rear axle play

beast_3

beast_3

Member
How much rotational play is acceptable in the rear axle?

I've seen the posts about front/rear & up/down play with the hub removed being due to inner seal wear. I'm concerned about play probably due to play in the differential; pinion/ring gear mesh &/or spider gears.

So how much rotation is OK?

Thanks!
Beast
 
Depends where one will be measuring; e.g., on circumference of;

a. Threaded part of axle; or,
b. Middle of keyway; or,
c. Outer rim of brake drum; or,
c. Rubber tire, (19"), or,
d. Rubber tire, (21").
 
With my right rear tire touching the ground, ****** in high gear (least slack) and the left rear tire in the air, I can rotate it back and forth about 1.5 inches at the tread.

I haven't had my rear end apart, but it feels and sounds great, and the ****** is like NOS inside.
 
I seem to remember that backlash between the pinion and the ring gear is supposed to be in the range of 0.010 and 0.014. One source on the 'net indicates

Some books say that backlash can be as great as .020, other say that .010 is the max.

So perhaps my number correct? And perhaps the actual number not that important?

Thinking this out further: It may be possible to extrapolate this amount from the 9" ring gear to the 28" tire diameter EXCEPT for the free play of the spyder gears. Each of these has it's own free play as well. And don't forget the free play that is developed by any looseness in the universal joint OR the transmission spline or gears?

Perhaps Tom's method of "this is what mine is" is perhaps the best comparison for you?

I might say that should yours be larger a large free play is NOT the end of the world. That is providing one has the proper tooth contact - which is determined by the use of blue layout dye when the gears are initially set up. As the gears wear tooth contact only gets better.

I think the only way to know for sure is to start at the beginning. When the banjo is disassembled, check your contact and backlash. (Bearing preloads are done individually and unmeshed and while important are not THAT important for an inservice axle.)

Generally, the Model A rear end is a pretty trouble free system. Ford used essentially the same setup through the late 1940s, and applied to it quantum leap changes in horsepower. I think if the rear end is not "HOWLING" then it is probably AOK.

Joe K
 
Hi Beast 3,

1. I have a never-used, re-built differential with all new bearings & new bearing races; new pinion & new ring gear (3:27); accuarately adjusted with dial indicators, (no guess work by feel); & everything accurately measured with an inch-pound torque wrench; and filled with oil, installed in car & ready to go in a few weeks.

2. With 19" wheels, & 4-Ply Rated Good Year Safety Tread Tires, the radius from the center of the rear axle to the rubber tire tread near the ground is approximately 14-1/2".


3. With the rebuilt transmission placed in 3rd gear, the passenger side 19" rubber tire on ground, & rotating "only" the 19" driver's side rubber tire back & forth, this driver's side wheel backlash (measured with back & forth movement between both the Right & Left axles), & measured at the driver's side tire tread near ground = + 7/16".

4. With a backlash measured at 14.5" = 7/16" = 0.4375"; the rear axle nut is 5/8" = 0.625"; hence, calling the requested approximate backlash at the axle threads "X", (on the driver's side only), we can find "X" as follows: X / 0.625" = 0.4375" / 14.5" ; therefore X = approximately 0.01885".

5. Therefore if one measures the backlash for both axles on only the driver's side at the axle threads at approximately 0.01885", it appears the backlash for each individual axle measured at the threads would be approximately 0.01885" / 2 = 0.09425" for each individual axle.

6. I had a "well" used differential from the late 1940's or early 1950's on my 1930 Coupe that had an approximately 5/8" similarly measured backlash in lieu of the new differential's 7/16" backlash.

Hope this information is helpful.
 
Last edited:
4. With a backlash measured at 14.5" = 7/16" = 0.4375"; the rear axle nut is 5/8" = 0.625"; hence, calling the requested approximate backlash at the axle threads "X", (on the driver's side only), we can find "X" as follows: X / 0.625" = 0.4375" / 14.5" ; therefore X = approximately 0.01885".

5. Therefore if one measures the backlash for both axles on only the driver's side at the axle threads at approximately 0.01885", it appears the backlash for each individual axle measured at the threads would be approximately 0.01885" / 2 = 0.09425" for each individual axle.


Gee, I love that kind of talk.
 
At the extreme limits of backlast the car won't move.

Some specs from a V8 book list diff gear backlash as .010, and axle endplay at .003-.006, and clearance of diff spyder gears to shaft of .005-.008 -- original nos and not worn A parts fit the same---it works out to barely perceptible play with no binding
As parts with more wear are used there will be more play, depending on how much noise you can tolerate, excessive play will be a clunk when going on and off the throttle .
 
Backlash(es) further inward along the tapered axle keyway would be slightly more than that at the axle nut threads requested above, because the axle has larger varying diameter(s) along the tapered axle keyway; hence, the Ford specified 0.010" would be close to "right-on".
 
Last edited:
To reply no. 10 above:

After looking at my handwritten notes & calcs, just a late night 12:44 a.m. misplaced typo decimal; hence, changing .09425" to .009425" is correct where indicated in reply #6 & #7.


Many thanks for same!
 
You must log in or register to reply here.
Back
Top