[SJMule]

I ate a bearing on my 69 after recently obtaining the original differential from my car from a prev. owner. (laughs)

The differential I removed from the car is a 2:78 posi with bolt in springs. The original 3:23 one legger has spring pockets and what appears as a thicker v brace cast on the bottom of the pumpkin ? Any ideas?

I plan on using my original "beefier" looking rear.

Lastly, what would the difference be between 3:42 vs 3:55 in a 69 GTO at freeway speed? Or performance. Want to have fun with this car, but still freeway it.

Thanks!

Mule

[SJMule]

I ate a bearing on my 69 after recently obtaining the original differential from my car from a prev. owner. (laughs)

The differential I removed from the car is a 2:78 posi with bolt in springs. The original 3:23 one legger has spring pockets and what appears as a thicker v brace cast on the bottom of the pumpkin ? Any ideas?

I plan on using my original "beefier" looking rear.

Lastly, what would the difference be between 3:42 vs 3:55 in a 69 GTO at freeway speed? Or performance. Want to have fun with this car, but still freeway it.

Thanks!

Mule

[RPM]

Since a 3.55 is a ~4% gear reduction vs 3.42 your engine would RPM ~4% higher. So if at 70 with a 3.42 you are spinning 3050 RPM like I am, you with a 3.55 would be turning 3172. Not a big deal. Acceleration-wise I doubt you'd be able to tell which gear was which.

[6D6GOAT]

i dont know about your first question, but here is a good rpm calc to see what your rpms on the freeway would be with any gear ration/trans setup.

http://www.5speedtransmissions.com/calculator.html

vic in redondo

['ol Pinion head]

3.42's are NOT an option for the 8.2 "BOP" rear.
3.42's were avail in the '68-70 Buick GS 10 bolt. The '68-70 Buick 8.2 does not share carriers, ring & pinions, or axles with any of the 8.2 "BOP" incarnations.

If the rear is not the confirmed original rear to the '69, one will need to ID what you have. To ID, one will have to examine the housing casting number & post back. It is also helpful to note how many (1, 3, or 4)access holes are machined in the axle flange, & whether the bolt-in axle has a seal next to the axle bearing or whether the axle uses a sealed bearing type axlebearing & axle seals up in he axle tubes.

[RedTiger]

I hate to jump into this thread, it sounds like you might know what my problem is too pinion head. I have a 8.2 housing with 3.42 gears and posi. The posi has 4 pinions and is a cone type. The axle flange on the good side has 3 holes and is outer seal type. Stamped numbers on the left had tube facing to the rear are N166. Casting number on same side facing rear on the center section is 67890 I can't get any 28 spline axle to fit except for the one that came in it and some incorrect inner seal style axle. The splines won't pass the Cone Clutch's splines.

[SJMule]

Thanks fella's! Was busy simply greening the underside and finally shot a pick. The one on the bottom is the original to my car. #600 WF

The one on top was installed by a prev owner. Haven't ground the snot out of it yet, couldn't get numbers off the normal place. Does appear that the tubes are plug welded on...Hmmm.

Thanx again I'll start a post of the changeout once I start install.

Mule

[Shadowjack]

Looks to me like you have a good comparison shot of an early narrow rear (top) and late wide one (bottom). The spring pads are a giveaway, of course, but look at the difference in how far the tube ends stick out from the control arm brackets. And of course the one with the additional reinforcing ribs is a later piece. It would be interesting to have an accurate measurement between the backing plate flanges on each one.

['ol Pinion head]

La Cabra,

Understand where you are coming from axle spline wise, there were many different versions of bolt-in 28 spline axles used from '64-72. Today, many folks just assume, in a search, that a GM muscle era axle had a certain kind of seal, 28 splines, & a certain length, then it will fit their application. Problem with this suppositition is GM Divisions all had their own axle (Differential) divisions, & up until late 1970 each had a lot of autonomy. Just one reason I stock a wide variety of used '64-72 axles & try & ID them all before putting them in the racks.

ID'ing your rear... Considering your original rear has an axle seal outboard on the axle, & has 3 holes in the axle flange, I would look the rear over closer, does it have U-bolts retaining the u-joint or straps with 7/16" headed bolts. The straps & 7/16" headed bolts are a tipoff for a 8.5 A-body rear... a very popular upgrade. Problem with jumping to the conclusion that your rear is an 8.5, is the 4 pinion cone carrier, the first 8.5 posi carriers (Warner-Motives), while cone style, were not 4 pinion but 2-pinion units.

All things considered,
-4 pinion carrier,
-3.42 gearing,
-external axles seals,
-& the kicker... 3 access axle hole acess flange. Am betting the 8.2 10 bolt rear you have is a '70 model Buick Skylark-GS piece. Basically a process of elimination as Pontiac A-body bolt-in axles always have one access hole in the axle flange, while Buick & Olds had 3 or 4 access holes & external axle seals & tapered axle bearings did not show up till the '70 model GM rears. Further, in sourcing a staight used axle, some care is going to have to be taken, as the most common "3 hole 28 spline external seal" axle is the "8.5 A-body" axle. This axle's 28 spline end is slightly different & will not slide in a 8.2 Pontiac 4 pinion carrier. Considering a '70-72 8.2 GTO axle will fit in the '68-70 Buick 4 pinion carrier, I seriously doubt the more common 8.5 A-body axle will fit in a '68-70 Buick 8.2 carrier, as such, one is going to need the '70 Skylark 8.2 10 bolt axle.

Hope this has not been too confusing, will try & ck in late tonight.

[RedTiger]

Thanks a ton, Pinion. I've been getting told by shops all over town that a 28 spline axle is a 28 spline axle, and for the most part they just wouldn't believe that it had to do with the splines. I don't know how much is cobbled together on the rear. The ring gear has "GMC" stamped on it. That normal? I haven't checked the ujoint hardware yet since it is at my shop instead of at home, but I'll take a look and report back on that. Here's a few pictures of it that I took the first time I tore it apart.
Photos of Axle

thanks again for the great explination

[78taman]

If you need a complete rear end for your car, I have one that will bolt right in. This would be an 8.5 rear end. It looks like you have an 8.2 from the pictures. The only thing you need to do is shorten the drive shaft 1 inch. These are much stronger than the 8.2. I can put whatever gears you would like.

[RedTiger]

where are you located? Also is it posi and how much?