Transmission noise at idle

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Jan 6, 2012 | 11:32 PM

JLMICCA

Thread Starter

Racer

Joined: Sep 2008

Posts: 343

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From: Marietta GA

Transmission noise at idle

This is now correctly edited: I have a '71 roadster that was converted from an automatic to 4 speed (GM bellhousing and Muncie...surprisingly is otherwise numbers matching). The prior owner had the 4 speed Muncie rebuilt by "Mr. Muncie" here in Georgia. The problem is that there is a slight sound coming from the transmission in neutral only when the clutch is engaged (pedal up). With the clutch disengaged (pedal down), there in no sound in any gear. My service manual from '63 states that may be from a damaged clutch gear bearing in the 3 speed transmission. (Hope this clarifies the question.)

Any thoughts as to what is causing this? Given the transplant issue, can this occur due to incorrect runout clearance at the bell housing?

Last edited by JLMICCA; Jan 7, 2012 at 02:50 PM. Reason: unclear question

Jan 7, 2012 | 06:57 AM

7T1vette

Team Owner

Joined: Jan 2006

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From: Crossville TN

Bad throw-out bearing in the clutch fork.

Jan 7, 2012 | 12:08 PM

Steve2147

Pro

Joined: May 2011

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From: BC

Need to clear up our terminology first. The clutch is disengaged when the pedal is "in" meaning at the floor, engaged is all the way out with your foot off the pedal.

If the noise goes away with the clutch disengaged, pedal depressed, the problem is internal to the trans.

If it is only there with the pedal depressed it will be the release bearing or pilot brg (bushing).

It is highly unlikely to be the result of an out of concentric bellhousing. The most common symptom of that would be jumping out of high gear.

With the trans in neutral and clutch engaged (pedal up), the input shaft is turning, one bearing there, the cluster gear is turning, 2 sets of rollers on a shaft, and 1, 2 and 3 gears on the main shaft are spinning on the output shaft. Each of those rides on a bushing. The noise can be any one or more of those gears or bearings. Edit, there's also a set of rollers in the back end of the input shaft that the frt of the output shaft runs.

Steve g

Last edited by Steve2147; Jan 7, 2012 at 12:11 PM.

Jan 7, 2012 | 02:14 PM

bpassmore

Racer

Joined: Sep 2009

Posts: 437

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From: Alvin Texas

You may have a normal condition, The Muncie trans had an anti- rattle device on the counter gear. It consisted of a thin spring loaded gear that contacted the input shaft gear to prevent the "gear rattle" when the gears were not loaded, in idle with clutch depressed. Most replacement counter gears don't have it, most re-builders remove it. It was probably not installed during the rebuild. This device was a problem if the trans was used in hard usage,racing.

Jan 7, 2012 | 02:48 PM

JLMICCA

Thread Starter

Racer

Joined: Sep 2008

Posts: 343

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From: Marietta GA

Thanks for all of the replies. I should have been much clearer when I made the post. I originally posted, "The problem is that there is a slight sound coming from the transmission in neutral only when the clutch is disengaged. With the clutch in, there in no sound in any gear." I should have posted, "The problem is that there is a slight sound coming from the transmission in neutral only when the clutch is engaged (pedal up). With the clutch disengaged (pedal down), there in no sound in any gear." Hope that helps. I will edit the original post.

Jan 7, 2012 | 03:53 PM

bpassmore

Racer

Joined: Sep 2009

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From: Alvin Texas

When the clutch is engaged (Pedal up) and in neutral the main gear is turning the countershaft, with no load. The gears have a small amount if clearance or slack between them. This slack makes the rattling sound you are hearing. When in gear the slack is taken up because they are loaded so the slack is eliminated and so is the sound you hear. The reason the noise is not heard with the clutch in is the gears are not turning.

Last edited by bpassmore; Jan 7, 2012 at 03:56 PM.

Jan 7, 2012 | 10:58 PM

JLMICCA

Thread Starter

Racer

Joined: Sep 2008

Posts: 343

Likes: 50

From: Marietta GA

Thanks bpassmore. From that explanation, it would seem I could just leave well enough alone. Simply a nuisance sound?

Mar 9, 2013 | 06:41 PM

Red69

Racer

Joined: Dec 2002

Posts: 306

Likes: 1

From: N. Charleston SC

My 69 makes the same noise discribe in this thread... Trans in nuteral... cluch engaged (pedel out)... Car at idel... Sounds like roller bearing rolling arround! Transmission about 1000 miles on it since rebuild.

Is this bearing noise something that is normal for a muncie?

Does it indicate an internal problem?

Could it indicate low gear lube?

Will it get worse?

Thanks!