1938 Buick Special rear axle ratios? Upgrades?

[carlisle1926]

I just bought a 1938 Buick Special that had been sitting idle for many years. I knew the engine was locked, but after buying the car, I could not roll it at all. The rear brakes were not stuck, but the transmission was FULL of water as well as the rear axle. So, now I will have to pull the engine and transmission for a rebuild. I removed the U-joint from the transmission and now the car rolls freely. I haven't opened the rear axle yet, but I would assume that it will need new bearings and possibly gears. So my question is, is it possible to use use the gears from a later model Buick? And since I would like to drive the car a bit faster than it would have in 1938, are there any better gear ratios available that will give me a higher road speed? I'm not opposed to swapping the entire rear axle from a later model if there is any benefit to that. Do any of you know of any options?

[jenz38]

Do you had think about an overdrive ?

look here, its out of an older thread :

http://forums.aaca.org/f165/overdrive-buick-straight-eight-343398.html

[1939_Buick]

You could put a gear set from a series 60, but very hard to find.

Look here bottom of post 5. I try to collect threads on changing straight 8 diff ratios'. There is a lot of information in the Torque Tube magazines in www.1937and1938buicks.com I have a list of the articles for reference.

Easiest way is get an 1950's diff with a better ratio and modify to fit your 1938 housing. Essentially you machine 0.25" off the new 3rd member housing and modify (cut/weld) the torque tube. The image below is scanned from 1937and1938buicks.com

Edited May 24, 2014 by 1939_buick
spelling (see edit history)

[Mark Shaw]

My 38 Special came to me with a 37 Century ring & pinion that required some modifications to fit in the 38. It cruises nicely at 60 mph, but finding an early Century rear end will be challenging. Installing a modified 50s diff as above may be easier in the long run...

[carlisle1926]

I'm going to give the 1950's rear end install a try. A friend of mine has an extra rear axle from a 1956 Special that he says I can have. I wonder if it is the same as a 1955 axle. If it will work, I will modify it to fit the 1938 housing as above. He also has a friend that is hot rodding a 1938 Special sedan and he doesn't need the transmission, but the engine is destroyed in it worse than mine. I'm assuming by the above diagram, that the 1938 Buick torque tube housing will slide over the 1955 housing after it is cut down to about 1-1/2ft in length. I'm having a hard time wrapping my head around that one.

[1939_Buick]

From my reading 1956 will not work. A different design. Need 1955 or older.

Anyway you need to check the ratio. The '56 may be no better than what you have now Many like 3.6 from 1953-54-55 dynaflow

The torque tubes do not slide over each other but are cut and butt welded. The length of torque tubes/drive shaft is not the same as the 1938.

Go to 1937and1938buicks.com and download "Torque Tube 1937-38 Club vol XIV (14) Issue 2 Pg 18 Nov-95" I have found 15 articles on these diff changes in 1937and1938buicks.com.

Edited May 25, 2014 by 1939_buick (see edit history)

[carlisle1926]

That's disappointing to hear that the 1956 Rear axles are different. My search for a 1955 axle now begins.

From my reading 1956 will not work. A different design. Need 1955 or older.

Anyway you need to check the ratio. The '56 may be no better than what you have now Many like 3.6 from 1953-54-55 dynaflow

The torque tubes do not slide over each other but are cut and butt welded. The length of torque tubes/drive shaft is not the same as the 1938.

Go to 1937and1938buicks.com and download "Torque Tube 1937-38 Club vol XIV (14) Issue 2 Pg 18 Nov-95" I have found 15 articles on these diff changes in 1937and1938buicks.com.

[1939_Buick]

That's disappointing to hear that the 1956 Rear axles are different. My search for a 1955 axle now begins.

Others will have more knowledge than me on this. Did you get the large email I sent you?

You have several years to chose from:- 1940 to 1955 with a suitable ratio

[carlisle1926]

Yes I got the email.

[pont35cpe]

Jason, the torque tube pinion gear is at the same level as the axles in the `38 rear end, where the `40-`55 the pinion is approx. 2" lower than the axles, which changes the angle of the torque tube between the transmission and rear end, torque tube is also a larger diameter. Tube may bottom out where tube passes thru frame X member. Also will eat up the U-joint in rear of transmission because of angle change, not a straight line thru engine/trans/torque tube.. I learned all this the hard way after modifying a `50 rear-end for my`36.. Also the rear end housing is 4" thick on the `40-`55, the `38 may only be 3 1/2", which means the axles wouldn't line up with the spyder gears.. I`m not sure about the `38 axles, maybe similar to my `36, they`re both the same length, where the `40-`55 axles one is longer than the other. When you call Dave Tacheny he can advise. Tom

[1939_Buick]

.. I learned all this the hard way after modifying a `50 rear-end for my`36 ...

There is a big differnce between a '36 and 1937 and later diff's. 1937 changed to hypiod with pinion shaft lower. Will post drawings later. Many guys have put 1950's 3rd member cw&p's into 1937-1938's and later cars.

[pont35cpe]

1939, you had me thinking I was out of my mind, so I went to my brothers and crawled under his `38 Special. Pinion center-line is same as axles, as I stated. Pinion may be lower on the larger series, I don`t know, I`m only familiar with the 40 series.. What is cw&p`s? Tom

[1939_Buick]

From the 1937and1938buicks.com site info looks like 1937 series 40 & 60 was when Buick first used hypoid (off set) configuration. And in 1938 series 80 & 90 went to hypoid.

[pont35cpe]

1939, my brothers `38 Special(40 series) is all original and does not have the hypoid configuration. Also there is a `37-8 torque tube assembly listed on ebay item #141132361475, picture is not real clear on my computer, sure doesn`t look like a hypoid set-up to me. Attention Jason/Carlisle1926!! Could you take a good picture of your torque tube and post it? I`m confused!! Tom

[1939_Buick]

This looks offset.

http://www.secondchancegarage.com/public2/1937-buick-journal-10-1.cfm

http://www.secondchancegarage.com/public2/1937-buick-journal-10-2.cfm

Have other images on my home computer

Edited May 28, 2014 by 1939_buick (see edit history)

[pont35cpe]

1939, Excellent!! Definitely a Hypoid type. I didn`t know `37 was leaf springs, another difference from `37 and `38. My brothers `38 has coil springs(must be the first year). I`ll try to get a picture of my brothers and post it(if I can figure out how) to show it is not a Hypoid. I know I`m a little crazy, but I`m not completely "nuts".. Tom

[Guest JR9162]

Carlsile,

The differential assembly (pumpkin) in the Special rear axle is interchangeable from 1941-1955. These all have 12 splined axle shafts. The 1950-1952 (and maybe 1953) Special axles are virtually the same width as your 1938 Special axle. As stated previously 3.56 (3.60) gears were available in the dynaflow equipped versions, and 3.41 gears were available in the 1954 Century. The 1938 propeller shaft (inside the torque tube) is 6 splines where it mates to the transmission, the 1941-1955 is 10 splines. You'll need to use the front portion of your 1938 torque tube and propeller shaft (cut and welded) mated to the 50-52 Special torque tube and propeller shaft. Going this route eliminates having to disassemble the pumpkin (differential). Machining material off the face of a latter differential to fit it inside a 1938 Special housing will require a rebuild of the differential. Regardless of either method chosen, you'll have to modify your torque tube and propeller shaft. You will probably need to use your 1938's rear radius rods and parking brake bracket to complete the conversion. You will need to convert the 1950-1952 Special housing to tubular shocks as well.

Search this index of the Torque Tube publications http://1937and1938buicks.com/The-Torque-Tube/Torque%20Tube%20Technical%20Index%20By%20Frank%20Freda.pdf for various articles regarding upgrading your 1938 Special's rear axle ratio. Be advised the 1938 Limited and Roadmaster has a different rear axle than the Special and Century.

A 1956 Buick axle and/or differential swap presents two issues. Axle shaft splines were increased to 30 in 1956, and I believe the complete assembly is somewhat wider than a 1938 rear axle assembly.

Edited May 28, 2014 by JR9162 (see edit history)

[Leif Holmberg]

Here are some ratios from 1940s and newer.

Leif in Sweden

[MrEarl]

What a great tech thread. and a great title for future searches. Giving it 5 stars now.

[pont35cpe]

Alright everyone!! I`ve just returned from checking out my brothers `38 again, and after cleaning all the "Mud-Dobber Hotels" off and reveling all the housing it`s no doubt a Hypoid.. Excuse me while I go wash the egg off my face... Tom

[carlisle1926]

I've been out of town working for the past few days in the FtWorth, TX, area, and I am just now seeing all the responses. I hauled home two engines, two transmissions and a 54 Special Dynaflow rear axle assembly. One of the engines is a 1948 248 and the other is a rebuilt 1938 248 out of a friend of mines car that he hot rodded. Both 1938 transmissions will need to be taken apart and have new bearings installed. The 54 Special axle should be a 3.60 ratio, but I will need to count the teeth on the gears to know for sure. So, I plan on using this 54 assembly to modify to fit my car. I was talking to a friend of mine about the issues with my Buick and he suggested that I go see a mutual friend that has a LOT of old car projects. He had three 38 Buick shells that he is hot rodding, so he let me have these parts off of them for a great price!

[1939_Buick]

. I hauled home two engines, two transmissions and a 54 Special Dynaflow rear axle assembly.

A very good haul.

As the 1948 248 has side engine mounts, you need to fit the front engine mount plate from the 1938. And as the '48 has a stepped intake manifold use the '38

By modifying the transmission end on the torque tube & springs supports,etc you may be able to use the complete rear axle assembly

Please keep us informed of progress

Edited May 31, 2014 by 1939_buick (see edit history)

[Guest JR9162]

The 54 Special axle should be a 3.60 ratio, but I will need to count the teeth on the gears to know for sure. So, I plan on using this 54 assembly to modify to fit my car.

No need to count the teeth. Just drain the lube oil (dope to you old timers) from the differential, remove the rear cover plate, and rotate the ring gear around until you can read the numbers stamped upon it. For instance a 4.10 ring and pinion will have 41/10 stamped on the ring gear (crown gear for those down under). Find the numbers and do the math.

Ok guys, found one, will look for more. Read the tech tips contained here: http://www.1937and1938buicks.com/The-Torque-Tube/Volume%20XIV%20Number%203%20(January-February%201996)%20(From%20Dug%20Waggoner’s%20collection).pdf

More: http://www.1937and1938buicks.com/The-Torque-Tube/Volume%20XXV%20Issue%201%20(Fall%202006)%20.pdf

Another method: http://www.1937and1938buicks.com/The-Torque-Tube/Volume%20XXIV%20Issue%204%20(March-April%202006).pdf

More: http://1937and1938buicks.com/The-Torque-Tube/Volume%20IV%20Issue%202%20(October%201985).pdf

Edited May 31, 2014 by JR9162 (see edit history)

[carlisle1926]

I haven't measured yet, but if the 54 Special axle that I have is the same width as the 38 axle, I might consider just removing all of the shock and spring hardware from my 38 and welding them onto the 54 axle. That would leave only the end of the torque tube to be changed out. I would prefer to do that over having to have 1/4" machined off of the 54 third member.

[Guest JR9162]

I haven't measured yet, but if the 54 Special axle that I have is the same width as the 38 axle, I might consider just removing all of the shock and spring hardware from my 38 and welding them onto the 54 axle. That would leave only the end of the torque tube to be changed out. I would prefer to do that over having to have 1/4" machined off of the 54 third member.

My sentiments exactly!

[MrEarl]

Re the rear end ratio, you may need to clean it up to see them but there should be numbers stamped on the bottom of the housing. 3/4 for 3.4:1 (50,60 and 70 series w/Dflow) 3/6 for 3:6:1 (40 series w/dflow) and 3/9 for 3.9:1 (3 speeds)

[74 Apollo]

There is a set of 1937 Century rear gears for sale in the Buick Bugle. Contact Bill 870-430-5277

[MrEarl]

BTT for this great thread. 

[MrEarl]

On 5/31/2014 at 1:37 PM, carlisle1926 said:

I haven't measured yet, but if the 54 Special axle that I have is the same width as the 38 axle, I might consider just removing all of the shock and spring hardware from my 38 and welding them onto the 54 axle. That would leave only the end of the torque tube to be changed out. I would prefer to do that over having to have 1/4" machined off of the 54 third member.

 

Any news to report back on on this swap?

[Jim Nelson]

Carlisle,  the 54 ratio's are:  3.6 for the standard shift.  All the dynaflows had the 3.4 ratio.  I'm putting the 3.4 in my 37 coupe.  It requires using the '54' third member which is machined -.250"  on the flange so the centerline of the axels matches the centerline of the '54' ring & pinion.  You WILL have to rebuilt the pinion bearings.  Mine had about 50,000 + miles.  I bought a '54' service manual to tell you how to repair thr '54' rear.   I am in the middle of the mod's and instillation.   I'll finish with a 60/65 mph car.  It's now a 50/55 mph car which in my area is way to slow.  I get run over now-- I don't believe in running my engines around 3000 + rpm.  I now run 2500 to 2800 rpm all day.  My 38 coupe has overdrive , with the original rear.  This gives me 2450 rpm and 65 mph.  I've driven that system  on +1600 mile trips.  Any questions on this,  e-mail me at :  oldbuickjim@gmail.com