Hi

I have a rx7 13bts5 and a rx7 fb 1982 12A, and want know what's a good oil to put on gearbox and rear transmition with oem lsd.

regards

 

85W90 Gear Oil. Buy one that comes with LSD additives or buy some LSD additives to put in there. Mobil 1 seems to have problems with our cars, so I would avoid that.

 

I run a roadranger CD50, a 50 weight made for eaton medium transmissions (660-860 ftlbs).

When I ran gear lube my transmission would rake in cold weather, and shifting into 3rd at the track. When switch to CD50 fixed the issue went away.

I'm just one person, have you searched the forum to see what other people run?

Gear oil is best left for rear ends, but it is the recammended oil from mazda.

I run Royal Purple in my differential (factory TII LSD) with off the sheft LSD additive

 

Synthetic oil works great, and most people consider it worth the extra money since the transmission and differential oil do not need to be changed very often. I like Red Line MT-90 in the transmission and 75W90 or 75W90NS in the differential. Other brands of synthetic oil will also work fine, such as Royal Purple, Amsoil, Elf/Total, etc.

The old Mobil 1 formula ate RX-7 synchros, probably due to massive amounts of sulfur. They supposedly fixed this, but I am too paranoid to use their products. Call me old and crusty, but I like sticking with GL4.

The RX-7 transmissions tend to have notchy shifting, especially in cold weather. Any type of synthetic transmission oil usually solves this problem.

Just so that others reading this do not get confused and try to put 20w50 motor oil in their transmissions, CD50 is approximately equivalent in "weight" to automotive SAE 90 gear oil.

 

..I agree 100 percent with EVIL..
I run synthetic,even though I can't afford it!.I just think it is good thing to do.It will make shifts smoother,and Save the gears,etc from wear and tear.
I use Redline.mt90 and additive in the rear and redline 75w90 in the trans.

 

Well if you have it in your car then you can obviously afford it.

If you think Red Line is expensive, you should see the pricing on the other brands. Current 75W90 Pricing at Summit Racing:

Red Line: $11/qt
PX3: $11/qt
Lucas: $15/qt
Royal Purple: $18/qt
GM Performance: $30/qt

Also, you only need to change the transmission and differential oil every 60 months or 60,000 miles. Crummy Coastal gear oil is currently about $4/qt at my local Autozone store. Given that you will need to buy 5 qts total, that is $20 for Coastal vs. $55 for Red Line, making the difference $35. While I realize that everybody has a different financial situation, I should hope that after 60 months even a panhandler could scrape up an extra $35. Then again, the cheapie Coastal gear oil should work just fine in a street car, even though the transmission shifting will probably feel pretty notchy.

Now that I look at it again, I should clarify that I was referencing transmission oil, not differential oil, and it is a personal preference. I have been using GL5 in my differentials for over 20 years with excellent results.