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Topic: Low speed knocking and bucking from rear end (Read 991 times) previous topic - next topic

Low speed knocking and bucking from rear end

A while back I was installing a 7.5 auburn posi in the bird and a thunderstorm started. I hurried the install because I couldn't leave the vehicle where it was and wanted to get it together just to move it. Well temporary somehow became permanent and now the rear end might have some issues. There is a higher than normal amount of whine from the rear at 50+mph. The bigger problem seems like a clunk from the rear especially on decel, more apparent right before the trans. downshifts gears, sometimes bucking and jerking also. I'm not 100 percent convinced the rear end is to blame, but it feels driveline related. I jacked up the rear end and in neutral turned the driveshaft. The pinion probably moved a good 1/4+" before the wheels moved.  I remembered setting the new ring and pinion tight with the original shims as I didn't have an exact shim pack to get the ideal backlash .
 Is the play in the pinion from the crush sleeve loosening and would that have an effect on the backlash? I would like to go back throught it and get it set up right but is that a waste of time since the new gears took a set. I would like to run the rear end hard and have it survive high torque if possible. Is it worth putting any more money into this 7.5?
[SIGPIC][/SIGPIC]88 t-bird: 5.0ho, gt40y, crane 2031, fms 1.7, paxton@5#, aod wide ratio, tci stall, performer rpm upper, 70mm bbk, pro m 60, 42#s, 3.73 7.5" posi, jba shorties, borla, upr x. 13.4 @ 104mph. cbaza, moates, tuned by decipha

Low speed knocking and bucking from rear end

Reply #1 –
If the pinion is moving in & out at all, then there is your clunking noise. And yes it will change the backlash everytime the pinion moves. Once the backlash changes, the rear will whine.
[SIGPIC][/SIGPIC]      STEVE ;)

Low speed knocking and bucking from rear end

Reply #2 –
If you plan on putting any power in front of the 7.5, I would think about an 8.8 swap. I broke a 7.5 in my '86 with a stock set up. Even worse it was on the line at the track!!!!
[SIGPIC][/SIGPIC]      STEVE ;)
 

Low speed knocking and bucking from rear end

Reply #3 –
I noticed some up and down looseness on the transyoke but, I'll have to pull the drive shaft to check the fore and aft movement of the pinion.
I guess I won't be going back to the track until I check it all out. Maybe I'm lucky I didn't get traction. :D
[SIGPIC][/SIGPIC]88 t-bird: 5.0ho, gt40y, crane 2031, fms 1.7, paxton@5#, aod wide ratio, tci stall, performer rpm upper, 70mm bbk, pro m 60, 42#s, 3.73 7.5" posi, jba shorties, borla, upr x. 13.4 @ 104mph. cbaza, moates, tuned by decipha