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Discussion Starter #1
Hey guys,

Wondered if anyone could help me out on a rear end question. I have a 69 XR7 with a 9" rear end. The tag says "WES-T1". 2.75 ratio.

I am wanting to change the gear ratio and also make it a posi. But I am unsure how many splines my axles might have. Is there a way to identify this number with having to pull the axles out?

Thanks
 

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If you look at the center of you rear wheels you will either have a round center or a square the round is 28 and the square is 32 I think thats right.
 

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Pchris
more then likely your car has 28 spline.99.9% sure of that.Ithink the big block cars(428cj,428scj, and the boss 302 cars) came with 31 spline axles.My70 had 28 spline until i had it rebuilt and put in a TORQ LINE limited slip differential .And ,ade a phone call to a mustang vendor for the 31 spline axles.As fot the rear gears 9` rear end gears are plentiful all depends on what you go with for the cars usage.For a 3 speed auto nothing more then a 3.50 for street and highway use.4 speed,5 speed,,AOD it varies but i wouldnt go up anything past a 4.11 setup. My car has a fmx w/ a shift kit and a stall speed but has a whimpy set of 2.75s but got 3.50s im gonna have installed at a later date.
hope this helps
thanks
pat
 

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Discussion Starter #4
The car has a 351W with a FMX transmission also. 2.75 gears just don't cut it.

I would like to order some new gears...that is the reason why I wanted to know what splines. Thanks for the responses.
 

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most models came with the 28 spline axles, the big block cars and Boss 302 models and i think also the Elim's came with 31 spline axles. I dont think they would come with that gear ratio, but I have seen 31 spline 3.89 open Nodular cases in some Shelby's. it takes approx. 400 lb/ft of torque to damage a 28 and about 600 lb/ft for 31. I've seen the factory axles, after someone has had some horsepower in their cars and the axles have twisted just outside of the 3rd member on the splines. also modern tire compounds which are much stickier than what was available back in the day combined with powerful engines increases likelyhood of failure.
 

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My buddy Terry's Boss 429 had evidently snapped its original 31-spline axles at one point. There was a patch on the back of the rear end housing where they had to cut it open to drive out the broken axle stub before the diff carrier would come out. After that, the car got 28 sline axles. The common reasoning at the time was that 28s would give and twist, whereas the 31s just snapped. They painted a line down the length of the 28-spline axles to measure twist. One of his 28s had a half-turn twist in it ans still showed no signs of wanting to snap.

I'm gonna be running 28s in AlphaCat and running mid-low 12s with it. I could have gone with 31s, but I already have the 28s, and also if I went with 31s I'd probably have to chance housings to the bigger axle bearing housing. If I start snapping the 28s, then maybe I'll go with aftermarket 33s and a big bearing housing.
 

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Cougrrcj, I was thinking the same about the housing sizes for the different bearing sizes and I talked to the folks at Moser the other day asking about axles for the narrowed rear I'm planning.

If I understood him right he said I could use the Mustang-Cougar small brg housing with any spline axles I wanted. mm
 
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