best tranny fluid?
 

I'm going to change the tranny fluid in my 90 GT w/ stock T5. Can someone tell me whats a good brand and weight synthethic fluid to use? ATF or manual?

A stock T5 takes regular ATF (mercon), You can upgrade to Mercon V, which is synthetic and has all the same additives and detergents than regular mercon has plus it's synthetic.
I've also heard of quite a few companies like Red Line fluids, and Royal Blue (i believe is the name) that offers synthetic fluid, which you can look it up on their website (Redline) or probably call Summit Racing, or whoever you're ordereing from to get the right fluid.

if you do go with a synthetic fluid, try to get one that doesn't have a friction modifier in it. manual transmissions actually work better if there is a little friction for the syncros (the blocker ring won't take as long to slow the gear and so it will be easier to shift).

If you use fluid without friction modifiers in it, you WILL destroy your synchronizers (sp?). They have a special lining on them, similar to that of a automatic's clutches, that will burn off.

no... a friction modifier is an additive that is added on top of the synthetic fluid; it is specifically engineered to allow smoother shifts than a regular (non-synthetic) fluid will allow. this modifier was designed for an automatic transmission so that the clutch mechanism would provide for smoother shifts... a friction modifier isn't good in a t5 because it won't allow the blocker rings (part of the synchronizer assembly) to grab the gear in order to slow it down or speed it up the way that it should, which would result in a harder shift.

the true benefit of synthetic fluid is that it will allow a longer service interval before you need to drain and refill the fluid in your tranny (which should be done about once a year with conventional fluids). of course, it's also a superior lubricant since the molecular structure is much more stable than a conventional fluid...

synthetic fluid will also cause your transmission to be just slightly louder than a conventional fluid.

Does Synthetic Redline fluid for T-5 Transmission D4ATF have friction modifer? Also, I've never heard anypne else say that a friction modifer is bad in a t5.

Also, why would synthetic be louder than regular fluid? And is it a noticable difference?

i just rebuilt my t5, so i did a LOT of research on every aspect... i read quite a few pages that said that you need enough friction for the syncros to work right, which makes sense... it's not friction in the way you're thinking though... friction as in it won't keep slipping and not grab the gear.

not sure why it would be louder, but then again, the sites that i read told me that people had that happen to them.

I use Amsoil in my tranny. Haven't had any problems with it.

I used Amsoil in my old T5 too.

Now, with my Tremec 3550, I use GM Snycromesh fluid as it is what is recommended by Tremec.

E

Do you use their Universal ATF or a specific weight of their Powershift fluid?

I believe it's the universal ATF. My neighboor is a whole saler of it and I get a few bottles from him. I'll have to go home and check out the bottles.