8 3/4 swap q's... help!

[74valiant]

i have a line on a 8 3/4 axle in a b body gtx. its not the original axle, but i do have stamp numbers. on the side it says 288 1489, and i beleive its a 3.23 gear. i was looking into the swap, and found out i need to move the spring perches in 1/2 inch. i knew that, but they also said that i had to change the driveshaft. is this true?? any way to identify a suregrip since the guy wont take the axle apart??


thanks for the help

 

[74fldart]

raise the rear off the ground or floor and turn an axle and watch both sides if they both turn the same direction it is a sure grip. the b body rear will fit without moving the perches just push the springs over and bolt in. if you have a 7/14/" rear now and switch to 8/3/4" you will have to shorten the dr. shaft. the u joints will probably be the same

 

[fishy68]

You better take an overall measurement from hub to hub and see how wide it is since you said it's not the original rearend from the GTX. It may be a bunch wider than an A-body rear and will make your tires stick way out of the fenders unless you run different wheels with more offset. The 489 case didn't go into use until mid to late 69 so it's possibly a newer/wider rearend.

 

[74valiant]

bought the rear. ill get some specs up and some pics

 

[74valiant]

ok, so these numbers are estimates...


backing plate to backing plate- 55.5
spring mount to mount-44.5
axle to axle-60 (axles are out of the housing a little,so its probably a little shorter)


whats this sound like it could be out of?

 

[fishy68]

Sounds like it's from a 68-70 B-body. That would make it 3" wider than a stock A-body rearend. And the perches are spaced at 1.-1/2" wider. That'd work ok if you use wheels with 1-1/2" more backspacing and move the perches in to 43" centers.

 

[74valiant]

thanks fishy68. im getting 16x7 or 16x8 for the car with 255/60/16 in the rear. what amount of backspacing you guys think on the 7 and 8 inch?? would 4in. be good for the 7 inch? 4.5 for the 8?


thanks for the help. just gotta find some ss springs, and this will be goin in!!:cheers:

 

[fishy68]

Well my 8 inch wide wheels are 3.75" backspacing on my 68 Cuda and pretty close. 4" would have probably been perfect. Not sure if your Valiant is the exact same fit but if it was I'd say 5.5 on the 7" and 6" on the 8's. Your best bet is to measure when you get the new rear in. Go with as much hanging back as you can that way they don't stick way out of the fenders. Also when you measure don't forget to figure in about 1" or so for the tire balloon effect. In other words if it's 7" from the outside of the brake drum to the spring (that's what the tire will hit first unless the springs have been moved inboard) don't go no more than 6" backspace.