Bad vibes help needed - The 1947 - Present Chevrolet & GMC Truck Message Board Network

hotrodhomi · 10-03-2005, 11:17 AM

I have a vibration at freeway speed (65-85 mph). Since I have had the problem I have done the following things to fix it:
I had the tires/wheels rebalanced.
I changed the bakes drums and rotors.
I had the driveshaft rebalanced.
I have pulled my hair out.
WTF

The vibration feels like it is in the back. The engine runs smoothly and I don’t think it is in the tranny. I can put it in neutral or first gear and match the RPMs to my RPMS at freeway speeds and I do not have the vibration.

I am not sure what to do next. Any Ideas?I think I have narrowed the problem down to the rearend. I think its either the differential or the axels.
How much should I pay for a used rearend if I decide to replace it? What years will fit with out any mods. Can I use one out of a 4x4?

My truck is a ’81 2wd swb with a th350 tranny and 3.08 gears.

*iceman7329* · 10-03-2005, 11:28 AM

Its most likely gona be the rearend. Our 88 Dodge does it to, and clanks when you put it in gear, the gear is shot in the rearend.

Eyegore · 10-03-2005, 11:52 AM

May want to check your transmission mount it could be worn out. Also were the u-joints replaced when the drive shaft was balanced? Can you get under the truck and move the shaft any clunking or play in it? Another thing raise the rear and check each wheel for play.
A 4x4 rear is different - 6 lug instead of 5.

hotrodhomi · 10-03-2005, 12:50 PM

The u joints were replaced. I don't hear or feel any clunking when I put it in gear. When I grap the drive shaft and try to twist it I dont feel any play. I haven't tried putting it in nuetral and checking for play. Would that make a diffrence. I wouldn't think it would. I've had the truck in the air and pulled the wheels straight out to check for slop...it felt tight.

Eyegore · 10-03-2005, 01:28 PM

Try moving the tailshaft of the transmission, transmission mount may be broken, sometimes their hard to spot.

hotrodhomi · 10-03-2005, 03:30 PM

I'll check that out when I get home. I'm leaning towards a bent axel but I can think of anything I did to bend it. I have a one tire fryer with 3.08 gears and my tires are of reasonable size. Hopefully I find it soon. Its annoying.

eagle23 · 10-03-2005, 05:15 PM

One other thing to check on the rear end is pinion bearing play. Grab the pinion yoke where it comes out of the diff, and see if it moves vertically. My '77 12 bolt does that (3.07 ratio) and I know it will either be overhauled or more likely buy a used one.

BTW, I most notice the vibration when I back off the gas ar freeway speeds, not at other times. No clunk going into gear, but I don't think a worn pinion bearing would do that.

And it could still be some of the other things people have mentioned so far.

Good luck and keep us posted!

BBC Beater · 10-10-2005, 03:40 AM

Flat spot in your tires?

10-03-2005, 11:17 AM	#1
hotrodhomi Registered User Join Date: Apr 2004 Location: Sacramento Posts: 3,737	Bad vibes help needed I have a vibration at freeway speed (65-85 mph). Since I have had the problem I have done the following things to fix it: I had the tires/wheels rebalanced. I changed the bakes drums and rotors. I had the driveshaft rebalanced. I have pulled my hair out. WTF The vibration feels like it is in the back. The engine runs smoothly and I don’t think it is in the tranny. I can put it in neutral or first gear and match the RPMs to my RPMS at freeway speeds and I do not have the vibration. I am not sure what to do next. Any Ideas?I think I have narrowed the problem down to the rearend. I think its either the differential or the axels. How much should I pay for a used rearend if I decide to replace it? What years will fit with out any mods. Can I use one out of a 4x4? My truck is a ’81 2wd swb with a th350 tranny and 3.08 gears.

10-03-2005, 11:52 AM	#3
Eyegore What Hump? Join Date: Apr 2003 Location: New River AZ Posts: 2,009	May want to check your transmission mount it could be worn out. Also were the u-joints replaced when the drive shaft was balanced? Can you get under the truck and move the shaft any clunking or play in it? Another thing raise the rear and check each wheel for play. A 4x4 rear is different - 6 lug instead of 5. __________________ Lil red 86 c-10 99 Sub 78 Camper Special w/ 454

10-03-2005, 01:28 PM	#5
Eyegore What Hump? Join Date: Apr 2003 Location: New River AZ Posts: 2,009	Try moving the tailshaft of the transmission, transmission mount may be broken, sometimes their hard to spot. __________________ Lil red 86 c-10 99 Sub 78 Camper Special w/ 454

10-03-2005, 11:28 AM	#2
iceman7329 Account Suspended Join Date: Mar 2005 Posts: 453	Its most likely gona be the rearend. Our 88 Dodge does it to, and clanks when you put it in gear, the gear is shot in the rearend.

10-03-2005, 12:50 PM	#4
hotrodhomi Registered User Join Date: Apr 2004 Location: Sacramento Posts: 3,737	The u joints were replaced. I don't hear or feel any clunking when I put it in gear. When I grap the drive shaft and try to twist it I dont feel any play. I haven't tried putting it in nuetral and checking for play. Would that make a diffrence. I wouldn't think it would. I've had the truck in the air and pulled the wheels straight out to check for slop...it felt tight.

10-03-2005, 03:30 PM	#6
hotrodhomi Registered User Join Date: Apr 2004 Location: Sacramento Posts: 3,737	I'll check that out when I get home. I'm leaning towards a bent axel but I can think of anything I did to bend it. I have a one tire fryer with 3.08 gears and my tires are of reasonable size. Hopefully I find it soon. Its annoying.

10-03-2005, 05:15 PM	#7
eagle23 Active Member Join Date: Feb 2004 Location: Atlanta GA Posts: 174	One other thing to check on the rear end is pinion bearing play. Grab the pinion yoke where it comes out of the diff, and see if it moves vertically. My '77 12 bolt does that (3.07 ratio) and I know it will either be overhauled or more likely buy a used one. BTW, I most notice the vibration when I back off the gas ar freeway speeds, not at other times. No clunk going into gear, but I don't think a worn pinion bearing would do that. And it could still be some of the other things people have mentioned so far. Good luck and keep us posted!

10-10-2005, 03:40 AM	#8
BBC Beater Registered User Join Date: Oct 2005 Location: Houston Posts: 57	Flat spot in your tires?



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