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Broken 727 Tail Housing Causes? #3060744
07/19/22 11:24 PM
07/19/22 11:24 PM
Joined: Apr 2016
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WNY
Moparrob68 Offline OP
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Cracked the tail housing on the first pass of the year. Looking for probable causes.
1968 Cuda tube chassis car 440/727
1/4" front motor plate, 0.090 mid plate, bolt through urethane trans mount
New 3.5" CM driveshaft, 1350 solid joints, 1" freeplay, same length as old 3" shaft
Ladder bars with coil overs, 1degree pinion angle, so there shouldn't be much movement in the front yoke
4200 two step chip on the trans brake.

Have been running this setup 4 years, last year it broke 2 rods in a violent explosion at the 1/4 mile finish line so I suppose the shock from that could have cracks it.
Just trying to avoid cracking another one as it wasn't a fun ride when the fluid got on the slicks at 135mph

IMG_3881.jpegIMG_3882.jpeg
Re: Broken 727 Tail Housing Causes? [Re: Moparrob68] #3060747
07/19/22 11:44 PM
07/19/22 11:44 PM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline
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The problem is you have too solid of a support (rear trans mount) and have enough flex in your chassis to break the tail housing. Maybe it was barelyholding up, and the engine failurepushed it over the limits. I run a mount that "floats" between rubber bisquits from bayonet end shocks. That gives it support, but i am carefull there is still a bit of give incase of severe stress. Running that deal since 1997, maybe i should check to see if i need new biscuits. 8.70s, no problems ever.


8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Broken 727 Tail Housing Causes? [Re: gregsdart] #3060799
07/20/22 06:48 AM
07/20/22 06:48 AM
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Tulsa OK
Bad340fish Offline
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Those poly trans mounts are really stiff, I'd put something much softer in there.


68 Barracuda Formula S 340
87 "Chrysler" Conquest
Re: Broken 727 Tail Housing Causes? [Re: Bad340fish] #3060800
07/20/22 07:12 AM
07/20/22 07:12 AM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline
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Originally Posted by Bad340fish
Those poly trans mounts are really stiff, I'd put something much softer in there.
👍


8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Broken 727 Tail Housing Causes? [Re: gregsdart] #3060805
07/20/22 07:46 AM
07/20/22 07:46 AM
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MI, usa
dvw Offline
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How far does the drive shaft set from being bottomed in the trans? If the motor is on a plate, does it have a fore/aft limiter? Other than a broken u-joint I've never seen another cause for a broken tail shaft. People say a solid mount will break them. But I've never run a solid mount. The only tail shaft I ever broke came from broken front u joint at speed. In that case of broken u-joints twice I've seen them bend the output shaft as well. Over a 15 degrees of bend.
Doug

Re: Broken 727 Tail Housing Causes? [Re: dvw] #3060812
07/20/22 07:59 AM
07/20/22 07:59 AM
Joined: Jan 2003
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Marion, South Carolina [><]
an8sec70cuda Online content
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I've broken two tailshaft housings w/ my cuda years ago. Both were due to twisted driveshafts. This was back when I had stock motor mounts w/ a torque strap and a poly trans mount. Car ran 10.40s then.


CHIP
'70 hemicuda...8 sec street car
'69 road runner 440 w/ Indy SRs
'69 road runner 440-6, 4 speed
'71 Demon 340
'73 Chrysler New Yorker
'90 Chevy 454SS Silverado
'06 GMC 2500HD LBZ Duramax...toy hauler
Re: Broken 727 Tail Housing Causes? [Re: an8sec70cuda] #3060817
07/20/22 08:17 AM
07/20/22 08:17 AM
Joined: Oct 2003
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W. Kentucky
justinp61 Offline
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I broke two years ago both due to bad u-joints, mine broke behind the trans mount. It appears to me with a front and mid plate if you run a rear transmission mount it would have to be in almost perfect alignment, at least with a rear mount that was very rigid.

Re: Broken 727 Tail Housing Causes? [Re: justinp61] #3060929
07/20/22 12:43 PM
07/20/22 12:43 PM
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Posts: 1,543
Apollo, PA.
B1MAXX Offline
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Even with the front and mid plate you need a limiter for front to back.

Re: Broken 727 Tail Housing Causes? [Re: Moparrob68] #3060930
07/20/22 12:43 PM
07/20/22 12:43 PM
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Posts: 19,364
PA.
pittsburghracer Offline
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Originally Posted by Moparrob68
Cracked the tail housing on the first pass of the year. Looking for probable causes.
1968 Cuda tube chassis car 440/727
1/4" front motor plate, 0.090 mid plate, bolt through urethane trans mount
New 3.5" CM driveshaft, 1350 solid joints, 1" freeplay, same length as old 3" shaft
Ladder bars with coil overs, 1degree pinion angle, so there shouldn't be much movement in the front yoke
4200 two step chip on the trans brake.

Have been running this setup 4 years, last year it broke 2 rods in a violent explosion at the 1/4 mile finish line so I suppose the shock from that could have cracks it.
Just trying to avoid cracking another one as it wasn't a fun ride when the fluid got on the slicks at 135mph





One degree or minus one degree. Nose up or nose down.


1970 Duster
Edelbrock headed 408
6.143@110.85 mph
9.73@135.05 mph shifting at 6700 RPM
422 Indy headed small block
5.982@112.56 mph
9.42@138.27

Livin and lovin life one day at a time




Re: Broken 727 Tail Housing Causes? [Re: pittsburghracer] #3060932
07/20/22 12:46 PM
07/20/22 12:46 PM
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Posts: 18,616
Las Vegas
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I would look very closely at our driveshaft....Every broken tailshaft housing I have ever worked on or seen was due to a bad driveshaft.


"I am not ashamed to confess I am ignorant of what I do not know."

"It's never wrong to do the right thing"
Re: Broken 727 Tail Housing Causes? [Re: Al_Alguire] #3061104
07/20/22 09:19 PM
07/20/22 09:19 PM
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SLO-KID Offline
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The faster I went with my previous ride the more this occurred. Ladder bar car. Did the fore/ aft deal, had the drive shaft “checked” twice. Finally replaced the driveshaft and no more breakage! Good luck!

(Artist formerly known as J-body)

Re: Broken 727 Tail Housing Causes? [Re: pittsburghracer] #3061113
07/20/22 09:35 PM
07/20/22 09:35 PM
Joined: Apr 2016
Posts: 67
WNY
Moparrob68 Offline OP
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1 degree nose down

Re: Broken 727 Tail Housing Causes? [Re: Moparrob68] #3061116
07/20/22 09:53 PM
07/20/22 09:53 PM
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Posts: 9,048
MI, usa
dvw Offline
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So no fore/aft limiter?
Doug

Re: Broken 727 Tail Housing Causes? [Re: dvw] #3061122
07/20/22 10:04 PM
07/20/22 10:04 PM
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Posts: 472
Lake Villa Il
INTMD8 Offline
mopar
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What's the front u-joint angle? Also what front slip yoke? (I've seen many sloppy billet ones which can vibrate like hell)


69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 595rwhp 475rwtq.
Re: Broken 727 Tail Housing Causes? [Re: dvw] #3061140
07/20/22 10:42 PM
07/20/22 10:42 PM
Joined: Apr 2016
Posts: 67
WNY
Moparrob68 Offline OP
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No fore/aft limiter

Re: Broken 727 Tail Housing Causes? [Re: Moparrob68] #3061145
07/20/22 11:27 PM
07/20/22 11:27 PM
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MI, usa
dvw Offline
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Originally Posted by Moparrob68
No fore/aft limiter


That would be my smoking gun. Unless the mid plate has some tubing across its length tied to the cage. That would leave all the fore/aft movement taken up by the trans mount. That transfers all the load to the tail shaft housing.
Doug

Re: Broken 727 Tail Housing Causes? [Re: dvw] #3061147
07/20/22 11:46 PM
07/20/22 11:46 PM
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Posts: 472
Lake Villa Il
INTMD8 Offline
mopar
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Wouldn't hurt to also check that the u-joints on the driveshaft line up. New doesn't always mean good and that's a newly introduced variable.

My experience is the same as Al_Alguire. Broken tailshaft almost always due to the driveshaft. (specifically approaching critical speed or imbalance)


69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 595rwhp 475rwtq.
Re: Broken 727 Tail Housing Causes? [Re: INTMD8] #3061177
07/21/22 04:59 AM
07/21/22 04:59 AM
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Wichita
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GY3 Offline
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We had a u-joint retaining clip come out and a u-joint cap come out.

The driveshaft had been shortened, rebuilt and had been in the car for thousands of miles.

It happened on a backroad at the top of second gear. Sliding around in transmisison fluid at close to 100 mph.

It didn't come fully apart but just the one missing cap caused the tailshaft housing to break and the tailshaft to bend.

I use another driveshaft shop now...


'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.

Re: Broken 727 Tail Housing Causes? [Re: SLO-KID] #3061337
07/21/22 01:25 PM
07/21/22 01:25 PM
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Las Vegas
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Originally Posted by SLO-KID

(Artist formerly known as J-body)


You could have just changed your username ya know, rather than "starting over"


"I am not ashamed to confess I am ignorant of what I do not know."

"It's never wrong to do the right thing"
Re: Broken 727 Tail Housing Causes? [Re: Al_Alguire] #3061522
07/21/22 09:58 PM
07/21/22 09:58 PM
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Originally Posted by Al_Alguire
Originally Posted by SLO-KID

(Artist formerly known as J-body)


You could have just changed your username ya know, rather than "starting over"


Not sure what happened….. one day I just couldn’t log in. Been lurking a couple weeks or better.

…..and I still have 3 727 tailshafts from “the good ole days” 😂







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