Rod Frazier Posted January 3, 2023 Share Posted January 3, 2023 OK, experts! I have a chance of buying the rear end from a '54 Century with the intention of using the higher gears in my '40 Century. My question is: Can I just change the ring and pinion, or do I have to change the pumpkin, or the complete rear axle assembly, or the whole deal including the torque tube? What's the simplest solution? Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted January 3, 2023 Share Posted January 3, 2023 34 minutes ago, Rod Frazier said: OK, experts! I have a chance of buying the rear end from a '54 Century with the intention of using the higher gears in my '40 Century. My question is: Can I just change the ring and pinion, or do I have to change the pumpkin, or the complete rear axle assembly, or the whole deal including the torque tube? What's the simplest solution? Rod, I changed the whole pumpkin. The entire axel assembly would be easier if it will work. You will enjoy the faster gear for cruising. Probably won't gain as much as I did as you already have a 4.9 or 3.6 and I had a 4.1,. What ratio is the 54? Ben Link to comment Share on other sites More sharing options...
Rod Frazier Posted January 3, 2023 Author Share Posted January 3, 2023 21 minutes ago, Ben Bruce aka First Born said: Rod, I changed the whole pumpkin. The entire axel assembly would be easier if it will work. You will enjoy the faster gear for cruising. Probably won't gain as much as I did as you already have a 4.9 or 3.6 and I had a 4.1,. What ratio is the 54? Ben The seller is checking the ratio but thinks it's about a 3.2 or 3.4. One of my Centuries has the 3.9 and the other one the 3.6. 1 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted January 3, 2023 Share Posted January 3, 2023 2 hours ago, Rod Frazier said: The seller is checking the ratio but thinks it's about a 3.2 or 3.4. One of my Centuries has the 3.9 and the other one the 3.6. Does he know the ratio is stamped on the bottom of the gear housing? Ben Link to comment Share on other sites More sharing options...
Fr. Buick Posted January 3, 2023 Share Posted January 3, 2023 The 54 Century had a 3.4 if it is a Dynaflow car. A manual trans would be a little shorter-legged, 3.9. Are you sure it will interchange back to 1940? I vaguely remember it only going back to 41 or 42. You should be able to confirm by searching these forums. If you can confirm that it will, then the easiest will be to keep all your original rear end and only swap out the pumpkin. Take it to a good shop for a look-over and adjustment if needed before installing. Beware the pin that holds the drive shaft onto the pinion is a lot of work to get out... Get a good punch and a big hammer! And support it with a sturdy jack stand right under the work area. Link to comment Share on other sites More sharing options...
Rod Frazier Posted January 3, 2023 Author Share Posted January 3, 2023 48 minutes ago, Ben Bruce aka First Born said: Does he know the ratio is stamped on the bottom of the gear housing? Ben I think so. He only lives about a mile from me but he's a very private person and it may take him a while to get back to me. The car has sitting in the field at least 20 years. Link to comment Share on other sites More sharing options...
Rod Frazier Posted January 3, 2023 Author Share Posted January 3, 2023 20 minutes ago, Fr. Buick said: The 54 Century had a 3.4 if it is a Dynaflow car. A manual trans would be a little shorter-legged, 3.9. Are you sure it will interchange back to 1940? I vaguely remember it only going back to 41 or 42. You should be able to confirm by searching these forums. If you can confirm that it will, then the easiest will be to keep all your original rear end and only swap out the pumpkin. Take it to a good shop for a look-over and adjustment if needed before installing. Beware the pin that holds the drive shaft onto the pinion is a lot of work to get out... Get a good punch and a big hammer! And support it with a sturdy jack stand right under the work area. Good to see that you and Ben agree. I have read elsewhere on this forum that the interchange is possible, but would be glad to hear if anyone has conflicting information! Link to comment Share on other sites More sharing options...
1939_Buick Posted January 3, 2023 Share Posted January 3, 2023 (edited) From what I have read 1954 into a 1940 is OK The torque tube is probably a different length. Buick changed often So get out the tape measure Better to change the complete pumpkin. Those gears have been operating in that housing for decades. Can take some effort to separate the torque tube drive shaft from the pinion shaft. Has a pin, that can be seen in some of the Buick parts books. If the torque tube length is the same a big win. Edit Several forum threads on this change, including https://forums.aaca.org/topic/305399-390-rear-gear-assembly-for-buicks/ https://forums.aaca.org/topic/352354-a-1940-1941-buick-question-regarding-rear-end-gearing/ Edited January 3, 2023 by 1939_Buick (see edit history) 1 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted January 4, 2023 Share Posted January 4, 2023 Everything I have read is 1940 -1955. I AM NOT CERTAIN about series in the older cars. The one I did in my 1950 came from a 1955 Century. I had that job documented in my thread but six years have disappeared from the middle of the thread. The entire pumpkin is removed with the pinion attached. I placed the entire assembly, torque tube, axel housing, everything, on saw horses. The trailing arms have to be disconnected from the mount near the front of the torque tube. I ground the rivets off. Used grade 8 bolts going back. Remove the flange bolts at the back of the torque tube. Then the pin mentioned above. Not easy is an understatement. THEN the drive shaft. See Old-Tank [ Willie Pittman] web site for a how to. I do not remember all the steps and sequences. Since the ring gear and pinion are never separated they require no adjustment. The steps to remove the pumpkin are documented in the 1950, and probably others, Buick Shop Manual. The 248 engine handled the 3.4 [ 3.36 ] well. Your 320 should have no problem. Ben Link to comment Share on other sites More sharing options...
Rod Frazier Posted January 4, 2023 Author Share Posted January 4, 2023 24 minutes ago, Ben Bruce aka First Born said: Everything I have read is 1940 -1955. I AM NOT CERTAIN about series in the older cars. The one I did in my 1950 came from a 1955 Century. I had that job documented in my thread but six years have disappeared from the middle of the thread. The entire pumpkin is removed with the pinion attached. I placed the entire assembly, torque tube, axel housing, everything, on saw horses. The trailing arms have to be disconnected from the mount near the front of the torque tube. I ground the rivets off. Used grade 8 bolts going back. Remove the flange bolts at the back of the torque tube. Then the pin mentioned above. Not easy is an understatement. THEN the drive shaft. See Old-Tank [ Willie Pittman] web site for a how to. I do not remember all the steps and sequences. Since the ring gear and pinion are never separated they require no adjustment. The steps to remove the pumpkin are documented in the 1950, and probably others, Buick Shop Manual. The 248 engine handled the 3.4 [ 3.36 ] well. Your 320 should have no problem. Ben Dang, Ben! I think you just talked me out of the whole deal! I'm going to Fredericksburg in April. Maybe I'll swing by your way and buy you a root beer float! 1 1 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted January 4, 2023 Share Posted January 4, 2023 11 hours ago, Rod Frazier said: Dang, Ben! I think you just talked me out of the whole deal! I'm going to Fredericksburg in April. Maybe I'll swing by your way and buy you a root beer float! I will accept!! The mod is not for the faint of heart. Most things good are not. It would be nice if the entire rear assembly would fit. Ben Link to comment Share on other sites More sharing options...
Jim Nelson Posted January 4, 2023 Share Posted January 4, 2023 Changed several rear ends to get a decent ratio. Removing the complete rear is the best way. Do not remove the ring and pinion as that requires - most likely - new bearings when it comes apart. The pinion has two bearings. One is a roller bearing (maybe two depending) in the rear of the pinion. Next to the ring gear. At the front of the pinion is a double row ball bearing. Each has a specific job. Checking the pinion for vertical play is important. By the book, it can only have a maximum of 0.0015 vertical movement. Then if that bearing is at the max. the factory requires you replace the front double row ball bearing. The ring gear has a different bearings still . Then when you have done all that, you have most likely had to pull the axels. If you did that you need to replace the outboard axel roller bearings. Those are 99.99 % never serviced because you have to remove the brake backing plates, to get to the bearings and relive. BTW. Those bearings are greased for lubrication. It requires two seals and roller bearing per side to create a cavity with the new roller bearings. Fill half way with new synthetic grease and put together. You got it apart so don't try to do it cheep. When you are done, you have a new - quite running - road geared rear end. Its not rocket science but you will need some one to help when needed. So, my last rear used a '54' dynaflo with the 3.4 ratio. Great ratio for a road car. Yes, pulling the drive shaft is not fun. Done it on two rear ends. I have 5 service manuals from 35 to 54. Each one has little nuances on how to best work on - repair your rear end. My best pin replacement used a grade 8 hex head bolt with a small locking nut to balance the drive shaft, after working hard to remove the factory pin. I ended up drilling the center out (make sure the drill is CENTERED ) . BTW, I have also installed over drive on my 1938 and 1935 Buicks. with the original 4.44 rear. This gave me a 3:11 rear ratio. That was easier as I removed the pumpkin and drive shaft / torque tube forward to the tranny. That guy still does it and does it very well. Send it to him and then when I got it back, assembled it, ran some wiring and it's done. Sorry for the long babble but it's all doable. BTW, all my cars are roadable - not trailer queens. 1 1 Link to comment Share on other sites More sharing options...
Rod Frazier Posted January 4, 2023 Author Share Posted January 4, 2023 37 minutes ago, Jim Nelson said: Changed several rear ends to get a decent ratio. Removing the complete rear is the best way. Do not remove the ring and pinion as that requires - most likely - new bearings when it comes apart. The pinion has two bearings. One is a roller bearing (maybe two depending) in the rear of the pinion. Next to the ring gear. At the front of the pinion is a double row ball bearing. Each has a specific job. Checking the pinion for vertical play is important. By the book, it can only have a maximum of 0.0015 vertical movement. Then if that bearing is at the max. the factory requires you replace the front double row ball bearing. The ring gear has a different bearings still . Then when you have done all that, you have most likely had to pull the axels. If you did that you need to replace the outboard axel roller bearings. Those are 99.99 % never serviced because you have to remove the brake backing plates, to get to the bearings and relive. BTW. Those bearings are greased for lubrication. It requires two seals and roller bearing per side to create a cavity with the new roller bearings. Fill half way with new synthetic grease and put together. You got it apart so don't try to do it cheep. When you are done, you have a new - quite running - road geared rear end. Its not rocket science but you will need some one to help when needed. So, my last rear used a '54' dynaflo with the 3.4 ratio. Great ratio for a road car. Yes, pulling the drive shaft is not fun. Done it on two rear ends. I have 5 service manuals from 35 to 54. Each one has little nuances on how to best work on - repair your rear end. My best pin replacement used a grade 8 hex head bolt with a small locking nut to balance the drive shaft, after working hard to remove the factory pin. I ended up drilling the center out (make sure the drill is CENTERED ) . BTW, I have also installed over drive on my 1938 and 1935 Buicks. with the original 4.44 rear. This gave me a 3:11 rear ratio. That was easier as I removed the pumpkin and drive shaft / torque tube forward to the tranny. That guy still does it and does it very well. Send it to him and then when I got it back, assembled it, ran some wiring and it's done. Sorry for the long babble but it's all doable. BTW, all my cars are roadable - not trailer queens. Thanks for all the details, Jim. If I keep my car with the 3.6 gears for longer tours, it's starting to seem like a waste of time and money to go through all that for very little change. If I decide to sell it, I could swap the entire rear assembly with the other car. And maybe I should look into the OD option, too. That would leave me with some lower gears for the mountains that surround my home. You wouldn't happen to live in northern Utah, would you? Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted January 4, 2023 Share Posted January 4, 2023 Rod, you are correct on recouping the cost. Maybe $25.00 per 1000 miles saved in gas at $3.00 per gal. But wear and tear on the drive train helps. An overdrive costs about 2-3 times a gear change. One gets a higher top [ smaller number] gear with od. More versatility since with od off one has the original gearing. I did lose that. Ben Link to comment Share on other sites More sharing options...
Rod Frazier Posted January 4, 2023 Author Share Posted January 4, 2023 24 minutes ago, Ben Bruce aka First Born said: Rod, you are correct on recouping the cost. Maybe $25.00 per 1000 miles saved in gas at $3.00 per gal. But wear and tear on the drive train helps. An overdrive costs about 2-3 times a gear change. One gets a higher top [ smaller number] gear with od. More versatility since with od off one has the original gearing. I did lose that. Ben Yeah, and my normal cruising rpm of 2500 would only get me about another 3.5 mph. I have no desire to run these things on the highway at 70 or 80 anyway, but 65 once in a while for an extended period would let me keep out of peoples' way a little better. I suspect your 50 is much more comfortable at speed. Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted January 4, 2023 Share Posted January 4, 2023 Same suspension and steering. Link to comment Share on other sites More sharing options...
Jim Nelson Posted January 4, 2023 Share Posted January 4, 2023 Your thoughts that if you have a 3.6 rear ratio, I would not change. No, I'm in flatland Florida so having the change to 3.6 or better works. But, living in big hill country, having the over drive lets me drive great in level country but down shift as low as you want. My '38 had a 4:44. rear so it was a 55 mph car. This way I can travel most anyplace even with 'normal gearing'. My 1935 has a 4.88 rear. That makes it a slow car -basically a speed bump in the areas I live in. With the OD in my 1935- 58 Vicky, I now have a 3.41 rear and slow crawl for regular busy driving. So, having OD. became a must if I wanted to go anyplace. Our 36-38 Buick Club is a driving club. So driving to any of our destinations required maybe driving 300 + miles to have our get together became 'must'. I live as an 'outlier' being I am along way just to get there - was a choice I made. Being necessary to drive on modern Inter-State highways means I needed to have 'tall gears' . So 'over drive' was my solution. I live in the Tampa / St. Pete area so keeping up with traffic was my thing. Its all in the choices you make. Our Buicks were built strong and drive miles that other pre-war cars can't stay with us. Our 'toy's are not cheep to keep up compared to modern cars. Brakes, tires, tune ups, shocks and low gas mileage compared to todays 25 / 35 mpg vehicles. I can trust my Buick to get me there and back. Things happen but that's life. 2 Link to comment Share on other sites More sharing options...
RiKi5156B Posted January 8, 2023 Share Posted January 8, 2023 I put a 3.60 third member and torque tube from a low mile 50 special with dynaflow in my 40 special sedan. Bolted right in no issues. 1/4" added to wheelbase. 1 1 Link to comment Share on other sites More sharing options...
Rod Frazier Posted January 8, 2023 Author Share Posted January 8, 2023 Thanks, all, for the good advice. If I get a good quote from the seller I'll make the buy and either stockpile the unit or offer it up to anyone else in need. 1 Link to comment Share on other sites More sharing options...
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