Is this a good idea?

[lukecp]

I posted a few weeks ago about a vibration problem i have been experiencing in my truck. The truck starts vibrating at about 75mph, and by the time i am pulling 85 or so it is unbearable. I have to pass on 2-lane roads alot, and in 3rd gear with the throttle wide open at about 95mph, it feels like the truck is going to fall apart.

Anyway....it may be either driveshaft or tire related. Since i'm not working right now, money is really tight, and i dont want to have to pay to get my tires balanced if i don't have to. So....can i jack the truck securley in the air, remove the rear tires, and possibly the brake drums, and start the truck, put it in gear, and rev it up until the speedometer reaches the speed at which i am experiencing the vibration? Would it hurt my driveline to be spinning at 85mph without any load on it?

This way...if i still had the vibration, i would know that it is driveline related....and if it is smooth, i will know that i need to get my tires balanced.

Thanks for any help

[72MARIO]

Where is the vibration ? If it is in the back move the back tire's to the front and see if the vibration moves. If not I would count on it being the drive shaft Hanger Baring.

Jacking up your truck in the air and running it is Frigging Nuts !

Try moving the tires first.

[lukecp]

It feels like its coming from the center of the truck....the carrier bearing and all U-joints are only 6 monts old so i don't think that it could be them...but who knows. I'm thinking that it may have threw a balance weight....

[cableguy0]

it could very well be the u joints or the carrier bearing most guys here replace the carrier bearing about every 6 months from what i have seen. DO NOT run the truck like that on stands way too dangerous. very good way to grenage an engine if you arent extremely careful

[lukecp]

Ok...thanks for the help. I was kind worried about having the driveline spin that fast w/o a load on it....didnt seem like a great idea, but i'm cheap, lol.

[cableguy0]

like someone suggested switch the tires from front to back and see if theres play in that carrier bearing its possible especially if your foot is anywhere near as heavy as mine which it seems it is

[lukecp]

Lol...my foot is fairly heavy

The truck sees 5000 rpm once or twice a week....i love the sound of the 4bbl wide open.

I will try swaping the tires...it will look kinda funky with 275/60's on the front and 255/60's on the back, lol.

[jakobs71chevy]

another quik and easy - go out and look around the tires for any missing wheel weights - another old wives tale is front end vibration is felt thru the steering wheel, in the rear you will feel it in your rear.

[71GMC_3/4T]

Since you're talking carrier bearing, I assume you have a 2 pc driveline. These are supposed to be "phased", which means the two drivelines have to be at a certain angular rotation with respect to the other when comparing yokes. My book (at home) tells how to do this. It's something like: place the two yokes so they are lined up, then rotate the rear ?? splines in ?? direction and slide together. I know they aren't supposed to be in line, and I also know you are supposed to mark them before disassembly, but I didn't. Mine vibrates also, so I always thought I put it back together wrong when I was uninformed. I don't drive that fast, so it isn't a problem for me, and I figured I'd get around to it some day...
Someone here should have the maintenance manual which states how the yokes are supposed to be phased.

[jcab]

I second, (or is it third?) the swapping of the tires front to back. If it is indeed a wheel balancing issue, when the unbalance tire is on the front, you will feel it in the steering wheel.

[cableguy0]

the best way is to mark the driveshafts before you take them apart and they will always line back up properly

[lukecp]

It is possible i have got the driveshaft out of phase.....but i'm not sure. I have had this vibration for quite some time, maybe a year, so it was there before i rebuilt the driveshaft. It has seem to have gotten pretty bad latley.

I just went out and checked the carrier bearing....there is maybe 1/8"-1/4" of up/down side/side play in the driveshaft, and the rubber looked pretty good. I have the drop down (aka...weak, lol) style bearing, so about 1/2 the play was because of the bearing hanger flexing. I think the U-joints are OK....the truck dosen't clunk when i put it in gear.

Soo...looks like i will be swapping tires around this weekend....if the tires aren't the problem, the shaft will go to the driveline shop.

Once again, thanks for all the help and stopping my crazy idea, lol

[Mudder]

Slow Down!!!!!!!!!!!!

Cheapest fix!

[palallin]

You beat me to it, Randy: Lucas, you're crazy driving that fast on these roads! I'd hate for ya to kill yourself before I get a chance to meet ya.

[lukecp]

Lol...i usually drive about 60-65 (mean speed of traffic), but every time i drive home on 63, i have to pass RV's or semi trucks putting along at 50-55

On the I44 75 (or faster....) is the average speed....and it is hard to drive that fast with the truck giving you a back massage, lol

[71GMC_3/4T]

Originally posted by cableguy0
the best way is to mark the driveshafts before you take them apart and they will always line back up properly

Oh, I wish I knew then what I should know now... Heck, mine was probably put together wrong by the PO anyway, lol. I'll bet he didn't know enough to chalk mark it either.

Yellow72Custom: Try putting a lot of weight on one of your tires, like a 3 oz. Put it on one tire (mark it so you'll know which one when you take it off). Drive the truck and compare the "seat of the pants" vibration to what you were feeling. If it's the same, it's probably a tire out of balance. If it's about 3 to 4 times slower, your driveline is out of balance. This is a lot easier than swapping tires. Your local tire shop should be able to give you a "test weight".

[68 Suburban]

My annoying vibration turned out to be a blown shock and an out of balance tire of the same corner. The combination made for a very annoying vibration inbetween 65-75. I first replace the shock and it got better. Then when I blew the front tire on my truck and had it replaced, i had the back tires balanced. No vibrations any more.

[oldsub86]

Running the truck on jack stands may not tell you much anyway as it won't be under the same load as when actually running on the street. I tried it on my truck this summer as I was looking for the source of a noise. It didn't help much.

Try to find someone with a similar truck and talk him into letting you try his wheels and tires for a few miles. We did that with my Suburban and my brother in law's pickup truck. Jacked the Burban up in the garage and took all 4 wheels off. Put them all on the pickup and went for a ride. Vibration was still there so we basically satisfied ourselves that it wasn't in the tires or wheels. He has since changed a few more things and still has it. We think it is in the auto transmission so he is living with it for now.

[71GMC_3/4T]

I thought the xfer case was going out on my '92 Z-71. I put her on jack stands and ran it at idle in 2nd to listen for the noise. I was relieved to find it was in the rear end and not the transfer case. As it turned out, the transfer case may have been cheaper to rebuild than the rear end. Cost around 800 for all new parts except the housing and axle shafts! I had someone else do the work since I don't like the 90wt smell and it was mid winter!

[rustyold69]

i would try running it on jackstands because it wouldn't rev any faster than it would if it were in neutral.