Dana 60 to 8 3/4 swap - Does size matter for the drive shaft?

[5hunert]

Has anyone here ever (successfully) re-used the slightly shorter drive shaft when replacing a Dana 60 with an 8 3/4?  According to the FSM, 8 3/4 equipped B bodies came with a 52.07 in driveshaft while Dana 60 equipped cars had a shorter 50.96 long driveshaft.  Will the lack of 1.11 inches in driveshaft length cause a problem? 
I'm trying to make my 69 Charger more interstate friendly for a long distance road trip this summer. Its a 440 auto that came with a 4:10 Dana as part of the A32 axle package. This is a blast around town but sux at 70MPH.  I located a correct 8 3/4 setup with 2.76 gears, but don't know if I also need to chase down the matching length drive shaft.  Back in the day when I was less informed, my crowd used to go the other direction and regularly replaced 8 3/4s with Danas without suffering ill effects. 

And yes, I'm holding on to the Dana in case the car ever becomes a numbers matching trailer queen.  Its just my experience that its a lot cheaper and easier to change out the entire housing than swapping out gears ratios in a Dana.

Thanks!

[cdr]

you will need the correct driveshaft .

[chargerbr549]

I thought I read somewhere lately that somebody makes different length slip yokes for a 727 that would eliminate the need for shortening or lengthening the driveshaft in some cases?

[BSB67]

I thought I read somewhere lately that somebody makes different length slip yokes for a 727 that would eliminate the need for shortening or lengthening the driveshaft in some cases?

That is not the issue.  You want the u-joint as close to the yoke support as possible without interference through expected motion.

If you were building a drive shaft, the common rule is for a min of 3/4" and max of 1" forward movement from rest position.

[bad88t-top]

I'm actually performing the same swap now on a 70 Charger.   What did you end up doing when you swapped yours?

[John_Kunkel]

The main thing you need to know on this subject is the difference in the dimension from the center of the axle shaft to the center of the u-joint.

Centerline of Axle Shaft to Center of Universal Yoke dimension for the 8 3/4" is 12.35" and for the 9 3/4" it is 13.47". As you can see, the difference is 1.120" so the driveshaft length must be adjusted accordingly when swapping rears.

[5hunert]

I'm actually performing the same swap now on a 70 Charger.   What did you end up doing when you swapped yours?

I ended up chasing down a 52" driveshaft.  I plan on putting the shorter shaft in at some point to see how it works.

[flyinlow]

I would be concerned with the amount of spline engagement. 1 1/8" less spline overlap could really stress the part of the spline still engaged when the yoke is pulled rearward.   For example, doing burn outs in reverse ,  accelerating hard over rough surfaces ( both bad ideas) or backing up a steep incline.

[c00nhunterjoe]

The 1 1/8 shorter length is because the rear is longer and will therefore bottom out the driveshaft against the tailshaft over bumps, or hard accel. Bad news.

[Bronzedodge]

Wow.  4.10 to 2.76 is a huge change.  You might hate it.  3.23 or 3.55 is a good all around gear.  A bit easier to swap center sections w the 8 3/4.

[5hunert]

Wow.  4.10 to 2.76 is a huge change.  You might hate it.  3.23 or 3.55 is a good all around gear.  A bit easier to swap center sections w the 8 3/4.

It should drop rpm at 60 mph from around 3000 rpm to 2100. I'm planning to drive from Seattle to Talladega.  Each 1mpg I can gain will equal about $300 in fuel cost. I'll probably stick some 3:23s in when I get back home.

[alfaitalia]

When I raised the gearing on my Jeep from 4.10 to 3.55...I was expecting a good improvement in mpg on the open road. What did I get?...well very close to no difference at all is what...barely measurable on tank top to tank to checks. If you think of each cylinder burning a "drop" of fuel every some it fires....then although you are burning less drops of fuel you are burning bigger ones...due to the extra load......especially on anything other than flat roads. Hills might mean you are in a lower cog too...making it worse. I'm not saying is won't be worth it...the lower revs, noise and more relaxed feel could be worth it alone....but don't expect the mpg improvements the maths might tell you to expect.

[A383Wing]

well, you must have done your math wrong......with him going from 4:10 to a 2:76 gear.....it will make a big difference in fuel mileage on the road trip next year

I made a run from Seattle to Canada back when 9-11 hit......fully loaded car, 3 adults also.....got 24.5mpg in the Daytona......