Rear End Twists on Acceleration
mightymoose_22
03-29-2005, 02:34 PM
Forgive me for not having all the info, but I can gather it as questions come up.
The Blazer is an early 70's model... I think a 72. The rear axle was taken off and taken to a shop to have the differential rebuilt. When reassembling a 4 inch lift was installed on the vehicle.
Due to the lift and the angle of the driveshaft from the transfer to the rear diff, 6 degree angle spacers were installed under the leaf springs so the drive shaft now sits at 15 degrees.
So... the problem.
After everything has been reassembled the rear end now jumps and twists on acceleration. I will try to describe: On a quick acceleration diff yoke clearly jumps up a couple inches and a twisting motion is very noticeable. On slow and smooth acceleration a vibration develops.
Unfortunately this problem was discovered on a test drive when the driveshaft popped out due to broken U joints, which were new. The extra movement in the shaft clearly broke the U joints. We thought the problem was due to the angle which is why the 6 degree shims were added, but then discovered the twisting and jumping movement later.
What would allow the differential to jump up like that? The large U bolts over the leaf springs are secure (does anyone know the specific torque for these?). The leaf spring bolts are secure (torque for these would be nice as well). The leaf springs are seated properly onto the axle... so what gives?
Are there any special reassembly considerations we should follow? Is it possibly something due to the differential not being rebuilt correctly?
Considering that the rear axle is one large piece, when the front of the differential jumps up a couple inches that means that the whole rear axle is rotating... I assume it has something to do with securing the axle. Aside from tightening the hell out of those leaf spring U bolts I don't know what can prevent that twisting.... and tightening the hell out of the bolts didn't help.
So please... any comments? Need any more info?
The Blazer is an early 70's model... I think a 72. The rear axle was taken off and taken to a shop to have the differential rebuilt. When reassembling a 4 inch lift was installed on the vehicle.
Due to the lift and the angle of the driveshaft from the transfer to the rear diff, 6 degree angle spacers were installed under the leaf springs so the drive shaft now sits at 15 degrees.
So... the problem.
After everything has been reassembled the rear end now jumps and twists on acceleration. I will try to describe: On a quick acceleration diff yoke clearly jumps up a couple inches and a twisting motion is very noticeable. On slow and smooth acceleration a vibration develops.
Unfortunately this problem was discovered on a test drive when the driveshaft popped out due to broken U joints, which were new. The extra movement in the shaft clearly broke the U joints. We thought the problem was due to the angle which is why the 6 degree shims were added, but then discovered the twisting and jumping movement later.
What would allow the differential to jump up like that? The large U bolts over the leaf springs are secure (does anyone know the specific torque for these?). The leaf spring bolts are secure (torque for these would be nice as well). The leaf springs are seated properly onto the axle... so what gives?
Are there any special reassembly considerations we should follow? Is it possibly something due to the differential not being rebuilt correctly?
Considering that the rear axle is one large piece, when the front of the differential jumps up a couple inches that means that the whole rear axle is rotating... I assume it has something to do with securing the axle. Aside from tightening the hell out of those leaf spring U bolts I don't know what can prevent that twisting.... and tightening the hell out of the bolts didn't help.
So please... any comments? Need any more info?
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