Moparts
Borked another 904 tail
Posted By: CJK440
Borked another 904 tail - 11/10/08 04:00 PM
Yesterday I had another 904 tail housing crack. It did it on Memorial day and I simply swapped the housing hoping it was a fluke. Guess it wasn't.
I plan to have the alum shaft checked for balance but I also want to check slip yoke engagement. What is the ideal distance from the end of the tail to shoulder of the slip yoke?? Could the slip yoke not be inserted enough cause my problem??
Anything else I should be looking into. The engine is on stock rubber biscuit mounts that aren't torn and has a stock rubber tranny mount.
Posted By: dizuster
Re: Borked another 904 tail - 11/10/08 04:29 PM
I had a 11.90's duster start breaking tailshafts before all of the sudden. Turns out the pinion snubber was broke, and it was letting the axle wind up an pull the yoke out. Fixed the pinion snubber and never had another tailshaft break...
Ideally the yoke should be pulled out 3/4"~1" from bottomed out in the trans...
Posted By: Cab_Burge
Re: Borked another 904 tail - 11/11/08 12:56 AM
I measure the length of the splines inside the yoke and then slide the yoke in all the way and pull it out half the length of the splines and measure to the center of the pinion yoke to get the proper driveshaft length, that is with the car sitting on the ground or on four jack stands so the weight is on the suspension just like it will be when I drive it. Some yokes are longer inside than others on the spline lengths
Posted By: MR_P_BODY
Re: Borked another 904 tail - 11/11/08 01:17 AM
3/4" is usually fine BUT it depends on the type
of rear suspension
Posted By: DaveRS23
Re: Borked another 904 tail - 11/11/08 01:56 AM
The last tail shaft I broke was due to excessive run-out on the tranny output shaft. Broke 2 tail shafts and could not figure out why, until I checked the tranny's output shaft with a dial indicator. Changed the output shaft and no more problems. To this day I don't know how the shaft got bent.
Posted By: torkrules
Re: Borked another 904 tail - 11/11/08 02:01 AM
Quote:
Yesterday I had another 904 tail housing crack. It did it on Memorial day and I simply swapped the housing hoping it was a fluke. Guess it wasn't.
I plan to have the alum shaft checked for balance but I also want to check slip yoke engagement. What is the ideal distance from the end of the tail to shoulder of the slip yoke?? Could the slip yoke not be inserted enough cause my problem??
Anything else I should be looking into. The engine is on stock rubber biscuit mounts that aren't torn and has a stock rubber tranny mount.
Couple of causes:
Output shaft bend
drive shaft bent
drive shaft out of balance
U joint not located properly, incorrectly installed, or moving withing the yoke.
excessive front u joint angle.
Posted By: turner
Re: Borked another 904 tail - 11/11/08 11:08 AM
Mine was due to an incorrect pinion angle
I broke several C4 tailhousings years ago because of a bent pinion. It doesn't take much!!!
Posted By: CJK440
Re: Borked another 904 tail - 11/11/08 09:07 PM
Suspension is all stock with repop 340 springs. I am running the factory snubber. With the stock springs there is not enough room for an adjustable snubber and the way the car squats on launch I am not sure the pinion can rotate up much.
My housing broke thru the speedo hole, forward of the tranny mount, not like the pic above.
The tranny is coming out over the winter to get freshened up so I'll get the mainshaft out and indicate it.
I'll check the D-shaft too.
What are you using for engine and tranny mounts?
i had this problem but with the 727 2 years ago, brand new driveshaft and it was just .018 out of balance. broke in the same place as yours turner
Posted By: CJK440
Re: Borked another 904 tail - 11/11/08 10:23 PM
Stock rubber biscuit mounts in the front and stock rubber rear.
Posted By: dartman366
Re: Borked another 904 tail - 11/11/08 11:49 PM
Quote:
Yesterday I had another 904 tail housing crack. It did it on Memorial day and I simply swapped the housing hoping it was a fluke. Guess it wasn't.
I plan to have the alum shaft checked for balance but I also want to check slip yoke engagement. What is the ideal distance from the end of the tail to shoulder of the slip yoke?? Could the slip yoke not be inserted enough cause my problem??
Anything else I should be looking into. The engine is on stock rubber biscuit mounts that aren't torn and has a stock rubber tranny mount.
are you posative they aren't torn or broke? I had one in a 68 coronet that I could of sworn was ok untill I jacked the motor up and it seperated, looked good while the motor weight was on it. 
Posted By: CJK440
Re: Borked another 904 tail - 11/12/08 01:21 PM
Quote:
Quote:
Yesterday I had another 904 tail housing crack. It did it on Memorial day and I simply swapped the housing hoping it was a fluke. Guess it wasn't.
I plan to have the alum shaft checked for balance but I also want to check slip yoke engagement. What is the ideal distance from the end of the tail to shoulder of the slip yoke?? Could the slip yoke not be inserted enough cause my problem??
Anything else I should be looking into. The engine is on stock rubber biscuit mounts that aren't torn and has a stock rubber tranny mount.
are you posative they aren't torn or broke? I had one in a 68 coronet that I could of sworn was ok untill I jacked the motor up and it seperated, looked good while the motor weight was on it.
I'll be double checking them when the motor is out this winter. I'll probably switch to the Mity mounts to be safe.
Posted By: QWK_ENUF
Re: Borked another 904 tail - 11/12/08 01:51 PM
put a truck housing on as they are stronger
Posted By: JohnRR
Re: Borked another 904 tail - 11/12/08 02:42 PM
Quote:
put a truck housing on as they are stronger
is there such a thing for a 904 ?
Posted By: dartman366
Re: Borked another 904 tail - 11/12/08 04:43 PM
Quote:
Quote:
put a truck housing on as they are stronger
is there such a thing for a 904 ?
Good question, if there is then I never knew about it. 
Posted By: QWK_ENUF
Re: Borked another 904 tail - 11/12/08 05:29 PM
Quote:
Quote:
Quote:
put a truck housing on as they are stronger
is there such a thing for a 904 ?
Good question, if there is then I never knew about it.
sorry , got 727 on the brain
Posted By: dartman366
Re: Borked another 904 tail - 11/12/08 05:34 PM
Quote:
Quote:
Quote:
Quote:
put a truck housing on as they are stronger
is there such a thing for a 904 ?
Good question, if there is then I never knew about it.
sorry , got 727 on the brain
That's ok, you are forgiven. 
Posted By: 727builder
Re: Borked another 904 tail - 11/12/08 09:33 PM
There is a 904 truck tail housing. And they appear to be beefier. Have one in my dart. May have another if you need it? Mel
Posted By: turbocolt2.4L
Re: Borked another 904 tail - 11/12/08 11:26 PM
get one off a full size van has the snapring cover on side.
Posted By: Quicktree
Re: Borked another 904 tail - 11/12/08 11:37 PM
Pinion Angle
Tired of breaking cases and drive shafts? There are many books that misled you on setting the pinion angle. For Drag Racing this is simple. You are trying to set the pinion angle to be parallel with the centerline of the engine & transmission on hard acceleration. To achieve this you must first figure out the parallel setting of the rear end to correspond to the angle of the engine & transmission, then add the proper amount of pinion angle. Add 1 deg. for 4-Link vehicles, 2 to 3 deg. for ladder-bar vehicles. Place stands under suspension to duplicate vehicle at ride height. Caution do not remove drive shaft without securing vehicle first. Take measurement with drive shaft removed.
Posted By: CJK440
Re: Borked another 904 tail - 11/13/08 02:42 PM
I checked the pinion angle relative to the tranny mainshaft centerline when I first broke it.
Posted By: CJK440
Re: Borked another 904 tail - 11/16/08 07:10 PM
Hmm, this looks less than ideal. Jackstands under rear axle.
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I think thats ok.
The shaft ends at the seal boot and you want 1" of room so it does not bottom out in yoke.
Posted By: dartman366
Re: Borked another 904 tail - 11/16/08 08:25 PM
I wouldn't want the shaft any shorter than that, mine the boot is about a 1/4 inch away from the very beginning of the radius, from the point you are showing how far will the yoke slip into the housing till it bottom's out?
Posted By: CJK440
Re: Borked another 904 tail - 11/23/08 03:30 PM
Got a chance to play in the garage today. Unbolted the shaft and drove it all the way in.
Looks like I am 1.5" from bottomed out.
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Posted By: CJK440
Re: Borked another 904 tail - 11/24/08 01:51 PM
The shaft is definately going in to check balance, think I should lengthen it .5-.75" while I'm there?
Posted By: JohnRR
Re: Borked another 904 tail - 11/24/08 02:02 PM
how will they LENGTHEN it ???
it looks to me like it is sticking out too far though
Posted By: DJVCuda
Re: Borked another 904 tail - 11/24/08 02:06 PM
Quote:
it looks to me like it is sticking out too far though
I agree
Posted By: LAR_414
Re: Borked another 904 tail - 11/24/08 02:20 PM
Something you may want to consider doing, since the car is up on jack stands.
Measure the angles:
-Get car as level as you can supported by suspension
-Use a plumb bob and masking tape on the floor to find the centerline of the CAR
-Now find the centerline of the Crankshaft / Transmission shafts. Use a plumb bob off the front pulley and off the trans yoke. Very easy to find where the engine / trans is POINTED relative to the CAR.
-Now find where the rear end is pointed. You can do this with a laser level on the rear axles / wheels,.....
-Everything should be lined up and parrallel to the car centerline.
If you have the rear pointed to the right and the engine / trans pointed to the left,....then you drive shaft is going to be at a crazy angle and want to swing like a hammock.....this can break stuff!!!!!!
I just went through this when setting up my Dana. I've got it all spot on!!!!!!
Posted By: CJK440
Re: Borked another 904 tail - 11/24/08 03:21 PM
Quote:
how will they LENGTHEN it ???
it looks to me like it is sticking out too far though
I think they talk dirty to it.
I figure they would cut the ends off and weld them to an new tube?? Perhaps its better to just make a new one....
Posted By: DJVCuda
Re: Borked another 904 tail - 11/24/08 03:41 PM
Quote:
Quote:
how will they LENGTHEN it ???
it looks to me like it is sticking out too far though
I think they talk dirty to it.
I figure they would cut the ends off and weld them to an new tube?? Perhaps its better to just make a new one....
Posted By: JohnRR
Re: Borked another 904 tail - 11/24/08 04:18 PM
Quote:
Quote:
how will they LENGTHEN it ???
it looks to me like it is sticking out too far though
I think they talk dirty to it.
I figure they would cut the ends off and weld them to an new tube?? Perhaps its better to just make a new one....
Not very impressive if it will only GROW a 1/2 "
as long as the yokes are good they can just put them on a new tube
Posted By: CJK440
Re: Borked another 904 tail - 03/23/09 06:06 PM
Let me wake this thread from the dead now that I got the rebuilt tranny/engine back in the car.
First off, the 2" measurement above is actually a little bit more. Maybe 2-1/8th. Its 2" when it was broken and must have had a gap.
Secondly, I verified the output shaft is straight on v blocks.
Third, I did find a truck tail and its very beefy but I still think I have a bad situation going on.
One thing that was really eating at me was why did I make a shaft that short?? I'm not that dumb, I wouldn't have ordered it like that. And why did it end up to be the OE length for my application but still be that far out??
One thing popped in my head. When I first ordered it I had an A body A833 in the car and now it has a 904. While the OAL of a 4 speed and a 904 is practically the same, I did have to buy a new slip yoke for the smaller 904 output.
Perhaps the aftermarket yoke is different than others???
Posted By: Dodgem
Re: Borked another 904 tail - 03/26/09 10:26 PM
Probably too late
Posted By: MR_P_BODY
Re: Borked another 904 tail - 03/26/09 11:52 PM
Quote:
Probably too late
In a drag car there is no way I would go to that
diamention, thats basically going 1.6" out, that
number is based on a production car that was ment
to have a ton of travel.... 3/4" - 1" is fine
Posted By: CJK440
Re: Borked another 904 tail - 03/27/09 12:05 AM
New shaft on its way. Should yeild 3/4-1" of pullout when all set.
I guess the stackup of differences of the 904 vs A833 coupled with the change in 29 to 26 spline yokes, plus swapping a stock mopar 7260 pinion yoke for a 1330 spicer yoke just didn't work in my favor.
I called mark williams after my new shaft came in. It has a 1.125 of room till it bottoms out. I thought it was a bit short. They said they like 3/4 to 1" on race cars. I was told not to sweat the extra 1/8th.
I know that they make different length pinion yokes so make sure you use all the parts that will be in place when racing.
Posted By: Quicktree
Re: Borked another 904 tail - 03/27/09 12:47 AM
Quote:
Mine was due to an incorrect pinion angle
there you have it 
Posted By: mbogina
Re: Borked another 904 tail - 03/27/09 04:51 PM
Another possible scenerio: IF the C-C dimensions for the shaft were stock length, and IF the replacement yoke was the same dimensions, and IF the Engine/Trans is in the stock location, then basically you only have 2 possible culprits for the shaft to be too short. The first would be the "stacking" of factory tolerances, the second would be that the rearend housing is not in stock location- perhaps the locating pin in the leaf springs has sheared. In the "olden days", we often redrilled the front spring hanger to shorten the wheelbase slightly, and flipped the front brackets upside down to lower the rear of the car and move the instant center up.
Posted By: HotRodDave
Re: Borked another 904 tail - 03/27/09 11:37 PM
Also if the body is bent even slightly it will change the length between the trans and diff. If it is bowed down like a smiley face the way it would be inclined to do after sitting on the wheels for almost 40 years then it would need a longer driveshaft.
Production tollerances could stack up quite a bit, think about the perches could be a hair off the body seams could be a hair off.
Posted By: CJK440
Re: Borked another 904 tail - 03/28/09 11:05 AM
Quote:
Production tollerances could stack up quite a bit, think about the perches could be a hair off the body seams could be a hair off.
When the shaft was made it was perfect for the 4 speed setup.
I think its just stackup. The 904 is a hair shorter than the A833, DrDiff says the 1330 yoke on my new 8 3/4 is a hair shorter than the stock 7290 yoke I used to have and the 904 slip yoke probably has a smaller dimension from the flange to the center of the U-joint center than the 29 spline I had before.