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Old 10-02-2021, 12:07 PM   #1
drolston
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Default Which Shaft is Broken

While cruising peacefully at 40 mph on a level stretch of road, Henry (my '41 coupe) failed to respond to a slight throttle movement. Engine would rev and clutch felt normal, but no go. Fortunately I was on a road with wide shoulders. No go in any gear, and the speedometer registered, so something broke back past the speedo gear.

Been there before, but it was always when doing some hot rod thing. This happened while just cruising. There was no clank or bang. I could hear a little rattle noise from the rear end. After getting home on a roll-back I popped the hubcaps and idled the engine in low gear. The shafts are locked tight to the hubs, so it is not a sheared key. Listened to both hubs with a bar to my ear and the rattle sound seems the same on both sides. Methinks drive shaft.

How do I tell for sure whether it is the drive shaft or an axle. Maybe pull the fill plug and see if the ring gear is turning with the engine in gear at idle?

Also, the rear end is original '41; will the axle be 16 or 18 tooth, and where might I find one? Same question for drive shaft. Can either be safely repaired by welding?
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Old 10-02-2021, 12:56 PM   #2
gajeepguy
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Default Re: Which Shaft is Broken

It's probably an axle key. In my hot rodding days I kept them in the glovebox at all times....-RG
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Old 10-02-2021, 01:01 PM   #3
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Default Re: Which Shaft is Broken

I'm thinking if the speedo is registering steady and varies with engine speed as you depress the accelerator, then something has failed behind the point where the speedo drive gear is located on the splined end of driveshaft. I'm thinking the driveshaft to pinion coupling, an axle shaft, or an axle key has failed. If it's not an axle key that sheared, then most likely that rear will need to come out.
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Old 10-02-2021, 01:06 PM   #4
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Default Re: Which Shaft is Broken

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Originally Posted by drolston View Post



After getting home on a roll-back I popped the hubcaps and idled the engine in low gear. The shafts are locked tight to the hubs, so it is not a sheared key.



Not Brokie!


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Old 10-02-2021, 01:30 PM   #5
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Default Re: Which Shaft is Broken

I had the same thing and it was an axle shaft.
Jack the rear end up and see if either of the rear wheels will pull outwards.
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Old 10-02-2021, 01:58 PM   #6
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Default Re: Which Shaft is Broken

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It would be my opinion that it is a broken axle. To answer your questions about repair or replacement, an axle cannot be welded satisfactorily, but they are readily available and fairly easy to replace. Identification of the exact axle in your housing can only be made by counting the teeth, 16 or 18, can be replaced by either in compatible tooth count, or by the replacement of both axles together with spider gear in a set of the different tooth count. Compatible axle sets for your housing range from 1935 to 1941, the axle shafts themselves being 32.85" in length.
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Old 10-02-2021, 05:25 PM   #7
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Default Re: Which Shaft is Broken

repaired on drive shaft that had stripped the splines in the coupler
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Old 10-02-2021, 06:10 PM   #8
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Default Re: Which Shaft is Broken

yes, when the splines finally let go, there is no noise, if you break an axle or driveshaft, you invariably hear the snap!
And yes, I have stripped the splines, it does and can happen!
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Old 10-02-2021, 09:13 PM   #9
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Default Re: Which Shaft is Broken

Quote:
Originally Posted by drolston View Post
While cruising peacefully at 40 mph on a level stretch of road, Henry (my '41 coupe) failed to respond to a slight throttle movement. Engine would rev and clutch felt normal, but no go. Fortunately I was on a road with wide shoulders. No go in any gear, and the speedometer registered, so something broke back past the speedo gear.

Been there before, but it was always when doing some hot rod thing. This happened while just cruising. There was no clank or bang. I could hear a little rattle noise from the rear end. After getting home on a roll-back I popped the hubcaps and idled the engine in low gear. The shafts are locked tight to the hubs, so it is not a sheared key. Listened to both hubs with a bar to my ear and the rattle sound seems the same on both sides. Methinks drive shaft.

How do I tell for sure whether it is the drive shaft or an axle. Maybe pull the fill plug and see if the ring gear is turning with the engine in gear at idle?

Also, the rear end is original '41; will the axle be 16 or 18 tooth, and where might I find one? Same question for drive shaft. Can either be safely repaired by welding?
After thinking about this a bit longer, before pulling the complete rear, the first thing I would suggest doing is pull those hub/drum assemblies and double check to make sure your problem is not a sheared axle key, and then if an axle is broken, you should be able to pull the broken end out of the axle housing. If by chance the problem is not a sheared key or a broken axle, then pulling the complete rear and torque tube for disassembly is in order.
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Last edited by JM 35 Sedan; 10-03-2021 at 04:09 PM.
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Old 10-03-2021, 05:43 AM   #10
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Default Re: Which Shaft is Broken

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After thinking about this a bit longer, before pulling the complete rear, the first thing I would suggest doing is pull those hub/drum assemblies and make sure your problem is not a sheared axle key, and then if an axle is broken, you should be able to pull the broken end out of the axle housing. If by chance the problem is not a sheared key or a broken axle, then pulling the complete rear and torque tube for disassembly is in order.

"After getting home on a roll-back I popped the hubcaps and idled the engine in low gear. The shafts are locked tight to the hubs, so it is not a sheared key."

He stated pretty clearly in his first post that it's NOT a sheared key! DD
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Old 10-03-2021, 06:11 AM   #11
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Default Re: Which Shaft is Broken

Although it would be nice to know precisely where the problem is, it's all moot, since the rear end will have to come out and apart in any case.
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Old 10-03-2021, 06:52 AM   #12
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Default Re: Which Shaft is Broken

You do not have to pull the rear end to replace a axle, just the ring gear side housing.
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Old 10-03-2021, 07:12 AM   #13
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Default Re: Which Shaft is Broken

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You do not have to pull the rear end to replace a axle, just the ring gear side housing.
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Old 10-03-2021, 07:49 AM   #14
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Default Re: Which Shaft is Broken

To each his own. I personally do not enjoy doing this job while lying under the car.
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Old 10-03-2021, 08:19 AM   #15
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Default Re: Which Shaft is Broken

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To each his own. I personally do not enjoy doing this job while lying under the car.
X2. I don't enjoy it either!
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Old 10-03-2021, 08:36 AM   #16
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Default Re: Which Shaft is Broken

To be exact only the left hand housing needs to be removed. I did this job when I broke a shaft on my 41 pickup. I covered it in some videos.
Part 1: https://youtu.be/t0AfzS5OLYE
Part 2: https://youtu.be/i26ZSqwFIF0
Part 3: https://youtu.be/8ToEl7O01P0
Part 4: https://youtu.be/MOVxQP0aZhg

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Old 10-03-2021, 08:39 AM   #17
JM 35 Sedan
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Default Re: Which Shaft is Broken

Of course you do not need to remove the rear on an early Ford with a closed driveshaft to replace a broken axle, BUT you never know what else that failure could have damaged internally unless you pull the rear and completely dismantle it, and check everything.
Also, if the rear is original and never been apart, it's likely the seals, gaskets, bearings, etc., may need replacing.
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Old 10-03-2021, 08:53 AM   #18
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Default Re: Which Shaft is Broken

My bet is an axle broken and you got lucky in that the hub/wheel couldn't move outward due to the brake shoes. When you idled the engine in gear was the Ebrake on? It would take a lot of abuse to strip the splines out of the coupling but it is over 80 years old. I have never heard of a main drive gear shearing off so does the speedo still work like suggested above? If the clutch disk came apart I would think it would be noisy but maybe not. Interested to see what this is.
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Old 10-03-2021, 08:57 AM   #19
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Default Re: Which Shaft is Broken

Agreed, it is really easy to remove the entire assy, and less painful to do it out from under the car!
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Old 10-03-2021, 12:24 PM   #20
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Default Re: Which Shaft is Broken

If you are going to disassemble the differential to replace an axle or perhaps the coupling, I think I would strongly consider replacing the bearings, seals and gaskets, especially if the differential is original, and be done with it. And it might be a good time to use 3.54 gears. And those gears will mean changing the turtle??!!!
Sorry to learn of the problem!!!
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