Rear Axle Question - '55 Chevrolet - Team Camaro Tech
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post #1 of 17 (permalink) Old Jan 20th, 13, 11:08 PM Thread Starter
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Rear Axle Question - '55 Chevrolet

I have a 55 Chevy 2nd series I am re-doing. But as I received it and even today = it has a stock 305 (not 350 - the seller ripped me off) with a 350 trans and a 2.56 rear end and it is NOT a dog in any sense of the word. She scoots quite well.
I have verified the 2.56 by counting teeth and by reading the "1 GM 3984822 1 77" code on the Ring Gear. Trouble is, I can not determine what it is from. I found "GM 18" cast on the passenger side of the differential housing and "1254333" on the drivers side. I can find a GM 8 but not a
GM 18. NOTHING on the passenger side axle housing, no stamped letters / numbers or other identification anywhere. The 1 and GM tell me it is a Chevrolet, produced by GM and the 1 77 appears to be telling me it was assembled in January 1977.
It has leaf springs and 9.5" diameter brake drums and 2" wide shoes. The axle has been flipped = is on TOP of the leaf springs. It has other tweaks - like a '89-'93 Chevy S10 front clip and the worst wiring I have even seen in any vehicle (got a new wire harness and I have modified a '69 Chevy 302 with a Roller Cam and 3-2s and a TH700R4 almost ready to go in (post rewiring) I am looking at a Chevy 12 bolt Posi 3.42 for leaf springs. It has drum brakes and may be 65 or 66. Unfortunately it has 6 lug axles and is priced at $500.00 as is = needs at least new axles.
I am a 73 yr old retired & partly disabled vet (ex-Submariner and RDT&E Diver) building my 1st street rod (since the mid-60s), so I am very short on knowledge, forgot a LOT over the years. I'm a dummy on rear-ends and suspensions. Any info / helps from you wise youngsters would be greatly appreciated. I live in the Clearwater-Largo area of Florida. Anyone nearby?
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post #2 of 17 (permalink) Old Jan 20th, 13, 11:27 PM
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Re: M21 and 3.42 ring & pinion

Murf, you dug up a pretty old thread.

First, thank you for your service.

The combination that was being talked about (2.56 rear axle ratio and M21 transmission - which has a 2.20 first gear) was generally being talked about as not ideal at take off from a stop. Your combination of 2.56 rear gear and TH350 transmission (which has a 2.52 first gear) would not be quite as bad off the line.

The 12 bolt you are looking at with 6 lugs is from a truck. Not ideal for use in a car.

I believe the 55 Chevrolet rear axle is about 60 inches wide from wheel mounting surface to wheel mounting surface. Others that are close to that width include 55-64 Chevy Cars, 67-69 Camaros, 68-79 Novas (and sister cars such as Pontiac Venturas) and some Mustangs/Cougars from the early 70s. Your best bet might be to find an 8.5 rear from a 73-79 Nova, but be sure it is an 8.5 and not a 7.5 rear. The 8.5 can be built to be almost as strong as a 12 bolt.

Follow this link to see how to correctly identify an 8.5 rear axle.
http://www.novas.net/forums/showthread.php?t=5066

Maybe we can have one of the moderators start a new thread for Murf?

Sorry I don't live closer. I am about 1500 miles away from your area.

68 Camaro SS 396 - 468 BBC now, M21, 12 bolt 3.73 coded housing but w/ 3.31 gears.
Looking for 68 Camaro with body number NOR 181016
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Last edited by bcm66; Jan 20th, 13 at 11:52 PM.
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post #3 of 17 (permalink) Old Jan 21st, 13, 03:55 AM
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Re: Rear Axle Question - '55 Chevrolet

Quote:
Originally Posted by surfmurf View Post
I have verified the 2.56 by counting teeth and by reading the "1 GM 3984822 1 77" code on the Ring Gear. Trouble is, I can not determine what it is from. I found "GM 18" cast on the passenger side of the differential housing and "1254333" on the drivers side. I can find a GM 8 but not a GM 18. NOTHING on the passenger side axle housing, no stamped letters / numbers or other identification anywhere. The 1 and GM tell me it is a Chevrolet, produced by GM and the 1 77 appears to be telling me it was assembled in January 1977.
It has leaf springs and 9.5" diameter brake drums and 2" wide shoes. The axle has been flipped = is on TOP of the leaf springs.

I am a 73 yr old retired & partly disabled vet (ex-Submariner and RDT&E Diver) building my 1st street rod (since the mid-60s), so I am very short on knowledge, forgot a LOT over the years. I'm a dummy on rear-ends and suspensions. Any info / helps from you wise youngsters would be greatly appreciated. I live in the Clearwater-Largo area of Florida. Anyone nearby?
Welcome, Murf, and Thank you for your time and your famliy's time in serving.

Agree with bcm66, truck axle, you're looking at - save your money.
I have seen, right after the date on the ring gear, two sets of numbers, as these are teeth count on the ring gear and pinion, ie, '10 41' = 4.10; '9 37' = 4.11.

Agree with you being a Chevrolet and circa 1977, but generally, rear GM brakes are 9" dia X 2" wide. Maybe rear axle from a Camaro/Nova?

Axle on top of the springs was an old school trick for height.
Pictures? Both, of your ride and rear axle? It would be interesting to see.

Yes, I did move this question to its own thread.

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post #4 of 17 (permalink) Old Jan 21st, 13, 09:57 PM Thread Starter
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Re: Rear Axle Question - '55 Chevrolet

Sorry about climbing on such an old thread - I'm pretty darn old myself. I'm a newbie here and haven't figured out blogs and forums yet. Been using 'puters since the mid-70s, but it all keeps changing so fast.

Thanks for the 12 bolt truck rear end advice. The darn thing just went up $100 to $600. Odd for something that is not selling.

OOPS, sorry guys - To clarify - my '55 2nd series is a '55.2 Chevy 3100 PICKUP (the '55.2 is the newer '55-'59 model, not the '47 to '55.1 model) and definitely not the famous car. Had a '55 Bel-Aire 6 cyl in '58. Put a 348 Tri-power with 4 speed in it. Car was stolen while on duty in Hawaii, but they didn't get the 348. Followed it with a '56 Vette 265 w/ 2-4s stock. My shotgun and I were the only "Howlies" in Corvettes Hawaii (a Kool group). Some years and a '57 Chevy Nomad, '63 T-bird and then a '69 Z-28 (the REAL Z) back in '69 and a '79 Datsun 280ZX and then a '87 Chevy Z-28 (again). I liked the '69 best of the two Z-28s. Others have come and not yet gone ('34 Ford Pickup and '90 S-10 4.3L EFI long-bed (was gonna combine the two), now gonna sell these 2 as a package. Also have '81 Silverado 350-350 with a complete '81-'82 'Vette rear and hydraulic dump bed I plan to sell. But I digress.

My current Pickup's rear is a 10 bolt and appears to be a 8.5" (hard to measure in the housing, but I am pretty sure I've got it right at 8.5" {versus an 8.2"}). The gearing is 16-41 for a 2.56 ratio, for sure. Ring Gear reads 1 GM 3984822 16-41 1 77 (I forgot the 16-41 in previous message). I have seen the 3984822 mentioned on a Nova web site, but no one verified it as being from a Nova. The ring gear bolts appear to have 3/4" heads, may be 11/16ths. Need to check closer.
I measured 9.5" across the Brake Drum ID. It may truly be a 9.0"". Don't know.
I have no idea what an M21 (or M20) transmission is. Mine '55 Pickup is a TH350 and will be replaced by a TH700R4 with the '69 302 engine. I got a good measurement across the WMS to WMS and it read 61.0". Odd, 'cuz none of the rear end info I have, so far, has a 61.0". Info has 60.5" and 62.0".
Should I keep the 10-bolt 8.5" (if it is 8.5")? I'd like to put a Posi in it if it is a good rear. BUT, with a 2.56 that tells me it is a type 2, which is not so good / strong. Rather have a type 3. As I said before, ANY advice is appreciated. You guys are way ahead of this old man.
PS - future messages will be MUCH shorter.
PPS - Anyone want to sell or swap or buy stuff?

Thank you for the "service" kudos guys. I am just one of 10s of millions, but I wasn't forced into service for Korea or worse, Vietnam, like so very many others. And I came home. Been watchin' wars on TV since the '50s and Iraq is the 1st to make me cry - repeatedly. I hate political wars, 'specially when those who send us don't go or send their own kids either. Back to the Draft.

Submarine duty was way-kool!!! R&D diving was far-out! Murf
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post #5 of 17 (permalink) Old Jan 22nd, 13, 04:01 AM
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Re: Rear Axle Question - '55 Chevrolet

Try here:
http://www.novaresource.org/axle.htm

Muncie trans is an alum cased four-speed manual and the M20, M21, and M22 signify internal gear ratios, but all are 1:1 final gear. M20, I believe has a 2.52:1 first gear ratio, but you would still be shy of initial gearing with a 2.56 axle ratio.

If you measured 9.5 inches across the drum, then so be it. The mystery continues...
And mystery solved...1977 Nova axle, er, brakes at least, 9.5"X2"
http://www.rockauto.com/catalog/more...022&cc=1057373

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Last edited by Everett#2390; Jan 22nd, 13 at 04:06 AM. Reason: Added brake size
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post #6 of 17 (permalink) Old Jan 22nd, 13, 08:46 AM Thread Starter
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Re: Rear Axle Question - '55 Chevrolet

Hello Everett; I checked the rockauto.com dimensions versus mine. Mine are: OD of Drum = 11 15/16" / ID = 9.5" / INSIDE Depth of Drum = 2 9/16" / OUTSIDE Height of Drum 3 1/8" / 5 bolt holes but 4.50" on the bolt pattern spread. Remeasured the drum holes and the axle stud spread again and again. Must be Murphy's Law on bolt holes.
That bolt pattern spread is, surprisingly, 4.50", not 4.75". I expected 4.75 'cuz it has Ralllye wheels (wheels and trim look just like my ole '69 Z Camaro's). Boy Everett, you are quick. 1977 Nova ! Does the "er" mean maybe?
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post #7 of 17 (permalink) Old Jan 22nd, 13, 10:20 AM
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Re: Rear Axle Question - '55 Chevrolet

I have shown the rockauto link as a reference, and yes, 9.5 inch ID.
er - used as a written expression for a hestitation.

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post #8 of 17 (permalink) Old Jan 24th, 13, 11:29 AM Thread Starter
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Talking Re: Rear Axle Question - '55 Chevrolet Pickup

Hey Ev - those are a pretty dangerous looking animals you have there! Is he / she attack trained?
Funny how those critters always seem to sit on their hip. One of my Wolf-hybrids does the same.

Last edited by surfmurf; Jan 24th, 13 at 11:32 AM. Reason: embelished
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post #9 of 17 (permalink) Old Jan 24th, 13, 05:32 PM
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Re: Rear Axle Question - '55 Chevrolet

You must be talking about Miss Bessie, newest arrival here about 13 months ago.
Just the way she sits, very skittish, abused earlier in her life plus a puppy mill breeder, and is afraid of dragonflies, flies, and anything catching her attention - very alert.
She ain't no attack dog, but a heck of a watchdog - barks at everything moving outside the window - grass, flowers, people, other dogs, flag, etc., but she is coming around.

Jake & Elwood, could care less, unless a dog in on their sidewalk...

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post #10 of 17 (permalink) Old Jan 28th, 13, 11:16 AM Thread Starter
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Question Re: Rear Axle Question - '55 Chevrolet

Two more data points found. I did find the stamping on the passenger side axle. I was not looking up high enough on the axle tube. It reads PH G70411.
I found the PH on a Camaro & a Nova web site. The Camaro site data does not correspond with the other Camaro PH data. The Nova's PH indicates a 2.56 Open, which is what I have. It was used in 77 & 79 Novas, but not 78. 75-79 are 4th Gen Novas.
I can not find the G70 or the 411 ANYWHERE. Also need to look for G7 and 0411. I did see a G72 on one web site. I will review every single number I have found so far and look on the TOP surfaces of the Differential housing, (darn hard to do for this older fella with a head bigger than 4") but so far nothing is on any of its TOP surfaces. I am expecting castings as I can not get my eyes up above the differential housing to see or even feel any stamped alpha/numerics.
Murphy's Law is gonna drive me nuts = but that will be a SHORT drive.
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post #11 of 17 (permalink) Old Jan 28th, 13, 01:53 PM Thread Starter
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Re: Rear Axle Question - '55 Chevrolet

OH - and I also learned I was measuring the axle wheel bolt pattern incorrectly. I was told to measure from a 1st bolt to a 3rd bolt. I measured bolt center to bolt center and got 4.50". On http://www.mrt-wheels.com/boltpattern.html and another web site i learned I need to measure from the farthest / back side of bolt 1 to the center of bolt 3 or to measure center to center and then multiply by 1.05
By the way - that web site has lots of info, whether you are an off road-vehicle person or not.
I also found using 1.06 as the multiplier comes a bit closer than 1.05.
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post #12 of 17 (permalink) Old Feb 14th, 13, 01:54 PM Thread Starter
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Re: Rear Axle Question - '55 Chevrolet

As best I can nail this rear end down - it appears it is a 1977 Nova. The 2.56 ratio denotes it should be a Type 2 differential, BUT the 8.5" Ring Gear and the rest of the info says it should be a Type 3 differential. The axle housing reads PH G70411. The PH confirms it as a 2.56 open. I am guessing my 1969 Z 302 with a reduced 10:1 CR, roller cam of 284-288 Duration & 510 530 Lift, and 3 Rochester 2 barrels with a 1 3/32" venture that Rochester says is a 278 CFM (each) = 834 CFM total (when lead-footing it) and a TH700R4 (2000-2400 stall) in the middle. I am guessing it would be maybe 350 HP +/- a Shetland pony or two, that the Type 3 rear should be fine - whereas the Type 2 is questionable. As a street vehicle, I believe the "C" clips would be OK as is. [I am thinking of obtaining a Positraction and maybe Disc Brakes as $$ provide (unless I can find a reasonably priced 12 bolt.] I am still unsure what rear end or even Type I have, just that it its a 10-bolt, 2.56 open, C clip with ?? spline axles, but in good shape and is 61.0" WMS to WMS ( = without drums mounted).
http://www.crankshaftcoalition.com/wiki/Rearend_identification[/url] says: "The 8.2" was used through 1971 in the X-body (Nova) and through 1972 in the A-body (Chevelle). The 8.5" corporate 10-bolt rearend began production in 1971 to replace the 8.2" and 12-bolt rearends. There was simultaneous use of the 8.2 and 8.5 during the changeover period, like in the Nova." That "changeover" should have been long-gone by 1 77 !

This seems to confirm the 77 Nova MUST BE an 8'5" and thus a Type 3 (stronger) rear and thus a "keeper".
SO - anyone have any comments, suggestions, wise cracks, OR REALLY GOOD INFO? Happy Valentines Day to any ladies out there.
Murf
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post #13 of 17 (permalink) Old Apr 22nd, 13, 09:34 AM Thread Starter
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Re: Rear Axle Question - '55 Chevrolet

OOPs - phrasing error on my part. The 2.56 ratio was STANDARD in '77 and '79. It WAS used in '78, but was not a standard ratio
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post #14 of 17 (permalink) Old Apr 22nd, 13, 10:25 AM
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Re: Rear Axle Question - '55 Chevrolet

So you decided to take what route?

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post #15 of 17 (permalink) Old Dec 10th, 14, 12:27 PM Thread Starter
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Re: Rear Axle Question - '55 Chevrolet

Quote:
Originally Posted by surfmurf View Post
hello everett; i checked the rockauto.com dimensions versus mine. Mine are: Od of drum = 11 15/16" / id = 9.5" / inside depth of drum = 2 9/16" / outside height of drum 3 1/8" / 5 bolt holes but 4.50" on the bolt pattern spread. Remeasured the drum holes and the axle stud spread again and again. Must be murphy's law on bolt holes.
That bolt pattern spread is, surprisingly, 4.50", not 4.75". I expected 4.75 'cuz it has ralllye wheels (wheels and trim look just like my ole '69 z camaro's). Boy everett, you are quick. 1977 nova ! Does the "er" mean maybe?
x

Last edited by surfmurf; Dec 10th, 14 at 12:30 PM. Reason: I had already responded, duh! Old age is only for the brave! ! !
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