# Drive line length?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Rolled, Oct 26, 2002.

1. ### Rolled1/2 ton status

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Here's what I have:
87K5
305
465
208
4" lift
35" tires
12 bolt rear

I just swapped out a 10 bolt for a 12 bolt and now I am wondering if my drive shaft is long enough. The 10 bolt sat foreward about 1.5 inches closer than the 12 bolt. I think the drve line is stock so it might have been too short for the 10 bolt as well. I am going to get a Suburban driveline and have it cut down to the correct length.

Here's my question:

What formula should I use to determine the correct length of the drive line?

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Hey bud,
When getting a new rear shaft you can use the old pathagoreon thoerm...or you can just stick your too short line in with about 1.5 inchs of slip yoke showing and measure how much longer that shaft has to be to come in contact with the yoke. (make sure you swap that 10 bolt yoke onto your 12 bolt to make ujoint tasks easier.)
For the P. Theorm..take (the height of the slip yoke center minus the height of the rear end yoke)squared + (parallel to the ground distance between the two yoke centers)squared = length of new shaft squared .....take the sqare root of your last answer for final calculation.
The front shaft should be fine for a 4 inch.
Blake

3. ### Rolled1/2 ton status

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So I need to put all but 1.5 inches of the slip yoke in the tranny? So if my slip yoke was 6.5 inches I would put it in 5 inches and then measure the missing distance to the rear?

Are you sure 1.5 inches is not to far in? If I have a heavy load in the back will the slip yoke bottom out?

Also, I tried to replace the 10 bolt yoke with the 12 bolt and they are different. The 10 has bigger u-joints and the collar around the spline is bigger so it would not even physically fit. I would have thought the 12 bolt would have the bigger parts but its does not. The brakes were also inferior on the 12 bolt. The 12 is out of a 78 (I think) and the 10 is from an 87. I guess GM upgraded over the years.

4. ### tRustyK5Big meanieStaff MemberSuper ModeratorGMOTM WinnerAuthor

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E-town baby!
The front shaft should be fine for a 4 inch.

[/ QUOTE ]

We just lifted a buddy's 89 4" and the front shaft needed to be lengthened...I'm assuming it was a little on the short side at stock height.

Rene

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Yeah, I would like to retract my statement of 1.5 inchs and now say about 2.25 inchs...my mind was playing tricks on me so i looked at a ruler.

Remember all drive shaft length measurements are from the centers of the yokes.

I heard that you have to change out that seal on the pinion to get a 10 bolt yoke to fit a 12bolt. I'm planning on doing this sometime so i could post part numbers on it for future swappers.

My front shaft is ok on length for my 6inch lift but the c/v joint is rubbing the tranny crossmember sometimes. If was an extreme wheeler i would get a longer one built.

Blake

6. ### Rolled1/2 ton status

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I just dropped it off at the driveshaft shop. I jusrt marked where it was and they said they would figuire it out for me. I'll pick it up today and post what what the measurement is.

For anybody reading who is doing something similar -

On my 87 with a 4 inch lift and a 1978 12 bolt, the slip yoke was only bitting 7/8 of an inch. With the 10 bolt it was bitting about 2 3/8 inch. The slip yoke is 6 inches.

7. ### Chaz88K51/2 ton status

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ok what ya do...mesure from one of the ears on the yoke on the axle to the seal on the transfer case...and tell the driveline shop that demention and they should be able to build a shaft as long as they know that demention..

8. ### Rolled1/2 ton status

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FYI for anybody doing the same thing.

The old shaft which was not original was 29.5" from center of yokes and the new one is 32.5". The slip joint goes in the transfer case 4.25" out of 6".

The shop charged me \$65 for the cut and weld and \$30 for a new spicer 1350 yoke and 2 u-joints. Total bill with tax was \$102.70.

9. ### imiceman441 ton status

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I changed the yoke from a 12 bolt to a 10 bolt, the seal is the only thing you need to change so it fits. The spline count is the same.
I don't remember the part numbers that was 10 years ago.

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