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Driveshaft Advice

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g3chevy / Mr Pontiac
Silverblack73ss
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Post by Silverblack73ss Thu Sep 14, 2017 8:52 am

I got word from my friend/mechanic after investigating why the rear seal was leaking in my TH350 trans that i have the wrong size driveshaft in. He said the one in the car is for a long tailed shaft transmission and i have a short tailed shaft trans. not 100% following, but does this make sense? is he talking about the yoke

Question is, does anyone know the length the driveshaft and yoke needs to be?

currently waiting on him to get a measurement to me on the correct size (car is currently 2 hours from me).

any information is greatly appreciated.

Thanks!
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Post by 73ss Thu Sep 14, 2017 5:33 pm

I have a spare driveshaft that I think came out of a 74 2-door malibu. NOT 100% sure, anyways it measures 59 1/8" from U-joint ear to U-joint ear. It doesnt have the yoke installed so I cant measure that .

It would be impossible to have a long tail 350 driveshaft in your car. There is a good 6" or so difference between a long 350 & a short 350. G3's had the short 350. The long ones were used in full size cars and some trucks.

You probably have a worn support bushing in the back of your trans which will make the yoke eat the seal. I think you can remove the tail of the trans to replace it without removing the whole trans. The yoke may be scored also causing the seal to fail
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Post by g3chevy / Mr Pontiac Thu Sep 14, 2017 6:19 pm

Yes, you can change the tailshaft bushing without removing the transmission. But you will need a special bushing driver to remove and install the new one. I'm sure a local transmission shop can replace it for a small fee. Here are a couple of pictures to reference of several short yoke driveshafts. Hope this helps.

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Post by Joe73 Thu Sep 14, 2017 6:50 pm

2 door and 4 door driveshafts should be different lengths since there is a 4" difference in wheelbase.

Another thing might be the length of your yoke. Someone might have switched it. You need a measurement from a 2 door car, center of the U joint to center of the U joint. Then you will know if you currently have the right driveshaft. Then you need an overall measurement which will tell you if you have the correct yoke.
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Post by bigredlaguna Thu Sep 14, 2017 7:55 pm

There are three sizes of tailshafts for the th350. 6, 9, and 12". If it is sized for a 9" tailshaft, then it it already the right size for a 700r4, so keep it around in case you want to swap in an overdrive.
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Post by pila Sat Sep 16, 2017 6:07 am

Some auto stores have the bushing & seal together in a kit. You will need the O-ring that goes between the tail housing and the main case on the trans, also.
Like mentioned, a trans place could fix it up for you, if you don't have the seal & bushing driver etc..

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Post by Joe73 Sat Sep 16, 2017 9:04 am

Ok, I had some time to grab some automatic driveshaft measurements for you.  I have a spare 73 ss driveshaft from a 350 with turbo 350 trans.  Here you go.

53 5/8" center of U joint to center of U joint.
55 3/16" overall length to the driveshaft itself, NOT INCLUDING THE YOKE.
60" overall length INCLUDING THE YOKE.
3 5/8" just the smooth part of the yoke.

Here's a good read if your considering swapping from a turbo 350 to a 700R4.

http://www.oldengine.org/unfaq/leadfoot/th350in.htm
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Post by 73ss Sat Sep 16, 2017 3:48 pm

Joe73 wrote:Ok, I had some time to grab some automatic driveshaft measurements for you.  I have a spare 73 ss driveshaft from a 350 with turbo 350 trans.  Here you go.

53 5/8" center of U joint to center of U joint.
55 3/16" overall length to the driveshaft itself, NOT INCLUDING THE YOKE.
60" overall length INCLUDING THE YOKE.
3 5/8" just the smooth part of the yoke.

Here's a good read if your considering swapping from a turbo 350 to a 700R4.

http://www.oldengine.org/unfaq/leadfoot/th350in.htm

Mine must be out of an El camino then.
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