I am trying to research which rear end is under my '57. What a surprise when I looked and found "no bolts". I was expecting to see 10 or 12 which is what I usually found in my other Tri-Fives. So I checked out the front driver side for casting numbers and saw 1246 over 3726898 with a large GM. Also looks like a small 10 or 16 after the GM. Any ideas?
That appears to be a stock rearend. The casting number is for a '55-'57 Chevy passenger car. If you are used to seeing 10 bolts or 12 bolts on the back of the differential, you are referring to a later, mid-60's to early 70's diff. Bob
A stock 57 differential would be a removable center section as you have pictured . If others you had were integral carrier , ( bolts on the rear) the differential had been changed , Chevy didn't have integral until 1965 .
Hello, All of our teenage high school Chevy Sedans had almost the same factory rear end. The center third member with different gears was "loaned" out to the 57 Chevy Bel Air from my own 58 Impala rear end. We had a stock 58 rear end that looked the same and accepted the same third member positraction center section. Years later, my 1965 El Camino had a completely different looking rear end with the exposed rear plate with nuts showing to the rear. Your unit from the 57, the center section (third member with the gears) gets removed from the front, after disconnecting the driveshaft and pulling out the rear axles. The axles do not have to come all the way out, but just enough to be free of the center gears. The Positraction unit or even the non-Positraction unit but with different gear ratios will pop out and be transferrable to any 55-58 units. The only odd ball thing is to add the Positraction gear oil if you have Positraction. Jnaki I changed the rear third member many times from a 4:11 gear ratio and popped in the complete 4:56 gear ratio on a weekly basis for weekend drag racing IN THE 58 IMPALA. It was worth the effort at the drags. When we borrowed the 4:56 gearing for my friend's 1957 Bel Air, modified 283 with dual quads, it gave him some extra performance off of the starting line. Finally, when we built our 1941 Willys Coupe, it had it own 56 Chevy complete rear end and the exchange of gear ratios was simple, since everything else was the same Chevy rear end models.
Thanks guys. That does make sense considering the other Tri-Fives were modified and i never thought about the rear end had been changed. One last question. I read on here the way to check the gear ratio was to jack up the car and rotate the rear wheel and count the rotation of the drive shaft. When I did it, I rotated the tire twice and the drive shaft turn 3.5 or maybe just over a half turns. Is that considered a 3.55 ratio?
Oh and am I correct in thinking that the original manual 3 speed was not the close ratio tranny? Weren't those just 4 speeds?
sounds like you have the 3.55 gears. The transmission should be a wide ratio. there is lots of info on the car here, you have to search for the vehicle info kit for 1957 chevy https://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html .
100% stock Tri-Five rear end; if it has a drain plug in the housing, then it's a 57. If the car originally had an automatic transmission, then the gears are 3.55, sticks had 3.70, and sticks with overdrive had 4.11's. 55-64 full size cars, 62-64 Chevy II/Nova, and 56-62 Corvette's used the same basic third members; stay away from the Chevy II/Nova's as they use very thin third member cases, and smaller bearings. I am Butch/56sedandelivery.
Those housings must be starting to get some value. I pulled the 57 rear end out of the 38 and replaced it with a nine inch Ford. Just because. I had went through three different pumpkins in the 57 rear end. My cousin needed the pumpkin for a car he was working on and I gave him the whole assembly. He used the pumpkin and then later bragged about selling the housing for $200 and he didn't even buy me lunch
It might be a 57-64 Olds Pontiac 9.3. If it is, you have one of the strongest differentials going.. Stronger then a 12 bolt by the way..
Plus it has the fill plug on the back and I don’t think Pontiac/Olds did that. Sent from my iPhone using The H.A.M.B. mobile app
As stated the 55-56 did not have a drain plug on the bottom but the '57 did. If yours is a '57 keep in mind that the axle bearings are larger than are the 55-56.
Your third member will fit '55 to '64 Chevy passenger cars and '55 to '62 Corvettes. 3.55 is a desireable gear ratio anymore.
In '55-'56, with 15" wheels, the manual transmission cars got the 3.70 gears (unless you had overdrive, in which case you had 4.11) and the automatics got the 3.55. In 1957, with 14" wheels, the manual transmission cars got the 3.55 and the automatics got a 3.36. So 3.55 gears would be correct for your car with manual trans.
57 axle is also different than a 55,56. I think it's a one year only. I broke drivers side a couple of years ago and was told that by a guy that worked on tri-fives for years. I guess they are getting harder to find.
Thats a stock 57 rear. I have the same rearend in my car. Sent from my iPhone using The H.A.M.B. mobile app
In 1955 there were ONLY 3 gear ratios: 3.55 (Powerglide tranny), 3.70 (3sp), 4.11 (3sp O/D) In 1957 they were: 3.36 (Powerglide tranny), 3.55 (3sp), 4.11 (3sp O/D) Chevy upped the ratios to compensate for smaller wheels on the 57
I just found some information on 3 speed manual transmissions in the link Squirrel provided. https://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html In this link for 1957 Chevy's it says there were only two options for 3 speed manuals. They were 3 speed overdrive or 3 speed close ratio. Based on this document if you have an original it would have to be one of those or else its not original.
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