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thrum thrum thrum
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73Gremlin401 View Drop Down
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Points: 946 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 73Gremlin401 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/17/2019 at 8:44am
Originally posted by CamJam CamJam wrote:

Double check your transmission mount. If yours is a 998 or 727 TorqueFlite the metal blade in the mount that attaches to the transmission can look good, but in fact can be separated from the rubber and be bottoming out metal on metal. My '72 was this way when I bought it. Discounted it a first because the mount looked fine, but when I took it out I could see the problem clearly. The thrum noise was exactly as you describe.


This is exactly what happened to one of mine as well.  'Looks good' can often be very deceiving.
73 Gremlin 401/5-spd.
77 Matador Wagon 360/727.
81 Jeep J10 LWB 360/4-spd
83 Concord DL 4-dr 258/auto
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tomj View Drop Down
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Points: 7544 		Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Nov/17/2019 at 12:13pm
same here, "looks fine" crumbles into pieces when the x-member removed. gravity holds the oil-soaked, torn, useless rubber parts in a facsimile of correct. The illusion ends when you remove it.

You might be able to test it by jacking the trans tail up and seeing if it separates, vs. wanting to lift the car. Of course requires care as jacking away without looking would tear even a new one.

On at least my 60's cars, dropping the trans x-member is easy. I'm sure it will hit the exhaust (i've only had single exhaust cars) but that's usually enough to get you arm into the greasy mess under there. I bet you remove the four sill bolts/nuts, the trans mount won't even hold the x-member up.
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
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george w View Drop Down
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Points: 2899 		Post Options Post Options   Thanks (0) Thanks(0)   Quote george w Quote  Post ReplyReply Direct Link To This Post Posted: Nov/17/2019 at 1:34pm
I have a similar situation with my 67 Ambassador DPL which has a 4 link rear suspension. The trans mount is good but I suspect that the upper rear control arm bushings are bad and to a lesser extent the lowers as well. I[m planning on having these replaced in the next week or two. Could worn bushings at the rear cause the same issue ?
Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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