1973 8.75" Question..

[MoparMilitia]

Hello all, Happy Friday!! Have a weird one, or maybe not. so i just swapped a 8.75" into my 71 b body, and everything went well. i have two cases, a factory 741 with 2.71 gears, open center and a 489 thats currently being built with a truetrac and 3.23's. so i tried the 741 case just to move the car around for the time being, popped it in, slid the axles in, bolted everything up, tires on. went to spin the pinion and... nothing? no rotation on either side tires. Yet, if you put the car on the ground in neutral, and roll it back and forth the pinion does spin the corresponding direction... im wating on a buddy to bring me a Moog 372 U joint (7260 to 7290), so i have no engine power to the diff just yet. is this normal? i would think with most open diffs atleast one tire would turn with input on the pinion... what could be the issue? when i had the 741 center section out everything spun normal, spider gears are moving, nothings blown... is there something in the carrier that could be chooched? im at a loss...

 

[Nate S]

Sounds bizarre. Are the tires moving but just much less than you expect? Remember there’s reduction in there. If the pinion spins with tires on the ground it has to go the other way too.

 

[MoparMilitia]

Sounds bizarre. Are the tires moving but just much less than you expect? Remember there’s reduction in there. If the pinion spins with tires on the ground it has to go the other way too.

Thanks for the reply! my thoughts exactly!! bizarre... tires move ZERO when i have the car up on the lift and i turn the pinion. But, you put the car on the ground and roll it to and fro, pinions moving fine. id be curious to see if i can mock the driveshaft up temporarily to see if the diff will hold with the trans in park.. thatll be my next test..

 

[MoparMilitia]

well theres that... just strapped the ujoint in, lowered the car down, put it in park and gave it a push.. off it went... no resistance what so ever, its like its still in neutral. little bit confused as to exactly what i would be missing here. like i said the entire assembly was completely fine outside of the car. spider gears are all in tact, im curious if somethings wrong inside the carrier? im not sure exactly what COULD be wrong in the carrier though.

 

[MoparMilitia]

well... im an idiot. apparently the HOUSING is a B body housing, but the axle shafts are for a A body... Axles measure 27 11/16" flat from the outside of the flange to the end of the splines.. i apparently need 30 5/8" for my b body.. would make sense seeing its not engaging the splines on the carrier. when installing the axles, i did feel it "pop" into place, but its just shy of meeting with the splines. Damn.. anybody have some 8 3/4 shafts laying around for a B body? lol..

 

[Nate S]

Well that’s funny, in a #%^*! Sort of way. If you needed ‘69 axles I’d give them to you.

 

[MoparMilitia]

Well that’s funny, in a #%^*! Sort of way. If you needed ‘69 axles I’d give them to you.

I very well may actually need 68-70 axles… measuring the actual axle itself, not the shaft.. from the inside of the carrier to the end of the axle tube flange I’m seeing 29 3/16”…. So this axles kinda funny, because the leaf perches are 47.3”, which is a 71-74 B body measurement, but my shafts are measuring 29 3/16”… which again, is 68-70… for a 71-74 8.75 it SHOULD want 30 5/8”… who the hell knows anymore lol.

 

[MoparMilitia]

Need ones with this measurement being 29 3/16”.

 

[RemCharger]

Start with the flange to flange measurement of the axle housing.

 

[MoparMilitia]

Start with the flange to flange measurement of the axle housing.

measurement on the inside of the flanges is 58 3/8", outside measurement is 59 1/4"

 

[RemCharger]

Sounds like maybe you have a 71-73 wagon housing?