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 wasn’t pressing on the clutch far enough, but it turns out that the clutch does not affect the noise at all.

It’s 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.

I’m thinking this is either the universal joint or something in the differential.

Can anyone offer any debug advice?


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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

Re: Noise in Drive Train
 

Yes, I am getting noise almost anytime I decelerate, regardless of the gear.


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Re: Noise in Drive Train
 

Thanks, I plan to check for this.

Re: Noise in Drive Train
 

Oh, boy... I've never had the rear end out of a Model A. This going to be a learning experience...

Re: Noise in Drive Train
 

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.

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.

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?

I’m thinking a spring spreader, new shackles (because they probably haven’t 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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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.
Marshall

Re: Noise in Drive Train
 

Marshall,

Thanks for posting. I’m 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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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.

Tom Endy

Re: Noise in Drive Train
 

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

Re: Noise in Drive Train
 

Yes, I checked the torque. It was fine.


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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.

Re: Noise in Drive Train
 

Did you check the lug nuts? a posibility

Re: Noise in Drive Train
 

The lug nuts were torqued correctly. Thanks for asking.


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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)—sometimes 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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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

Noise in Drive Train
 

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

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

https://uploads.tapatalk-cdn.com/202...48ca81aefa.jpg

The end cap came off, but the arm doesn’t want to budge away from the vertical tube.

https://uploads.tapatalk-cdn.com/202...00452778b0.jpg


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Noise in Drive Train
 

Hmmm… Does the bolt holding the other end of the shock link have to come off too before the shock link will wiggle free? If so, do I need to scribe an index mark on it before taking that end loose so the I won’t put it back on later in an incorrect orientation? Is there an incorrect orientation?


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Re: Noise in Drive Train
 

Remove the arm from the shock, nut and bolt, use a fat blade screwdriver to spread the arm where the arm attaches, leave the arm and link on the rear end. Those links can be a PIA

Noise in Drive Train
 

I’d rather avoid having to remove the shock arm from the shock. A friend sent a YouTube video that suggested removing the two shock bolts from the inner frame rail, and that “looked” easier to do. However, the shock arm all REALLY does not want to come out of the tube.

Any ideas?

https://uploads.tapatalk-cdn.com/202...34ba019667.jpg


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Re: Noise in Drive Train
 

Does anything inside the tube put pressure on the ball that would prevent it from exiting the hole in the tube?


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Re: Noise in Drive Train
 

Re: Noise in Drive Train
 

My shock looks like it’s missing item 2 in the diagram from Bratton’s.

https://uploads.tapatalk-cdn.com/202...ce13c07fe1.jpg


I’ll try pressing down on the ball to see if that makes a difference.


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Re: Noise in Drive Train
 

I agree with "Big hammer" and find it easier to just remove the bolt and nut from the shock arm and slide the arm off the shock's shaft, leaving the ball part of the arm still inside the link. It may help to insert a chisel or flat blade screwdriver in the arm's split opening behind the bolt to spread the opening a little bit. Move the rear axle up and down with the floor jack to facilitate an easier arm removal and re-installation. You'll find the "sweet spot" where the arm will be easiest to pull or pry off.
However, if pieces are missing from inside the link as you suspect, now is the perfect time to rebuild the link's guts. This will make the shocks more efficient and also eliminate an irritating knocking noise when the car hits a bump or hole in the road. Missing internal shock link parts will definitely create a rattle that is hard to diagnose with the wheels still in place, especially inside the rear shock links.
By the way, you can't put the shock arm back on incorrectly and still be able to install the bolt. There is a groove in the shock's shaft for that bolt. Any other orientation of the arm over the shaft will not allow the bolt to be inserted through the rear of the shock link arm.
Marshall

Re: Noise in Drive Train
 

It went in, so it's gotta come out.

Re: Noise in Drive Train
 

I always just remove the two bolts that holds the complete shock and let it hang.

Re: Noise in Drive Train
 

I finally got back to this today. I got the shocks off; now, the next problem is getting the universal top clamshell off. There isn’t enough clearance to get a normal 9/16” socket on the bolts, and there are lots of obstructions for two 9/16” wrenches.

Any ideas?


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Re: Noise in Drive Train
 

I did this recently and just used wrenches, lots of flipping of the wrenches but that’s how I did it.

Re: Noise in Drive Train
 

There your wrenches grind them to fit, still a pain.

Re: Noise in Drive Train
 

I hope you have taken the floorboard out. If so, there should be plenty of room for your wrenches.

Noise in Drive Train
 

I have a Tremec T170 transmission. So, taking the floorboard out doesn’t help because the universal is in a different position. (I took out the floorboard before I started disconnecting the drive line.) The drive shaft and radius rods have been shortened to accommodate the extra length of the T170 transmission.


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Re: Noise in Drive Train
 

I finally finally got the universal out of the car. This is my first time removing the differential to get to it.

This fell out of the universal area as I pushed back the torque tube.

https://uploads.tapatalk-cdn.com/202...33f7b01e71.jpg

Once upon a time, that was probably a bolt. I didn’t see a washer.


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Re: Noise in Drive Train
 

https://uploads.tapatalk-cdn.com/202...8297c300c8.jpg
https://uploads.tapatalk-cdn.com/202...b699559bcc.jpg
https://uploads.tapatalk-cdn.com/202...b98a8ef6d8.jpg
https://uploads.tapatalk-cdn.com/202...a98b1f55c1.jpg
https://uploads.tapatalk-cdn.com/202...09f1ab2da5.jpg


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Re: Noise in Drive Train
 

That bolt was probably the noise I’ve been hearing in the drive train.


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Re: Noise in Drive Train
 

The universal feels “notchy” to me, and I’d like to replace it (if I can find one) while I have it apart.


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Re: Noise in Drive Train
 

As long as you have the rear axle out, you might consider replacing all the bearings and races in the rear axle. It’s not difficult if you take your time. Check out Tom Endy’s article - referenced above. Rock Auto carries the bearings and races at a significantly lower price than other vendors. We can give you part numbers if you decide to do this.

And - if you go this far, I’d suggest going ahead and taking the spring apart and cleaning, painting and greasing the leaves.

It may take 2-3 days to do all of this, but you’ll never have a better chance to do this, and you’ll be pleasantly surprised with the results. I’ve done this on both of my cars in the past couple of years……and please use a spring spreader.

Good luck - Jim

Noise in Drive Train
 

I wish I had the time, but I’m working long hours at work.

The car has been down for months as it is, I don’t think I have the skill set yet to take this on. I have a restored bell housing that I need to install at some point too, but I’m electing to put that off to a later date as well. I don’t want to change out a bunch of parts and inadvertently create more problems.

Thanks for the suggestion though. It definitely makes sense.


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