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post #1 of 4 (permalink) Old 11-16-2016, 02:33 PM Thread Starter
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Thump when shifting


I have a 1994 Trans Am LT1 engine with 4L60E automatic transmission. A while back I was taking a turn from a stop at a decent acceleration and wham! all the sudden it felt like I went over a speed bump. I had my sister look at it and determined it was a bad transmission mount. So, I replaced it and shortly after it happened again. Sister checked again and same problem. I upgraded to the aftermarket (polyurathane I think) transmission mount and still does it. I am now somewhat savvy with my car now and checked and it is fine and installed correctly, however, whenever I add any gas whatsoever passed a easy shift it feels like I went over a speed bump and feels like it's coming from the shifter area. Is there anything that would cause this other than transmission mount? Like torque converter or something? Or is my transmission just screwed and need a rebuild? Any help would be appreciated.
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post #2 of 4 (permalink) Old 11-16-2016, 08:30 PM
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If you continually have issues with tearing up transmission mounts I would check out the motor mounts as being your root cause failure. That being said, bad motor mounts can allow for the exhaust to it the floor under hard acceleration. The torque arm mount is likely trashed as well.

1996 Pontiac Firebird, 396 ltx, 24x, forged eagle crank, 6" compstar rods, 5cc forged pistons, LE custom billet 263/271 .688/.688 108 LSA, LE ported AFRs, Pacesetter LTs, 200hp Nirtous Outlet plate, 4L80E, Moser 9" w/4.30 & trutrac
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post #3 of 4 (permalink) Old 03-07-2017, 09:59 PM Thread Starter
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So, its been a while and finally got around to checking. The torque arm looks ok, however, when I jiggled the torque arm near the transmission it did move a little with a little force. Is that normal? Or do I need a new mount?
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post #4 of 4 (permalink) Old 03-08-2017, 06:51 AM
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Torque arm should take quite a bit of force to move it. It's made to keep eng/trans in line with rear end under extreme driving conditions.
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