewhere to align those shafts, but nobody has been able to volunteer it yet.

I have also wonder if either one of the yokes where the shafts slide in are worn and making it wobble?

Wonder Wonder Wonder. Time to get off my duff and talk to some of the local talent and let them look at it.
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1997 Silverado 3500 LWB Vortec 454, headers 4.11 posi. Victory Red WOW!
1976 Oldsmobile 98 Regency four door 42,000 miles original paint. This is still a car!
1990 Oldsmobile 98 Touring Sedan 34,000 miles
1983 Hurst/Olds 30,000 actual miles
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1972 Hurst/Olds-a work with no progress
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Old 12-30-2008, 03:38 PM   #9
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Re: Driveline vibration

The slip joint is more than likely worn, just hold the two shafts, near the slip shaft and work them back and forth, if there is a fairly obvious amount of movement, might not be a bad idea to just have a completely new shaft made.


Yeah on the call in for pricing, as ever shaft is a little bit different and they more or less custom build your shaft to your specs (all shafts are custom built, but they can put a bigger yoke, you's might be a 1'2" shorter than all the rest of the driveshafts, etc, etc. Sit down when you call them, as I am sure by the way their reputation proceeds them here and other boards, their pricing is in line with a shop with that type of name synonamous with quality and bullet proof performance!!

I wasn't trying to harp on your driveline shop, just most shops, have a basic spin balancer, whereas balanced at typical highway speeds are way different.
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Old 12-30-2008, 07:48 PM   #10
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Re: Driveline vibration

I had this problem on my '47 panel. It is driveshaft related. If all the joints, pinion angle and stuff checks out, check the drive shaft length. Mine turned out to be just a hair too short. Vibration showed up after a tranny and rear end change.

Steve,
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Old 04-15-2021, 12:01 PM   #11
Rich72C10
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Re: Driveline vibration

Sorry to dig this up, but I have this same noise / vibration. Comes in around ~38 ends around 45 MPH. Say I am staying right at 40 MPH due to speed limit. If I give it a bit of gas or passing to 45 or above, don't hear/feel it.

Wished the OP followed up with a solve but guess no chance as he hasn't been around since 2017

I found a local shop that will look at it and if any balancing needs to be done there is a top shop in the town north of me that they can take it too. I suppose this is next on my list (after they finish installing all my Moog parts / CPP sway bar for a frontend refresh).

If I get this done/solved - I'll update.
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Old 04-16-2021, 06:10 PM   #12
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Re: Driveline vibration

Likely not the same but.....one time i had a vibration in an old Caddy, did the rotors, got a tiny bit better, did the driveshaft, still better but not gone, fixed a brokent tranny mount while I was at it, which didn't help much but you know....process of elimination......turned out my tires were very old (still looked great though due to low mileage) and one was just starting to lose a tread. Centrifugal force caused that slight bulge in the traction surface became more pronounced as the speed increased.
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Old 04-17-2021, 04:46 PM   #13
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Re: Driveline vibration

I always say if the vibration goes away at a higher speed it is tire balance. It's pretty hard to get a good balance on truck tires. My 76 had a vibration right at 55 mph since I got it. I would just try to drive at 60 mph where the vibration goes away. I just bought new tires and they took a lot of weight to balance them. My vibration is now at a different speed but I can still speed up to make it go away. I can live with it.

Some shops have the old balancers that spin the wheel fast. With the new balancers you just spin the wheel by hand once or twice but they give a lot better balance. My truck got balanced with the old style balancer because that is where I bought the tires. If I was a little more OCD I would take them to another shop and get them balanced on a newer machine.
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