Will '39 ring & pinion gear fit a '38?

[Pete Phillips]

I have located a 3.6:1 ring & pinion gear for a '39 Century. I have a friend/customer with a 1938 Special who wants the lower numerical gear ratio to replace the 4.4:1 in his Special. Something tells me that '39 ring & pinion won't fit other years, or am I mistaking the front of the driveshaft for '39-only ?  Anyone know if this '39 ring & pinion will fit a '38 Special?

Pete Phillips, BCA #7338

[Erndog]

According to my Hollander, they are only interchangeable if they are both either an 80 or 90 series.

[Jim Nelson]

Option,   I believe the '39' rear end is unique thus swapping gears may not work.    If you like you car,  see if you can find a '38' rear  end complete and change it.  (BUT,  you still need a 3.90 or 3.60  gear set.).   Or, for a  complete 1940 or 41  rear with a  3.6 rear ratio.    I don't know for sure but you would probably not visually see the difference.   BUT,  you would have a great cruising  car.    Next option,  I put an over drive in my  '38-46s' and loved it.   cruise  2350 rpm and drive easily 65 mph all day long.   Best $2300 spent for drive ability.   Again,  the only visual that you would see is the push/pull knob under the dash and the turn on electrical button.    The fellow who does it is in Circleville Ohio.     He has been doing it for years.   ( I put one in each of my two Buicks ).   My 1935-58 had a normal 4.88 rear so it was a 'slow' car.   With the OD,  it became a nice car with a 3.41 rear.    Now a nice 60 mph cruising car.     JMHO but I have experience in this option.     I'm prejudice,  as I would keep the original  '39' rear and run with the OD.    ( p.s.,   I like floor shifters - - -) . 

[Jim Nelson]

BTW,   if your '39' has the same 4.44 rear ratios that the 37 and 38 had,  the OD system gives you a  3.11 rear.    No problem as you won't use the OD until you engage it around 34 mph.   That puts your car in good rpm's as you have already been in  third gear.   

[Jim Nelson]

Sorry for my confusion.   I had a '38'.  (just sold it to a friend),  so the OD in a 38' makes a good option.   Ignore my ramblings on the '39' .      So if you go that way,  my mod's might be nice.   E-mail me if you want more details.   oldbuickjim@gmail.com   

[Bloo]

I too believe the 37-38 40 and 60 series ring and pinion sets will interchange with each other, but not 39, however I am not close to my books to verify it. I imagine a crowd of 39 40 series owners is gathering in @Pete Phillips' front yard about now....

[buick looks fine for 39]

I had a nos 1938 390 ring and pinion and compared it to a a 39. The inside diameter of the pinion bearing surface was different between the 2 years making it non-interchangeable.

                                                                                           Thanks

                                                                                              Leif

[1939_Buick]

On 5/3/2022 at 12:13 PM, Pete Phillips said:

I have located a 3.6:1 ring & pinion gear for a '39 Century. I have a friend/customer with a 1938 Special who wants the lower numerical gear ratio to replace the 4.4:1 in his Special. Something tells me that '39 ring & pinion won't fit other years, or am I mistaking the front of the driveshaft for '39-only ?  Anyone know if this '39 ring & pinion will fit a '38 Special?

Buick seemed to change the transmission & differential design-part numbers often during the '30's. 1940 and later more stabilised.

Even with the same diff ratio the part numbers can be different.

For 1938 S40 (option?), 1939 S40 (not an option?) , 1939 S60 (option) ring part number 1303392  47/13 3.6 ratio is the same. Ring carrier is the same. [would need to check my parts books to be 100% sure. The parts book number have discrepancies].  However the pinion is different

 

Some years ago some one in the forum fitted a 1939 39/10 3.9 to a 1938. He had to machine/sleeve the pinion shaft to get it to work. Was far from a bolt in.[will search for details] As a wild guess would be a the same with the (rare) 47/13 3.6 r&p set Parts 1303392/1310356.

 

Edit

From an email

Quote

I did install the 1939 3.90 ring & pinion into my 1938 housing and it was successful and quiet running but this is not a bolt in swap that can be done without some experience in setting up differential gears. It also requires at least a dial micrometer with a magnetic base. A universal pinion depth measuring tool is also very helpful.

The biggest difficulty with this swap is the front pinion bearing. The '39 bearing is different from the '38 and the pinion shaft diameter is also different so you can't swap the bearings. I tried several options to remedy this and finally arrived at a solution that worked. I had to take the pinion and the retainer to a machine shop and machine 1/8" from the pinion bearing seat and also 1/8" from the front of the retainer face. Even after doing the machine work I still had some difficulty getting the gears to present an acceptable wear pattern.

I'm planning to do another set and if that one is successful I will do an article and publish it in the Torque Tube magazine.

I think I would consider using the whole carrier assembly from the '39 and cutting and welding the torque tube from the '38 onto the '39. This would eliminate all of the gear set up issues.

 

 

Edited May 9, 2022 by 1939_Buick (see edit history)

[Jolly_John]

The '39 Special straight eight handles a 3.90 rear end very nicely for highway cruising. No strain at 65 to 70 m.p.h., and with very responsive acceleration to getting up to that speed (speaking from experience). I don't know if a 3.60 would be a little "tall" for the small series engine torque curve. Just throwing that out. John

Edited May 4, 2022 by Jolly_John (see edit history)