T56 Fluid PROBLEM/Question

**NastySS** · 05-20-2010, 07:45 AM

Hello all,

First of all, why the heck do the T-56's run Dextron III auto fluid instead of Gear Oil (like 75W-90) like every other manual trans I have owned? When I bought my 2001 SS new, I changed the trans fluid to Mobil 1 Dextron III. At the time, I did not know there was Synthetic in there already. There is nothing in the manual (that I saw) about changing the Trans Fluid at periodic intervals in the maintenance sections. I was not used to having to do this, as I have always owned a manual trans with gear oil in it. At about 70,000 miles after coming back from a 500 mile trip, my trans started making some unnerving noises, and I had some difficulty getting the shifter into gears. I immediately changed the trans fluid to Mobil 1 Dextron III again.

This oil change stopped most of the noise and the shift issues. I do know however, that some damage was done to the trans from not changing the oil sooner, although it does not seem to have gotten any worse since the oil change. If I take it past about 4 grand in 1st gear, it it hard to get it into second and will grind a little when I shift. If I go gently in first, it shifts fine into 2nd. It still makes a little noise in the first few gears, that I can only hear when I drive close to something that can reflect the sound back to me, for example a cement wall in the center of a roadway.

I am very conscientious about maintenance, I am actually very pissed at Chevy for not mentioning the need to change the Dextron III Manual Trans fluid. If I did it earlier, I would have not damaged my T-56! Any comments about my issue would be appreciated. Is there a better fluid for me to be using than Mobil 1, as I plan to change it again in the next week or so. Although it has only been about 6,000 miles since my last change, I know there is still a little of the beat up fluid still in there from the last change, and I want it all out.

Thanks for reading,

Tom

**km346** · 05-20-2010, 09:38 AM

FWIW ATF is the recommended fill for a lot of manual transmissions. Both ford and Chevy manual transmissions that ive owned had ATF factory fill.

That being said Ive always run a non synthetic DexIII in my t-56. Ive read that synthetics don't mix well with the paper blocker rings and can cause problems. GM states that Dex VI (a synthetic) should not be used in the t-56. The TSB that i have read says to use GM P/N 88861800 manual transmission and transfer case fluid. I would try draining out that mobil 1 and filling it with the GM fluid or any non synthetic dexIII. But by the sound of it, your transmission may need a rebuild.

**km346** · 05-20-2010, 09:44 AM

Found the TSB figured id post it up.

MANUAL TRANSMISSIONS AND TRANSFER CASES
The content of this bulletin does not apply to manual transmissions or transfer cases. Any vehicle that previously required DEXRON®-III for a manual transmission or transfer case should now use P/N 88861800. This fluid is labeled Manual Transmission and Transfer Case Fluid.

Recommendation/Instructions:

Manual Transmission fluid part number 88861800 U.S. (88861801 Canada) is currently available through GMSPO. Current and past model vehicles listed above with either a manual transmission or transfer case that REQUIRE Dexron III should use the above listed manual transmission fluid. This fluid is a direct replacement for Dexron III in manual transmissions and transfer cases. DO NOT use Dexron VI in place of the manual transmission fluid in any manual transmissions or transfer cases as a failure may result.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

**Cutlass** · 05-20-2010, 06:03 PM

yep I've heard the T56 is not compatible with synthetic ATF, also.

**NastySS** · 05-21-2010, 07:32 AM

I just called Mobil 1, and obviously they tell a different story. They say their Synthethic (By the way, has no mention of DexIII on the bottle) is perfect for the T-56, and highly recommends it. The guy I spoke to says he has used it in several T-56 trannies, and he also said Mobil 1 provides their Synthetic for Corvette T-56 Trannies. This is of course, what I would have expected him to say.

He did say he recommends it to be changed every 30,000 miles, and is shocked the GM says the DEXIII "Does not need to be changed" like the Factory Car Manual indicates on page 6-24.

**shady milkman** · 05-21-2010, 07:41 AM

Originally Posted by NastySS

I just called Mobil 1, and obviously they tell a different story. They say their Synthethic (By the way, has no mention of DexIII on the bottle) is perfect for the T-56, and highly recommends it. The guy I spoke to says he has used it in several T-56 trannies, and he also said Mobil 1 provides their Synthetic for Corvette T-56 Trannies. This is of course, what I would have expected him to say.

He did say he recommends it to be changed every 30,000 miles, and is shocked the GM says the DEXIII "Does not need to be changed" like the Factory Car Manual indicates on page 6-24.

this is tremec's response from 08'

-Dexron III is THE most highly recommended all round choice, specifically Texaco/Havoline brand.

-Dexron VI- Still being evaluated and tested, NOT recommended for the T-56 at this time and has caused issues so far in preliminary evaluation.

-Syncromesh- Not really recommended, but can be used in high temp high stress applications(drag racing, very hot climates etc.) since it is thicker than dexron III for some added protection.

-Synthetic- Mobil 1 is the only brand advisable to use and tested by Tremec, can cause shifting issues in colder climates.

**shady milkman** · 05-21-2010, 07:42 AM

however i am big on just running no synth for transmissions anywho so id go dexIII no synth and be good.

**shady milkman** · 05-21-2010, 07:43 AM

and i hate mobil 1

**NastySS** · 06-06-2010, 06:17 AM

Hi ,

Just wanted to update everyone. Three days ago, I drained out the Mobil 1 Synthetic Dexron III, and put in Valvoline Max-Life NON-Synthetic DexIII. When I drove the car after getting it off the lift, I noticed an IMMEDIATE POSITIVE DIFFERENCE. The slight noises that the trans made in 1st and 2nd gears, reduced about 50% immediately. Since the few days I have been driving the car, it seems to have gotten even better, and the noises are nearly imposible to hear now. I can now safely say that putting Synthetic DexIII in your T-56, IS NOT A GOOD IDEA, as so many of you have stated.

Thanks all of you who provided input and your expertise! You all just may have saved my tranny! I am taking a 1000 mile road trip next week, so that will be the deciding factor, but I am very optimistic. Thanks again!

Tom

**Cutlass** · 06-06-2010, 09:20 AM

Good info for future reference!! Thank you for the update. I'm not even sure whats in mine and now I think I wanna drain and refill it. Glad it seems to be fixed for you

**35th-ANV-SS** · 06-06-2010, 12:02 PM

Definitely good info. Thanks for sharing your update.

**NastySS** · 06-07-2010, 04:39 AM

Hey, no problem. Glad to be of help as many of you have been to me!

**Homer J** · 06-07-2010, 05:30 AM

Originally Posted by Cutlass

Good info for future reference!! Thank you for the update. I'm not even sure whats in mine and now I think I wanna drain and refill it. Glad it seems to be fixed for you

how do you drain the fluid?

**NastySS** · 06-07-2010, 05:51 AM

There are fill and drain plugs on the side of the transmission. They accept the square end of a 3/8" ratchet or a 3/8" ratchet with a 3/8" extension on it. The fill plug is about half way up the side of the trans on the Driver Side. The drain plug is at the bottom and side of the trans on the passenger side (At least on my 2001 SS), but very close to the rear of the trans. You just remove the drain plug, and let it drain out, hopefully into a container you will use to recycle the fluid. The T-56 takes 4 Quarts to refill.

The 2 plugs are nearly impossible to see unless the car is jacked up, or up on a lift. To refill the trans, you will need some sort of pump to get the oil up into the fill hole, as there is no room above the fill hole to "Gravity" fill it.

Good Luck,

Tom

PS...Note that this is the process for a 6-speed manual T-56 Trans. If you have an Automatic transmission, the process will be much different.

**Cutlass** · 06-16-2010, 06:38 PM

I changed my T56 fluid out 5 days ago or so. It may be all in my head but it sure seems to shift a lot smoother. Less notchy then before.

**NastySS** · 06-17-2010, 05:28 AM

Hey Cutlass,

How many miles are on your T-56, and is this your first trans oil change?

No,,,,it is not in your head!!! The fluid DOES need to be changed at intervals NOT DIVULGED by Chevrolet. Changing it does positively affect the performance of your T-56!

I will be writing a letter to Chevrolet, expressing my distain at their statement on page 6-24 of the Manual that states "The manual transmission fluid does NOT need to be changed". This is total BULL, and because I believed them, I have a partially damaged transmission. I will be sending the letter to the office of the CEO, and I will be respectfully requesting a new transmission. Now, I do not expect to get one, but it sure can't hurt to see what they have to say for themselves.

It is true that the latest fluid change to a Non-synthetic Dex III has greatly improved the shifting and reduced noise. If I had done it sooner than 76,000 miles, I would most likely have no damage to the trans at all.

**Cutlass** · 06-17-2010, 05:23 PM

I have 99,000 miles but only owned it since 86,000. This is the first time I've changed the fluid but I remember the previous owner telling me he changed it. I believe him because the fluid that came out was bright red and looked fairly good. Knowing the previous owner, it may have been synthetic ATF in there.

**Mr. Luos** · 06-17-2010, 05:29 PM

NEVER drain and just fill with 4 quarts. This can happen to those that fill at the shifter (like myself).

Make sure you fill with the fill plug open. Draining it never releases all 4 quarts (although it comes close). Fill until the plug starts draining. Stop.

I use Mobil 1 in mine. If there are 8-10 second T56 cars running it without issue, so can I. Of course, those transmissions are upgraded, so....take it as you will.

**km346** · 06-17-2010, 06:53 PM

Originally Posted by Mr. Luos

NEVER drain and just fill with 4 quarts. This can happen to those that fill at the shifter (like myself).

Make sure you fill with the fill plug open. Draining it never releases all 4 quarts (although it comes close). Fill until the plug starts draining. Stop.

I use Mobil 1 in mine. If there are 8-10 second T56 cars running it without issue, so can I. Of course, those transmissions are upgraded, so....take it as you will.

Thats not exactly the best logic...
The problem seems to be the paper blocker rings swelling due to the synthetic fluid and causing shifting issues. As you mentioned Im sure 8-10 second cars have been upgraded to carbon blockers. Whatever works for ya its your trans-mixer not mine.