F23 Transmission Rattle

[Rauq]

ZZP recommends Redline MT-90 for the F35. most of what I've read says the F23 doesn't really care, but most say ATF over gear oil (which is thicker than ATF). I did find someone talking about overfilling with a specific gear oil on a J-body circle track application, but I can't find it again.

 

[D&dgoblin69]

I get a rattle in 5th gear iam using gear oil 75w. So atf in a manual transmission?

 

[Rauq]

My '06 Cobalt owners manual says DexIII for the F23. DexVI is an approved replacement for all DexIII applications. I can't say 75W is wrong or needs to be replaced or that ATF will fix a rattle, but if you want to try it that doesn't seem like a bad idea to me. If you're going that route, do try 2.6qts through the vent plug on the top instead of 1.8qts through the side fill plug.

 

[Dsteinhorst]

Couple thoughts to add to this.
I consider Pennzoil synchromesh a good fluid and have used on several transmissions over time. It helped wake up my notchy F23.

If you go above factory fill level, you may get leakage out the vent during hard cornering. I lost fluid at a couple autocrosses until I drained to the standard fill line. I had maybe an extra pint over factory.

 

[CaptFrank2001]

Just refilled my Trans yesterday. Valvoline DEXRON VI.

 

[Scott #321]

Mine rattles and made me think something is wrong in my new F23. No woories though been holding fine. I use BG synchromesh and have added 10%Lucas to thicken it a little. anything over the standard fill line like the TSB states to help with rattle caused fluid leakage into the clutch and eventual slipping.

 

[Rauq]

If you're leaking fluid with a 2.6qt fill, you probably have a leak like I did. There's two seals that can leak on the clutch master cylinder, and if you opened the trans up, this plug could theoretically leak as well.

I don't see how a 2.6 qt fill would cause a leak otherwise.

 

[CaptFrank2001]

I Believe the F23 capacity is 1.8 Quarts. I confirmed this by fully draining then adding 2 quarts of Dexron VI. I then removed the upper fill limit drain plug and app. 2 Oz. drained out.

I read this: "Overfilling the Getrag F23 transmission can lead to unusual noises, potentially including rattling or grinding, as the excess fluid can create air pockets and reduce lubrication effectiveness."

And this: "Potential Problems with Overfilling:

• Foaming: Excess oil can create air pockets, causing the oil to foam and reducing its ability to lubricate properly.
  
  • Noise: Foaming oil can lead to unusual noises, including knocking, tapping, or ticking sounds.
    
    
  • Grinding: While overfilling may initially mask the rattle, some owners have reported that it can lead to grinding noises in third and fourth gears.

 

[Rauq]

Generally speaking, yes, overfilling isn't a good idea, but there's a GM TSB for F23 noise, and they specifically recommend a 2.6qt fill to mitigate. They also mention that overfilling beyond 2.6qts can lead to fluid leaks out of the breather/fill port, which is interesting in that the caution isn't with regards to leaks inside the bellhousing.

I'm not sure where you're quoting from, but for what it's worth I've never come across suggestions that 2.6qts causes more problems than it solves.

If you're getting fluid leaks into the bellhousing with 2.6qts of fluid and not at 1.8qts, and your input shaft seal and throwout bearing face seal are in good condition, then that's a good data point for folks to learn from. Sorry I can't be of more help.

 

[Scott #321]

Generally speaking, yes, overfilling isn't a good idea, but there's a GM TSB for F23 noise, and they specifically recommend a 2.6qt fill to mitigate. They also mention that overfilling beyond 2.6qts can lead to fluid leaks out of the breather/fill port, which is interesting in that the caution isn't with regards to leaks inside the bellhousing.

I'm not sure where you're quoting from, but for what it's worth I've never come across suggestions that 2.6qts causes more problems than it solves.

If you're getting fluid leaks into the bellhousing with 2.6qts of fluid and not at 1.8qts, and your input shaft seal and throwout bearing face seal are in good condition, then that's a good data point for folks to learn from. Sorry I can't be of more help.

Mine leaked around the TO bearing seal but the seal looked fine on when I inspected it. Synchromesh is very thin maybe even thinner then DexIII. Staying with standard fill and adding the 10% Lucas solved my problem.

 

[Desert Sasqwatch]

Overfill on any gearbox will create foam, which creates excess heat and pressure, that leads to shortened oil life and reduced lubrication. The GM bandaid bulletin was not a fix and it guaranteed they will be seeing that gearbox for continued revenue after it starts to fail. Some gearboxes are just noisy by default (or design) and doesn't necessarily mean there is something wrong with it. The transmission in the Goblin sits out in the open and the 'normal' noises it makes are more apparent. Most competition gearboxes make noises that are wholly unacceptable to the general public. My $0.02.

 

[Rauq]

Overfill on any gearbox will create foam, which creates excess heat and pressure, that leads to shortened oil life and reduced lubrication. The GM bandaid bulletin was not a fix and it guaranteed they will be seeing that gearbox for continued revenue after it starts to fail.

2.6 quarts is not necessarily overfilled, but is higher than the original fill spec. I manufactured transfer cases for a number of years, and the fill spec was enough fluid to get the job done. You could have added 30-40% more fluid in those units without worrying about frothing. Like many other LSJs, Goblins, and tracked cars in general, I run an extra quart of oil. That doesn't shorten oil life, reduce lubrication, or guarantee that a motor provides continuous revenue for the manufacturer, either.

 

[CaptFrank2001]

Generally speaking, yes, overfilling isn't a good idea, but there's a GM TSB for F23 noise, and they specifically recommend a 2.6qt fill to mitigate. They also mention that overfilling beyond 2.6qts can lead to fluid leaks out of the breather/fill port, which is interesting in that the caution isn't with regards to leaks inside the bellhousing.

I'm not sure where you're quoting from, but for what it's worth I've never come across suggestions that 2.6qts causes more problems than it solves.

If you're getting fluid leaks into the bellhousing with 2.6qts of fluid and not at 1.8qts, and your input shaft seal and throwout bearing face seal are in good condition, then that's a good data point for folks to learn from. Sorry I can't be of more help.

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Did I miss something? I see no mention of F23 in the GM TSB.

 

[Rauq]

RPO M86 and M94 = F23

 

[ah.b.normal]

There is a lot of insulation in a Cobalt forward of the driver! And as mentioned, none between a Goblin driver and the trans. In GM's crusade of ending NVH it could be an acceptable noise?, but certainly worthy of keeping an ear on! Remember also, a Goblin uses solid motor mounts as well.

 

[CaptFrank2001]

RPO M86 and M94 = F23

That GM TSB refers to the F23 as used in the Pontiac Sunfire and Grand Am. It even says that in the TSB under "models". The M86 and M94 are actually GETRAG axle codes. Not sure any of that TSB applies to the F23 as used in the Cobalt. But it looks like we are in agreement that overfilling beyond 1.8 Qts is a bad idea.

 

[Rauq]

But it looks like we are in agreement that overfilling beyond 1.8 Qts is a bad idea.

Agree to disagree...

And for the record, F23 is the Getrag axle code. M86 and M94 are GM RPO codes. I think M94 is the pre-Ecotec J-body F23. The '08 Cobalt LS my F23 came out of had the M86 RPO code. If it'd come out of a Saturn Vue, it'd still be an F23 with a 4.41 ratio and MG3 RPO code.