b-body rear in a-body

[humbulayed]

for those that dont kno yet picked up an 8 3/4 from the swap meet on saturday he said it was out of a 69 roadrunner its complete paid 400 and it already has 4.5 in bolt pattern and 4.56 gears its been recently rebuilt nothing looks worn at all its painted and looks real great even the brake parts aren't worn or even rusty.....now i did the math and its 1.8 inches longer on each side compared to the 7 1/4 in my dart sport...now obviously the spring perches need to be moved and thats not a problem but i really dont wanna shorten the tubes and axles and respline cause i dont have the money and some say it looks "right at home" under an a-body, if anyone has ANY pictures of an A-body with a non shortened b-body axle underneath that would help i just wanna get an idea of what it looks like, if i have to we can change backspacing but i dont wanna get the no-dish look, and also what would my top speed be with 4.56 gears. Its not a daily driver just a weekend warrior but i prefer to get out on the highway every once in a while.....

[superbee1970440]

I think you are gonna have to narrow it, unless you want your car all jacked up in the back with the wheels sticking out, like Joe Dirt.
As far as top speed....what's your combo?
With an auto, small block & normal sized street tires, about 55mph, unless you really wind it out.
Deep gears like that are no fun on the street.

[derek peters]

cut the pads off one at a time. use a grinder to remove the welds off of the pads. take the first one off and put the rear on a pair of blocks, leaving the other original spring pad in place. if you set it on the blocks the original pad will hold the pinion angle correct, and you simply locate the new pad 1,3/4 inch inboard, and tack weld it in place, with the new one in place cut the other one off, put it back on the blocks, position the new one and tack weld. double check everything before welding. i like to double and even tripple check everything before finnal welding. it will not be to wide. the rear end is only 3 inches wide to begin with. simply get rear wheels the same width, but with 1.5 inches more back space. problem solved. you may have to prop the pinion up to keep the rear end ballanced when it is setting on the blocks, just make sure the pads set level on the blocks

[moraycen]

If you are going to use it in your Dart sport it will be fine. Just move the pads in. I used a 69 "B" body 8 3/4 i my 74 duster (same as dart sport) with 15x8 centerllines, I believe they had a 5in backspace and 295-50s it all worked out great. I think I have a pic of it when I had cop car wheels on it,Ill have to look , if I find it ill post it.

[Jacksdad]

I have to agree with moraycen. The axles on these things are way too narrow for the rear fenders anyway. I have a '73 Duster and it could certainly benefit from another 1 1/2" either side to bring the wheels out - they're buried so far under the car it looks ridiculous. You shouldn't have a problem with the wheels not being dished enough.

[humbulayed]

and what about drive shart? shorter?! longer!? same!?

[humbulayed]

also could anyone recommend a gear ratio? (318, 302 heads, gasket match 1.88/1.6, 450/450 ,ed performer, ed, 650, hedmen headers, 904 trans, not sure on tire size yet figure as much as i can get (around 28 or 29) i want just enough gear to make it through the quarter and decent on the highway

[moraycen]

I do beleive you will have to shorten it 1 1/2 to 2 ins Im not 100% sure how much, but you will have to shorten it.
Gears if you go with a 275 60 tire you can get away with 391 s.

[humbulayed]

from what i measure they dont need shortening, that is, if i dont use a 275 which is over a 10 1/2 inch tire....and y shorten if you dont have to plus it already has the desired 5 on 4 1/2 inch bolt pattern....if you look under the car from the rear it looks to narrow as is

[humbulayed]

lol ahh i apologize moraycen, i thought you were referring to the tubes and axles.....thanks for the info on the driveshaft im sorry once again i misunderstood

[humbulayed]

too ask another question my father owns a tool and die shop he does alotta welding and CNCing and whatnot......would the drive shaft have to be balanced again?would i have to take it somewhere? or can he just cut and weld?

[Jacksdad]

You could always try the suck it and see approach. Shorten it if you need to and see if you get a vibration. I guess the balancing wouldn't be thrown off too much if you drew a line in chalk and made sure you aligned the marks as you weld it. Cutting through the original welds and sliding the UJ back into the shortened shaft would be the best way to do it. I remember my Dad joined two different shafts together in the middle on a custom project, but he slid another piece of tubing inside to bridge the join and welded it in place with spot welds drilled through the outer tubing before he butt welded the whole thing together. He put it on the car and spun it with a piece of chalk next to it to see if it was curved, and used a torch and a wet rag to shrink the long side, then took care of the inbalance with a hose clamp that he kept twisting around until it smoothed out. That was a few years ago in Britain and we didn't have the luxury of local driveshaft shops that could do the job without it costing an arm and a leg (plus my Dad was old school and didn't bat an eyelid at fabricating stuff - he was good and knew it). It's not that expensive over here to have an experienced shop do it, but if your Dad's up for it, make the most of it.

[humbulayed]

thank you i'll run it past him and see what he thinks, im not an experienced welder yet but im atleast gonna try and move the perches on my own he can handle the driveshaft

[ehostler]

There is an axle measurment diagram in the archives. It has all of your axle dimensions. Based on those dimensions, going form a 7¼ to an 8¾, the drive shaft will need to be 2¼" shorter.

You can shorten it yourself; however, I would recommend that you take it to a driveline shop and have it balanced.

[moraycen]

If you do shorten it yourself make SURE you line up the U joints with each other!!!

[humbulayed]

i figure i'll get an estimate from the driveshaft shop and if its too much then diy....thanks for all the info, much appreciated

[JDart270]

does any one have pictures yet ive got a 65 dodge dart that i want to replace the rear end in and a 8 3/4 had come into thought but my car has curved out wheel wells so i dont know if a bigger axle would be a hinder or a helper but anyone with pics would help the thought process thanks

[humbulayed]

yea i would still be interested in seeing an example if anybody has one

[mopar_man72]

I have a pair of caravan rims on my duster to use as rollers. the tires it came w/ had major tread seperation. anyway, the offset won't work on the rear, but they look right at home on the front. since the B body axel is wider then your stock one you could use newer FWD wheels. only thing to keep in mind is don't go wider then the rims on the front, you'll rub the tierod ends. I think the ones I have on are 205 or 215/70/15.