M6 Fluid Flush

[Joe K. 99 Zeee!!]

I had an A4 in my last F-body. This is the first time I've had an M6. I understand that in auto cars, if the fluid hasn't been flushed for say 50,000 miles, it isn't a good idea to do it as it could dislodge buildup and lead to tranny failure. Would this also apply to an M6? I wouldn't think so, but I thought I'd ask. The owners manual doesn't even specify changing the fluid at all...ever. I have 77k on mine and am going to at least drain and fill the tranny fluid. I don't believe it's ever been changed.

[bn_bullet]

Joe,

IMHO, it's a good idea to change the tranny fluid in the M6 every 25K or so. It doesn't really hold that much fluid (only a few quarts) and is fairly easy to do. To my knowledge you can do no harm in changing the fluid as long as the proper quantity and type (Dexron) is put back in. Good luck with it.

Brian

[TraceZ]

I run B&M QuickShift Synthetic in mine, or at least I think that was what it was called. It shifts very smoothly.

I dont see any way that changing the fluid in a high mile M6 could hurt it. There is no valve body, no pumps... it's just a box of gears and bearings with a seal on each end.

[fastTa]

The T-56 is one of the few manual transmissions that do not use gear oil. They use GM Synchromesh or Dexron III.

The best thing to run in a T-56 is GM Synchromesh. Penzoil also makes a synchromesh product, but I have my reservations about using Penzoil products. Some say it is also OK to run plain ole Dexron II.

BTW GM has now switched to Dexron VI.

You DO NOT want to run any type of synthetic on a pre-99 T-56. I took an ASE class on GM transmissions and they showed us several extremely worn blocker rings from the use of regular ATF synthetics.

GM Synchromesh has special additives and the proper additive pack to work specifically with the T-56/

In a T-56 there are blocker rings that have a friction surface on them, much like a small clutch disc. These blocker rings are what engage the steel gear and makes your shifts go much more smoothly. On 98 and earlier T-56's, the blocker ring clutch surfaces were organic and were slotted. The 99 and later T-56's were lined with carbon fiber and were not slotted.

The 98 and earlier T-56's are susceptible to pre-mature blocker ring wear with the use of sythetic oil due to the follwing two reasons.

The organic blocker ring clutch surfaces being organic(paper) need to have the proper oil (GM Synchromesh) to engage properly and to experince a long service life. Synthetic ATF's generally contain a high detergent additive pack and do not contain the correct limited slip additives to make the paper blocker ring clutch surfaces engage correctly.

Additionally, a significant portion of aftermarket synthetic ATF's are non-silicone based and are therefore hygroscopic, meaning they absorb water. Obviously this will saturate the paper lined blocker rings and eventually wear the lining off. The 99 and later carbon fiber lined blocker rings are immune to both of these known issues with synthetic ATF.

GM Synchromesh is specifically made to be non-hygroscopic.

[TraceZ]

So should I dump the B&M TrickShift and go with the GM stuff ASAP?

[fastTa]

So should I dump the B&M TrickShift and go with the GM stuff ASAP?

If it were my car, yes.

I had my doubts to whether or not this was true, but after seeing those burnt up blocker rings I was convinced.

[Joe K. 99 Zeee!!]

Being that I have a '99 though, I should be fine with Dexrong III or IV, right?

[fastTa]

Being that I have a '99 though, I should be fine with Dexrong III or IV, right?

Well you should have the carbon fiber blocker rings, but to be sure I think there was a specific RPO code for the later T-56's. Don't quote me, but I think it's M12.