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11-06-2002, 11:00 AM | #1 |
Registered User
Join Date: Oct 2002
Location: San Diego, CA
Posts: 51
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Just got 71 K5 home last night! HEEELP!
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!
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1971 K5 Blazer- SOLD 350/TH350/4.10's fr/rr w/posi rear 4" Suspension lift, 33" tires 1996 GMC Sierra 4x Daily Driver- Flow, K&N New Toy- 1994 Chevy Z71 6" Procomp suspension 15x12" Alcoas w/BFG MT's Flowmaster |
11-06-2002, 11:13 AM | #2 |
Ain't we cute?
Join Date: May 2002
Location: Friendswood, TX
Posts: 700
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Things you mentioned are the first things I would look at, plus the carrier bearing if it's a 2 piece DS. Good luck!
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69 C10 2WD LWB Fleet 350/350 power front disc conversion (6 lug disc kit from gmcpauls) and new engine, PS, A/C, fresh fluids, SHE DRIVES! FOR SALE $3900 |
11-06-2002, 11:55 AM | #3 |
STL-KKN
Join Date: Aug 2001
Location: Tomball, Tx
Posts: 182
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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.
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1969 C10 350/POWERGLIDE 1991 1500 EXTCAB 350 Formally: collegeK5er |
11-06-2002, 12:09 PM | #4 |
Senior Member
Join Date: Aug 2002
Location: Valley Center KS
Posts: 3,525
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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 |
11-06-2002, 12:15 PM | #5 |
STL-KKN
Join Date: Aug 2001
Location: Tomball, Tx
Posts: 182
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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
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1969 C10 350/POWERGLIDE 1991 1500 EXTCAB 350 Formally: collegeK5er |
11-06-2002, 12:16 PM | #6 |
Registered User
Join Date: Oct 2002
Location: San Diego, CA
Posts: 51
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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.
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1971 K5 Blazer- SOLD 350/TH350/4.10's fr/rr w/posi rear 4" Suspension lift, 33" tires 1996 GMC Sierra 4x Daily Driver- Flow, K&N New Toy- 1994 Chevy Z71 6" Procomp suspension 15x12" Alcoas w/BFG MT's Flowmaster |
11-06-2002, 12:48 PM | #7 |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,723
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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.
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44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
11-06-2002, 01:12 PM | #8 |
Goodbye Darlin'
Join Date: Nov 2001
Location: Coupeville, WA USA
Posts: 330
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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.
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1971 Blazer CST SOLD! Last edited by 71Blazer; 11-06-2002 at 02:39 PM. |
11-06-2002, 01:44 PM | #9 |
Registered User
Join Date: Feb 2001
Location: East Central, MO
Posts: 11,336
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Instead of shims!
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.
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11-06-2002, 01:50 PM | #10 |
Registered User
Join Date: Oct 2002
Location: San Diego, CA
Posts: 51
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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
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1971 K5 Blazer- SOLD 350/TH350/4.10's fr/rr w/posi rear 4" Suspension lift, 33" tires 1996 GMC Sierra 4x Daily Driver- Flow, K&N New Toy- 1994 Chevy Z71 6" Procomp suspension 15x12" Alcoas w/BFG MT's Flowmaster |
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