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strange vibration, when under light power,2000rpm

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amc401t10 View Drop Down
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    Posted: Oct/21/2015 at 4:41pm
strange vivbation when at or below 2000rpm.
any touch of the gas pedal and she vibrates like a tire out of ballence,let off gas and vibration goes away. it was worse when first started and cold. never completely goes away once warm.
checked pinion and u-joints and tail shaft bushng, all is well.
iam thinking ballencer or tq convertor.
ps its done this for a long time, thought it was the tires, just installed 4 new tires, rides a lot better but vibration under power below 2000rpm is still their.
any ideas?
pss when my 2200 stall converter came in about 15 years ago the starter gear was made on the convertor(for mopar) ,the trans shop ground the welds off and used behind my 727.
pss if u rev the engine in park, around 2000 rpm she vibrates some, but its rurning the ballencer and tq convertor both, which one?
thanks
does the after market make a ballencer for a 401?
1-owner 74 gremlin x 401, t10,3.73 12 bolt,750carb,reed 250@50 cam, roller rockers,msd,offy int.
72 amc matador 401 727
84 j10 ,360, 727
1970 4-door rebel sleeper(455 pontiac,turbo 400)
79 spirit,4.2
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 6:53am
Also check the rear axles. You may have a spun hub. An easy way to check is to pull the hub cap and mark the nut and hub with a crayon/chalk. Drive until you get the vibration then check. If marks not lined up you have a spun hub. Tightening the nut won't help, you need a new hub (hard to find) or a complete used axle and hub. A new hub has no splines cut into it. The force of installing embeds the axle splines into the slightly softer hub, mating the two for life. The right rear is the one that usually spins, but the other can. AMC didn't specify a retorque interval because they last well over 10 years/100K miles. I always retorque if I don't know when/if it's been done before. Every 20 years is usually good. It gets retorqued when the wheel bearings or seal is changed, AMC probably figured that was enough. If you get a used axle you may have to pull the hub and change the brake backing plate.

This is a weak point in the design, but since they last 30-50 years under normal driving it's not a design flaw. Not good for over 400 hp either, especially in a heavy car.  Your Gremlin should be okay, unless you're running slicks or sticky tires -- then it's going to spin eventually. In a built car like that I'd order one-piece axles from Strange or some other company.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amc401t10 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 8:42am
I have re torqued my hubs each year. it vibrates in park when reving the engine around 2000rpm, its gotta be something turning while engine is reving. I am leaning toward the tq convertor since the trans shop ground the starter ring off for my trans.
the balancer hasent sliped, timing mark right on.
whats strange is that it is worse when cold,again makes me think tq convertor,(fluid thicker when cold),as it warms up most goes away.
anything else in the trans that could cause this?
thanks
1-owner 74 gremlin x 401, t10,3.73 12 bolt,750carb,reed 250@50 cam, roller rockers,msd,offy int.
72 amc matador 401 727
84 j10 ,360, 727
1970 4-door rebel sleeper(455 pontiac,turbo 400)
79 spirit,4.2
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FuzzFace2 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 9:09am
Any way to undo the converter and push it back so you can run the motor to see if that is it?
Check with a converter rebuilder to see if they can balance the unit or just replace it with the right one.
Dave ----
TSM = Technical Service Manual

75 Gremlin X v8 for sale
70 Javelin 360/auto drag car
70 Javelin 360/T5 Street car
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 10:16am
Didn't catch that it vibrated in park... obviously not hub!  I would suspect the TC also. 
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toolmanxiii Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 1:12pm
are you using a 401 flexplate?
 Aftermarket companies also drilled the ring gear to fine tune the balance on converters . if they cut it off it's out of balance .
I've even seen some with weight plates welded to them .
The trans shop should have known just cutting the ring off would throw off the balance . it's a wonder it has not ripped the pump out or the rear main.
I'm unsure what you mean by balancer .


Edited by toolmanxiii - Oct/22/2015 at 1:15pm
71 360 Hornet sst 83 2wd 360/727 Eagle wagon (crashed)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 4:24pm
Originally posted by amc401t10 amc401t10 wrote:


any ideas?
pss when my 2200 stall converter came in about 15 years ago the starter gear was made on the convertor(for mopar) ,the trans shop ground the welds off and used behind my 727.
pss if u rev the engine in park, around 2000 rpm she vibrates some, but its rurning the ballencer and tq convertor both, which one?
thanks
does the after market make a ballencer for a 401?


So this is a MOPAR converter?
I guess I thought engine balance was a function of the flex plate, but to be honest if the shop took a MOPAR converter and dealt with it to turn into an AMC application converter, it makes sense to me that it is the wrong one and very well could be a contributor to a balance problem as described.

I have used 2200 rpm stall converters, but I had no problem ordering and getting the proper AMC ones.

70 390 5spd Donohue
74 Hornet In restoration
76 Hornet, 5.7L Mercury Marine Power
80 Fuel Injected I6 Spirit
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toolmanxiii Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 4:35pm
Originally posted by uncljohn uncljohn wrote:

Originally posted by amc401t10 amc401t10 wrote:


any ideas?
pss when my 2200 stall converter came in about 15 years ago the starter gear was made on the convertor(for mopar) ,the trans shop ground the welds off and used behind my 727.
pss if u rev the engine in park, around 2000 rpm she vibrates some, but its rurning the ballencer and tq convertor both, which one?
thanks
does the after market make a ballencer for a 401?


So this is a MOPAR converter?
I guess I thought engine balance was a function of the flex plate, but to be honest if the shop took a MOPAR converter and dealt with it to turn into an AMC application converter, it makes sense to me that it is the wrong one and very well could be a contributor to a balance problem as described.

I have used 2200 rpm stall converters, but I had no problem ordering and getting the proper AMC ones.


That's what I get . a 727 is a "Dodge" trans . I have seen it done before with similar results . only worse. I have a 2500 stall in my Eagle. Ordered it from Hughes . first one cane with ring gear , when I called and told them AMC they had no problem shipping the correct one . they even paid return freight .
Summit Racing Part Number: HUP-24-25  incorrect

Summit Racing Part Number: HUP-24-25-360BAL  correct 



Edited by toolmanxiii - Oct/22/2015 at 4:39pm
71 360 Hornet sst 83 2wd 360/727 Eagle wagon (crashed)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amc401t10 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2015 at 8:37pm
Looks like its time for a converter!
Thanks
1-owner 74 gremlin x 401, t10,3.73 12 bolt,750carb,reed 250@50 cam, roller rockers,msd,offy int.
72 amc matador 401 727
84 j10 ,360, 727
1970 4-door rebel sleeper(455 pontiac,turbo 400)
79 spirit,4.2
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/24/2015 at 9:25am
Depending on the thickness of the balancing weights and their relation to the converter feet, you might be able to unbolt the converter from the flexplate and run the engine briefly to see if there's any change without the converter.

My setup wouldn't allow this, but it was custom balanced and the weight hit on the feet when I tried to rotate the engine with the converter decoupled.
1968 AMX 390 w/T5
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