Just got 71 K5 home last night! HEEELP!

[into1000101]

I haven't even gotten under it yet, but I had to drive it 90 miles last night and there is what I would consider a severe vibration in the drivetrain somewhere. The reason I know that is when I let off of the gas and coasted, it stopped vibrating, and as soon as I got back on the gas it would persist. It has a 350/TH350/NP205 to a 12 bolt rear w/ 4.10:1 posi.

My first instinct is:

Driveshaft unbalanced
U joints toast
Play in pinion bearing?
undesireable driveshaft angle (4" suspension lift)

The gd owner didn't say ONE word about this. Plus it didn't have seatbelts and the seats were not completely bolted down. SCARY ride!

Anyways, I love the truck, but it isn't even driveable right now. Plus I am nervous, because with this much vibration, I know it has transferred to the transmission and crank over time.

Any pointers?

Thanks!

Russell

Pics soon!

[jmil1974]

Things you mentioned are the first things I would look at, plus the carrier bearing if it's a 2 piece DS. Good luck!

[cacauba]

i had an 81 with a mild lift and once a year i had to replace the u-bolts. i know the angle was off but didn't want to spend the money to shim the driveline.

[Ackattack]

Yeah, I bet it is pinion angle. The pinion angle changes slightly under load, and if it's already off, the additional change can make the vibrations.

I just got shims for my truck for like $10, took away a lot of vibrations

[cacauba]

ok really i was just too lazy, but i miss typed, it was the u-joints that i had to change out often. i would change them, and ad some shims and take it for a ride. let us know

[into1000101]

Southpa-

The vehicle came in from out of state, and it is a very nice vehicle pending an inspection to find the source of the vibration. I am not asking for a lecture on buying a used vehicle.

I don't exactly know why, but the way you worded that offended me. Seemed unnecessary.

Everyone else, thanks! I will probably find what is wrong tonight. Where did you guys get your shims at? I forgot I am dealing with a VERY short wheelbase vehicle. A 4" on this blazer is probably the same as a 6 or 8" on a truck.

[Mike C]

I would suspect u-joint damage. A u-joint with no bearings under load can get out of phase significantly. Start there. An out of phase drveshaft should pulse under load or coast. With no lift on the truck you should have no troubles with the u-joints. With 4" you might. I wound up with a CV shaft on the back of my Jimmy. Also make sure the pinion bearing is not bad and the pinion nut is tight. Another thing to check is that the U-bolts holding the rear to the springs could be loose.

[71Blazer]

Another Blazer problem I've encountered is a heavy clunk when shifting into/engaging reverse. It is certainly louder with worn u-joints but even when they're fresh it still does it. WHY?

I've had two K5's and both were u-joint eaters. In the '84 with a 4" lift I replaced one or the other u-joint every 8 months until I had the drive shaft lengthened. The drive angle because of the short wheelbase can get very wrong very quickly especially with a lift.

The 71 I currently drive blew out the yoke on the transfercase when that u-joint went bad. But typically the u-joint at the rear axle goes bad first. Shims seem to help there.

[Mudder]

i would just drop the transfer case 2 inches using all the bolts and spacers that are already there. There should be a spacer on each of the cross member bolts. use those spacers and bolt the cross member up to the bottom of the frame. use caution that you dont crash your distributor when you let it down. Mine has been like that for years and have never had trouble with u-joints or viberations.

[into1000101]

You guys are awesome! Thanks for the quick replies. My old 82 GMC High Sierra had 6" suspension lift for years with one set of ujoints even though the angle was far less then ideal. I didn't realize how really nice I did my 82 until I drove this.

Here is a link to my old 82:

http://temp.corvetteforum.net/c4/int...llaneous.shtml