Banjo rear end! ring and pinion

Brendan

Brendan

Well-known member
could you just change the ring gear from a 37 tooth to a 34 tooth to give you a 378, with out changing the pinion gear? because they both have a 9 tooth pinion. what would happen?
 
No, you can't do that with early Ford gears. The pinions may have the same tooth count but I can assure you the profile of the pinion teeth are different for those two ratios.
 
Brendon, we did that more than once back in the 50's, used to drag a 39 coupe at Sanford Me. We just slipped in another ring to change ratios, never changed the pinion. Walt
 
this is for my Model A. I have some bad axles in it. I bought another rear end and it has 378s in it so since I had it apart I was wondering if I could just change the ring gear?
 
A 4.11 ring gear is thicker than a 3.78. The pinions are different diameters to accomadate this. What you propose is not going to work. If you could re-shim enough for it to mesh, it will fail immediately as the pinion teeth are different as well.
 
This is gonna be interesting..... one person says one thing and another person says the exact opposite.
It was pointed out to me recently that some people here post opinions based on things they've read, not actually done, and it made me realise that I might be guilty of that too. So, I have resolved to think about my actual experiences before I hammer the keyboard. Consequently I have absolutely no advice to offer on this topic. :D
 
bassman/nz said:
this is gonna be interesting..... One person says one thing and another person says the exact opposite.
It was pointed out to me recently that some people here post opinions based on things they've read, not actually done, and it made me realise that i might be guilty of that too. So, i have resolved to think about my actual experiences before i hammer the keyboard. Consequently i have absolutely no advice to offer on this topic. :d
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amen !
 
Brendan, Your bad axles have nothing to do with the banjo, only the axle housings and spider gear. Why not leave the banjo alone and just match up the axles and spider on your rebuild?
 
Well we did that once and it made one hell of a noise when we got it back to gether. I think we junked the car.
 
Ring gears have to be cut to form a ratio. If you have a given number of gear teeth cut into a ring then the spacing and width have to be equal on all of the teeth around the circle. The pinion that works for that ratio has to have teeth that are spaced to fit the ring teeth. The outer diameter of the pinion and the thickness of the ring have to be variable to get specific ratios to work with both parts and still have good fit to each components tooth count for the specific ratio entended at manufacture.

After gears and pinions are cut for basic fit, they have to be matched for fine tuning of the fit usually by honing with specialized equipment. Once they are a matched set, the serial numbers are etched into both parts so as to lessen the chance of incompatible parts being put together. If a person ever gets a gear set to work with mismatched serial numbered gears, they would be lucky. This is even if the parts are both of the correct ratio.
 
Ol' Ron said:
Well we did that once and it made one hell of a noise when we got it back to gether. I think we junked the car.
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Ol' Ron, you crack me up :D We did many "impossible" things when we were kids. Sometimes they even worked for a short time. Some of us are lucky we made it through those days. Maybe that car you junked was the same one that Walt is talking about ;)
 
If I remember correctly from back in high school mechanical drawing, we would draw two lines at right angles connected at one end, kind of like the letter "L." The lengths of each would be the pitch diameter which (I'm pretty sure) is the diametral pitch times the number of teeth?? Number of teeth divided by the diametral pitch?? Anyway, the more teeth, the longer the line. Then, lines would be drawn perpendicular to and at the center of each of the two lines. Then, a line would be drawn from the intersection of the second two lines to the intersection of the first two lines. This would show the angle at the pitch circle for the two gears. If different ring gears were going to be be essentially the same basic diameter, the diametral pitch would vary which would vary the pitch diameter of the pinion. So, even if the pinion tooth count would be the same, the pitch and diameter would be different. If anyone can understand this, would you please explain it to me? Thanks!
 
It will NOT work.Even tho the pinions have the same number of teeth the diameters are different.About 30 yearsago,a friend wanted me to rebuild his A rear end,He gave me all the seperate pieces & I was to assemble it for him.I had the housings apart numerous times & could not get the mesh even close & it always had way to much backlash.Eventually,it turned out that the gears were from 2 different gearsets..which were 3.78 & 4.11 which he had thought wouldwork as they had the same tooth count on the pinions.I spent many hours on that job with no pay as I was doing it for a friend.
 
I've never done it and I would be skeptical EXCEPT that Walt
Dupont says he did it successfully.
I think Walt has more experience than all of us together and if he says he did it I would try it.
It's not all that much work and if you don't like the results you can do something else.
Let us know how it works.
 
Brendan, If you have a matched set of 3.78:1 ring and pinion gears that will fit the banjo rear of your Model A, those are the gears you should use. As I mentioned at Tahoe, I changed the gears in my '35 from 4.11 to 3.78 and installed all new seals and bearings as necessary prior to doing the Cross Country Tour. It took a lot of time to get pinion and carrier bearing preloads set correctly and getting the gear backlash set was also time consuming.
As much as I respect Walt Dupont's knowledge and good advice for flathead engine building and many other areas of expertise on these early Fords, I think his post here could mislead you and others into making a mistake and wasting a lot of time and money. What he did back in the 50's to make a run down the drag strip will not work long term for you today on a car you want to drive on the road.
If or when you decide to make a gear change and replace that axle, send me a pm and I will send you step by step instructions with pictures on how I setup the rear in my '35. It should be a very similar procedure for doing your Model A.
There is also a procedure with pictures posted on the H.A.M.B. about how to rebuild a banjo rear. I used some of the same methods/procedures that he described but found some of his info misleading as well.
 
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columbiA said:
It will NOT work.Even tho the pinions have the same number of teeth the diameters are different.About 30 yearsago,a friend wanted me to rebuild his A rear end,He gave me all the seperate pieces & I was to assemble it for him.I had the housings apart numerous times & could not get the mesh even close & it always had way to much backlash.Eventually,it turned out that the gears were from 2 different gearsets..which were 3.78 & 4.11 which he had thought wouldwork as they had the same tooth count on the pinions.I spent many hours on that job with no pay as I was doing it for a friend.
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This is correct. Matching gear sets are designed to transmit force over a wide surface area while maintaining oil between the gears. The machining tolerances are very critical. That is how strength and minimal wear are achieved. A mismatched set is weak and will wear out quickly even if you can get the teeth to mesh. Sometimes a mismatched pair of the same ratio design can be setup to work together OK with a little luck. The idea of using a pair from different ratio designs is just not going to work anywhere successfully in my opinion.
 
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