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Old 06-17-2020, 03:22 PM   #1
ML28
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Default Ring/Pinion Question

Are rings and pinions always matched and lapped as sets? What happens if you match a NOS ring from one set to a NOS pinion from another?
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Old 06-17-2020, 04:05 PM   #2
BRENT in 10-uh-C
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Default Re: Ring/Pinion Question

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Are rings and pinions always matched and lapped as sets? What happens if you match a NOS ring from one set to a NOS pinion from another?
This has long been a topic of controversy here. No where on the A-4610-* Pinion Gear print nor the A-4210-* Driving Pinion print do I find where it states the gears were machined as a set. Where the argument comes in is when you read the Ford Parts Price List books when it lists the A-4209-AR/B/C as "matched". The reason I feel they were listed as 'matched' is because the 3.78 ratio (9-34) and the 4.11 ratio (9-37) shared the same teeth count on the pinions however they were a different pitch of teeth and were not interchangeable. Now when you look at the early parts books when the 3.70 ratio was the only R&P available, it lists them as A-4210 and A-4610 available separately -or as a A-4609 set. Since there is not any mention on the original prints of the two being lapped or mated, it is my opinion this was not an operation that was performed until after the Model-A era. As for your NOS gears, the key is to make sure you have the correct 9 tooth Pinion that mates to your Ring Gear.
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Old 06-17-2020, 05:04 PM   #3
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Default Re: Ring/Pinion Question

Not sure about cars but for AA's the 12/24/30 and 1/16/31 Chicago Service Letters
states that the gears are now matched and that old stock of the unmatched gears
should be returned to the branch for credit.
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Old 06-17-2020, 05:39 PM   #4
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Default Re: Ring/Pinion Question

Both valid points cited above. If you want to take the time,set it up dry with prussian blue on the teeth,impression the gear set,disassemble and check contact pattern,eliminate the doubt. Gear hobbing is done in runs,pinions are run on one hobber,ring gear on another,set matching would take a jig instead of an axle assembly and imprinting the pattern as I suggested above.
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Old 06-17-2020, 05:39 PM   #5
BRENT in 10-uh-C
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Default Re: Ring/Pinion Question

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Not sure about cars but for AA's the 12/24/30 and 1/16/31 Chicago Service Letters states that the gears are now matched and that old stock of the unmatched gears should be returned to the branch for credit.
Hey Bob, thanks for that. I will go look to see if I can find anything regarding passenger vehicles.

Interesting that Ford waited until the last 8 months of production to start this 'matching' process with the AA. If the same applies to the passenger chassis, I should try to find a later (1931) A-4209 print and see if it mentions 'matching' on the print or the EI.
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Old 06-17-2020, 08:35 PM   #6
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Default Re: Ring/Pinion Question

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I personally believe that the ring & pinion were not lapped prior to installation at the Ford factory. First I don't think Henry would have wanted to waste the time when they will be lapped in after about 500 miles. Second, I have taken hundreds of original R&P's out of Model A rear axle assemblies over the years and have found one thing in common. All have a serial number stamped on the end of the pinion gear. When you clean up the ring gear and hold it at an angle to the light you will see same the same number written with an electric etching pencil on the flat side. The numbers are large and written by hand.

My theory is that a worker pulled a pinion gear from one stock bin, and the ring gear from another and then wrote the number on the ring gear before he installed it in a rear axle assembly.

I have heard people state that they have successfully mated up an R&P that came out of different rear axle assemblies. I would think after a few thousand miles it may lap in. I for one, however, would not do it because it could be initially noisy and result in customer complaints.

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Old 06-17-2020, 10:31 PM   #7
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Default Re: Ring/Pinion Question

Years ago I helped a guy with a rear axle that we assembled with a ring gear from one axle and a pinion gear from another. I wasn't too confident about the outcome but that is what we had to work with. The resulting assembly was smooth and quite from day one. So, evidently it can be done.
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Old 06-18-2020, 01:33 AM   #8
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Default Re: Ring/Pinion Question

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My theory is that a worker pulled a pinion gear from one stock bin, and the ring gear from another and then wrote the number on the ring gear before he installed it in a rear axle assembly.
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Tom Endy
Tom, I doubt The management would go for such a waste of time. I believe the gear sets were lapped and numbered.
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Old 06-18-2020, 09:45 AM   #9
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Default Re: Ring/Pinion Question

Technically, wearing-in of new gears as a matched set is lost after the gears have some service wear. From experience, mixing ring & pinion gears works fine so long as the gears are properly meshed.
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Old 06-19-2020, 08:48 AM   #10
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Default Re: Ring/Pinion Question

Lapping machines were developed after road speeds became higher and rear axle problems started to become apparent. The way the pinion gear is mounted on the drive shaft makes it more difficult to set up for lapping than the integral pinion shafts that came along in the V8 era. If I had to guess, it was likely that they began to lap them either late in production or they only did it for replacement parts after production switch to the 1932 models.

Prior to lapping, the gears were basically bedded in during break in of the car. Hobbed gears are relatively smooth on the tooth drive surfaces but they are not all the same microscopically. Lapping beds them in as a set prior to production and gives the gear tooth surfaces a very smooth finish. Gear hobbs wear and as they wear, things change microscopically till the hobb cutter is worn out.

Mixing worn gears is always risky. They might work OK and they might not. The only way to find out is to set up the contact pattern & backlash and then run them. If backlash isn't consistent when checked in several locations then there will likely be problems later on.
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Old 06-19-2020, 10:52 AM   #11
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Default Re: Ring/Pinion Question

I've used an un-matched 4.11 gear set. There was a slight noise at about 45 MPH otherwise they were very good.
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Old 06-19-2020, 11:47 AM   #12
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Default Re: Ring/Pinion Question

My Coupe has just about 50,000 miles on mismatched ring & pinion. These gears, running in SAE 140 synthetic gear oil, are quiet and have been trouble free. These gears have been up 80+ mph.
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Old 06-19-2020, 07:56 PM   #13
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Default Re: Ring/Pinion Question

Most like to re-use ring and pinion gears that were originally assembled together. If there is any wear at all, that's only good if the contact position of the pinion to ring gear is adjusted in exactly the same position. Otherwise it would be pretty much the same as using gears that never lived together.
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Old 06-20-2020, 08:02 AM   #14
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Default Re: Ring/Pinion Question

It's basically all about contact. At least a set that has run a long time generally has even contact even though it's worn. The contact pattern will change a bit but backlash will have a noticeable increase. I've set up a lot more main rotor transmission gear sets for the helicopters than I have rear axles but they will all run OK if the bearings have enough preload and the contact pattern/backlash are within limits. I always set up used gears closer to max limits than minimum. As long as they are within the acceptable range, they will run OK.

If gears have uneven wear and backlash varies too much, the set should be replaced. To run stuff that should be replaced is counter productive. One person may be OK with it but they will likely pass it on to the next guy and they won't be happy when they find completely worn out gears with gear oil that looks like metallic paint.

Last edited by rotorwrench; 06-20-2020 at 08:09 AM.
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