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  #1 (permalink)  
Old 09-17-2009, 10:08 AM
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Default Rear End Noise

I'm running a 9" Ford positraction rear with 3.50:1 gears and yesterday I began a grumbling noise from the rear. It only happens when I make a right turn. I am running rear disc brakes with integral e-brakes and at first I thought it might have been the right rear e-brake, or even caliper hanging up, but it doesn't sound like the noise is coming from the brakes.

I suspect that the problem may be in the differential.

Any members proficient with rear end troubles? If so, I'd appreciate any ideas as to what the problem may be.

Any help will be greatly appreciated.

Thanks,

Tony
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Old 09-17-2009, 10:39 AM
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Grumbling or roaring is usually the sign of a bearing or a universal joint.

If not IRS, then I would start by looking at the outboard axle bearing. You can pull the axle then spin the bearing by hand and see if it feels rough.

A differential bearing would probably make noise at all times and it would be more prominent at higher speeds.
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Old 09-17-2009, 11:53 AM
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I have a 8.8" with "posi-trac". You need to run the Ford friction modifier along with the diff oil. There are clutches in the track-loc that need the modifier to get lubricated. After adding the modifier, turn the car in tight left and right hand circles, (not doing donuts), about 8-10 turns in each direction.

Here's a couple sites that have it.

http://www.mustangmagicparts.com/m19...-mod19546.html

http://www.stangmods.com/M-19546-A1-...er-p/00364.htm

I used redline shockproof gear oil in mine so I used their friction modifier from Summit.
http://www.summitracing.com/parts/RED-80301/

Hope this helps.

Dan
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Old 09-17-2009, 12:15 PM
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If this is a new sound, its probably not a good sign. There are lots of Internet sites dedicated to how to work on a Ford 9", such as http://73-79.com/tech/ford9/. These help you see what's going on inside.

Getting the axles out for inspection and bearing/seal replacement is no big deal, though actually replacing bearings will require a shop press and the right tools. Its a common job so there should be plenty of shops around you that can handle it if you choose to remove and reinstall the axles yourself after servicing. If the problem is in the 3rd member itself, that gets a tad bit more involved but is still something you should be able to at least remove yourself (though its bulky and heavy.) Any good 4-wheel drive or rod shop should be able to check out and repair a Ford 9". If it were mine, I'd change the gear oil first and see what that looks like. If your diff oil is real dirty, just changing oil could help because the posi-trac needs clean gear oil that has the limited slip additive in it, or you need to add the additive. I would then run it by a shop that deals in these axles and have them give a listen. They may tell you its nothing more than a noisy traction-lok. If that doesn't yield success then I'd the pull the axles and inspect the bearings. And if all that's good, its time to drop the 3rd member.

FYI, if you wind up needing serious help, the folks at John's 9 Inch Factory are awesome and build a great rear end, I've got one in my Hurricane and its friggin' bullet proof.
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