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Old 08-23-2020, 04:18 PM   #1
Conaway2
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Default Rear axle questions

Reassembling the rear axle this afternoon, and have a couple of questions. I‘Ve replaced both carrier bearings and races, but am re-using the pinion bearings and race. Pinion and ring gears are the original ones - they show some wear, but overall look pretty good. Wear pattern on the ring gear teeth is right in the center of the tooth, per the article by Jack Richard in Vol 6 of the ‘how to restore your Model A’ series by MAFCA.

I have 0.026” in gaskets on the passenger side, and 0.010” on the driver side, which gives a carrier bearing pre-load of about 5 lbs using the twine and fish scale measurement method described in the article. Pinion bearings are preloaded to about 10-12 inch-lbs, as measured with a small torque wrench.

How much backlash should I expect with used pinion and ring gears ? I’ve read that it should be 0.010” to 0.020”, but I suspect this axle has more backlash than that. I’ll have access to a dial indicator tomorrow, so will be able to get a measurement.

I added a 0.010” shim behind the driver side carrier bearing to allow me to use more gasket thickness, so the only remaining adjustment I can make is to have 0.030” of gaskets on the passenger side and 0.006” on the driver side.

Realistically, can I adjust backlash on used gears to the 0.010” to 0.020” range ??

Thanks - Jim
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Old 08-24-2020, 11:10 AM   #2
Jim Brierley
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Default Re: Rear axle questions

I recommend .008"-.010" of backlash. .020" is too much. You can also change backlash by moving the pinion in or out.
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Old 08-24-2020, 11:41 AM   #3
Conaway2
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Default Re: Rear axle questions

Jim - thanks for your reply. Hadn’t thought about moving the pinion gear. I think I will go ahead and replace the pinion bearings and race. With used ring and pinion gears, is it realistic to get backlash where you recommend it ?

Thanks - Jim
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Old 08-24-2020, 07:01 PM   #4
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Default Re: Rear axle questions

Removed the pinion bearings and race today - the bearing closest to the pinion gear literally fell apart when it came off; all rollers were badly worn on one end. New bearings and race are ordered - I suspect this is part of the reason I was having trouble with the backlash adjustment.
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Old 08-24-2020, 07:40 PM   #5
Tom Endy
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Default Re: Rear axle questions

The only way you can move the pinion gear forward or aft is to either add a shim between the first bearing and the forward side of the pinion gear, or take a cut on the forward end of the gear, depending on which direction you want to move it

I think you will find that Henry designed the assembly such that the gear contact between the ring & pinion is pretty much in the center and moving the pinion fore and aft is not necessary.

The way to adjust the backlash is to move banjo gaskets left-right. This will move the ring gear in or out away from the pinion gear, which is stationary and straight down the center line of the car. If you don't have the latitude, add shims under the carrier bearings and compensate for it by adding more banjo gaskets. you can even jockey carrier bearing shims left-right to to adjust backlash. It can be a tedious process.

Articles I have read claim that the backlash can be as much as .020. I think that is too much. I believe it should be less than .010. I usually set it around .003 t0 .005. You can measure it with a dial indicator by turning the drive shaft back and forth and feeling for when a tooth on the pinion gear touches either side of two teeth on the ring gear. I don't bother with a dial indicator, I have done enough of them I can tell by feel where the backlash is.

It is important that you do have some backlash, otherwise you will have binding between the gears as the pinion gear teeth will be bottoming out in the ring gear. So when you think you are there rotate the drive shaft to run the ring gear through 360 degrees and stop and check that there is backlash every few degrees.

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Old 08-24-2020, 08:24 PM   #6
Conaway2
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Default Re: Rear axle questions

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Thanks for responses and comments ! New pinion bearing and race are ordered and should arrive by Friday. Adjusting the fit of the rear axle is much more complex than I ever margined. In the 50+ years I‘ve owned and driven Model A’s, I’ve never worked on a rear axle, so this old dog is learning some new things !
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Old 08-25-2020, 12:17 PM   #7
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Default Re: Rear axle questions

Yes, very realistic.
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Old 08-25-2020, 11:47 PM   #8
larrys40
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Default Re: Rear axle questions

Conaway,
Like Tom I have done many rear axles. My experience and setup is exactly Tom's. After doing many you get a feel for it, although so I can relay my setup to the customer I like to check the backlash so I know what it is and it is stated. I concur with Tom's assessment of the pinion setup, I have never shimmed or had to change the pinion in or out. If it is off it is probably because the pinion bearings aren't fully seated.

Larry Shepard
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Old 08-30-2020, 04:07 PM   #9
jdpalmer
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Default Re: Rear axle questions

Glad you got new bearings. I had a noise I thought was transmission so I took it out rebuild it. Later same rough noise and then the rear end went totally out the pinion bearings completely gone. Now all new parts and higher speed gear runs smooth as modern car.
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Old 08-30-2020, 05:09 PM   #10
Aarongriffey
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Default Re: Rear axle questions

I have done many, but only a few model A rear ends. Did the last one last October.
I NEVER leave them with less than .020 backlash. Never.
Too much backlash, within reason” doesn’t hurt a thing. Too little can cause howl.
Too little can also cause it to throw teeth at high speed. I’d shoot for .022, if it comes out at .018 to .022” I’d leave it alone.
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Old 08-31-2020, 07:06 AM   #11
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Default Re: Rear axle questions

Quote:
Originally Posted by jdpalmer View Post
Glad you got new bearings. I had a noise I thought was transmission so I took it out rebuild it. Later same rough noise and then the rear end went totally out the pinion bearings completely gone. Now all new parts and higher speed gear runs smooth as modern car.

I did the same thing! At least both of us have good fresh transmissions now
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Old 08-31-2020, 12:19 PM   #12
Jim Brierley
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Default Re: Rear axle questions

Ask 10 Model A guys a question, you get 12 answeres. Listen to all, then make-up your own mind. Proof is above.
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