When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I'm looking for recommendations on what kind of transmission fluid to use on my 1988 Firebird formula with a 5 speed manual transmission. It has a 305 engine if that makes a difference. Anyways what kind do you guys recommend, brands types etc... I don't mind paying more for the better fluid especially if it would help with longevity in the long run. How much do you need if you are changing the fluid in the transmission? Anything else that I should know? Amsoil is supposed to make good motor oil. Is that actually the case? If so how is their transmission fluid? That is the direction I am leaning at the moment.
Last edited by Penguin James; Jun 15, 2025 at 06:06 PM.
Reason: To ask a few more questions.
All for the low price of 92 bucks a quart. Which makes me guess that the original stuff has been discontinued and that is why you guys are recommending Dexron 3. Or am I missing something here or just way over thinking things? I have found some other brands that say they are the GM part number 12345349 or Syncromesh transmission fluid should I use that or go with Dexron 3? AMSOIL 5W-30 Manual Synchromesh Transmission Fluid is what I am thinking of getting right now. Am I reading that right that if I am changing the fluids I need 32 oz of transmission fluid? Anyways thanks for the help. I got this old Firebird and finally have it to the point where it is running again but I don't know how old all the fluids are or when they were changed last so I am thinking it can't hurt to get all the fluids changed so I just don't have to worry about it.
Last edited by Penguin James; Jun 16, 2025 at 12:43 PM.
Re: What kind of transmission fluid do you recommend?
"Dexron/Mercon" at the parts store. It is Dexron III.
GM 88900333.
No engine oil. No gear oil. Both will cause blocker ring material failure. No Dexron VI. That has too low a coefficient of friction.
Using "heavier" gear oil is thoughtless-think. ATF is completely fine for lubrication. You don't improve lube in a gearbox by using something physically thicker unless the thinner product breaks down at operating temp. ATF doesn't. You DO improve lubrication by using a product that will continually remain fluid, resist aeration, and coat wear parts. ATF does this great. The breakdown of T5 units is largely due the cheap *** bearing design and shaft support at the maindrive/mainshaft piloting which flops 3rd around, and the counter nose with vibrational casting wear. All of which happens with gear oil in early, and with ATF in late units.
Which makes me guess that the original stuff has been discontinued and that is why you guys are recommending Dexron 3. Or am I missing something here or just way over thinking things? I have found some other brands that say they are the GM part number 12345349 or Syncromesh transmission fluid should I use that or go with Dexron 3? AMSOIL 5W-30 Manual Synchromesh Transmission Fluid is what I am thinking of getting right now. Am I reading that right that if I am changing the fluids I need 32 oz of transmission fluid? Anyways thanks for the help. I got this old Firebird and finally have it to the point where it is running again but I don't know how old all the fluids are or when they were changed last so I am thinking it can't hurt to get all the fluids changed so I just don't have to worry about it.
