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Best lubricant for transmission and differntial

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i was thinking of changing the transmission and differential fluids, what is the best lube to buy, stick with original or go for Royal Purple stuff, the car has 93000 mils.
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A lot of people around here swear on Royal Purple, which makes my decision towards RP too. So far I had the RP on my tranny and it works just fine.

Some people reported smoother shift, but I don't feel the difference between RP and stock.
 

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When I put my UUC clutch setup in, Rob recommended and mix of different Redline products in the tranny. I read some bad press about RL causing some ill effects. Anyway I got scared and took out the Redline and put in Royal Purple Synchromax. The smoother shifting and reduced noise made me think that my Indy guy somehow installed my transmission better. Very pleased!

I had also bought RP for an oil change, but after reading repeated stories about shearing, I stayed with my Mobile 1.

I have not researched RP's gear oil, but I think the results would mimic what the Synchromax did for my 6-speed.
 

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When choosing a rear diff. fluid, please make sure to get the 75W-140, not the 75W-90.
Yep. That's the spec'd oil. I think it's important to get the right one (75w-140), as the shear loading in the diff is probably pretty high, what with the tremendous HP and torque of the engine, and the high weight of the car. As long as you use oil with a limited slip differential additive package (RP MaxGear already has it; no need to mix it in), it should be quiet, but I worry what wear you'd get if you use the lighter weight lube.
 
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