According to Ogre's Fiero Cave...

Fluid Guidelines for Manual Transmissions.

There have been many posts in the forums about what oil to use in the Fiero manual transmissions. I've been digging around in paperwork for a while to find which oil GM recommends in the different Fiero manual transmissions vs. the info in Haynes and other sources. This item is confusing to say the least.

I’m up to three documents from ALLDATA and GM. These documents specify one of three oils is to be used. Yes, I know this conflicts with Hayne's book that says use motor oil in the transmission. I'm still trying to figure out where that info came from and if any of it is valid. (It wouldn't be the first time that rag was wrong.)
Fluid type and capacity by transmission

This table is correct based on the listed TSB's.
Transmission Oil Cap, U.S. Pint Cap, Liters TSB # & Date
4 speed GLS 6.0 2.8 na
5 speed, Muncie STF preferred, MTF 4.0 1.9 88-7-17, 2/88
5 speed, Isuzu STF preferred, MTF 5.4 2.5 88-7-31, 5/88

It states that for my 4 speed manual transmission on my 84 Fiero, I should use GLS.

However, according to my previous thread, https://www.fiero.nl/forum/Forum2/HTML/107718.html, I am told to use synchromesh transmission fluid.

I am confused as to which one I should be using. After doing a search on this forum, it seems most use synchromesh on all manual transmissions. Is this true? Should I use synchromesh instead of GLS?

Thank you for all of the help!

The factory recommended lube for the 84 4 speed is 5w 30 motor oil. I've been using Mobil 1 5w 30 for seven years or so. Many say that GM later changed to sycnromesh fluid for later model trannies but I've never seen anything on that fluid for our 84's.

I have the Muncie 4 speed. It felt like the synchroes were on their last legs. I tried Mobil 1, and 5w30, but the correct answer was Synchromesh Fluid.

If you ask a GM Mechanic they have been using Synchromesh in all the manual trannies for years. There was guidance out on it from GM.

The difference is like having a new transmission. Believe me.

Use it.

Arn

quote Originally posted by Arns85GT: I have the Muncie 4 speed. It felt like the synchroes were on their last legs. I tried Mobil 1, and 5w30, but the correct answer was Synchromesh Fluid. If you ask a GM Mechanic they have been using Synchromesh in all the manual trannies for years. There was guidance out on it from GM. The difference is like having a new transmission. Believe me. Use it. Arn

So is there different grades of synchromesh? Like is there a 5w30 synchromesh? Or is there just a "one size fits all" synchromesh? What do you use in your 84 tranny?

Thanks!

i got my 4spd 84 recently. This is my first manual car as well so how do i tell (or what to look for) when the syncro starts to go? Also, how do you flush/change fluid on the 4 spd?

quote Originally posted by megahaas: i got my 4spd 84 recently. This is my first manual car as well so how do i tell (or what to look for) when the syncro starts to go? Also, how do you flush/change fluid on the 4 spd?

As would be done with any old used car I would buy, flush the coolant, brakes, and transmission. You do not know when the previous owner performed these jobs (unless they gave you detailed descriptions and receipts). Plus, it gives the new owner a sense of confidence that their systems are clean and running smoothly.

Royal Purple Synchromax. After using it you'll never go back to anything else.

quote Originally posted by RyanFromMichigan: Royal Purple Synchromax. After using it you'll never go back to anything else.

Thanks for the advice. Is this the general consensus amongst most? Is there a GM or NAPA brand that is just as good or better?

Thanks! Much appreciation

Royal Purple is available through Summit Racing or locally at Pep Boys. I wouldn't go cheap with a fluid as rarely changed as manual trans oil. A premium synthetic is the best insurance you can get to keeps shifts smooth and reduce wear for longer life.

quote Originally posted by RyanFromMichigan: Royal Purple is available through Summit Racing or locally at Pep Boys. I wouldn't go cheap with a fluid as rarely changed as manual trans oil. A premium synthetic is the best insurance you can get to keeps shifts smooth and reduce wear for longer life.

Is there a GM brand that is recommended through TSBs or something of that matter, though?

Thanks! I will probably end up getting the royal purple and be like the artist formerly known as Prince

EDIT: It appears from this thread that GM and Chrysler recommend Penzoil Synchromesh
https://www.fiero.nl/forum/A...090907-2-092293.html

[This message has been edited by FirstDrCar (edited 04-04-2010).]