? on 7 1/4 to 8 3/4 rear end

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johnmucci

johnmucci

moparmucci
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I have a 66 dart that I am putting a 360 in it. I am also going to swap out the 7 1/4 for an 8 3/4 rear end. Will my existing driveshaft fit?? if not, does anyone know how much it will have to be cut?? Or does anyone have one that will bolt in??? Thanking you in advance, John
 
There are many posts on this, so search.

Pretty sure the driveshaft will have to be cut, which most drive-shaft shops can do fairly cheap.

I kind of recall the later slip yokes have different splines, so if you are changing the tranny you need a later yoke.

If you are keeping the 66 tranny, you need a spacer ring for your smaller torque converter snout to fit in the 360 crank hole.
 
Whats in it for a transmission? I just put a 8 3/4 and a 727 in my demon(108" wheel base). It was originally a slant 6 with a 3spd manual. I had to cut it to around 46 1/2"
When you get everything in (tranny and rear) push your slip yoke in the back of the tranny all the way, then pull it out about an inch, then measure from the center of the caps in the slip yoke to the center of the caps in the rear yoke. That should give you the length you need
 
Ah DUH,,, sorry about that, it has the stock 904 automatic transmission in it and I am using that. The engine builder is getting me the torque convertor and flex plate as the motor is going to be dyno tuned before I get it. Will I still need that spacer ring or should the builder know this? and where can I get it if so? Thanks!
 
You will definetely need to shorten the drive shaft and the best way to come up with a length is to measure the actual distance especially since you're replacing the rear. Have all the car weight on all 4 tires, put the tranny slip joint all the way forward into the tranny until it stops (gentley) then withdraw it on the splines 1". Now measure from the tranny yoke cup area center line to the rear end yoke cup centerline and give that dimension to a reputable drive line shop. Make sure they balance the drive shaft after ends have been welded.
 
Had that done on my 1972 dart back in the day , shaft had to be cut down . I brought mine to a shop , they cut it down balanced it and made sure it fit properly . never had a problem after that .
Nice car you have , going to go well with 360 , 8 3/4 is needed for sure . I must have blown 4 7 1/4 diffs before I got smart and put in an 8 3/4 .
 
Pre 1968 torque converters have a different spline count. Better off with a later trans for converter selection and part throttle kick down is a bonus.
 
BillGrissom said:
There are many posts on this, so search.

Pretty sure the driveshaft will have to be cut, which most drive-shaft shops can do fairly cheap.

I kind of recall the later slip yokes have different splines, so if you are changing the tranny you need a later yoke.

If you are keeping the 66 tranny, you need a spacer ring for your smaller torque converter snout to fit in the 360 crank hole.
Click to expand...

Ok, so where can I buy a spacer ring?????
 
johnmucci, cut the driveshaft 2.25 inches (2 1/4"). That is the difference in the
distance of the axle centerline to the yoke u joint centerline when going from a
7 1/4 to an 8 3/4. Orv
 
Im sure you know this already, but your also going to need 8 3/4 shock plates and new u-bolts
 
Measure, measure and cut once. Standard rule of thumb. Just be sure the weight of the car is on the suspension when you measure it.

My suggestion is to find a local shop that will cut and balance, call them and ask them what they want you to measure.
 
johnmucci said:
Ok so where can I buy this spacer ring??? anyone
Click to expand...
Since nobody knowledgable answered, I relate what little I know. There are two fit issues.

1. The torque converter must match the crankshaft snout. Early torque converters have a smaller snout than later cranks. Not sure of the cut-off year (early 70's?). Might have been with the switch from forged to cast cranks. I don't know where to buy the spacer ring. Search FABO to find several posts.

2. The input shaft splines on the transmission must match the splines on the torque converter. If you put a later torque converter in an older transmission, it will seem to fit, but will just spin uselessly without turning the input clutch. Many posts on this "what the heck" issue. I understand you can change the input shaft in an older tranny, but requires taking the transmission half apart. If so, replace clutch plates (cheap, ~$2 ea for standard plates), at least measure your steel plates, and install new rubber. A "banner kit" includes these (no steels). Might be better to install a later rebuilt tranny, as others suggest. Should fit fine since '66 started the lever shift housing, which continued forever (even late model transverse Torqueflites). Of course, shipping costs are a b***, so if resourceful, modifying yours could be best.
 
OK THE MYSTERY IS SOLVED!!! I took my tranny and stock converter to my engine builder(Dan Costello @ Performance Only in Delray Beach Fl. He called Hughes and explained the situation(which he has seen before and they are building a special order converter so it fits my tranny and the 360 crank at no additional charge than if I was buying one from stock!! Dan said he could make the spacer but why if Hughes will build one. Thanks for all the input, learn something new everyday!!! Thanks A bodies!
 
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