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Old 09-11-2020, 09:50 AM   #1
some mech 3
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Default Loud Noise when car decellerates while i n first and second gears

This is a follow-up to a Dec 12 post titled Transmission Assembly. To identify the metal-banging noise I have rebuilt the transmission and put in a new U-Joint, clutch, and pressure plate. These did not remove the noise. The noise is a continuous banging until I push down the clutch pedal. In ordinary driving the car runs beautifully. I welcome your insights. Thank you.
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Old 09-11-2020, 02:07 PM   #2
Floats
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Default Re: Loud Noise when car decellerates while i n first and second gears

Mech 3,
I canít help, but I believe I have a similar problem. I think it is the crankshaft moving forward when the inertia of the car is driving the engine. Ie gearing down and using the engine to slow down. I believe the drive train was not designed for this Ďabuseí
The crankís fore and aft movement specs are just a few thou.
Furthermore, I believe poor restoration/babbeting and modern driving techniques( gearing down in order to slow down) does not bode well on the crank thrust washers/supports.
I could be mistaken and will let you know if and when I have had the opportunity to drop my oil pan.
Honestly, I think that is the noise you are referring to.
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Old 09-11-2020, 05:17 PM   #3
some mech 3
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Default Re: Loud Noise when car decellerates while i n first and second gears

Floats: I like your reasoning. Clearly, it's a situation of inertia of the car in opposition to the crankshaft with all its moving parts. But what is colliding to make the noise? How do I correct it? Thanks.
Sam
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Old 09-12-2020, 01:08 AM   #4
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Default Re: Loud Noise when car decellerates while i n first and second gears

If the noise is the crank moving back and forth the sound should change if you just hold the clutch pedal down a little keeping the throw out bearing against the pressure plate.
Some years ago a guy was installing a rebuilt engine in a ‘30 roadster and used a flywheel bolt so long that it broke piece off the rear main cap.
Since the pan was on the engine he didn’t notice the broke main.
When he drove the car the oil poured out.
So I had another cap rebabbited by guessing how the thrust would turn out.
Well it came out to .032” of back and forth play in the crank but we bolted the pan back on and they’ve been driving it ever since. About 20 years.
Still no leaks and no noise.
I would first look for a U joint problem. But it has a new one? Hmm.
Loose flywheel?
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Old 09-12-2020, 05:45 AM   #5
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Default Re: Loud Noise when car decellerates while i n first and second gears

Thanks Aaron,
Iíll try that.
However, I recently removed the pan in order to check the shims on the mains and also to confirm the crank end play. The end play was way out and I decided to have the engine redone but have not gotten around to it.
I will try the clutch trick.
Mech 3,
Yep, if I remember correctly the crank moves back under power and forwards under engine braking. The limit is very little, just a few thou. Mine moves quite a bit, I did measure it, but decided to redo the engine and promptly forgot the exact measurement, but it was a few mm. I have no idea who touches what in order to make the noise.
Will let you know when I find it, but I don't know when Iíll get there.
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Chris
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Old 09-12-2020, 08:28 AM   #6
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Default Re: Loud Noise when car decellerates while i n first and second gears

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Chris and Aaron: I'm going to try the keeping-the throw out bearing pressing on the pressure plate. Also, I neglected to say the engine has been rebuilt and has less than 100 miles on it.
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Old 09-13-2020, 12:51 PM   #7
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Default Re: Loud Noise when car decellerates while i n first and second gears

I'm just throwing this out there for something to think about; Could your noise be coming from the drive shaft bearing located at the front of the torque tube just aft of the speedo gear. If bad it could cause the u-joint and drive shaft to whip on deceleration. around. Not something that is checked often.
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Old 09-13-2020, 05:57 PM   #8
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Default Re: Loud Noise when car decellerates while i n first and second gears

I had a noise somewhat like and found that after thirty years my flywheel had worked loose,took a while to find it you may want to give it a thought good luck
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Old 09-14-2020, 08:36 AM   #9
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Default Re: Loud Noise when car decellerates while i n first and second gears

Woody: I don't think it's the flywheel because the car drives very well when not decelerating. Thanks.
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Old 09-14-2020, 08:49 AM   #10
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Default Re: Loud Noise when car decellerates while i n first and second gears

Ruth: I think your suggestion is quite possible. When I had the rear end and the transmission out of the car I checked the rotation without noise, and I never thought of the torque tube bearing. To all of you contributors: we all think this is a unique and puzzling noise problem in that the car runs very well except when I decelerate. The easy solution is not to decelerate while in first and second gears. I don't need to do this except when going down a very steep hill. Thanks.
Sam
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Old 09-14-2020, 08:53 AM   #11
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Default Re: Loud Noise when car decellerates while i n first and second gears

To all of you: Keep the suggestions coming.
Sam
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Old 09-14-2020, 11:02 AM   #12
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Default Re: Loud Noise when car decellerates while i n first and second gears

Decelerating is generally when the power train is unloaded and starts to push back the other way due to engine braking. Any thrust loading in the transmission changes from thrusting some aft to thrusting some forward. If it doesn't make the noise in high gear then that gives an indication that it may be something related to the cluster gear and the input shaft. Braking in high gear goes straight through the main shaft to the input shaft but braking in 2nd goes through the counter shaft cluster to the input and same with the 1st gear plus the change in any thrust loading that might exist there. Something is moving around more than it should.

If it was rear drive aft of the transmission then it should do the same thing in all three gears.
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Old 09-15-2020, 01:04 PM   #13
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Default Re: Loud Noise when car decellerates while i n first and second gears

rotorwrench: I like your analysis. It makes a great deal of sense. Now it remains to find out what is moving around more than it should. I removed all the gears, shafts, and roller bearings.; everything moved as it should with no sloppiness. It appeared in very good
condition. Thanks, rotorwrench.
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Old 09-15-2020, 01:58 PM   #14
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Default Re: Loud Noise when car decellerates while i n first and second gears

A long starter bolt rubbing on flywheel?
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Old 09-15-2020, 10:29 PM   #15
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Default Re: Loud Noise when car decellerates while i n first and second gears

I went back and read your Dec 2019 thread regarding this problem. At that time, you described this as a "screeching noise" when decelerating in 1st & 2nd gears.

In this thread, you are describing the noise as a "metal banging noise".
Have the symptoms of the problem changed with the work you have done ? Metal banging sounds more serious than screeching.

With a rebuilt engine, I'm going to assume that the thrust clearances are correct, and therefore going to rule out the engine as source of noise due to deceleration.

I would agree with the logic of rotorwrench... that the problem is in the transmission... as the noise only occurs in 1st and 2nd gears. As he stated, in 3rd gear the shafts are directly coupled and you stated that the noise does not occur in 3rd gear.

I would want to see if you could also recreate the problem in reverse.... although it may be more difficult to duplicate the forces from accelerating / decelerating / engine braking while driving backwards.

You indicated that you rebuilt the transmission, but didn't give any detail as to what you found or replaced. Let us know what you kept vs what you replaced when rebuilding the transmission.

Is it possible to upload an audio file of the sound it is making? Might help to diagnose the problem.
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Old 09-18-2020, 11:30 AM   #16
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Default Re: Loud Noise when car decellerates while i n first and second gears

To all contributors: I have made an audio tape of the decelerating noises. However, I need very explicit directions on how to upload the file from my pictures and get the tape to you. I look forward to hearing from you.
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Old 09-18-2020, 12:29 PM   #17
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Default Re: Loud Noise when car decellerates while i n first and second gears

You can check the wear on the torque tube bearing . Remove the speedo drive and push a heavy screwdriver up and release on the spiral gear . There will be a bit of lash where the spiral is seated on the driveshaft but only a very little .If it does move up and down appreciably then the Hyatt bearing and most likely the sleeve as well is worn . I dont think this is the cause in this case but worth checking I think .

John in sunny afternoon Suffolk County England .
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Old 09-19-2020, 09:40 AM   #18
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Default Re: Loud Noise when car decellerates while i n first and second gears

Are you sure that the noise isn't coming from the rear axle assembly, and being transmitted up the torque tube?
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Old 09-19-2020, 10:28 AM   #19
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Default Re: Loud Noise when car decellerates while i n first and second gears

^^^What he said,classic ring and pinion issue ^^^ under load its fine,decell it get noisy
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Old 09-19-2020, 06:39 PM   #20
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Default Re: Loud Noise when car decellerates while i n first and second gears

Except that he says it only occurs in 1st and 2nd gear...
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