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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 84Silverado4x4 on August 21, 2014, 10:14:07 pm
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Not sure if anyone can point me in a direction but I will explain what I have going and see if anyone can help. I have an 84 chevy half ton short box 4x4 with a full suspension lift. I believe it to be a 8" lift but it is between a 6 or 8 for sure. I have a noise that comes when I coast mainly in overdirve though I can hear it for a split second when I let of the gas in drive also. The truck doesn't make a noise or vibration at any other time.... I just replaced the engine, transmission, front and rear driveshafts and rebuilt the tcase. However I still have the noise. The lift kit has a shim to help put the pinion angle better for the drive shaft and I'm wondering if that is enough or the problem? There really isn't a vibration but mainly just a noise when coasting and really only in overdrive. The noise was the same with the old transmission and did it at the same time so I can rule that out.
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remove one drive shaft at a time to isolate the front or rear axle
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remove one drive shaft at a time to isolate the front or rear axle
This and report back. Also, what kind of noise. Clunking, grinding, whistling ?
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I think its from the center or rear portion of the truck but It's doing it in 2 wheel drive. The sound is kind of like a fishing rod letting line out when you have a bite...lol thats the best way I can describe it. Only a minor vibration when it's making the noise...otherwise it drives great....just mainly when coasting in overdrive that i hear it.
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As Irish said, remove the front drive shaft and drive around to eliminate the front all together. The sound you said seems to me like it is from tension, like when something that rotates is too tight, it will or can make a whining sound.
You said you have a shim, I assume on the rear axle to help correct the pinion angle at the rear pumkin, how is the transfer case angle ?
On jeeps this was always a problem because of the short wheel base vehicles they are. If the angle is too great it can cause a slight bind which you would normally only hear when decelerating or coasting. As the engine is powering down the road it likes to twist just a little and can take the pressure off the bind, that is why you only hear it at those times. Just a theory at this point without you doing some legwork still.
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The front drive shaft seems to be good. I used the 1" spacers that comes on the transmission/tcase crossmember and installed them in between the frame and crossmember. This almost completely removed the noise but I have a LS engine in my truck and it had to sit so far back in the engine bay it was very close to the firewall. To give the engine more clearance from the firewall I cut the tcase drop spacers down to 1/2 an inch and my noise isn't as bad as before but still there....I'm guessing my only option is to get the pinion angle better and pointed up more to eliminate the noise. Does anyone know about what degree shim I would need to make it right. There is a shim now but I don't know the degree. It looks to be about 1/4" thick on the big end. I'm guessing it must be close as I don't have any vibrations and I only hear the noise when coasting in overdrive.
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you can buy an angle finder from pretty much any hardware store for like 10 bucks. then just google pinion angle and there are youtube vids all over on how to figure your angle and what degree shim you need
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Did you isolate the front from the back, or are you just assuming it is not the front ?
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I took the front drive shaft off and it still does it. I have an angle finder but I'm not sure what degree shim I need as there is already a shim in between the axle and leaf spring but I'm not sure what degree it is. Is there a way to tell by measuring the thick portion of the shim without removing it? I use the truck as my daily driver and would like to have the correct shim ordered and on the way so the only down time I have is swapping the new shims in rather than having to pull them out to measure and have to put it back together again to drive it until the new shims arrives.
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hook the front shaft back up and remove the rear.
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This might sound crazy. But I had an old Nissan truck that would do this as well. Turned out it was the heat shield on the catalytic converter was loose. Something about letting off the gas would cause that thing to rattle. But no other time really. Does your truck have a cat? If so, check that.
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You definitely have a driveshaft angle problem. It might also be compounded by worn u-joints or slip yoke - or an out of balance/bent driveshaft.
(http://www.therangerstation.com/tech_library/images/pinion_angle_bad_angles.PNG)