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Broke 727 Tailshaft... Why?
#359389
06/27/09 11:03 AM
06/27/09 11:03 AM
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Joined: Jan 2003
Posts: 4,288
Danville, NH
Mopar_Mike
OP
master
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OP
master
Joined: Jan 2003
Posts: 4,288
Danville, NH
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Went to check out a small trans leak and low and behold see the crack around tailshaft. Starts at the speedo cable and up and around..
What could have caused this?
67 Coronet 3800#, 500hp 440, 727 with 3300-3500 stall. I put about 15 runs on the car so far this season. I have solid engine mounts and the poly trans mount.
This Sux..
RS23L7 4-Speed
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Re: Broke 727 Tailshaft... Why?
[Re: Mopar_Mike]
#359391
06/27/09 11:14 AM
06/27/09 11:14 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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If your car has alot of flex in it the poly mount could be too stiff, 3/4" max for the drive shaft movement... they tend to break where your did... thats the weak point in the tail shaft... also make sure the drive shaft isnt bottoming out in the trans... do you have engine limiters 
Last edited by MR_P_BODY; 06/27/09 11:16 AM.
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Re: Broke 727 Tailshaft... Why?
[Re: MR_P_BODY]
#359392
06/27/09 11:29 AM
06/27/09 11:29 AM
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Joined: Jan 2003
Posts: 4,288
Danville, NH
Mopar_Mike
OP
master
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OP
master
Joined: Jan 2003
Posts: 4,288
Danville, NH
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The only vibration I feel is just before I hit the traps. But I am thinking it is just suspension/wheel balance... ?
I am about to pull the driveshaft, I will check to see if it bottoms out, but I am not sure I understand the play?
...Also, I was foot braking the car and held it back to around 3200-3300 rpm and then would launch the car. Think maybe I torqued it too much and it broke that way?
Last edited by Mopar_Mike; 06/27/09 11:36 AM.
RS23L7 4-Speed
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Re: Broke 727 Tailshaft... Why?
[Re: Mopar_Mike]
#359393
06/27/09 11:39 AM
06/27/09 11:39 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
The only vibration I feel is just before I hit the traps. But I am thinking it is just suspension/wheel balance... ?
I am about to pull the driveshaft, I will check to see if it bottoms out, but I am not sure I understand the play?
Bottom out the shaft in the trans, then when you pull
it back to mount it on the diff you shouldnt have
more than 3/4" movement.... but if its too long you
could be bottoming out in the trans(as the rearend
gets closer to the same level the drive shaft is
getting pushed into the trans)
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Re: Broke 727 Tailshaft... Why?
[Re: 65dragnet]
#359400
06/27/09 03:00 PM
06/27/09 03:00 PM
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Joined: Aug 2003
Posts: 3,101
cincinnati ohio
mcat4321
master
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master
Joined: Aug 2003
Posts: 3,101
cincinnati ohio
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Quote:
Quote:
my dad had a problem when he would lift after the stripe it would break the trans . he tried mounts , shafts, shocks and a ton of other things. he went through 4 housing . new leaf springs fixed the problem. its getting to the point where age HAS to be considered on parts, if they are beat on or not
That is usually caused by by pinion angle being wrong 
the set pinion angle had nothing to do with it.
going from under heavy load to relaxed had the pinion moving because of the front of the spring being shot , it would let the rearend yolk move up and down too much.
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Re: Broke 727 Tailshaft... Why?
[Re: mcat4321]
#359401
06/27/09 03:19 PM
06/27/09 03:19 PM
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Joined: Jan 2003
Posts: 32,394
Quicktree
I Win
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I Win
Joined: Jan 2003
Posts: 32,394
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Quote:
Quote:
Quote:
my dad had a problem when he would lift after the stripe it would break the trans . he tried mounts , shafts, shocks and a ton of other things. he went through 4 housing . new leaf springs fixed the problem. its getting to the point where age HAS to be considered on parts, if they are beat on or not
That is usually caused by by pinion angle being wrong
the set pinion angle had nothing to do with it.
going from under heavy load to relaxed had the pinion moving because of the front of the spring being shot , it would let the rearend yolk move up and down too much.
pinion angle has everything to do with it  what the heck do you think happens when the rearend yoke moves up and down to much?
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Re: Broke 727 Tailshaft... Why?
[Re: Quicktree]
#359402
06/27/09 03:56 PM
06/27/09 03:56 PM
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Joined: Aug 2003
Posts: 3,101
cincinnati ohio
mcat4321
master
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master
Joined: Aug 2003
Posts: 3,101
cincinnati ohio
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Quote:
Quote:
Quote:
Quote:
my dad had a problem when he would lift after the stripe it would break the trans . he tried mounts , shafts, shocks and a ton of other things. he went through 4 housing . new leaf springs fixed the problem. its getting to the point where age HAS to be considered on parts, if they are beat on or not
That is usually caused by by pinion angle being wrong
the set pinion angle had nothing to do with it.
going from under heavy load to relaxed had the pinion moving because of the front of the spring being shot , it would let the rearend yolk move up and down too much.
pinion angle has everything to do with it what the heck do you think happens when the rearend yoke moves up and down to much?
thats why i put the "set" pinion angle.. changing it with shims or rewelding the perch would not stop the problem. the leafs was the problem.. thats like saying running over a chunck of steel didnt cause the wreck, the flat tire did..
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Re: Broke 727 Tailshaft... Why?
[Re: 7sec.cuda]
#359407
06/28/09 08:12 AM
06/28/09 08:12 AM
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Joined: Apr 2005
Posts: 399
metro detroit
turner
enthusiast
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enthusiast
Joined: Apr 2005
Posts: 399
metro detroit
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Quote:
wrong pinion angle or drive shaft is to long
I broke my tail shaft housing, due to an incorrect pinion angle, mine broke on the finish line after I got out of the throttle, I believe my driveshaft was too short and pulled out of the trans too far.
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