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Username Post: what ratio is this differential        (Topic#353531)
junky 
Valued Contributor
Posts: 3429

Loc: Northeast CT
Reg: 06-27-10
10-20-18 05:29 PM - Post#2749133    

I picked up a differential, but don't know what the gear ratio is. When I turn yoke 1 3/4 turns, the axle will make one complete revolutions. Can you determine what the gears are from this information? thanks Junky

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 




YOUNG57 
Frequent Contributor
Posts: 1217

Loc: Tennessee
Reg: 12-06-10
10-20-18 09:36 PM - Post#2749148    
    In response to junky

“the axle will make one complete revolutions”
Both axles need to turn together to get a good count.



 
pvs409 
"8th Year" Gold Supporting Member
Posts: 2907
pvs409
Loc: Sergeant Bluff, Iowa
Reg: 01-10-05
10-20-18 09:43 PM - Post#2749149    
    In response to junky

  • junky Said:
I picked up a differential, but don't know what the gear ratio is. When I turn yoke 1 3/4 turns, the axle will make one complete revolutions. Can you determine what the gears are from this information? thanks Junky



There are factory stamps on the passenger side of the third member stamped into the metal that are tied to the original gear radio(61 to 64’s). There are two letters and numbers, the 2 letters indicate the rear
end ratio.
Paul

57 BelairHT 283/270hp 4 spd
62 ImpHT 327/300 4 spd
62 Imp CV SS 327/300HP 700R4 (sold)
62 Imp HT SS 409/482 stroker 4 spd
62 Imp SS 409 - 5 spd Convertible
http://paulstensland.com


 
Verne_Frantz 
Member #574 "61-64 Subject Matter Expert"
Posts: 5773
Verne_Frantz
Loc: Hightstown,NJ USA
Reg: 08-22-00
10-21-18 06:54 AM - Post#2749174    
    In response to junky

It's probably a 3.55 open rear.

Verne



 
omarine 
Silver Supporting Member
Posts: 270
omarine
Loc: San Diego
Reg: 06-29-15
10-22-18 07:47 AM - Post#2749237    
    In response to junky





61 Impala bubbletop, 283, 2bbl Rochester, generator, points and drum brakes- daily driver
'49 Harley Davidson FL - Panhead


Edited by omarine on 10-22-18 07:50 AM. Reason for edit: No reason given.

 
Gene_Schneider 
Ultra Senior Member
Posts: 12282

Loc: Wisconsin..USA
Reg: 09-27-02
10-22-18 11:34 AM - Post#2749249    
    In response to YOUNG57

There will be two letters and two numbers stamped into the differential housing, front, right side at about the 9:00 O'clock location

ChevGene 1934 Master sedan 1939 Master DeLuxe Town Sedan 1950 Styline DeLuxe Power Glide 1957 Nomad 283 PG 1963 Corvair Convertible


 
raycow 
DECEASED
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raycow
Loc: San Francisco, CA
Reg: 11-26-02
10-22-18 12:48 PM - Post#2749258    
    In response to junky

Gene is correct about both the probable ratio and the stamping. However, I usually find it easier to determine the ratio by counting shaft revolutions instead of looking for the stamp (which on some cars can be difficult to see or read) and then decoding it.

Jack one rear wheel off the ground and turn it TWO revolutions with the transmission in neutral and the parking brake off. The number of driveshaft revolutions will equal the axle ratio. If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both wheels off the ground and turn either wheel only ONE revolution. Count the driveshaft revolutions the same as for an open rear.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
junky 
Valued Contributor
Posts: 3429

Loc: Northeast CT
Reg: 06-27-10
10-22-18 04:42 PM - Post#2749283    
    In response to raycow

The complete rear is out of the car. I did hold one axle, and turned the driveshaft 1 3/4 turn, for the other axle to make one complete revolution. I did find a stamping and the first letter looks like a partial B second letter is also a B and then the number 2. The second number is illegible. It has a round solid tag at 1 o'clock.
A little paint remover brought up the last digit. It is a 4. There is a big space between the 2 and the 4.

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


Edited by junky on 10-22-18 05:21 PM. Reason for edit: add additional information

 
Shepherd 
Frequent Contributor
Posts: 2080

Loc: Lake George, NY
Reg: 11-11-15
10-22-18 05:29 PM - Post#2749289    
    In response to junky

If it's exactly 1.75, then it is most likely 3.55.



 
Verne_Frantz 
Member #574 "61-64 Subject Matter Expert"
Posts: 5773
Verne_Frantz
Loc: Hightstown,NJ USA
Reg: 08-22-00
10-22-18 08:39 PM - Post#2749308    
    In response to Shepherd

  • Shepherd Said:
If it's exactly 1.75, then it is most likely 3.55.



I thought I already covered that.

Verne



 
junky 
Valued Contributor
Posts: 3429

Loc: Northeast CT
Reg: 06-27-10
10-22-18 09:02 PM - Post#2749311    
    In response to Verne_Frantz

The stamped code BB according to the 348-409 website is a 3.36. I will get a picture in the morning. What do the two numbers mean .. they are 2 and 4 or 24?

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
Shepherd 
Frequent Contributor
Posts: 2080

Loc: Lake George, NY
Reg: 11-11-15
10-23-18 05:13 AM - Post#2749324    
    In response to Verne_Frantz

You said, probably, just agreeing with your assessment. Lol



 
Verne_Frantz 
Member #574 "61-64 Subject Matter Expert"
Posts: 5773
Verne_Frantz
Loc: Hightstown,NJ USA
Reg: 08-22-00
10-23-18 05:49 AM - Post#2749326    
    In response to junky

Besides the two letters to designate the original ratio, there should be 4 numbers: Month 01-12 and day 01-31.

Verne



 
DZAUTO 
Member #51
Posts: 8906

Loc: Mustang, OK, USA
Reg: 12-25-99
10-23-18 07:17 AM - Post#2749333    
    In response to Verne_Frantz

If everything is all original, then the solid round tag is the key. It indicates 3.36.





 
beagrizzly 
"11th Year" Gold Supporting Member
Posts: 2123
beagrizzly
Age: 70
Loc: south texas
Reg: 08-04-12
10-24-18 11:52 AM - Post#2749437    
    In response to junky

Junky,

I think you misunderstood Ray. He meant to turn the axle exactly two full revolutions, and count the driveshaft revolutions. Mark your yoke, and mark it again when done. Get it exactly. There isn't much difference between a 3:36 and a 3:56 ratio.

Watch it closely. It will make at least 3 full revolutions before you get close. Then if it goes another 1/3 turn, you have a 3:36. If it goes a half turn, you are looking at a 3:56. A little over 4, and you have a 4:11, and so on.

However many turns you get there is your actual ratio.

This rule of thumb has worked for me since I was a child. That was when dinosaurs still roamed the earth.

Griff

if you're gonna be a bear..................

1960 Biscayne (the 6T)
2005 Yukon XL
2007 GMC Sierra Classic 8.1
2009 Silverado
2011 Escalade ESV


 
Tri5man 
Valued Contributor
Posts: 3898
Tri5man
Loc: Possums Crotch, KY
Reg: 06-26-07
10-24-18 12:51 PM - Post#2749442    
    In response to beagrizzly

If you read he original post he said he just picked up the differential and wanted to know the ratio. No where does it say its currently installed in a car. Doubt all the information about determinating the ratio on a differential installed in a car will answer the OP's question.
Still good information.

Gary



 
grs 
Contributor
Posts: 164

Loc: Texas
Reg: 07-04-14
10-29-18 11:08 AM - Post#2749884    
    In response to Tri5man

Count the number of teeth on the ring gear and the pinion gear. Then you divide the number of the pinion gear into ring gear.



Edited by grs on 10-29-18 12:10 PM. Reason for edit: No reason given.

 
raycow 
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raycow
Loc: San Francisco, CA
Reg: 11-26-02
10-29-18 01:08 PM - Post#2749904    
    In response to grs

What if my X-ray vision module is in the shop for annual maintenance, and I don't want (or am not allowed by the owner) to pull the center section?

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
junky 
Valued Contributor
Posts: 3429

Loc: Northeast CT
Reg: 06-27-10
10-29-18 03:06 PM - Post#2749922    
    In response to raycow

for a little clarity, here are the pictures of the spare differential that I asked about originally.





Based on your chart above, this is a 3:36 differential.

This is where it gets a little weird, since the differential in my car has the same BB stamping, but the tag has a second hole in it, which would designate that it is a 3:55.

This is the date code on my differential.



And here is the tag picture.



Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


Edited by junky on 10-29-18 03:09 PM. Reason for edit: No reason given.

 
A White Sport Coupe 
"9th Year" Silver Supporting Member
Posts: 426
A White Sport Coupe
Reg: 08-19-10
11-07-18 02:13 PM - Post#2750682    
    In response to junky

Hello,

The tooth count is stamped on the ring gear. Divide the large number by the small number.

Bob


 
DZAUTO 
Member #51
Posts: 8906

Loc: Mustang, OK, USA
Reg: 12-25-99
11-07-18 03:11 PM - Post#2750686    
    In response to A White Sport Coupe

  • A White Sport Coupe Said:
Hello,

The tooth count is stamped on the ring gear. Divide the large number by the small number.



It's also stamped on the end of all Chevy pinion gears like this.
10-37-GM = 3.70 ratio





 




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