Machine later gears for 1934 axle

D

Duke

Senior Member
I would like to go to a 3.78 or 3.54 to replace the 4.11 in my 1934 axle. I have to shorten my driveshaft so that is not a concern (going in a 32). Is the machine work on a set of 1940 3.78 worth the time? Has anyone done this and know the number of hours vs new gears at $595?
 
1938-40 gears have a 6 spline pinion.You need to find a set of 35-36 10 spline . If its 3.78 you have to have the pinion gear bearing surface machined to use the 33-34 pinion bearings.35 and later pinion bearings will not fit in the 33-34 banjo(to large) If its 3.54 the top of the 11 tooth pinion gear will have to be machined (to fit thru the banjo opening)as well as the pinion bearing surface. Finding a good used set of 3.54's is not easy. In 1968 I had a 35 3.54 pinion fitted to a 34 banjo by Cook's Machine in L.A. They also shortened the driveshaft(necessary). $20 back then.The ring gear will not need to be machined.Last set of true 33-34 3.54's I saw for sale was $750 and that was awhile ago.


Here is a thread on the HAMB
https://www.jalopyjournal.com/forum...6-ford-3-54-gears-in-a-33-34-rear-end.672981/
 
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As Sheldon is aware, I did this same job in 08, 10-spline 3.78 from a 37 Ford, into a 34 banjo. My experience was the same as his. At that time the guy that did the crankshaft grinding at Johnson Machine in Monrovia CA, did the pinion modification. He was a flathead guy, and knew exactly what to do, including the slight step on the pinion bearing surface. I don't recall what I paid for machine work, but I remember it was dirt cheap, I'm thinking $25. I already had the gears, bearings, etc, so the total job was very inexpensive. The driveshaft shop charged very little, also.
 
If you have access to a lathe its an easy job, I have done quite a few, use an insert tool to turn the pinion bearing down to the 33/34 size,(copy the old 33/34 pinion dimensions) use the same insert tool to machine the tips of the pinion teeth to just slip into the 33/34 housing,(no more) use an oil stone to debut the teeth after this, make a spacer to take up the difference in pinion bearings under the pinion nuts,( I think about 1/2 inch) let me know if you want the exact dimensions, bore the inside of the 10 spline on the 33/34 drive shaftto allow a tap fit of a 6 spline coupler cut in half and weld it intaking care to drill the retaining pin hole in the right place,

Lawrie
 
Worth the $595 of new gears. It is most likely a break even or a monetary loss. It is a lot of fun and rewarding.
 
Do you have the 3:78's or do you need to buy them? If I were you I would base my decision on performance not price. Depending on your tire size and transmission and weight, the 3:54's my be better suited for your car.
 
I did it about 5 years ago. Local crank grinder did the pinion for 50 bucks, then I did the drive shaft myself. The ring gear tips do not always have to be trimmed, mine did not, but some do. Only worth it because I had the 3.78's in stock, and could do the drive shaft myself.
 
Thank you everyone for the help, especially Deuce Lover who phoned from France to help me.
I currently only have 4.11 gears. I can find later Ford 3.78 easily vs the cost of a new set of 3.54.
 
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