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Old 09-24-2022, 08:37 PM   #1
shew01
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Default Noise in Drive Train

I just got back from a 300 mile tour with a number of Model A friends, and I noticed a noise in the drive train about halfway through the trip. I initially thought I wasnít pressing on the clutch far enough, but it turns out that the clutch does not affect the noise at all.

Itís a thump thump thump sound, and it does not seem to appear as long as I have a load on the drive train. However, when I let off the gas, I sometimes hear the thump thump thump sound, especially at low speeds, around 5-10 mph.

I was in a parking lot near home, and I especially heard it while coasting in neutral.

Iím thinking this is either the universal joint or something in the differential.

Can anyone offer any debug advice?


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Old 09-25-2022, 03:21 AM   #2
Marshall V. Daut
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Default Re: Noise in Drive Train

It could be the universal joint, as you suspect. But usually when the U-joint is going bad, there is an accompanying increased vibration upon deceleration. Otherwise, the symptoms are the same as you describe.
It could also be the large nuts loosening on the drive shaft where the gear enters the center carrier of the rear end. The repo tang with its multiple ears is not very good. The tangs are too short to be bent over the nuts properly. Sometimes that retainer ring has been left off completely. If that bearing retainer's ears were not bent over properly or they are too short or the retainer is missing, the forward nut will start backing off the pinion gear threads, followed by the large nut next to the center carrier. When that second nut starts to back off, then the noise and vibration begin upon deceleration because of the increased lash between the pinion and ring gears. If allowed to continue, vibration will be felt and a loud scraping noise will be heard. As the nuts continue to loosen, both will become more noticeable upon deceleration, but largely disappear under acceleration.
To test for this condition, place the rear end on sturdy jackstands, put the transmission into neutral and have someone turn one of the rear wheels forward while you lie right under the rear end housing, slightly forward. If the nuts have loosened up, you will hear scraping as a rear wheel is turned by hand. Then have your helper rock one wheel back and forth about 1/4 turn each way. You should hear scraping or clunking if those nuts have loosened up.
If you do hear scraping or any noise emanating from right in front of the center carrier in the rear end, the fix is not fun. The rear end has to come out so that the torque tube can be removed in order to tighten those two large nuts next to the pinion gear. The large nut nearer to the gear is the one that is critical to be tight. The other one just acts as a back-up to keep that one from loosening. Tighten the nut closer to the gear so that the drive shaft can be turned by hand, but with some effort. Too loose and the rear end will make noise. Too tight and you run the risk of burning out the pinion bearings. Be sure to alternately bend the ears on the retaining flange between the two pinion gear nuts alternately so that one ear bends over the rear lock nut and the next one bends over the front nut. You'll have to turn the foward-most nut until the ears on the retaining flange can be fully bent over the flat side of each nut. Once the forward-most nut has been tightened, you should be able to turn the drive shaft with one hand, feeling a firm resistance.
When removing the drive shaft to effect this repair, don't forget to first remove the thin lock ring in front of the speedometer drive gear. Then the speedometer drive gear, roller bearing and thrust washer can be slid off the front of the drive shaft. After the bolts in the rear of the torque tube have been removed, the torque tube will slide right off. Remove the speedometer drive housing at the bottom of the front of the torque tube first!
Marshall
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Old 09-25-2022, 04:42 AM   #3
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Default Re: Noise in Drive Train

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Originally Posted by Marshall V. Daut View Post
It could be the universal joint, as you suspect. But usually when the U-joint is going bad, there is an accompanying increased vibration upon deceleration.
Yes, I am getting noise almost anytime I decelerate, regardless of the gear.


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Old 09-25-2022, 05:00 AM   #4
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Default Re: Noise in Drive Train

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Originally Posted by Marshall V. Daut View Post
To test for this condition, place the rear end on sturdy jackstands, put the transmission into neutral and have someone turn one of the rear wheels forward while you lie right under the rear end housing, slightly forward. If the nuts have loosened up, you will hear scraping as a rear wheel is turned by hand. Then have your helper rock one wheel back and forth about 1/4 turn each way. You should hear scraping or clunking if those nuts have loosened up.
Thanks, I plan to check for this.
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Old 09-25-2022, 05:03 AM   #5
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Default Re: Noise in Drive Train

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Originally Posted by Marshall V. Daut View Post
If you do hear scraping or any noise emanating from right in front of the center carrier in the rear end, the fix is not fun. The rear end has to come out so that the torque tube can be removed in order to tighten those two large nuts next to the pinion gear. The large nut nearer to the gear is the one that is critical to be tight. The other one just acts as a back-up to keep that one from loosening. Tighten the nut closer to the gear so that the drive shaft can be turned by hand, but with some effort. Too loose and the rear end will make noise. Too tight and you run the risk of burning out the pinion bearings. Be sure to alternately bend the ears on the retaining flange between the two pinion gear nuts alternately so that one ear bends over the rear lock nut and the next one bends over the front nut. You'll have to turn the foward-most nut until the ears on the retaining flange can be fully bent over the flat side of each nut. Once the forward-most nut has been tightened, you should be able to turn the drive shaft with one hand, feeling a firm resistance.


When removing the drive shaft to effect this repair, don't forget to first remove the thin lock ring in front of the speedometer drive gear. Then the speedometer drive gear, roller bearing and thrust washer can be slid off the front of the drive shaft. After the bolts in the rear of the torque tube have been removed, the torque tube will slide right off. Remove the speedometer drive housing at the bottom of the front of the torque tube first!
Oh, boy... I've never had the rear end out of a Model A. This going to be a learning experience...

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Old 09-25-2022, 08:32 AM   #6
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Default Re: Noise in Drive Train

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Hello, a lot of previous posts on rear axles on the barn , also many of the repair manuals go over them , and can always ask here . Good luck.
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Old 09-25-2022, 08:35 AM   #7
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Default Re: Noise in Drive Train

Also you will need a spring spreader , use caution when removing the rear shackles, a lot of tension in that rear spring.
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Old 09-25-2022, 06:02 PM   #8
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Default Re: Noise in Drive Train

Marshall left some good test ideas above, and I plan to check them out as soon as I can.

Assuming this is a universal joint problem, what parts should I have on hand before starting this project?

Iím thinking a spring spreader, new shackles (because they probably havenít been changed in a long time), a universal joint rebuild kit, new cotter pins, any gaskets?

Should I be replacing anything else (to save future labor) when I get the car apart?

Are any other special tools needed other than a spring spreader?


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Old 09-25-2022, 06:36 PM   #9
Marshall V. Daut
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Default Re: Noise in Drive Train

You won't need a spring spreader unless you plan on disassembling the rear end and/or rear spring for a complete restoration of the leaves. To replace a bad U-joint or to tighten the pinion gear nuts, you need only to remove the rear end with the rear spring left in place. It is much more work and potentially more dangerous to disconnect the rear spring from the shackles in order to drop the rear end. Just put a large C-clamp over the center of the rear spring once the rear end has been lowered. That will protect against a broken or weak center bolt allowing the spring leaves to separate all of a sudden. I know some guys prefer to disconnect the rear spring from the rear end first, but I have found it easier and faster to drop the entire assembly. The one time I removed the rear end with the spring left inside the rear crossmember, I had a heck of a time getting the spring hangers back in place while struggling beneath the rear fenders = not much room. Whatever way you choose to drop the rear end, just be aware that it's a heavy and awkward animal.
To check and/or replace the U-joint, the rear end has to come out and be rolled back a foot or two so that the U-joint can be removed. If the U-joint is good, but the pinion gear nuts have loosened up, you only need to remove the torque tube once the rear end has been lowered and pulled out from beneath the car. Use a strong floor jack to lower the rear end. Don't use one of those dinky Harbor Freight Chinese aluminum floor jacks. Use a large, sturdy floor jack with a wide circular platform for the center of the rear end to sit on while it is being lowered and raised back into position.
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Old 09-25-2022, 06:50 PM   #10
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Default Re: Noise in Drive Train

Quote:
Originally Posted by Marshall V. Daut View Post
You won't need a spring spreader unless you plan on disassembling the rear end and/or rear spring for a complete restoration of the leaves. To replace a bad U-joint or to tighten the pinion gear nuts, you need only to remove the rear end with the rear spring left in place. It is much more work and potentially more dangerous to disconnect the rear spring from the shackles in order to drop the rear end.
Marshall,

Thanks for posting. Iím green at this, and the YouTube video I found used a spring spreader to disconnect the springs. I REALLY was NOT looking forward to having to use a spring spreader.


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Old 09-25-2022, 07:33 PM   #11
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Default Re: Noise in Drive Train

Anytime you remove a rear end from a Model A you should use a spring spreader. The spreader takes the spring tension off the shackle bolts so they can be disconnected. The rear is then dropped out of the car and the spring remains attached to the frame where it is safely retained.

If you plan to remove the spring, you should collapse the spreader to remove the spring tension first. The spring is then safe to remove.

When you remove a rear end from the car with the spring attached to it all the spring tension is being held by a 3\8 hex bolt and it is dangerous. The bolt was not meant to hold that much tension when new. It could be 90 years old and rusted. If the head should pop off the bolt the top leafs will fly 20 feet in the air and take your head with it if you are standing over it.

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Old 09-25-2022, 08:13 PM   #12
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Default Re: Noise in Drive Train

https://www.santaanitaas.org/wp-cont...vised-2014.pdf
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Old 09-26-2022, 08:04 AM   #13
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Default Re: Noise in Drive Train

Are your rear wheel hubs properly torqued? I recently had a similar noise and found a loose left rear axle nut. Dr Foot
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Old 10-09-2022, 10:52 AM   #14
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Default Re: Noise in Drive Train

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Are your rear wheel hubs properly torqued? I recently had a similar noise and found a loose left rear axle nut. Dr Foot

Yes, I checked the torque. It was fine.


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Old 10-09-2022, 03:03 PM   #15
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Default Re: Noise in Drive Train

Prefer the spring spreader route since the spring is solidly held in the conformal saddle. Among the parts you may need to change be sure to add bushings and possibly the reamers necessary to finish the job. The journals on my shackles were D-shaped in crossection and chewed up the bushings. Be advised that finding a quality U Joint can be a challenge. An NOS or used but still tight unit may be the way to go. The first "new" unit I bought was almost as bad as the one that needed to be replaced. Above all, exercise care with the spring. Let us know how it goes.
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Old 10-09-2022, 06:18 PM   #16
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Default Re: Noise in Drive Train

Did you check the lug nuts? a posibility
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Old 10-09-2022, 06:29 PM   #17
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Default Re: Noise in Drive Train

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Did you check the lug nuts? a posibility

The lug nuts were torqued correctly. Thanks for asking.


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Old 10-09-2022, 06:35 PM   #18
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Default Re: Noise in Drive Train

This noise has come and gone a number of times since I originally posted. Driving home from a club event on Saturday, I started getting a vibration and sometimes a crunching/thumping sound (at low speed)ósometimes a vibration could be felt in high gear. I'm guessing the noise/vibration is not the clutch, but I need to check the adjustment on it anyway. I'm thinking this may be the universal joint. I have Monday off as a holiday; so, I'll finally have some time to work on it.

I have an engine stethoscope somewhere in my garage. Once I find it, I plan to take a listen to the differential and universal joint, and before I take this thing apart, I plan to re-read this thread.


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Old 10-09-2022, 08:14 PM   #19
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Default Re: Noise in Drive Train

I agree with Tom Endy in post #11 - use a spreader and take tension off the rear spring. Having removed rear axles with and without a spreader, I always use one now. They are not expensive.

I also think Marshall is probably right in post #2 about the noise. I had the same issue after my first rear axle reassembly.

Good luck - Jim
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Old 10-10-2022, 01:51 PM   #20
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Default Noise in Drive Train

I got the car up on jack stands and Iím trying to figure out how to disconnect the shocks.

Iím using the Les Andrews book as a guide, but I must be doing something wrong.



The end cap came off, but the arm doesnít want to budge away from the vertical tube.




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