Longer drive shaft needed ?

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Higgins56

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My Car
1971 Mach 1 Fastback now with 503 CID 4 bolt block with AFR Bullit heads , Edelbrock Performer RPM AirGap intake and ProSystems carburettor 1050.
4 sp Toploader with 9" Wavetrac rear.
Caltracs and shocks at the rear.
I have a brand new   cro moly drive shaft that fits nicely in its current set up...

Problem is that my bellhousing is not the correct one.

When installing the correct one - the  dimension  of the crank shaft is not exactly correct.

The difference  between the bellhousings is  half an inch, meaning that the shaft  would be half an inch short.

Is this critical ?

The Toploader output shaft ( 31 spline)  is anyway ab. 4 inch in contact  with the  drive shaft.

 
How much of the driveshaft yoke at the transmission is showing with the suspension loaded. I like to see an inch so if the suspension was to become compressed things don't break.

 
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How much of the driveshaft yoke at the transmission is showing with the suspension loaded. I like to see an inch so if the suspension was to become compressed things don't break.
Thanks Mikes73 for the comment !

I have to measure it when I have the new  bellhousing !

 
No problem man, if you have an inch or inch an half or so you will be good, less than an inch is no bueno.

 
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Mikes 73,

I am just thinking what you are saying... so I understood that it is good to see the drive shaft yoke at least an inch from the transmission tail end - right ?

But the more it shows the yoke out of the transmission tail end, the less yoke is in contact with the output shaft.... did I understand somthing wrong ?

Would the optimum be that the whole yoke is in contact with the output shaft ?

In my case when chancing the bell housing the transmission actually " escapes" half an inch from the yoke's end....

 
An inch to inch and a half of the input shaft of the driveshaft yoke sticking out of tailshaft housing will be fine, man now I am confused haha:<) an inch showing of the driveshaft yoke input shaft showing would be more ideal though.

 
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You will probably be fine with it as is. While I don't like to have as much showing as has been suggested here, the shaft has plenty of spline engagement to handle an additional 1/2 inch. As the driveshaft does move when the suspension moves, there has to be enough play that it doesn't bottom out against the transmission or pull out at extreme suspension travel.

It boils down to simple geometry. The shaft is the bottom line of a right triangle. The suspension travel is the vertical side so you are solving for the hypotenuse A squared + B Squared = C squared that is to say you are determining the maximum length change from level to full suspension travel.

a fixed length shaft of 50" will be A. A squared is 2500

suspension travel squared is B. B squared so if suspension travel is a max of 6" (up or down) B squared is 36

2500+36= 2536

The square root will now show you the shaft length at full travel or 50.36"

You would need a full inch of clearance if you had 10" of suspension travel with a driveshaft for one of our cars. Even at full droop, you don't have that much travel.

 
My friends all way 250+ so I like to have that extra wiggle room especially when high jumping railroad tracks on the back roads.My chit don't sit. Thanks Jeff for the in depth explanation that a simpleton like me can understand.

 
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An inch to inch and a half of the input shaft of the driveshaft yoke sticking out of tailshaft housing will be fine, man now I am confused haha:<) an inch showing of the driveshaft yoke input shaft showing would be more ideal though.
THanks again

still  confused but now on a higher level  ;)

A simple drawing would make it clear in a second - I think - this is however no rocket science anyway.

 
You will probably be fine with it as is.  While I don't like to have as much showing as has been suggested here, the shaft has plenty of spline engagement to handle an additional 1/2 inch.  As the driveshaft does move when the suspension moves, there has to be enough play that it doesn't bottom out against the transmission or pull out at extreme suspension travel.

It boils down to simple geometry.  The shaft is the bottom line of a right triangle.  The suspension travel is the vertical side so you are solving for the hypotenuse  A squared + B Squared = C squared that is to say you are determining the maximum length change from level to full suspension travel.

a fixed length shaft of 50"  will be A.  A squared is 2500

suspension travel squared is B.  B squared  so if suspension travel is a max of 6" (up or down) B squared is 36

2500+36= 2536

The square root will now show you the shaft length at full travel  or 50.36"

You would need a full inch of clearance if you had 10" of suspension travel with a driveshaft for one of our cars.  Even at full droop, you don't have that much travel.
Thank you for this  info.

In my current case the  drive shaft yoke play is  nearly zero.... I wonder how much should  it be  to give sufficient play.

I do understand  the  problem with "zero" play against the transmission - it must be avoided.

So -  without doing any measurements I would say that in this case the  coming  half an inch play is  welcome.

 
Thanks Higgins lets see if we can do this

              -------[#################################]

front of driveshaft.                                                      back of driveshaft

On this part ------ of the driveshaft slip yoke I like to have about an inch sticking out of the back of the transmission where the seal is and the driveshaft slip yoke slide in so when the rear suspension go up and down it doesn't make bad things happen to various parts of the transmission.

I hope my detailed diagram helps man. If you need more in depth high tech help private message me and I can give you my phone number to offer further assistance ::thumb::

 
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An inch to inch and a half of the input shaft of the driveshaft yoke sticking out of tailshaft housing will be fine, man now I am confused haha:<) an inch showing of the driveshaft yoke input shaft showing would be more ideal though.
THanks again

still  confused but now on a higher level  ;)

A simple drawing would make it clear in a second - I think - this is however no rocket science anyway.
I had the chance today to look under the car and  what I see was that the driveshaft yoke was showing ab an inch out of the trannys  tail.

My friend said that it looks alright, however I remembered when I installed it that iI pushed the  yooke as far it gets  into the  trannys tail and I just  could  fit to the differential's end. That gave me the impression of  "zero play".

 
Thanks Higgins lets see if we can do this

              -------[#################################]

front of driveshaft.                                                      back of driveshaft

On this part ------ of the driveshaft slip yoke I like to have about an inch sticking out of the back of the transmission where the seal is and the driveshaft slip yoke slide in so when the rear suspension go up and down it doesn't make bad things happen to various parts of the transmission.

I hope my detailed diagram helps man. If you need more in depth high tech help private message me and I can give you my phone number to offer further assistance ::thumb::
Sorry for the delayed answer - YES  we  are thinking the same way.

Thanks  a lot !

 
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