So a guy offered to let me have a core 55 Chevy rear axle. Said third member is junk but housing is good and the axles should also be good. I have a pristine 3.36 geared open differential from a 58 Chevy. I've read where 57+ p case into 55/56 Chevy axle housings required some clearancing. Is that just on the p case? Or would even some clearancing need to be done for my non posi third member?
The only caveat I know of is that if you used axle shafts from a non posi rear with a posi center, you have to grind about 1/8 of an inch of off the ends of the shafts for clearance.
When a young guy I purchased a third member from a totaled 56 Chevy state patrol car & found the ring gear was much bigger & wider yet the same ratio, had to grind the factory housing relief a tad to permit it to fit, seems I recorded part numbers at that time.
Hello, When we were teenagers, we had a gaggle of Chevy sedans as our hot rod race cars and cruisers. Two 55 Chevy sedans, a 56 post model, a 56 Bel Air Hardtop and of course, my 58 Chevy Impala. prior to 1960, we also purchased a 56 Positraction Chevy rear end from our local s****yard. It was in excellent condition with a few additions/changes, fit right into our 1940 Willys Coupe we were modifying to race in the gas coupe/sedan cl***es. The 56 Chevy had a 4:11 Positraction unit and our 58 Impala also had a 4:56 Positraction unit. So, now we had an interchangeable item to go back and forth. As long as we continued to use the smelly special Positraction oil with each changeover. It was my first heavy (pun intended) duty third member swap as a weekly job. My brother wanted to have a chance to win against other stock cars using his 4:11 rear gears, with everything else even. The top opponents had 4:56 Positraction gear as approved by the tech committee. So, of course, he wanted to race on Saturdays using the 4:56 gears. As anyone knows, 4:56 is not the most friendly everyday street set of gears a it makes the motor work overtime. My weekly job was to get under the 58 Impala on Thursday after school and complete the swap each week. Jnaki They both fit easily, as long as you remember to put in the specific Positraction oil if using the complete unit. If not, then normal GM rear axle oil is standard. Do they fit other 55-58 Chevy rear axle housings? Yes. At one time, our 40 Willys Coupe had a 56 Chevy Positraction rear axle housing. We put in the 4:56 gears + the smelly oil. The Impala had the 3:78 gears non Positraction. So, where were the 4:11 Positraction gears? My friend and I installed the Positraction 4:11 gears in his 57 Chevy Bel Air Hardtop for a weekend and then extended it for a couple of weeks, of “extra” fun. YRMV
@Johnny Gee posted a chart, I saved it, will see if I can find it. This made sense to me at the time…
Hello, One last thing, as far as cruising around in a powerful 348 /280hp Impala, it was interesting as the 4:56 Positraction gears were in place. The Impala was ready for any challenges or situations on the dragstrip or street encounters. But, the motor did wind up high RPMs, as we cruised down the highway. The 4:11 Positraction gearing was good for any encounter, with the 280hp making up for any other thing missing other than a little more quickness off of the starting line. Overall, it was the best for highway cruising and drags if necessary. If we ran with the Bruce Slicks neatly tucked under inside of the rear fender openings, it was almost unstoppable. The black on black on black was always good for some intimidation. Ha! But, with those Bruce Slicks and the C&O Stick Hydro transmission + the 4:56 gears, nothing went faster on the So Cal streets at the time. If we were doing some road cruising, like the two separate times we had planned on a trip to San Diego from Long Beach, we put in my friend's 3:55 stock gears with no Positraction. Now, it was a great highway cruiser and at freeway speeds + the long stretches along the coast, it was a great riding sedan. During the holiday season, even in snowy conditions, the 4:11 Positraction proved do well on the upper elevations in the local So Cal mountains. Once the carbs were adjusted, the Impala was a great running/handling car during the snowy months and vacations. Jnaki Overall, the 4:11 Positraction gears were the best overall, daily driver to school, cruising on Fridays/Saturdays and holding our own at the dragstrip. Grip, acceleration and power... what more could one ask for in a street sedan, even during the custom car/hot rod phase? Thanks for the memories, @themoose Note: At the time of our backyard garage sale of our left over parts from our 1940 willys coupe build, one of the first things to sell fast as soon as the ad came out in January 1961 was the 56 chevy rear axle housing as noted: Positraction wording was left out due to cost of the ad and space. YRMV
I built a '23 T with a '55 Chevy rear axle and a 327 and 4.11 gears. The housing actually twisted and the center section ended up pointing skyward, necessitating a change to a 12-bolt. If you are planning to put a significant amount of power through the axle I would choose a stronger unit.
3:36, 3:56, 3:70(most) non posi. 3:08 can be had but I don't think it was available in '55. 3:70 was most standard shift cars. 3:56 for auto's. Think 3:36 was an option. Just fyi, i've had plenty of 'em, they are weak and prone to noise. EasyPeasy and you're o.k.
The housing twisted like a candy cane or barber pole. Between the ladder bar rear suspension and the pig. The pig ended up out of alignment to the driveshaft by about 10 - 15 degrees. The housing was less than 3" in diameter and the wall thickness was thin. Full disclosure - I used drag slicks from time to time. A 10 second ride.
Hello, Good advice, but for every build, folks have their own construction goodies to show and tell. Our 283 stock SBC long block motor with added on, 6 carbs on top and an Isky Cam. Not a super high horsepower unit for the LaSalle transmission and a 4:11 Chevy Positraction rear axle set up. But, it was supposed to be a daily driver/weekend racer. Gas Coupe and Sedan cl***es were originally set up for that purpose. The Reath Automotive folks told us that the 4:11 Positraction unit was pretty strong and should work well. When we approached Joe Reath again on our 2nd rebuild of the new 292, after month of racing, we originally wanted to go 1/8 over and ½ inch Reath Stroked Crank for a full 352 cubic inches. He suggested a 1/8th over to 292 and stock it full of blower spec parts to go along with a new 671 supercharger now coming on the market for SBC motors. So, our friend in Los Angeles was also fine with that notion and said he had a way to get a new 671 blower drive for us. A week later, we had a new, before the full speed market blast, Isky-Gilmer Belt Drive Kit and Edlebrock manifold. It had not been shipped to the full speed shops in So Cal, as yet. Jnaki So, now, luckily my brother had saved enough to get the full “blower spec” parts suggested by Joe Reath. He gave us a new crank as we spent a lot for all of the special parts for the new 292 cubic inch SBC motor. No dyno runs, but Reath Automotive folks estimated at least a 500 hp motor with the 671 and 6 Strombergs on top. At the time, we were flabbergasted at that suggestion. we just wanted a smooth running motor to use at the drags and then finish it for our daily street driving. Yes, we had options for the blower pulleys +/- Joe Reath also said our drive line and ch***is set up was perfect for the new horsepower and motor set up. He suggested a Two Port Hilborn Injector System in a few months as the pipeline said one was in the making for the 671 on an SBC motor. When Joe Reath came over in the Lion's Dragstrip pits, he was impressed at what we did and how the motor sounded. Then he told us to stop by his shop for some "hot" spark plugs. Ha! My brother was already making plans with an infusion of cash and had set up an order of the Hilborn System, a new wider set of M&H Slicks and a set of Halibrand Mags all around. I also installed the 4:56 Positraction gear set up from our 58 black Impala tow vehicle into the 56 Chevy axle housing. Everything fit perfectly, including the smelly Positraction oil straight from the local Chevy parts dealer's counter. The all new stuff was going to be ok for the driveline we had in our original build, despite the increase in horsepower we now had and would have in the future… YRMV
Busted a tooth off the pinion on my 55 BelAir in front of my then girlfriend’s ( now wife of almost 52 years) house. I paid a retired neighbor of my aunt $10 for the pumpkin from a 58 Chevy sitting on sand, with no wheels. Jacked it up with a bumper jack, pulled the axles, driveshaft, and differential with the car precariously perched on that tippy jack. Looking back, I could have been crushed, and there was nobody within a half mile to recover my body.
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