Just completed fluid changes in the Tremac MN6 speed and rear diff.

MN6 - after much researching, I opted for the Royal Purple ($8/quart - 4.1 quarts required) Synchromax. Luckily, I had the C6 up on the lift, so the process was pretty easy. Simply use a 3/8" socket wrench (no socket) to remove the "fill" plug first (located higher on the driver side near the "DEXRON III" sticker. Once this is removed, the draining process will be easier as this will serve as a vent. Then, remove the drain plug (again using the 3/8" drive). Be careful as the fluid will be hot (no duh...) Upon complete draining, reinstall the drain plug then fill until the fluid starts to run out of the fill hole. I opted to use a $15 fluid transfer pump I got at the parts store - made quick work of the fill.

Rear diff - I wanted to use Royal Purple for the diff as well, but couldn't locate 75W-90, so I went with Mobil 1 synthetic ($10/quart - 1.5 quarts required) and supplemented with a posi additive (available at GM or the parts store). Again, first remove the top "fill" plug located on the diff - located behind the exhaust on the upper right. This requires a 10MM Allen (hex head) wrench. That's the easy one to remove. The drain plug is located directly on the bottom on the diff, which facilitates easy fluid changes. Problem is it's difficult to get the wrench into the plog and then having enough clearance to loosen. If you don't have a 10MM Allen wrench, a 3/8" Allen wrench will work. The plug is not that tight, so you won't have to worry about jacking it up. Was easiest to simply put the bottle spout into fill hole and squeeze. I then refilled the bottle with the other bottle and continued to it was full. Remember to add the posi additive! (Royal Purple does not have a need for this additive - so says the website)

Results:
MN6 - shifts much better. most of the "notchiness" is gone and makes me happy I left my B&M shifter installed.

Diff - no notable difference, but there wasn't a known problem before.

In a nutshell, I think these were excellent preventive maintenance actions. I would, however, wait until you have at least 2,000 miles on before the swap as the rear diff needs some time to mesh - and I've read it's best when that is done with a non-synthetic.

Total job cost - $70
Total time - 1 1/2 hour

 

for track events, or situations when the trans is likely to get hot, I recommend using Pro Blend's ATF additive. Tremec actually suggested it to me back in my T1 days (2000), and I've used it ever since.

It is like "water wetter" for your trans.

 

I swapped out the diff and tranny fluids exactly as you did. Waited until over 3000 miles to allow "break in". Pleased with the results. The most noticeable difference in my situation was the smoothing out of the 1 to 2 shift, which was quite notchy and hesitant, especially when cold.

 

Any ideas about getting the trans oil out of the oil cooler on the Z51 model?

Thanks!
J

 

according to the manual, there are quick-disconnects for the pipes. Disconnecting them should allow most of the fluid to drain out, albeit messy. Just be sure that when you re-fill, you run the fluids back into the cooler (by running in on the lift), then topping off the fluids.

You need to make your you DON'T OVERFILL either the trans or diff, as it will cause them to leak. Also, the extra fluid actually increase temperatures due to the extra fluid friction on the gears.

 

How bad would it be if I switched to brands but didn't drain the external cooler on the Z51? I want ot go with R. Purpole.

 

Anyone have any negative information regarding the above? Where the majority of the fluid is replaced, but remnants of a previous fluid exists?

hmmm

 

No problem-you will have a mild blend. Fluids are compatiable

 

There really is no way to completely remove all the existing fluid. There will always be some medium left upon the gears, inside case, etc. As stated, these fluids are compatible. I, too, have the Z-51 option and chose not to mess (literally) with the small amount remaining within.

 

I changed engine, transmission and differential lubes yesterday at 3K miles. No good reason, just excessive maintenance.
I used all Mobil One products - 5W30 oil, ATF and 75W90 gear lube - with additive, of course.
I found that a Bondhus (sp?) ball-end hex driver helps a lot on the differential drain. These things work up to about a 30 degree angle. Also, being a little worried about getting used oil on the spring, I stuck a little plastic trough above it to divert the oil.
I got about 3 3/4 quarts or a little more ATF into the transmission, which is about right for a drain and fill - remember the 4.1 quarts is for a rebuild. ATF sticks to the gears and won't all come out.
The shift does seem slightly smoother now, although I've never considered it to be a problem anyway.

 

One followup on this. My engine oil looked about as expected, a little dark but fine. The transmission fluid looked like new. The differential oil was fairly dark with some metallic traces in it. I don't think this is unusual for a positraction differential, but it does seem like changing it out fairly early isn't a bad idea. My Z28 called for changing it at 7500 miles then at 30K (as I recall) after that.
I think I'll make a point of changing this fairly often, although the owner's manual doesn't say anything about it that I can find.

 

How Much do you add to a C6 6 speed. Good place to get it?

 

http://performanceunlimited.com/cobr...additives.html

 

...this forum, and the consensus on products to use, I performed this change on my car.

Saturday I installed my B&M shifter. Definitely liked the throw, but because of the decreased mechanical advantage there was quite a bit more effort per shift - even in what used to be the buttery 4-6th gears.

(but I wanted to see how the shifter performed with oem fluids)

Sunday, I went through my first jacking experience - yikes (thanks again to this forum for helpful information). Then swapped the trans fluid with ProBlends TransCool (as DavidFarmer mentioned) and RoyalPurple Syncromax.

Both days I drove around for an hour or so (too much fun).


End results - h**y c**p!! Night and day difference. The improvement due to the RP isn't even funny. It shifts like it felt before, maybe even smoother (and that's with the decreased mech. adv. in the B&M).

Thanks for recommending this change guys.