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Unread 09-26-2013, 05:16 PM   #1
DezertTJ
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9" in TJ

I know a 9 in a tj is common, but I'm needing some help. Its a low pinion 9 and I'm going to be running iro brackets in the stock mounting locations. 2.5" lift with 1.25 bl and 1" mml. Now what I'm lost on is what's a good pinion angle to set these brackets for? I was reading the directions that came with the iro kit for an 8.8 and they said 6*, but that doesn't even seem close. I've heard 13* is good. I would measure it under the jeep, but at the moment there is no 3rd member. Is it ok to measure from the top of the 9 at the flat spot? Don't know if this is considered advanced tech, but any help is good. I will be running an sye when it gets done

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Unread 09-26-2013, 09:50 PM   #2
Jeepin72
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Can I assume that the suspension lift is the one on the Jeep now? If so, what is the pinion angle now? Then, do you know if the pinion yoke will be in the same distance from the t-case as it is with the D35? Or is the 9" longer or shorter? That should give you an idea where to tack in the brackets.

Since both are low pinion, it would make sense that they are similar. Do you have adjustable arms to allow for adjustment?

I recommend tacking the brackets in and then mock it up and cycle it. Then pull it and finish weld.
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Unread 09-27-2013, 12:01 AM   #3
DezertTJ
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I'm pretty sure the 9 is longer. Ill go with a stock pinion angle or maybe a little more and use adjustable arms to refine it. I did some research on some 9" pinion angles in tjs and some people are running 20*, which seems like a crazy amount
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Unread 09-27-2013, 06:38 AM   #4
Jeepin72
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My 14 bolt is sitting at 19 degrees. Granted I have twice the lift and a tummy tuck and moved the axle back about 6 inches!
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Unread 09-27-2013, 02:32 PM   #5
fratis
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Wait until you put a third member in. A 9" does not mesh the pinion and ring gear in the same way a 35, 44, or 60 does and this makes a low pinion lower then the standard housing.
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Unread 09-27-2013, 03:04 PM   #6
rchase559
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Quote:
Originally Posted by fratis
Wait until you put a third member in. A 9" does not mesh the pinion and ring gear in the same way a 35, 44, or 60 does and this makes a low pinion lower then the standard housing.
I believe you are looking for the term "hypoid offset"
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Unread 09-30-2013, 06:17 AM   #7
Gordon-0
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Quote:
Originally Posted by rchase559
I believe you are looking for the term "hypoid offset"
Almost.
"Axial offset". When gears have an axial offset, they are known as "hypoid" gears.

Among other things, hypoid gears have much smoother engagement but need higher quality oils because of this constant sliding along the gear face.

With normal gears, the drive face of the pinion contacts the drive face of the ring gear but there is no sliding along the face.
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Unread 09-30-2013, 02:05 PM   #8
biffgnar
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Quote:
Originally Posted by DezertTJ View Post
I'm pretty sure the 9 is longer. Ill go with a stock pinion angle or maybe a little more and use adjustable arms to refine it. I did some research on some 9" pinion angles in tjs and some people are running 20*, which seems like a crazy amount
Pinion on a 9" LP third member is long and low. Can be a PITA in a TJ actually. As far as angles go, for me with 4" SL, 3"+ gained from TT and that low pinion third in the rear (so call it 8+" of driveline lift) I'm just under 21 degrees at ride height. I wouldn't want to be much higher or rear driveshaft would be binding up when axle sagged. To get to 21 required an SSYE on my 231 (and pretty much ruled out a bigger TC for now). With 12" of travel in the rear split roughly 50/50 I don't bind at full sag but I think I'm very close to the limit. Oh, I shouldn't forget I did have TW do extra clearancing on my yokes and CV joint which I think is definitely helping prevent bind with this setup.
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Unread 09-30-2013, 05:13 PM   #9
DezertTJ
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I'll have to tack them in and line it up to get it correct, but I'll start with 15* and go from there. Thanks for the help guys
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