Thndrstrkz

I am putting in a new clutch soon and figure " What the hell why not change the trans fluid while I am there". I have used Mobil ATF ( not synthetic) previously. This would be my second time changing the trans fluid and I have 112,000 miles on it. I know GM doesn't have a service interval but I figured at least every 50k would be suffice? I would prefer to use Redline in my trans,however I am not sure whether to use D4 ATF or MTL? Any help on this topic will be GREATLY appreciated!!!

dailydriver

If you're going to use one of those the D4 is the one. Just know that the jury is out on whether or not which synthetic Dex 3 will or will not; let the synchros engage, swell the blocker ring materials (especially in your '99), or eat the adhesive holding the blocker ring material on. Or this can all be just an "urban myth", no one (including Tremec and the "experts") seems to know!!

Ryan02SS

iTrader: (3)

I've used the D4 before and shift quality was great. I can't blame the D4 for my trans locking up in neutral on the 3-4 shift at the track but it was filled with it. My Father and I tore the tranny apart and found nothing wrong. Beefed it up while it was apart and have been running Mobil 1 Syn ATF since rebuild. Shifts very smooth with the M1 and I have no complaints. Many writeups i've seen say not to use Synthetic in older T56's. Like dailydriver said above nobody really knows anything.

INMY01TA

iTrader: (1)

I've used D4 for years and just switched to MTL about 4 months ago. I think the D4 shifted better and I'm gonna switch back when the weather warms up a bit.

CTSmechanic

iTrader: (2)

I used Red Line in my 00' T56 and less than 3 months later she was in the shop gettin rebuild..... I guess the Red Line really pisses the non kevlar blocker rings off...

chucky2

Thndrstrkz- There are many opinions on this, and as dailydriver points out, no one seems to have all the answers (I've looked around on this topic a lot...and basically come to the conclusion that the people who have the resource to definitively settle this - Tremec, GM, Ford, etc. - simply don't care to...so, it'll never be put to rest).

You should probably take a long, slow, read read through the below thread...I believe it addresses most options, concerns, and viewpoints on the subject. The mods ought to make it a sticky...

Which T56 fluid?

I realize the thread is long, but I think it's worth it to be informed in the end...

Hope this helps...

Chuck