F23 Transmission Rattle

Grayson

Active Member
Hey everyone,
I got my Goblin driving yesterday and it all runs great! However I am getting a weird rattle for the transmission when I let the clutch out all the way. This happens in both neutral and in gear. I figured I would make a thread as I didn't really find a thread that might address this issue.

Before I take my trans back off I wanted to see if anyone else had any ideas of what it might be so here's the info.

Donor was a 2007 SS/SC and we swapped the F35 trans for a brand new F23 trans from DF. This came with a brand new throwout bearing as well.

From my research everyone says that it is the intermediate shaft bearing or the throwout bearing that would cause that rattle noise because it only happens when the clutch is all the way out. However, I have a hard time believing that either one of these things would be it because it is a brand new trans from DF.

It seems like it might be the clutch but I didn't have any issues with it before we tore the car down.

We have bled the clutch and brakes multiple times. My first thought is there is a tiny amount of air in the system. I believe I bled it correctly but is there a specific bleed procedure for the clutch that may be causing the issue?

Any advice is welcome, especially if its something I can try before taking my trans off again.... I have a video of the rattle that I can post once I get it off my camera if that is helpful to anyone is diagnosis.

Grayson - Goblin #488 SS/SC F23 manual trans
 

Gtstorey

Goblin Guru
Air won't really have any affect when the clutch is engaged (pedal is released).

Did you check the airgap on the throwout bearing?
 

Grayson

Active Member
Air won't really have any affect when the clutch is engaged (pedal is released).

Did you check the airgap on the throwout bearing?
I think we did. It matched the old trans when we took it out. That would definitely be something we check if we remove the transmission.

Would a rattle suggest too much air gap or too little?
 

Gtstorey

Goblin Guru
Not sure how matching old and new can matter if you changed to a completely different transmission type. You have to measure it to account for all of the variables of flywheel, clutch, throwout bearing and transmission.
 

Grayson

Active Member
Not sure how matching old and new can matter if you changed to a completely different transmission type. You have to measure it to account for all of the variables of flywheel, clutch, throwout bearing and transmission.
That would make sense and probably the issue. We will check that. Again, not entirely sure if we matched it to the old or if we measured based off the ZZP video instructions.
 

Rauq

Goblin Guru
There was a TSB on early F23 vehicles that overfilling the fluid level would reduce or eliminate certain types of noise the F23 might make. 2.6qts instead of of the 1.8qts called for, and requires filling through the vent cap on the top instead of the level fill port on the side. I just used a Dex VI fluid as it's supposed to supersede all Dex III applications, which the F23 originally called for. I put in two quarts and most of a third like this and haven't had any weird noises from my F23, but it was a 60k mile used unit when I put it in.

While I'm sure GM wouldn't say there's a break in period on a new trans, having worked in similar auto manufacturing, there may be an NVH reduction after putting a few miles on new gears and putting some new fluid in it. Might be worth doing a drain and (over)fill to see if that helps before you try pulling the trans.

Edit: additional input, in my opinion the absolute best way to bleed a Cobalt clutch is with a pressure bleeder. The line from the master to the bleeder can be done super easily. Then do the pedal down - crack bleeder open - close bleeder - pedal up to bleed the portion from the bleeder to the slave.

What clutch and flywheel are you using?
 
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Grayson

Active Member
Ok, so someone sent me a forum link for fieros that use the same trans. It seems to be just a common thing with the F23s.
Does anyone else who runs an F23 on their Goblin also have this sound?

 

Grayson

Active Member
There was a TSB on early F23 vehicles that overfilling the fluid level would reduce or eliminate certain types of noise the F23 might make. 2.6qts instead of of the 1.8qts called for, and requires filling through the vent cap on the top instead of the level fill port on the side. I just used a Dex VI fluid as it's supposed to supersede all Dex III applications, which the F23 originally called for. I put in two quarts and most of a third like this and haven't had any weird noises from my F23, but it was a 60k mile used unit when I put it in.

While I'm sure GM wouldn't say there's a break in period on a new trans, having worked in similar auto manufacturing, there may be an NVH reduction after putting a few miles on new gears and putting some new fluid in it. Might be worth doing a drain and (over)fill to see if that helps before you try pulling the trans.
I might try that. I haven't looked yet but where is the drain for the fluid on the F23. Also, seems to be some deliberation on what fluid to use in the trans to reduced or eliminate the noise fully.

Did you have a rattle when you installed your F23 at first or did you just start with it overfilled?
 

Rauq

Goblin Guru
I think my edit missed your reply. Additional input, in my opinion the absolute best way to bleed a Cobalt clutch is with a pressure bleeder. The line from the master to the bleeder can be done super easily. Then do the pedal down - crack bleeder open - close bleeder - pedal up to bleed the portion from the bleeder to the slave.

What clutch and flywheel are you using? I'm using a ZZP aluminum flywheel and South Bend Stage 3 clutch and pressure plate. OEM F23 slave cylinder. It does chatter a little, and the trans does seem to rattle a little if the engine is being lugged, but nothing I would think is abnormal or atypical.

I might try that. I haven't looked yet but where is the drain for the fluid on the F23. Also, seems to be some deliberation on what fluid to use in the trans to reduced or eliminate the noise fully.
There's a drain plug on the bottom. I think I had to grind down a hex key to get it to fit in with the subframe right next to it. There's also a fill plug on the side of the trans, don't use that one. To overfill you have to go through the vent cap on the top.
Did you have a rattle when you installed your F23 at first or did you just start with it overfilled?
I never noticed a rattle. I did overfill it from the start. I had a pretty decent fluid leak upon the first install from a bad input shaft seal on a brand new slave cylinder, so the fluid level did drop at some point in time, but I still never noticed a noise. I've had 2.6 quarts in it since I fixed that fluid leak.
 

Grayson

Active Member
I think my edit missed your reply. Additional input, in my opinion the absolute best way to bleed a Cobalt clutch is with a pressure bleeder. The line from the master to the bleeder can be done super easily. Then do the pedal down - crack bleeder open - close bleeder - pedal up to bleed the portion from the bleeder to the slave.

What clutch and flywheel are you using? I'm using a ZZP aluminum flywheel and South Bend Stage 3 clutch and pressure plate. OEM F23 slave cylinder. It does chatter a little, and the trans does seem to rattle a little if the engine is being lugged, but nothing I would think is abnormal or atypical.


There's a drain plug on the bottom. I think I had to grind down a hex key to get it to fit in with the subframe right next to it. There's also a fill plug on the side of the trans, don't use that one. To overfill you have to go through the vent cap on the top.

I never noticed a rattle. I did overfill it from the start. I had a pretty decent fluid leak upon the first install from a bad input shaft seal on a brand new slave cylinder, so the fluid level did drop at some point in time, but I still never noticed a noise. I've had 2.6 quarts in it since I fixed that fluid leak.
I'm not entirely sure what Clutch im running as it was on my donor before hand. I'm going to try and drain and over fill the fluid and see if that works. If it still chatters then I will probably pull my trans and remeasure air gaps and inspect clutch.

Is there a specific trans fluid I should use? Seems like the fiero people are very opinionated about it. There is an autozone down the street from me so preferably something that I can pick up from there.
 

Stretch2126

Well-Known Member
I have an fx400 clutch and aluminum flywheel and it makes noise. Especially chattery when it’s real hot out on engine decel.
 

Rauq

Goblin Guru
I know mine definitely does. Noisier after the LSD install too it seems.
I've also only run my F23 with an LSD so I've not heard any comparison.

I'd note too that you're going to hear more engine and transmission noises in a Goblin than in something else with a hood and windshield and insulated firewall. It's important to try to assess what's a normal noise and what's not. But if you're convinced what you're hearing isn't normal, I'm not going to tell you that it is.
 

Grayson

Active Member
I've also only run my F23 with an LSD so I've not heard any comparison.

I'd note too that you're going to hear more engine and transmission noises in a Goblin than in something else with a hood and windshield and insulated firewall. It's important to try to assess what's a normal noise and what's not. But if you're convinced what you're hearing isn't normal, I'm not going to tell you that it is.
Here is a video, listen at the end of the video when I pull my foot off the clutch and start getting out of the car you can hear the rattle.

 

Gtstorey

Goblin Guru
As usual, I can't tell anything about a noise from a video. I hear what you are talking about, but hard to judge what it might be. But it seems to be only setting still with it in neutral and clutch engaged. Might still be a throwout bearing dragging.
 

Grayson

Active Member
I think my edit missed your reply. Additional input, in my opinion the absolute best way to bleed a Cobalt clutch is with a pressure bleeder. The line from the master to the bleeder can be done super easily. Then do the pedal down - crack bleeder open - close bleeder - pedal up to bleed the portion from the bleeder to the slave.

What clutch and flywheel are you using? I'm using a ZZP aluminum flywheel and South Bend Stage 3 clutch and pressure plate. OEM F23 slave cylinder. It does chatter a little, and the trans does seem to rattle a little if the engine is being lugged, but nothing I would think is abnormal or atypical.


There's a drain plug on the bottom. I think I had to grind down a hex key to get it to fit in with the subframe right next to it. There's also a fill plug on the side of the trans, don't use that one. To overfill you have to go through the vent cap on the top.

I never noticed a rattle. I did overfill it from the start. I had a pretty decent fluid leak upon the first install from a bad input shaft seal on a brand new slave cylinder, so the fluid level did drop at some point in time, but I still never noticed a noise. I've had 2.6 quarts in it since I fixed that fluid leak.
What fluid did you use when you re filled your trans? Im about to go buy fluid.
 
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