For the manual transmission, Synchromesh works excellent. I've cleaned up so many notchy transmission draining out trans fluid and refilling with Synchromesh. If you don't want to pay GM's price, pick up some Pennzoil from your local parts store. 4 qts...



For the 4L60 cars, Amsoil DEX III works oustanding. I've seen 10-15 degree temp drops JUST by installing the fluid (full evac & refill). This is what the bottle looks like...




These are the fluids we use in my shop.

 

Is the Pennzoil a synthetic blend? My T56 has no problems with synchro's but does seem to have a very slight leak at the rear (a few drops appear between the tranny and diff'). Will a synthetic blend increase the leakage?

 

GM changed their recommendation in a bulletin that was issued 3 or 4 years ago.

GM bulletin highlights: "Any vehicle that previously used DEXRON-III for a manual transmission or transfer case should now use p/n 88861800 (88861801 in Canada) Manual Transmission and Transfer Case Fluid. All licenses for DEXRON-III expired at the end of 2006 and will not be renewed. Fluids sold in the market after that date bearing claims such as "suitable for use in DEXRON-III applications" or similar wording should be avoided, because 'DEXRON-III' fluids are no longer checked and policed by GM and therefore may not be the originally tested and approved formulation."

 

... somewhat. I would not use a Dexron VI fluid in a manual - the viscosity is much lower than a Dexron III fluid. But, I would (and do) ignore GM's disclaimer to buy their new fluid (part 88861800). There are many fluids on the market labeled to meet the superseded Dexron III spec, which was the spec for our C5s. These are all reputable companies whose best interest would not be served making products which don't meet a spec, whether it is superseded or not.

I have been using this, which is AMSOIL's primary recommendation for the T56, since 2007 in my 02 Z06 at the track without problem:
AMSOIL Torque-Drive Synthetic Automatic Transmission Fluid (Product Code ATD1G)

More than happy to get AMSOIL products for forum members at dealer wholesale pricing, about 25% below retail, via the AMSOIL Preferred Customer Program. Drop me a PM if interested.

 

ah ha, i knew there had to be some difference regardless of the claimed compatibility

also makes sense with the 4x4 jeep guys who often have 200k + mile transmissions. lower viscosity in a high mile trans would be the kiss of death.

didn't know their was a viscosity difference

 

And for that concern, in my high mileage daily drivers (have 192k on an 03 Chevy Trailblazer EXT with 5.3L and AWD) I do use the AMSOIL Sig Series Multi-Vehicle ATF which is a Dexron III formulation vice AMSOIL's ATL which is a Dexron VI formulation. In the Vette I use the Torque Drive ATF, which is also Dex III formulation.

FYI, AMSOIL's Torque Drive ATF (Dex III) has a viscosity of 7.4 cSt at 212F, AMSOIL's Sig Series Multi-Vehicle ATF (Dex III) has a viscosity of 7.5 cSt at 212F. For comparison, their Sig Series Low Viscosity ATF (product ATL)(Dex VI) has a viscosity of 5.9 cSt at 212F.

 

Well, this is all a bit confusing! The Amsoil Torque Drive seems to have the proper viscosity, yet the Pennzoil Synchromesh seems to have better additives for a manual transmission. Did GM transmission designers sacrifice sychro' wear for better cold weather shifts when they spec'd the fluids? GM Manual Transmission and Transfer Case seems to be the ideal combination (viscosity and additives). The Honda MTF sounds do-able, also.

 

I'm about to change the fluid in my T56 which was rebuilt not too long ago, I have used syncromesh in the past and the shifting was alot less notchy. Does the amsoil make the shifting not as notchy as well?

 

In general, MTFs such as the Pennzoil Synchromesh have a viscosity about 30% higher than required for Dexron III. It doesn't look like Pennzoil lists the viscosity for their Synchromesh, but they do list that it meets GM Specification 9985648. AMSOIL's equivalent MTF which meets the same spec has a viscosity of 9.7 cSt at 212F. The 30% or so increase in viscosity will increase pumping friction losses and result in less net HP and reduced mpg. I personally wouldn't use an MTF in the GM T56 application. If you look up the actual Tremec spec, they list an ATF spec as well. I'd stick with a Dexron III spec fluid of your choice.

 

Well, I've seen the Pennzoil listed for 9.3 cSt at BITOG. The GM Manual Transmission and Transfer Case Fluid has ~ 7.5 cSt, which is almost the same as Dexron III. Other MTF's with similar cSt's include BMW, Honda, VW, Ravenol, and Royal Purple. Castrol has a full synthetic with a 8.0 cSt. Although I hear what you're saying with friction losses and higher viscosity, my particular T56 has a very slight leak, I think from the seal on its' output shaft, and I wonder if the slightly higher viscosity will attenuate the leak or help the seal???

 

You probably wouldn't see any noticeable difference.

 

I just found this in the "sticky" at the top "One of the Best Threads ever posted"...

I too find it confusing as hell if you read through everyone's opinions of what fluids to use in your manual transmission, when compared to what GM says to use... ie; GM recommends Dexron 3 (or 4 ATF).... and then others on here recommend GM Synchromesh Manual Trans. Fluid... and then should it be Synthetic Fluids or Non-Syn Fluids?... What is correct? and What is fact?

BTW my car is a 2000 M6, and I too hope to make the right decision in choosing my service replacement fluids.


HOPEFULLY this info here is reliable...

STICKY = "Manual transmissions -- Replacing the transmission fluid often helps shifting. Early transmissions have paper blocker ring that require Dexron III ATF compatible (usually organic) fluid because some synthetics will destroy the paper blocker rings and subsequently the transmission. Later transmissions, and all rebuilt transmissions, have Kevlar/carbon fiber parts that allow the use of synthetic fluids.

I believe the 1998 - 2000 transmissions have the paper blocker rings. The safe transmission fluids seem to be: GM Synchromesh PN #12345349, Honda ATF-Z1, Royal Purple Synchromax, Amsoil ATF, O’Reilly Dexron III ATF."


The following transmission fluids may be unsafe for early transmissions: Redline D4 ATF, Mobil 1 ATF, Royal Purple Max ATF.

http://forums.corvetteforum.com/c5-t...must-read.html
__________

 

Well, first I want to say thanks C66 for offering the deal on the Amsoil. In the end, I went with the Pennzoil because it was so readily available at my local Autozone. Here's what I did: after draining out the transmission, I wiped the joint of the case that houses 5th, 6th and reverse gears. It was that joint that was leaking. I cleaned it, thoroughly, with acetone and then applied a thin layer of Seal-All all along the bottom and half-way up the sides of the joint. Cleaned the old red sealant off the threads on the drain plug, wrapped it in teflon tape, and tightened it down. Then, I re-filled with the Pennzoil Synchromesh ( a little more than 3.5 quarts). I let the Seal-All cure for 24 hours, drove the car 10 miles, then checked the joint: no leaking! I know that eventually I'll have to remove the rear-end and re-seal the case, but I'm hoping my temporary 'fix' will let me do it at leisure this winter...

 

Watch out, here comes more disinformation...

I bought the Pennzoil Synchromesh and brought it to a local place to do the drain/fill just a few minutes ago. They didn't believe it was right and dug around on Pennzoil's website for a while. The shop owner found a tech support number on the site and called. The Pennzoil person he spoke to said not to use this in my '02 Z06. The shop then refused to put the Synchromesh in for me. They wanted to use Dexron III, but didn't have enough to do it, so they couldn't do anything at all. Now I'm stuck finding another shop that will put something in.

Yay! Total confusion... Grr.

 

I don't find this surprising. The spec was Dex III and I doubt any major company would say it is okay to another spec fluid as it would open them up to liability claims.

 

Well, I've put over 300 miles since I've applied the Seal-All and the leak seems to have disappeared. I've noticed no difference in the performance using the Pennzoil, but will probably drain it again and replace it with the Amsoil. The Pennzoil didn't cost much ($8.99/qt) and I figured that if the Seal-All didn't stop the leak, then I'd fill it with what was the easiest to procure. Now that I know the Seal-All works, I'll drain it and fill it with the proper viscosity fluid.

 

This is my question as well. I could not find DexIII anywhere, so I bought Mobil 1 Synthetic ATF "All vehicles". Have just put it in, but haven't lowered or driven the car yet. This is in a "later" T56...

 

No input on ^this^?

 

same here. i drained mine & pried the trans/diff apart then put a bead of black RTV on the mating surface from about the middle of each side down around the bottom. tightened it all back up & filled it with some O'Reilly Dexron ATF.

just put about a hundred miles on it yesterday with some pretty spirited mountain driving & the garage floor's still clean after sitting about a day & a half

 

Zebra - How were you able to reach/remove the top bolts that hold the trans' & diff' together? I didn't "pry" them apart in-situ and couldn't imagine how they could be separated at all without pulling them both out of the vehicle.