Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 10-02-2020, 09:51 AM   #1
Bob Bidonde
Senior Member
 
Bob Bidonde's Avatar
 
Join Date: May 2010
Location: Long Island, NY
Posts: 1,959
Default Rear Axle Taper - What It Does

The taper on the rear axle is there to center the axle concentric with the brake drum assembly. Torque from the axle to the wheel is transferred by the shear key between the axle and the drum.

Applying a lot of nut tightening torque to the rear axle is not a good practice because:
>it increases the frictional force that resists removing the brake drum. In turn, this leads to the use of tools that may damage the axle's threads;
>it deforms the tapered joint, and eventually the brake drum rubs against the brake backing plate;
>it raises the tension stress in the axle at the inboard end of the taper where there is a stress riser due to the key slot and the abrupt change in the axle's cross section. This reduces the fatigue life of the axle.

It has been said many times that no torque wrenches were in use when the Model "A" was manufactured, so the assembly line worker was snugging the axle nut. The point is that there is no technical need to apply a torque more than is necessary to snug the brake drum onto the axle and engage the shear key in the process. Because someone publishes a book specifying 100 ft-lbs or more does not make the practice right.

My experience is that a snug with a wrench not exceeding 50 ft-lbs is adequate.

Okay you all. Fire away!
__________________
Bob Bidonde
Bob Bidonde is offline   Reply With Quote
Old 10-02-2020, 10:16 AM   #2
john charlton
Senior Member
 
john charlton's Avatar
 
Join Date: May 2010
Posts: 937
Default Re: Rear Axle Taper - What It Does

It has been my belief that the key should not be loaded. If the taper in the hub and taper on the axle are within spec when the axle nut is correctly torqued there is a mechanical bond between the two . I always clean both tapers with thinners and make sure they are bone dry before fitting . I think the key is not designed to accept radial driving load it is the taper bond that does the job . If you assembled it all without the key I would guess it would work just fine . I have often thought of trying it . The key stops initial rotation as you torque up .

John in same place same weather .
john charlton is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 10-02-2020, 10:29 AM   #3
d.j. moordigian
Senior Member
 
d.j. moordigian's Avatar
 
Join Date: May 2010
Location: Fresno, Ca.
Posts: 3,613
Default Re: Rear Axle Taper - What It Does

Quote:
Originally Posted by john charlton View Post
It has been my belief that the key should not be loaded. If the taper in the hub and taper on the axle are within spec when the axle nut is correctly torqued there is a mechanical bond between the two . I always clean both tapers with thinners and make sure they are bone dry before fitting . I think the key is not designed to accept radial driving load it is the taper bond that does the job . If you assembled it all without the key I would guess it would work just fine . I have often thought of trying it . The key stops initial rotation as you torque up .

John in same place same weather .
John,
I agree with what you say...also, lapping the taper of the axle too the hub
is a big deal..makes for a good fit.
djm
d.j. moordigian is offline   Reply With Quote
Old 10-02-2020, 11:05 AM   #4
David R.
Senior Member
 
Join Date: Aug 2016
Location: West Virginia
Posts: 352
Default Re: Rear Axle Taper - What It Does

Same technology of a morse taper drill chuck attachment.
David R. is offline   Reply With Quote
Old 10-02-2020, 11:08 AM   #5
Conaway2
Senior Member
 
Conaway2's Avatar
 
Join Date: Apr 2019
Location: Mt. Pleasant, SC
Posts: 265
Default Re: Rear Axle Taper - What It Does

A somewhat related question.....

The driver’s side rear drum occasionally rubs against the backing plate. I have one 010” axle shim in place, which apparently is not enough, and I can barely tighten the nut enough to get a cotter pin in the axle. I plan to add another shim, but am worried I won’t be able to fit a cotter pin at all...and the axle threads are pretty worn.

I’m sure I’m not the only person to encounter this issue - is there an easy fix ?

Thanks - JIm
Conaway2 is offline   Reply With Quote
Old 10-02-2020, 11:19 AM   #6
1931 flamingo
Senior Member
 
1931 flamingo's Avatar
 
Join Date: May 2010
Location: new britain,ct 06052
Posts: 8,771
Default Re: Rear Axle Taper - What It Does

Sponsored Links (Register now to hide all advertisements)
Take a grinder to the rear of the brake drum facing the backing plate. Also make sure the backing plate isn't bent.
Paul in CT
1931 flamingo is offline   Reply With Quote
Old 10-02-2020, 11:42 AM   #7
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 5,953
Default Re: Rear Axle Taper - What It Does

When I was really young we had a fella that would just snug the axle nut. He apparently also insisted the key handled the strain. The car would have to be towed back after awhile. Sometimes just a key installed correctly would fix it, sometimes it took more.
The man was eventually fired, there were other issues too.
Many years later a fella in town had a 29 sedan he drove the wheels off of, drove it everywhere. Happened to see him along the road and pulled him to the garage. I found the key sheared [ other side loose too] and it dawned on me. So I asked him how long ago this was done and who worked on it. Guess what, yep it was him. But now he needed a hub and axle. A real PITA considering.
The tapers are there for a reason. Maybe 100# isn't necessary and 50# would work, but, just snugging, like this man would do, doesn't make it.
Patrick L. is offline   Reply With Quote
Old 10-02-2020, 02:56 PM   #8
hotrodart
Senior Member
 
hotrodart's Avatar
 
Join Date: May 2010
Location: Shenandoah Valley Virginia
Posts: 148
Default Re: Rear Axle Taper - What It Does

Your skepticism of the axle preload specification is way off base. You have been lucky with only 50 ft-lbs....or maybe you simply "baby" your car.



The taper on the axle is designed by the engineers to make sure the hub and axle rotate as one unit (by pure friction) with the maximum torque of the engine, and maximum resistance from the tires (friction between the tire and road surface)......with some margin of safety added. The key should take no load at all with the proper preload (ft-lbs). The proper preload depends upon the taper angle, materials involved (steel in this case), and total contact area between the axle taper and the hub. I have never seen the design figures that Ford used, but a reasonable guess for automotive applications in the '30s would be about 75% (non-lapped tapers).
hotrodart is offline   Reply With Quote
Old 10-02-2020, 03:41 PM   #9
Joe K
Senior Member
 
Joe K's Avatar
 
Join Date: Jul 2010
Location: Cow Hampshire
Posts: 3,613
Default Re: Rear Axle Taper - What It Does

Quote:
Originally Posted by Conaway2 View Post
A somewhat related question.....

The driver’s side rear drum occasionally rubs against the backing plate. I have one 010” axle shim in place, which apparently is not enough, and I can barely tighten the nut enough to get a cotter pin in the axle. I plan to add another shim, but am worried I won’t be able to fit a cotter pin at all...and the axle threads are pretty worn.

I’m sure I’m not the only person to encounter this issue - is there an easy fix ?

Thanks - JIm
Sounding like an issue inside the "pumpkin." Natural tendency is for the spider gears to "push apart" the two axles. Wear in the rear bearings (usually brinelling which usually doesn't affect the bearing geometry until the very end) will result in the axles "receding" from each other and improve clearance between the brake drum and backing plate. That is improve "occasionally" - given slop in the rear end (i.e. spider gears worn or improper preload of the carrier) it is possible the drum may occasionally contact the backing plate?

In a rear rebuild there is "spec" for the looseness around the spider gears. Tom Endy may be able to comment on this further. You may be able to get a sense of this with the drum off (or even on.)

We have commented in another thread on the possibility of "stretch" occurring in the rear hub as it is forced on the taper. A new hub might cure it - or try swapping the one rear hub for the other and see if the issue follows along?

Easy fix? You did that already (Shim.)

Joe K
__________________
Shudda kept the horse.
Joe K is offline   Reply With Quote
Old 10-02-2020, 03:48 PM   #10
rotorwrench
Senior Member
 
rotorwrench's Avatar
 
Join Date: Jun 2010
Location: San Antonio, Texas
Posts: 12,044
Default Re: Rear Axle Taper - What It Does

The taper shaft design has been around since the dawn of the industrial revolution. It's a simple way of joining a shaft with a hub and not have problems with fretting as was the norm with splined type designs as long as they are maintained in clean and tight condition. Shear keys were added to protect the shaft from breakage if the taper joint started to loosen. A sheared key is dead give away that the joint was too loose. The male and female tapers must be clean as a steam whistle before assembly. No oil or lube of any kind. It's good if the key is snug in both keyways but it will load up against a loose key pretty quick in service. Ford made the axles strong enough to take a torque of 100 Ft/Lbs but I don't know if that is what was intended or not. Suffice it to say that it should have been tightened to a level that it could just barely reach a cotter pin alignment with a fairly long handled breaker bar type tool. The torque should be rechecked after a period of driving that would be sufficient to apply multiple torque loads in both forward and reverse gears.

A good way of dealing with wear and tear problems with these friction joints is to start looking for parts that are in better condition than the problematic parts. Folks can keep beating the horse but one day it's going to break and leave the owner on the side of the road.

It's natural for worn out tapers to pull inward far enough for the drum to rub the backing plate. If it's that worn then start looking for better parts. Shims make a poor fit for a tapered shaft type joint.
rotorwrench is offline   Reply With Quote
Old 10-02-2020, 04:13 PM   #11
john in illinois
Senior Member
 
john in illinois's Avatar
 
Join Date: May 2010
Location: Illinois
Posts: 1,942
Default Re: Rear Axle Taper - What It Does

The taper drives the hub. If it gets the hub gets driven by the key it usually cracks the keyway.

John
__________________
Welcome each day
john in illinois is offline   Reply With Quote
Old 10-02-2020, 04:22 PM   #12
Synchro909
Senior Member
 
Synchro909's Avatar
 
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 5,289
Default Re: Rear Axle Taper - What It Does

I was taught that the drive is provided by the taper and that the key is only to hold thigs while they are tightened or to ensure alignment if orientation was important, which it is not with the axle.
I have just replaced an axle and hub on a car that the previous owner didn't keep the nuts tight. Both axle and hub were badly galled. I am absolutely certain that if I reassembled the old hub and axle, even with a good key, it would fail very quickly. I've also seen axles where he drive side of the keyway is broken out. That only happened because the drive was not being done by the key, not the taper.
I generally respect Bob's posts but on this, I'm afraid I have to respectfully differ.
__________________
Accidents hurt. Safety doesn't.
Synchro909 is offline   Reply With Quote
Old 10-02-2020, 05:47 PM   #13
bbrocksr
Senior Member
 
Join Date: May 2010
Location: Yakima Washington
Posts: 630
Default Re: Rear Axle Taper - What It Does

Quote:
Originally Posted by Bob Bidonde View Post
The taper on the rear axle is there to center the axle concentric with the brake drum assembly. Torque from the axle to the wheel is transferred by the shear key between the axle and the drum.

Applying a lot of nut tightening torque to the rear axle is not a good practice because:
>it increases the frictional force that resists removing the brake drum. In turn, this leads to the use of tools that may damage the axle's threads;
>it deforms the tapered joint, and eventually the brake drum rubs against the brake backing plate;
>it raises the tension stress in the axle at the inboard end of the taper where there is a stress riser due to the key slot and the abrupt change in the axle's cross section. This reduces the fatigue life of the axle.

It has been said many times that no torque wrenches were in use when the Model "A" was manufactured, so the assembly line worker was snugging the axle nut. The point is that there is no technical need to apply a torque more than is necessary to snug the brake drum onto the axle and engage the shear key in the process. Because someone publishes a book specifying 100 ft-lbs or more does not make the practice right.

My experience is that a snug with a wrench not exceeding 50 ft-lbs is adequate.

Okay you all. Fire away!
The taper transmits the torque not the key. If the nut is not torqued properly the tapers will slip shearing the key. Once the key has sheared it ruins the tapers and they will not hold as designed.
Bill
bbrocksr is offline   Reply With Quote
Old 10-02-2020, 07:06 PM   #14
1crosscut
Senior Member
 
1crosscut's Avatar
 
Join Date: Feb 2011
Location: Lincoln, Nebraska
Posts: 1,461
Default Re: Rear Axle Taper - What It Does

Quote:
Originally Posted by Conaway2 View Post
A somewhat related question.....

The driverís side rear drum occasionally rubs against the backing plate. I have one 010Ē axle shim in place, which apparently is not enough, and I can barely tighten the nut enough to get a cotter pin in the axle. I plan to add another shim, but am worried I wonít be able to fit a cotter pin at all...and the axle threads are pretty worn.

Iím sure Iím not the only person to encounter this issue - is there an easy fix ?

Thanks - JIm
Jim if you add another shim and the nut won't go on far enough to fit a cotter pin you can sand some of the back side of the nut off allowing the pin to be fit.
__________________
Dave

It'll feel better when it quits hurting.
1crosscut is offline   Reply With Quote
Old 10-02-2020, 07:13 PM   #15
shew01
Senior Member
 
shew01's Avatar
 
Join Date: Sep 2016
Location: Roanoke, VA USA
Posts: 877
Default Rear Axle Taper - What It Does

Quote:
Originally Posted by 1931 flamingo View Post
Take a grinder to the rear of the brake drum facing the backing plate. Also make sure the backing plate isn't bent.
Paul in CT

Can that throw the wheel out of balance?

Iím asking because my brakes squeal.
Sent from my iPhone using Tapatalk
shew01 is online now   Reply With Quote
Old 10-03-2020, 09:59 AM   #16
ryanheacox
Senior Member
 
ryanheacox's Avatar
 
Join Date: Apr 2013
Location: Northwest CT
Posts: 1,047
Default Re: Rear Axle Taper - What It Does

Quote:
Originally Posted by shew01 View Post
Can that throw the wheel out of balance?

Iím asking because my brakes squeal.
Sent from my iPhone using Tapatalk
Brake squeal is usually caused by not tapering the ends of the brake linings.

Sorry Bob, I also agree that the key is only there to keep things aligned/stationary while assembling.
ryanheacox is offline   Reply With Quote
Old 10-03-2020, 10:56 AM   #17
shew01
Senior Member
 
shew01's Avatar
 
Join Date: Sep 2016
Location: Roanoke, VA USA
Posts: 877
Default Re: Rear Axle Taper - What It Does

Quote:
Originally Posted by ryanheacox View Post
Brake squeal is usually caused by not tapering the ends of the brake linings.
Iím sure that is true on some (possibly most) Model As.

However, the previous owner warned me about upcoming brake squeal when I purchased the car a little over a year ago. He told me his work around was to spray (but not soak) a little WD-40 around the crack between the drum and the backing. That definitely works, but Iím not all that happy spraying WD-40 anywhere near the brakes.


Sent from my iPhone using Tapatalk
shew01 is online now   Reply With Quote
Old 10-03-2020, 12:24 PM   #18
Conaway2
Senior Member
 
Conaway2's Avatar
 
Join Date: Apr 2019
Location: Mt. Pleasant, SC
Posts: 265
Default Re: Rear Axle Taper - What It Does

After reading all the comments, I think I need to find another carrier/axle assembly that’s in better condition than the one I have. I recently replaced all the bearings and races in the rear axle assembly and adjusted bearing preloads and gear backlash - following the article by Tom Endy. However, the ring and pinion gears show a lot of wear, as do the axle tapers.
Conaway2 is offline   Reply With Quote
Old 10-03-2020, 01:13 PM   #19
KR500
Senior Member
 
KR500's Avatar
 
Join Date: Mar 2012
Location: Addison,ll.
Posts: 387
Default Re: Rear Axle Taper - What It Does

Locking TAPERS have been used almost since the beginning in metal working machinery. Mills, grinders, lathes, and drill presses have used Morse and other standard years to retain hubs, chucks, and other components. I believe a 7 degree taper and less are considered locking tapers.
KR500 is offline   Reply With Quote
Old 10-04-2020, 11:37 AM   #20
Bob Bidonde
Senior Member
 
Bob Bidonde's Avatar
 
Join Date: May 2010
Location: Long Island, NY
Posts: 1,959
Default Re: Rear Axle Taper - What It Does

For those of you who believe that the tapers transmit torque, try driving your Model "A" with both shear keys removed. The only way a taper transmits torque is via friction. Talk to someone who was driving a Model "A" when a shear key failed. I will bet that you will hear the axle spun in the drum. When a shear key fails, no torque is transmitted while accelerating or braking. By the way, if the tapers on your axles have groves in them, that's evidence that the drum did spin on the axle.
__________________
Bob Bidonde
Bob Bidonde is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 09:32 PM.