Bad rear end gear oil experience.

Pentalab

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An open differential is ok for the 4 L V6. The oem traction lok LSD is a poor excuse for a LSD at the best of times for the GT. The rebuild kit is cheap, and the GT-500 carbon fiber rebuild kit is only $20.00 more. But the CF discs won't last long... they melt. The real solution is the eaton tru-trac...with it's 3.5:1 bias ratio. Maintenance free, just use 80W-140 dino gear oil + a rear axle catch can.
 

Anti

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Thank you 1950StangJump$. You are on point with my original issues, findings, and solutions.

All others in the thread, further discussion of what FM is for, what actually causes whining, and what doesn't isn't needed. lol I am WELL aware of how a stupid diff works, especially an LSD, and what causes what. lol

Stage 3 proto, please don't hijack threads.
 

08MustangDude

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I have had the pinion gear jump teeth, but that was in a Geo tracker.
No other RWD car I had, had ever done that before, nor after. The
ring gear wants to climb the pinion gear every time you stomp on the
gas, that is what changes the pinion angle when you accelerate. If the
pinion gear is loose, bad bearings, or pre-load, it can go crooked when
you stomp on it, and jump teeth. It's not all THAT common, but it has
happened.

Banging is usually too much play in the drive line, which happens as soon as
you step on the gas. Too much lash in the diff, or bad universal joints. I just
had a set go bad in my Silverado. Stepped on the gas, BANG, and it wouldn't
move... BOTH the front and rear U-joints broke...

However, I suppose a tooth jump can sound like that depending on how it
travels through the car... It's like a very VERY loud "tang" or "ting" sound,
depending on how the sound transmits through the drive-line.
 

Riptide

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FWIW, I had a one tire fire after dumping friction modifier into the rear diff on my 2006 car. The synth I put in there already had the additive. Too much, and I had a problem. Drain and fill it was fine again.

Different car but I swapped the gear oil in my subaru out with OEM stuff and ever since it whines. IDC about it honestly but I know that whatever fluid I had in there before the OEM stuff did not make this noise.
 

DiMora

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This is like an oil thread. Opinions will always vary, and there is no right or wrong answer. With that said, when folks start experimenting beyond what the OEM recommends, it can always lead to trouble. Although Amsoil / Royal Purple are probably fine products, I hate Amway-like pyramid schemes, so I avoid that stuff.

I want to be able to walk into a Wal-Mart or any Auto Parts store and get what I need. So I run Mobil 1 or Lucas products.

I put an Eaton Detroit True-Trac in my car and run Lucas gear oil in it. Zero issues.

If I was on the OEM clutch pack I would run Motorcraft, Lucas or Mobil 1 WITH the Ford friction modifier.

Why run Royal Purple which *may* work when you can run something without modifier in it, add the correct modifier...and you know it *WILL* work?

Keep it simple.
 

Anti

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This is very true.

Odd thing is my mobile1 said it has FM in it, but they must have it wrong some how. In the future I will just get it without and by the FM separate, for sure.

Of course now I have thought about new gears and lsd once I replace my 2 piece drive shaft to rule out the carrier bearing, but I don't know which lsd to go with.
 

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