Clutch shudder

[Baker7888]

Hey guys, 78 Malibu, carb LT1 with T-10 four speed, G body mechanical clutch kit. Using a 10.5” flywheel for an 87 Camaro and a 10 spline clutch for a 63 Vette (what the trans was originally in)

I have a decent little clutch shudder from a dead stop that I was hoping would work itself out but hasn’t. Definitely worse if there is any incline. The engangement has also been somewhat difficult to pinpoint, partly cause I am fighting an off idle bog (edelbrock 750) and thinking the cheap G body clutch pedal and linkage kit may not be perfect geometry (fork possibly). I do have it adjusted correctly.

Anyhow my main question is lately I have noticed what sounds like an engine knock when the car is idling low (usually when it’s cold) however when i push the clutch pedal in the sound goes away. The car runs and drives fine, has good power, so I would rather not tear into it during the last nice stretch of weather we are having here in the fall. Just thought I would get some thoughts and feedback ahead of time what may be going on. The transmission also likes to kick out of 2nd gear when not under a load and it leaks. And I’m also always looking for 5th gear. So needless to say I am not a huge fan of this transmission however I would like to run the setup I have. I did have it looked at before I installed it (was clean and supposedly rebuilt) and the transmission shop said it looked great and “whoever rebuilt it did a great job”. I know these things are kind of leakers to begin with….My main concern is the poor driveability due to the clutch shuddering and the embarassing light knocking noise when it is idling around 5-800 rpms. Thoughts???

 

[UC645]

If the knock goes away when you depress the clutch pedal, that sounds like the engine’s thrust bearing.

I wouldn’t be running that engine for much longer if that’s the case.

As far as shudder, all down to the type of clutch. As per your other thread from May you went with a “stage 2” from Zoom. Not sure how much I trust that nomenclature, as upgrade stages are just marketing jargon. Clutch type- such as full face or paddles and type of friction material have a lot to do with chatter or shudder when starting out. More aggressive materials like ceramic will chatter on the street, but aggressively grab when you dump the clutch. So if your clutch is of that variety, that’s likely the culprit of your shudder.

Here’s a couple of links from Summit to clarify:

How do I choose the right clutch?

help.summitracing.com

What are the different types of clutch discs?

help.summitracing.com

 

[Baker7888]

If the knock goes away when you depress the clutch pedal, that sounds like the engine’s thrust bearing.

I wouldn’t be running that engine for much longer if that’s the case.

As far as shudder, all down to the type of clutch. As per your other thread from May you went with a “stage 2” from Zoom. Not sure how much I trust that nomenclature, as upgrade stages are just marketing jargon. Clutch type- such as full face or paddles and type of friction material have a lot to do with chatter or shudder when starting out. More aggressive materials like ceramic will chatter on the street, but aggressively grab when you dump the clutch. So if your clutch is of that variety, that’s likely the culprit of your shudder.

Here’s a couple of links from Summit to clarify:

How do I choose the right clutch?

help.summitracing.com

What are the different types of clutch discs?

help.summitracing.com

Thank you. I agree, it is marketed as a “stage 2” clutch but looks pretty stock to me. What causes the thrust bearing to shudder? It was new upon install is actually a bronze bushing, not a bearing

 

[Texas82GP]

You're referring to the pilot bushing. The thrust bearing is part of the rear main bearing.

Any chance the knocking you are hearing is the throwout bearing contacting the pressure plate forks when the clutch is disengaged?

 

[Baker7888]

You're referring to the pilot bushing. The thrust bearing is part of the rear main bearing.

Any chance the knocking you are hearing is the throwout bearing contacting the pressure plate forks when the clutch is disengaged?

Very well could be. And knock may be the wrong word. But its a lightly audible noise below 800 rpm, and pushing clutch in makes it disappear. To the above, how would I determine this?

 

[Texas82GP]

Very well could be. And knock may be the wrong word. But its a lightly audible noise below 800 rpm, and pushing clutch in makes it disappear. To the above, how would I determine this?

Remove the clutch inspection cover and visually verify that the throwout (clutch release) bearing isn't touching the pressure plate fingers when the clutch pedal is in the full up position. The engine doesn't need to be running for this inspection.

The purpose of the spring that pulls forward on the clutch fork is to ensure that the throwout bearing doesn't touch the pressure plate fingers when the clutch pedal isn't pushed in.

If the throwout bearing is touching the fingers on the pressure plate while the clutch pedal is all the way up, then the throwout bearing is 'running' all the time and will suffer a short life. The clutch linkage is normally adjusted to prevent this but it is possible this is your problem, and is easy to check. If the throwout bearing is only lightly contacting the pressure plate fingers, it could be bouncing on and off of them and make a knocking sound.

 

[Baker7888]

Remove the clutch inspection cover and visually verify that the throwout (clutch release) bearing isn't touching the pressure plate fingers when the clutch pedal is in the full up position. The engine doesn't need to be running for this inspection.

The purpose of the spring that pulls forward on the clutch fork is to ensure that the throwout bearing doesn't touch the pressure plate fingers when the clutch pedal isn't pushed in.

If the throwout bearing is touching the fingers on the pressure plate while the clutch pedal is all the way up, then the throwout bearing is 'running' all the time and will suffer a short life. The clutch linkage is normally adjusted to prevent this but it is possible this is your problem, and is easy to check. If the throwout bearing is only lightly contacting the pressure plate fingers, it could be bouncing on and off of them and make a knocking sound.

Well, that answer deserves a like for sure. I played with adjustment early on and thought i was just looking for a certain amount of free play at the pedal. I will definitely check this weekend. I have some bigger accelerator pump nozzles coming as well.

Would a stiffer spring at the fork help this?

 

[Built6spdMCSS]

My SS has clutch chatter..which is perfectly normal for the type of clutch I have. Probably the same thing you have. Some do it, some don't.

Very light chattering noise while idling in neutral. Slight push on the pedal and it goes away.

 

[Baker7888]

My SS has clutch chatter..which is perfectly normal for the type of clutch I have. Probably the same thing you have. Some do it, some don't.

Very light chattering noise while idling in neutral. Slight push on the pedal and it goes away.

Hmm. Well that had been my suspicion all along. Didnt bother me until a bystander thought it was engine knock. Kind of embarrassing at the moment. I guess i’ll look to see if the throwout has contact and if not i might move on. I do want to pull the transmission at some point but can also live with it as is.

 

[Texas82GP]

Well, that answer deserves a like for sure. I played with adjustment early on and thought i was just looking for a certain amount of free play at the pedal. I will definitely check this weekend. I have some bigger accelerator pump nozzles coming as well.

Would a stiffer spring at the fork help this?

I wouldn't think so, unless if the spring you are using is substantially softer than stock. You want to be sure the throwout bearing isn't contacting the pressure plate fingers when the pedal is all the way up or it won't last long. The throwout bearing is meant to "run" only when the pedal is depressed. If it's running all the time, it will wear out very quickly and will start screaming. Then you're pulling the transmission to replace the throwout bearing.

Regarding the leaks....Those old 4-speeds are pretty easy to work on. No internal disassembly is required to address leaks. Make sure your speedometer drive isn't leaking. Beyond that, it's just gaskets and seals. Also thread sealant (not RTV) is advisable on the bolts that go right into the case where the oil is present.

Are you sure it's the transmission that is leaking? Oil on the clutch disk can cause chatter.