differential question

[W-motorhead]

I am planning to replace the ring and pinion set in my '63 Biscayne to a more cruising friendly gear ratio. I think the axle ratio is 4.11 or possibly 4.56. I cannot tell from the external markings on the differential housing and I have not removed the pumpkin to count the gear teeth. At 70 mph, the engine speed is 4000 rpm. It gets very noisy at higher speeds, although the 409 doesn't give a damn and keeps pumping out power.

My question for the group is whether ring and pinion gears are the same size for positraction versus standard differentials. Show Cars and Ecklers sells gear sets for a wide range of axle ratios (3.08, 3.36, 3.55, 3.73, and 4.11), but they make no distinction between posi and standard.

Dan Fults

 

[Phil Reed]

Makes no difference Dan. Totally interchange.

 

[Don Jacks]

Yes,but the diffenencial carriers are different between the 3 and 4 series.The 4 series gears are thinneer in the ring gear requiring a spacer to use on a 3 series diff.unit! You should know that,Phil.I'm dissapointed in you!

 

[Blk61409]

You will need to know which carrier you have. The pinion gear is smaller the lower the ratio or the higher the ratio number and as a result the ring gear must be thicker. To accommodate these differences Chevrolet made 2 different carriers. On, I believe 4:11 and up the ring gear carrier has the ring gear flange off set for the difference in the pinion gear diameter. You can determine what ratio you have without removing the rear end by raising the rear of the car, mark the drive shaft and a rear wheel, rotate the wheel one revolution and county how many times the drive shaft turns. Be sure and put the trans in neutral. One hiccup in all of this is if someone put a 4:56 gear on a 3:08 carrier they would have used a ring gear spacer and you would definitely need to know that before ordering a gear. It's possible you could remove the drain plug and put a bore scope in and see about the spacer.
Probably completely confused by now.

 

[61BUBBLE348]

Could you source another pumpkin with the right ratio and then do a Saturday morning swap over.

 

[models916]

You are going to have to pull it. Could be a 3 series with a spacer. Very common to put the big gear on the 3 series posi. No way to know without looking at it.

 

[W-motorhead]

Once again, very helpful advice from the 409/348ers! The wheel rotation test, suggested by Blk61409, indicates that I have a 4.56:1 ratio. I'll remove the pumpkin to see if there is a spacer. I'll let you know what I find.
Dan Fults

 

[yellow wagon]

Yea it's really easy to pull the pumpkin. Then you know for sure. Make sure you have a set of retainer plate gaskets and some gear oil + posi additive on hand if you slap it back together

 

[Phil Reed]

My question for the group is whether ring and pinion gears are the same size for positraction versus standard differentials.

Dan Fults

Yes,but the diffenencial carriers are different between the 3 and 4 series.The 4 series gears are thinneer in the ring gear requiring a spacer to use on a 3 series diff.unit! You should know that,Phil.I'm dissapointed in you!

Look at Dan's question Don. According to 64 reprint parts book: #3867386 OPEN carrier fits 57-59 Pass 1st design and 59-64 Pass 2nd design. NO mention of different carriers for ANY gear ratio. Yes...there are 3-series and 4-series Posi units but GM only lists one OPEN carrier for use with either 3-series or 4-series gear sets. And that's the way I interpreted Dan's question.

 

[Don Jacks]

Yeah,yeah,sure,sure.........Excuses ,excuses...you just dont want to admit that you blew it.

 

[Phil Reed]

Don.....I realize that public apologies are difficult....just look at our politicians. So if it would be easier for you...........a PM to me would be acceptable!!!!!!!!!!!!!!!!!!

 

[Don Jacks]

If we didnt love you so much,we wouldnt pick on you,Phil.As for an apology,I can do that..............the third day after hell freezes over!!!!!!

 

[1961BelAir427]

I'll apologize to Don. I apparently missed his birthday last friday?? Sorry man....hope you had a great one!

 

[Don Jacks]

Thanks Jason,but the 28th is only the day I get to celebrate this year.My REAL birthday dosent come around until next presidential election year.

 

[1961BelAir427]

That can't happen soon enough. You just reminded me of a friend who is also a leap year baby. I forgot to send him a card.

 

[W-motorhead]

I pulled the differential from my '63 and determined that I have a series-3 positraction with 4.56:1 gear ratio. May I ask those following this thread to look at the attached photos and tell me if am correct about this being a series-3 and whether there is a spacer between the ring gear and the carrier flange?
Dan Fults

 

[Blk61409]

Yep, see the spacer between the carrier flange and the ring gear?

 

[Don Jacks]

You are indeed correct.Now all you have to decide which gear you want.3.36 would be a really good highway gear IF you're running the factory cam,or a mild performance [hyd] cam.If you've got a healthy cam in it,then no taller than 3.55.

 

[W-motorhead]

Many thanks, guys. I'm running one of Aubrey Bruneau's fairly aggressive hydraulic cams (236 degrees duration @ 0.05 lift). I'm thinking about the 3.36 gear set. Would it be shameful to consider 3.08 for a 409?

 

[tripower]

I run 3:23's but have a 3:27 1st gear. I think the 3:36's or 3:55's would be great.