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Old 05-28-2019, 01:19 PM   #1
ringgold
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Default TH400 Slip Yoke Engagement

Putting together my car and finally got a driveshaft made. Did the usual bottom out the yoke all the way in the trans and pull out 1" to measure for a shaft. Gave the builder the info I collected and got a shaft made. Install it and notice there is more than 1" of the yoke exposed outside of the trans. I do some measuring and come up with this. This is all Th400 stuff and the output shaft has the o-ring on it so I found a counterbored yoke to use with this output shaft.

output shaft diameter 1.33"
output shaft sticks out .5" past the seal
amount of yoke inserted into the tail housing is roughly 1.53"
amount of yoke exposed outside of housing is roughly 1.875"
Splines start roughly .55" inside the yoke

All of these measurements were taken with the rear axle on jackstands, so the rear had weight on it. My friend says that I'm good to go, but I'm learning some new stuff and wanted to ask others. I read that spline engagement should be the same as shaft diameter and about as important is that the yoke is in the tail shaft housing bushing. Looks like the yoke is in the bushing and that I have an inch or so of spline engagement. I know the more the better and you want the u-joint close to the housing with enough room so that it doesn't bottom out. Will what I have work fine or do I need to contact the drive shaft builder and let him know it's too short?
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Old 05-30-2019, 11:00 AM   #2
Eman85
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Default Re: TH400 Slip Yoke Engagement

Put the car on the ground and look at the yoke. When you measured did you have the yoke and use it to measure for the center of the u-joints? How did you measure for the shaft? Was the car on it's tires when you measured?

Last edited by Eman85; 05-30-2019 at 11:01 AM.
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Old 05-31-2019, 10:09 PM   #3
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Default Re: TH400 Slip Yoke Engagement

"Did the usual bottom out the yoke all the way in the trans and pull out 1" to measure for a shaft. Gave the builder the info I collected and got a shaft made."

"All of these measurements were taken with the rear axle on jackstands, so the rear had weight on it."

Measured from center of the yoke U-joint holes with the yoke pulled 1" out from the trans to the top of the rear 8.8 pinion flange with the suspension weighted.
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Old 05-31-2019, 10:29 PM   #4
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Default Re: TH400 Slip Yoke Engagement

OK, did they make the shaft the length you measured? Did you put the car on the ground and see if the depth of the yoke changes? I don't like the jackstand method, rather have it on the ground, on 4 boxes or on a drive on lift.
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Old 06-04-2019, 12:33 AM   #5
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Default Re: TH400 Slip Yoke Engagement

It looks to be shorter than the measurements I gave them. I did put the car on the ground, but doesn't look like it changed.
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Old 07-14-2019, 09:17 AM   #6
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Default Re: TH400 Slip Yoke Engagement

No expert here (have worked at ATI about a hundred years ago) but I see a lot of questions that were not asked.

Is it in a passenger car? is the passenger car at normal ride height?

1 piece drive shaft length and yoke engagement is always a compromise of sorts, so if the car is lowered there will typically be very little movement so the yoke can be stuffed pretty deep.

Conversely if the car has a 60s look and is jacked up in the back a deep yoke stuffing on a 400 is a sure way to knock the center support out of the planetary gears.

With the back of the shaft disconnected push the yoke as far forward as you can and make a note of its position, make sure you have at least a half inch to spare at full suspension compression and axle wrap-up (the position of the rear end will change with worn bushings and in addition various GM front clips will shift around during use causing movement of the engine/trans to rear axle).

Last but no least make sure the yoke and bushing are tight.....this is by far the most important factor in any failure scenario.

Good luck and honestly 3/4" of splines properly engaged will be fine strength wise IMHO.....compare the strength of a full circle of splines to a small contact area of a few teeth of planetaries or spider gears and you can see its not really a weak point as long as the yoke/shaft is stable in its bore.
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Old 07-15-2019, 02:56 PM   #7
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Default Re: TH400 Slip Yoke Engagement

Quote:
Originally Posted by bottlefed1 View Post
No expert here (have worked at ATI about a hundred years ago) but I see a lot of questions that were not asked.

Is it in a passenger car? is the passenger car at normal ride height?

1 piece drive shaft length and yoke engagement is always a compromise of sorts, so if the car is lowered there will typically be very little movement so the yoke can be stuffed pretty deep.

Conversely if the car has a 60s look and is jacked up in the back a deep yoke stuffing on a 400 is a sure way to knock the center support out of the planetary gears.

With the back of the shaft disconnected push the yoke as far forward as you can and make a note of its position, make sure you have at least a half inch to spare at full suspension compression and axle wrap-up (the position of the rear end will change with worn bushings and in addition various GM front clips will shift around during use causing movement of the engine/trans to rear axle).

Last but no least make sure the yoke and bushing are tight.....this is by far the most important factor in any failure scenario.

Good luck and honestly 3/4" of splines properly engaged will be fine strength wise IMHO.....compare the strength of a full circle of splines to a small contact area of a few teeth of planetaries or spider gears and you can see its not really a weak point as long as the yoke/shaft is stable in its bore.
Thanks for the reply. I had forgot that I even made this thread till a few minutes ago.

It is a passenger car and weight will be applied to the rear of the car if I'm ever able to do drag week, which is a goal of mine. The car is roughly stock height. It may sit a little higher in the rear due to new springs that I installed. I have not been able to put a few hundred pounds on the rear yet to see how much the shaft may move inwards.
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