U joint problem? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gman · 02-22-2003, 12:17 AM

Need some expert help. When letting foot completely off gas pedal quickly, there is a heck of a bang or slapping sound which sounds like its coming from the driveshaft area. It also does it when accelerating after coasting. There's obviously slop somewhere but I'm not sure whats causing it. U joints? And if so, how do you tell which one? How do you tell a bad u-joint? Any help would be greatly appreciated.

*Piston* · 02-22-2003, 12:32 AM

Couple of different ways to check them.
If you have a level area of ground and a working parking brake (or wheel blocks) leave the transmission in neutral, crawl underneath. Grab the end of the drive shaft (both ends, one at a time) and move the shaft back/forth, up/down, then take the drive shaft in one hand and the rear diff yoke in the other and twist in opposite directions. If the noise is that loud, you'll be able to see the movement. Any movement at all indicates its time to replace THEM, do both while the shaft is out.

While we're talking about them, if you have a shudder, vibration or noise from the drive shaft its time to pull the driveshaft out and physically move each u joint to check for binding, any stiffness or binding at all means its time to replace THEM. In your case though, the best way to check them is with the driveshaft in place.

If nothing is found wrong, there's a chance your differential has too much backlash (worn ring/pinion) But this will be a deeper thump rather than a clanging noise.

ChevLoRay · 02-22-2003, 09:41 AM

You need to check the center support, too. I have seen them detonate at inopportune times....like we ever have a breakdown in the driveway. My sons' '69 SWB had the center support break loose from the mounting, which was still bolted-in. After replacing all of the u-joints, and the center support, no more problems.

baggedblaz · 02-22-2003, 02:35 PM

its a 4x4 shorty? there shouldn't be a center support bearing? should have a one piece driveshaft..

EdB · 02-22-2003, 11:21 PM

you need to mark the shafts and reassemble them the
way they were. They are balanced as a unit.

This one of those lessons I learned the hard way.

EdB

gman · 02-23-2003, 06:30 PM

Thanks for the replies. Been gone all weekend. I'll be checking them soon like you folks said. Correct.....its a SWB 4X4.

02-22-2003, 12:17 AM	#1
gman Registered User Join Date: Nov 2000 Location: Ogden, Utah Posts: 290	U joint problem? Need some expert help. When letting foot completely off gas pedal quickly, there is a heck of a bang or slapping sound which sounds like its coming from the driveshaft area. It also does it when accelerating after coasting. There's obviously slop somewhere but I'm not sure whats causing it. U joints? And if so, how do you tell which one? How do you tell a bad u-joint? Any help would be greatly appreciated. __________________ 72 Chevy SWB Custom Deluxe K10, 350/SM465, PS, PB, Fact. Air 2000 Harley...Wide Glide

02-22-2003, 09:41 AM	#3
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	What about the center support? You need to check the center support, too. I have seen them detonate at inopportune times....like we ever have a breakdown in the driveway. My sons' '69 SWB had the center support break loose from the mounting, which was still bolted-in. After replacing all of the u-joints, and the center support, no more problems. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

02-22-2003, 02:35 PM	#4
baggedblaz Registered User Join Date: Jan 2002 Location: Layton,Ut Posts: 196	its a 4x4 shorty? there shouldn't be a center support bearing? should have a one piece driveshaft.. __________________ '82 chev swb 4dr 2wd project '72 2wd blazer LT1/4L60E "SURFSIN" bagged 20's '71 2wd blazer '95 chev 2wd Xcab swb

02-23-2003, 06:30 PM	#6
gman Registered User Join Date: Nov 2000 Location: Ogden, Utah Posts: 290	Thanks for the replies. Been gone all weekend. I'll be checking them soon like you folks said. Correct.....its a SWB 4X4. __________________ 72 Chevy SWB Custom Deluxe K10, 350/SM465, PS, PB, Fact. Air 2000 Harley...Wide Glide

02-22-2003, 12:32 AM	#2
Piston Account Suspended Join Date: Oct 2002 Location: Olathe, KS Posts: 2,300	Couple of different ways to check them. If you have a level area of ground and a working parking brake (or wheel blocks) leave the transmission in neutral, crawl underneath. Grab the end of the drive shaft (both ends, one at a time) and move the shaft back/forth, up/down, then take the drive shaft in one hand and the rear diff yoke in the other and twist in opposite directions. If the noise is that loud, you'll be able to see the movement. Any movement at all indicates its time to replace THEM, do both while the shaft is out. While we're talking about them, if you have a shudder, vibration or noise from the drive shaft its time to pull the driveshaft out and physically move each u joint to check for binding, any stiffness or binding at all means its time to replace THEM. In your case though, the best way to check them is with the driveshaft in place. If nothing is found wrong, there's a chance your differential has too much backlash (worn ring/pinion) But this will be a deeper thump rather than a clanging noise.

02-22-2003, 11:21 PM	#5
EdB Registered User Join Date: Jan 2003 Location: Gulfport Ms Posts: 401	you need to mark the shafts and reassemble them the way they were. They are balanced as a unit. This one of those lessons I learned the hard way. EdB



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