[1stgenbird]

I admit that I don't know a lot about the rear diffs, but I hear the term "4 pinion rear end". What does that mean, how does it differ from a 3 pinion?
I have a spare 67 rear end with two radius rods and I read that if there are two rrs, then it's a 4 pinion rear.
I'm not sure whether it's a posi or not. The axle is somewhat rusty and I can't see the code.

[b-man]

Your posi diff comes with either 2 small spider gears (pinions) or 4, both the 2 and 4-pinon diffs will have 2 large side gears that engage with the axles.

The 4-pinion posi has more strength and will distribute the load amongst 4 small spider gears rather than just 2.

Pull the rear cover and investigate, knowing codes or the number of traction bars/radius rods won't do you any good if any repair work or parts replacement has been done inside the axle housing over the years.

[AG]

All '67 4 speed cars had two RRs, autos had one. Nothing to do with gear ratio or posi non-posi.

[Cammer-6]

here we go again

actually the rear end ratio does tie into this

OHC-6 1 bbl with auto trans got no radius rods unless it had the 323 rear
then it got 1
OHC-6 1 bbl manual trans(which includes both 3 speed and 4 speed,column or floor shift,got 1 radius rod.

All others with manual trans got 2 rods,this included 3 speeds, both floor and column shifted,4 speeds floor shifted.

[phoenixpnr]

Originally Posted by Cammer-6

here we go again

actually the rear end ratio does tie into this

OHC-6 1 bbl with auto trans got no radius rods unless it had the 323 rear
then it got 1
OHC-6 1 bbl manual trans(which includes both 3 speed and 4 speed,column or floor shift,got 1 radius rod.

All others with manual trans got 2 rods,this included 3 speeds, both floor and column shifted,4 speeds floor shifted.

I heard that manual open rears only had one and 400 manual cars had two, any truth to that?
What is the rule on auto 400 cars? I have a Auto 400 open car which has one, that makes sense to me, but did auto 400 posi cars have two? Or did the second one have more to do with gear ratios, say 3.55 and numerically up?

Sorry if this has already been gone over!

[Region Warrior]

From ones i've seen(maybe 10), all "N" housings have HD guts.
Look for a raised "N" on top/front of case.
But like b-man said, no tell'n if sometn's been replaced over the years.

[Pete67FB400]

Originally Posted by b-man

Your posi diff comes with either 2 small spider gears (pinions) or 4, both the 2 and 4-pinon diffs will have 2 large side gears that engage with the axles.

Does these pictures I took of mine when the cover was off a few years ago show enough to tell what I have? I know it is a 3.08 posi unit, but I don't see any pinions in these shots.

Thanks,
Pete
67 400 coupe

[phoenixpnr]

That is a 2 pinion unit.
I could be wrong but I thought only 3.55 (factory) and up recieved the 4 pinion units.

[rexs73gto]

The N means it is a NODULAR rear end

[Cammer-6]

Originally Posted by phoenixpnr

That is a 2 pinion unit.
I could be wrong but I thought only 3.55 (factory) and up recieved the 4 pinion units.

3.36-4.33 rears were 4 pinion
not sure that 4.33 applys to Birds tho as no one has come forward with a legit one that I know of.

['ol Pinion head]

All factory 64 & 65 Pontiac 8.2 Safe-T-Track & Olds 8.2 Anti-spin units were 2 pinion units.
All '64-65-66 model production 8.2 Pontiac housings were gray iron... very susceptible to pinion deflection under high torque loads. Pinion deflection is big reason why all gray iron GM 8.2 rearends blow up when exposed to heavy torque loads, no matter what posi carrier (rebuilt 4 pinion, eaton, auburn) & good aftermarket axles are installed in it. The weakest gray iron housings ever cast were used in '64-66 Olds & Buick 8.2 rears, they are junk.

4 pinion cone type 8.2 Pontiac Safe-T-Track carriers were introduced for '66 models with the low ratio 3.36-4.33 gearsets. They were also used by Oldsmobile in '66. Pontiac dealers were advised to replace destroyed '64 & 65 two pinion Safe-T-Track units with the 8.2 HD 4 pinion Safe-T-Track carriers.

If one has a Pontiac 8.2 2.56 or 2.78 Safe-T-Track rearend, it is a 2 pinion, as no 4 pinion units were made for the high ratio (2.56 & 2.78 rears).

Mid ratio 4 pinion Safe-T-Track units were produced in early (through '69) & '70-72 8.2 Pontiac styles. The mid ratio 8.2 Pontiac carrier was used with 2.93, 3.08, & 3.23 8.2 Pontiac gearsets. While there were many 4 pinion Safe-T-TRACK rears built with gray iron housings, there never was a 8.2 HD SAFE-T-TRACK rear built with the mid ratio gears & 4 pinion carrier.

To qualify as HD SAFE-T-TRACK, the 8.2 Pontiac rear was built with the nodular housing and the 4 pinion carrier AND the special forged axles. Tons of '67-72 Pontiac 3.55 SAFE-T-TRACK rears were built with nodular housings, but with the the standard duty '67-69 or '70-72 Pontiac 8.2 axles.

Buick built their own HD 8.2 BUICK 10 bolt rear from '68-70. It takes it's own gearsets (like their 2.93's, 3.08's, 3.42's & 3.64's) & its own different series 4 pinion posi carriers. These Buick 4 pinion 8.2 posi carriers had different spline side gears & their own stagger for different ratios. If one is not careful buying used parts they can end up with a 4 pinion Buick posi carrier for intended Pontiac 8.2 usage.. The '68-70 Buick 8.2 posi unit & single track carrier takes a 12 bolt carrier bearing on the drivers side & normal 10 bolt carrier bearing on the passenger side

[phoenixpnr]

Originally Posted by 'ol Pinion head

All factory 64 & 65 Pontiac 8.2 Safe-T-Track & Olds 8.2 Anti-spin units were 2 pinion units.
All '64-65-66 model production 8.2 Pontiac housings were gray iron... very susceptible to pinion deflection under high torque loads. Pinion deflection is big reason why all gray iron GM 8.2 rearends blow up when exposed to heavy torque loads, no matter what posi carrier (rebuilt 4 pinion, eaton, auburn) & good aftermarket axles are installed in it. The weakest gray iron housings ever cast were used in '64-66 Olds & Buick 8.2 rears, they are junk.

4 pinion cone type 8.2 Pontiac Safe-T-Track carriers were introduced for '66 models with the low ratio 3.36-4.33 gearsets. They were also used by Oldsmobile in '66. Pontiac dealers were advised to replace destroyed '64 & 65 two pinion Safe-T-Track units with the 8.2 HD 4 pinion Safe-T-Track carriers.

If one has a Pontiac 8.2 2.56 or 2.78 Safe-T-Track rearend, it is a 2 pinion, as no 4 pinion units were made for the high ratio (2.56 & 2.78 rears).

Mid ratio 4 pinion Safe-T-Track units were produced in early (through '69) & '70-72 8.2 Pontiac styles. The mid ratio 8.2 Pontiac carrier was used with 2.93, 3.08, & 3.23 8.2 Pontiac gearsets. While there were many 4 pinion Safe-T-TRACK rears built with gray iron housings, there never was a 8.2 HD SAFE-T-TRACK rear built with the mid ratio gears & 4 pinion carrier.

To qualify as HD SAFE-T-TRACK, the 8.2 Pontiac rear was built with the nodular housing and the 4 pinion carrier AND the special forged axles. Tons of '67-72 Pontiac 3.55 SAFE-T-TRACK rears were built with nodular housings, but with the the standard duty '67-69 or '70-72 Pontiac 8.2 axles.

Buick built their own HD 8.2 BUICK 10 bolt rear from '68-70. It takes it's own gearsets (like their 2.93's, 3.08's, 3.42's & 3.64's) & its own different series 4 pinion posi carriers. These Buick 4 pinion 8.2 posi carriers had different spline side gears & their own stagger for different ratios. If one is not careful buying used parts they can end up with a 4 pinion Buick posi carrier for intended Pontiac 8.2 usage.. The '68-70 Buick 8.2 posi unit & single track carrier takes a 12 bolt carrier bearing on the drivers side & normal 10 bolt carrier bearing on the passenger side

Wow what a mess! So I guess the lesson that we can take from this, is to count the axle splines! Definitely a nice insight as to why the nodular center sections were used.
'ol pinion head, just curious, what were the Chevy 12 bolt center sections made of?

['ol Pinion head]

It's really not a mess, its actually easy to understand, if you look at it as a continuation of improvements as power levels rose as the torque loads increased with more powerful engines. Through the 60's GM had 4 divisions building A-bodys in the US, & each division basically had its own gear & axle assembly at least enough autonomy that in '68, 69, & 70 each division had its own rears. GM, Ford, Chysler all increased the strength of their rearends in their highest performance vehicles as the decade rolled on. Warranty claims is not what they wanted, so they upgraded... at least behind their performance engines.

In GM's case, the common Chevy 12 bolt was not the General's strongest factory A-body or F-body rear. Not unless you happened to to have been one of the very few who ordered a COPO Chevelle, an L78 or LS6 Chevelle, or COPO Camaro, or an over the GM counter version of one the truly HD 12 bolts for those cars. The rest of Chevrolet Divisions Chevy 12 bolt offerings, the vast majority of Chevy 12 bolts built had weak axles coupled with their really weak link: the brittle spider gear/side gear combination. Truth be known, the 30 spline standard duty Chevelle 12 bolt axles lack a lot in strength to the best bolt-in 10 bolt axles, thus counting axle splines really won't tell the whole story. In the case of factory Pontiac 8.2 axles, it wont tell if a 28 spline sealed bearing axle is a regular light standard axle or if is is one out of HD SAFE-T-TRACK rear. As far as metallurgy of the 12 bolt Chevy center housings I have not studied that a ton. Would love to compare a 69 BE coded Camaro 12 bolt to the '69 BV I have in my racks. Both are 4.10 positraction Camaro units, the BE has all the good stuff & has a different casting number on the hsg. Nodular iron, a good bet.

More on axles... the bolt in axles out of '64 or 65 Olds Cutlass or 442 or Buick Skylark or '65 GS will bolt right in a '64 or '65 Pontiac 8.2 rear, and are the same strength std duty axle. Now what about the fellow who just bought a early GTO or LeMans project car & over the previous years, the Pontiac's original rear was swapped with the weak early Buick 8.2 out a '64-66 Cutlass or '64-66 Buick Skylark. They look nearly identical, but the strength of the gray iron center section early Buick 8.2 is not near as strong as the "weak" gray iron Pontiac 8.2 housing out a '65 Tempest, LeMans or GTO. Olds even specified the Pontiac 8.2 in many of its higher torque application '66 442's. that housing was just Pontiac's standard '66 gray iron 8.2 housing rear. Not the nodular 8.2 Pontiac housings which first started showing up in '67 Pontiac A-body 3.55 Safe-T-Track applications. The nodular hsg 8.2 was really needed behind really strong applications like the '66 L79 W30 442. Olds instead dropped the 8.2 & developed the type "O" 10 bolt rear which lasted a few years.

[phoenixpnr]

Originally Posted by 'ol Pinion head

It's really not a mess, its actually easy to understand, if you look at it as a continuation of improvements as power levels rose as the torque loads increased with more powerful engines. Through the 60's GM had 4 divisions building A-bodys in the US, & each division basically had its own gear & axle assembly at least enough autonomy that in '68, 69, & 70 each division had its own rears. GM, Ford, Chysler all increased the strength of their rearends in their highest performance vehicles as the decade rolled on. Warranty claims is not what they wanted, so they upgraded... at least behind their performance engines.

In GM's case, the common Chevy 12 bolt was not the General's strongest factory A-body or F-body rear. Not unless you happened to to have been one of the very few who ordered a COPO Chevelle, an L78 or LS6 Chevelle, or COPO Camaro, or an over the GM counter version of one the truly HD 12 bolts for those cars. The rest of Chevrolet Divisions Chevy 12 bolt offerings, the vast majority of Chevy 12 bolts built had weak axles coupled with their really weak link: the brittle spider gear/side gear combination. Truth be known, the 30 spline standard duty Chevelle 12 bolt axles lack a lot in strength to the best bolt-in 10 bolt axles, thus counting axle splines really won't tell the whole story. In the case of factory Pontiac 8.2 axles, it wont tell if a 28 spline sealed bearing axle is a regular light standard axle or if is is one out of HD SAFE-T-TRACK rear. As far as metallurgy of the 12 bolt Chevy center housings I have not studied that a ton. Would love to compare a 69 BE coded Camaro 12 bolt to the '69 BV I have in my racks. Both are 4.10 positraction Camaro units, the BE has all the good stuff & has a different casting number on the hsg. Nodular iron, a good bet.

More on axles... the bolt in axles out of '64 or 65 Olds Cutlass or 442 or Buick Skylark or '65 GS will bolt right in a '64 or '65 Pontiac 8.2 rear, and are the same strength std duty axle. Now what about the fellow who just bought a early GTO or LeMans project car & over the previous years, the Pontiac's original rear was swapped with the weak early Buick 8.2 out a '64-66 Cutlass or '64-66 Buick Skylark. They look nearly identical, but the strength of the gray iron center section early Buick 8.2 is not near as strong as the "weak" gray iron Pontiac 8.2 housing out a '65 Tempest, LeMans or GTO. Olds even specified the Pontiac 8.2 in many of its higher torque application '66 442's. that housing was just Pontiac's standard '66 gray iron 8.2 housing rear. Not the nodular 8.2 Pontiac housings which first started showing up in '67 Pontiac A-body 3.55 Safe-T-Track applications. The nodular hsg 8.2 was really needed behind really strong applications like the '66 L79 W30 442. Olds instead dropped the 8.2 & developed the type "O" 10 bolt rear which lasted a few years.

I take it that the casting numbers are different between the early buick olds 8.2 rears and the pontiac ones.

[Old Goat Racer]

Since 'ol Pinion head mentioned Chevy 12 bolts, can you tell us if the Pontiac 12 bolt of 70-72 is stronger or weaker in any way? I believe the housing & axles are different but the gears & posi are the same ?? Thanks, OGR

['ol Pinion head]

Sent you a PM

[Doug Hopkins]

Originally Posted by Region Warrior

From ones i've seen(maybe 10), all "N" housings have HD guts.
Look for a raised "N" on top/front of case.
But like b-man said, no tell'n if sometn's been replaced over the years.

My 67 326 2bbl. 3-speed came from the factory with a N housing and it was a 3.08 open economy rear,and had two radius rods. All V8 (326 & 400) stickshifts came with two radius rods per the 67 Firebird service manual. N housing had nothing to do with a performance option, it was what the housing was made of. Same as the crankshafts nodular iron. The HD Safe-T-Trac (4 pinion posi) was an option often refered to as HD axle assembly.

[Doug Hopkins]

Originally Posted by phoenixpnr

I heard that manual open rears only had one and 400 manual cars had two, any truth to that?
What is the rule on auto 400 cars? I have a Auto 400 open car which has one, that makes sense to me, but did auto 400 posi cars have two? Or did the second one have more to do with gear ratios, say 3.55 and numerically up?

Sorry if this has already been gone over!

You are right this has been gone over. So here it is (attachment) straight from the 1967 Firebird Service Manual. The second bar had nothing to do with gear ratio or posi. As you can see in the attachment the V-8 auto.trans. had one on the R.H. side, so you car is correct. The only 1967 firebirds that came with two bars were the 6-cyl./4bbl. manual trans. and all V-8 manual trans. Only Firebird with none would be the 6-cyl./1bbl. unless the car was equipped with 3.23 gear ratio. (see the *)

[Region Warrior]

Originally Posted by Doug Hopkins

My 67 326 2bbl. 3-speed came from the factory with a N housing and it was a 3.08 open economy rear,and had two radius rods. All V8 (326 & 400) stickshifts came with two radius rods per the 67 Firebird service manual. N housing had nothing to do with a performance option, it was what the housing was made of. Same as the crankshafts nodular iron. The HD Safe-T-Trac (4 pinion posi) was an option often refered to as HD axle assembly.

Learned som'tn new. Thanks.
Was surprised to find mine has 4 pinion's w/a 3.36 gr.

[silverbullet07]

I've been looking into my rear as well. I have a 68 zm that is suppose to be a 3.36. It looks like a hd 4 pinion and it has the N stamp. However it looks like someone has but in 2.73 gears ..

I think I would like to switch it back to 3.36 but will test it on the road to see how it does.