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Username Post: Bad vibration & noise        (Topic#341256)
Forum Newbie
Posts: 95

Reg: 08-03-15
12-14-16 06:06 PM - Post#2666127    

New gm 502 in 86 Chevy 1 ton 2 wheel drive truck with 4 sp manual transmission and a gear vender overdrive . Have about 3000 miles on it. Started getting a bad vibration and noise only in overdrive. Called gear vender and did some tests that they said to do. Was determined to be worn clutches in overdrive. They have sent me 3 rebuilt units and still have a bad vibration, although different from one to another,and at deferent speeds.Now their trying to tell me it's the motor and or flywheel. The vibration only seems to happen while in overdrive. Has anyone ever had this problem?

"15th Year" Gold Supporting Member
Posts: 18770
Loc: Colorado Springs, CO
Reg: 08-08-04
12-16-16 02:49 PM - Post#2666388    
    In response to Dynamutt

If you have made sure that the overdrive doesn't have a bent output shaft, and you have made certain that the driveshaft is balanced and the U-joints are in good condition:

You likely have a problem with the engine, transmission and overdrive mounts. These mounts need to be nearly solid, to prevent the overdrive from flopping around, causing a vibration. You also need to make sure the overdrive is firmly mounted to the output of the transmission, any loose fasteners will cause a vibration.

It is probably vibrating because when the overdrive isn't engaged, the torque is output out of the back of the transmission, and the transmission mount along with the engine mounts absorb all of the reactive torque and transmit it into the frame. In this instance the overdrive acts like a very expensive small driveshaft in between the transmission and the real driveshaft, and no torque is transmitted to the overdrive mount. However, when the overdrive is engaged, the reactive torque is then transmitted to the end of the overdrive instead of the end of the transmission, through the engine mounts and the overdrive mount (if you have one, and you should), instead of the transmission mount. That is why you need a very good mount on the overdrive and the transmission both. I realize that it is common for people to just hang the overdrive on the back of the transmission, but this is like hanging a cheater bar on the back of the transmission, one that forces the back of the transmission to move around. So, make sure the mounts are good and solid, on both the transmission and overdrive, and use polyurethane mounts if you can.

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