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rear end gears


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Guest imported_JPIndusi

I remember reading somewhere that on some years the axle ratio was stamped on the bottom of the rear end housing. I'm sorry but I cannot locate reference.

Joe, BCA 33493

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Good Morning Brian: Yes, the number of teeth for both the ring and pinion

were at one time stamped on the very underside of the housing/central hub. I have used

a steel brush to clean the housing to read the numbers and at times they

have been scraped or lightly stamped so they could not be read. If they

cannot be read the ring has the part number stamped on the side and can be

located by simply spinning the ring until the number comes up. The part

number mates with the pinion number so only the ring number is required to

look up in the parts book. Hope this helps. Patrick W. Brooks

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Guest imported_JPIndusi

Thanks Patrick for confirming my memory on the ratio being stamped on the bottom of the housing.

As a senior citizen, it feels good to know I am not losing it yet.

Joe, BCA 33493

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I got curious (ok, and a tad inebriated, it's Saturday night), so just went down to the garage and crawled underneath the rear-end of my 38 with a light, a rag, and a wire brush ... found "40" right on the bottom of the diff; not sure what that's saying, though I *know* it's a 4.4-1 ratio.

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That may be the number of teeth on the ring gear. Look more and you may find the number or teeth for the pinion which would be something like 9 which gives a ratio of 4.444444....to 1. To find this divide the number of teeth on the pinion into the number of teeth on the ring gear and this will give you the ratio. A lot of times these numbers are stamped in the gears along with the part number. <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" /> Dave!

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If you can crank the engine you can find out the ratio. Raise one of the rear wheels from the ground. Put a mark on, e g the lowest point of the wheel. Put in highest gear, crank the engine some full turns and notice how many turns the wheel turns. Remember that the wheel turns two times faster if one wheel is fixed. Example: If you turn the engine four full turns and the rear wheel tyrns two full turnd the rear end will be 1:4.

Jan

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  • 2 weeks later...

Do you or anyon else know what the actual #s of the rings and pinions that make up the various ratios. I am having a difficult time trying to get across to the owner what he has to look for. He has come up with 42 or 43 gear rings(give or take he says). He says he can't get easy access to the pinion to count them. Without the pinion # or a clue as to any differences in the ratios I'm having a hard time finding out what rear end he has. Just for your knowledge he had sold the 38' buick(he's not sure what model it was) and the rear end was a spare.

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  • 2 weeks later...

the gears are supposed to be 3.90s but do I need the whole rear end or just the ring and pinion gears. Also what do you have to go through to replace the gears. I haven't seen them yet but will it hurt them if they are rusty ? Pretty simple questions but as a novice any answers will help out. Brian

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The rear end isn't the hard part--it's the torque tube. The rear ends on these cars are like the Ford 9-inch where the ring and pinion are removed from the axle housing as a unit (actually, as part of the torque tube). Getting the original pinion off the torque tube and reinstalled on yours is the challenging part. It is a press fit with a 1-time seal and isn't really designed to be serviced. An experienced shop can probably handle it, but don't just take it to your local garage and see if they can figure it out. Most shops won't even know what a torque tube is, and if they don't, go somewhere else. I'm sure someone here has done the job and that they'll chime in with more information. Where's The Old Guy when you need him? <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" />

The ring gear is riveted to the carrier assembly. You can probably bolt it on using some Grade-8 or better bolts and either lock washers, nylock nuts or some Lok-Tite (or a combination of all 3). Just make sure you check clearances so that the bolt heads and nuts don't hit anything. It's been a while since I was inside mine, and I can't recall whether the rivets need to be flush or not. It will be obvious once you open it up whether you have room for a nut and bolt or if you have to find someone to rivet it back in.

You definitely don't want to install rusty parts in your differential case. But I'm sure it's only surface rust and not serious. Use a chemical rust remover or a wire wheel to knock it off and get it nice and clean before you install it. This is the easy part. <img src="http://forums.aaca.org/images/graemlins/laugh.gif" alt="" />

Hope this helps. Good luck with the job!

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Matt

I have stayed out of this conversation because I don't know about the 38 rear ends.The 37-38 club had an article in their news letter about using later gears, but I don;t have it available. When I changed the set up in my 40, I used the center section (pig) from a 55 (3.42) and installed the drive shaft and torque tube from my original unit. It was quite a chore removing them, and the big problem was getting the drive shaft to run true. There is a section in the 40 shop manual that explains how it should be done, but I did not have the equipment available , so I locked the rear end to the floor,and used my hydraulic jack to bend the drive shaft. It took 3 times before I got the vibration out of the drive line at 70MPH

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Guest imported_JPIndusi

I had the rear end changed on my 1948 Special from the 4.44 to a 3.36 to 1 from a later model Buick, probably a 1955. I wanted a 3.60 but couldn't find one and was shipped a 3.36 that I was told was a 3.60. However, it seems to work out OK. The work was done by a fellow, then on Long Island, but now in upstate NY. He removed the entire assembly from the car, separated the torque tube and radius rods from the housing, then removed the original pinion from the driveshaft by grinding down the rivet/roll pin and driving it out. Next he removed the old pumpkin and installled the replacement pumpkin into the housing, connected the original driveshaft to the new pinion shaft with a roll pin, then connnected the torque tube to the pumpkin.

I have had it up to 70 MPH with no problems, although with 6:50X16 tube type bias ply tires and drum brakes I am cautious about high speeds. I generally keep it at 60 MPH and below.

My understanding is that the housings are identical from 1940 to 1955. There was a lengthy and detailed article on adapting these pumpkins to 1937-39 Buicks but I would have to search for it. As I recall there was a fair amount of machining, cutting, welding and balancing.

Joe, BCA 33493

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