8 3/4 rearend from a 67 pickup going into a 86 D150 2wd that currently has a 8 1/4. Will driveshaft shortening be needed? Thanks

Forgot to mention truck is an automatic/904 not a 727

That will depend on how much room was left on the driveshaft going into the trans. I would say no, or it will be pretty tight.

I have a 88 d100-440/727 A-body 8 3/4

I can measure the shaft for you if you like.

I cut mine to fit when I built my truck from scratch.

The center-of-axle to center-of-u-joint dimension on the 8 1/4" is 11.69" and the 8 3/4" is 12.35" so you need to shorten the driveshaft .66".

If it's a two piece shaft you may have enough room to slot the center bearing mount. When I converted my 92 diesel to lockup I did not have to shorten the shaft and that is a 1.125" difference.

well I bolted the rear-end in, got the driveshaft in, it is so far in the transmission tail shaft that the yoke is jamming into the tailshaft seal, so yes..looks like it will have to be shortened.

I can remember someone on here years ago giving me a hard time cause I shorten mine up. Was basically saying I had no idea what I was saying....anyways....I had shorten mine up....been a long time now....don't remember how much....but....

to be exact. it is best to have the yoke bottom out in the trans and measure from center to center of u-joint cap at static ride height, then subtract 1"

some say 1" to 1.5"

I always go 1" and have it balanced. I also look for the 6270 yokes and the 4" tubes from long wheel base vans/trucks.

The intended use for the truck may also affect the clearance required.

I find the factory clearance to be more than generous. The factory ride height is pretty high too.

I had an 87 D100 and did the same 8 1/4 rear to 8 3/4 swap. Like Kunkel said, factory numbers require a slight trim but I did not shorten mine and had plenty of yoke to seal clearance. Even at a lowered ride height plus towing and overloading the bed the yoke only went forward another 1/8".

If you have clearance but the balloon seal is touching. They also have rear transmission seals without the balloon.

I have a seal on the transmission with no balloon and the yoke it jamming into the seal. Maybe a lot of people that did the conversion have had 727 trucks and they have had more driveshaft clearance? mine is a 904 (A999) transmission.

which has a longer shaft than a 727

what measurement do you get with yoke bottomed out in trans center of cap to center of cap?

the difference should still be what John said .66

I wager you need to chop off 1" that will get you off the seal lip and have room to slip.

I went from a slant six/833od to a 440/727. same length. Put the 8 3/4 rear under it, and had to shorten driveshaft about 3/4" for it to be right. I run a driveshaft shop, so that wasn't an issue!

I agree with Old goat.
I had to do the same thing

I took the driveshaft to a machine shop to get 1" taken off and rebalanced if needed. I will install it tonight and see what happens and give an update. Thanks

UPDATE: The driveshaft bolted right it, everything looks good. ill finish a few small things (replace some wheel studs, bleed brakes) and hopefully the truck will be back on the road tonight and hopefully it pulls harder with these 3.91s, the 8 1/4 I replaced had 2.90s.

going from a 2.90 to a 3.91 is going to be noticed. depending on tire size.

my 88-440 truck turns a 29x15x15 M/T 2600 RPM @ 55 MPH with 3.91sg gets 10 MPG

2.76 turns 2000 RPM @ 55 MPH gets 12.5 MPG but topend is UNLIMITED! 4800 RPM @ 130 MPH flying mile.