Medium Duty vs Heavy Duty Safety Track
 

How do you tell if you have a medium duty or heavy duty 4 pinion safety track carrier ? The service manual says that the medium duty carrier is gray iron and the Hd carrier is nodular iron but does not say how to tell the two apart.Is there a N cast in the nodular carrier like there is on the center section of the rear end or a part number that is cast in it that will tell me what I have ? Thanks.

there is some info here http://forums.maxperformanceinc.com/...hlight=nodular

Thanks for the help but I'm trying to find out how to ID. the carrier that the ring gear bolts to.That thread was mostly about the N housing itself.I packed home a 4 pinion carrier that came out of a 4 speed 69 SJ Grand Prix and want to know how to tell if it is the HD version before I pay for it.

The 1969 G medium duty 4-pinion carrier hold 2.93 - 3.23 gears and the heavy duty unit holds 3.36 - 3.90 gears.
Thus the ring mounting surface is less offset on the heavy duty unit compared to the medium duty gear carrier.

I think the grand prix 10 bolt carrier is different from the gto 10 bolt carrier

why would GM do that? the housing is different because the tubes are smashed to lower the car..but the carrier, i just cant see gm using a diff carrier on a car thats built on the same line..its a G Body 69-72 a stretched A body

im no expert.

From MPC:

i see..but thats a housing diff..and post-t i aint arguing...im investigating..

but what roger is talking about is the housings and bearingings..i have pulled 3.23 posi units and gears right out of a GP and had them put in Lemans rears..

as far as i know the only diff is early and late..sometime the ring gear bolt size changed and early can be converted

i will link this to roger and he can help answer the orig question

I'm investigating also I don't exactly know if the carriers are the same between a 69 gp and a 69 judge. The last shortcut I posted supposedly shows a medium duty carrier from a 69 gp. OP posted question about 69 gp in judge section

Have owned nearly a dozen 3.23 4 pinion Safe-T-Track rears, quite a few I bought over the last 20 years in '69 GP parts and project cars with XF 428's. Have parted out most of these rears. The HD 4 pinion MID RATIO carrier was used in all of them. The rearend, itself, is not a HD Safe-T-Track, doesn't have the nodular housing and doesn't have the HD forged axles.

Post, All the factory '69 3.23 geared Pontiac A body rears, I've worked on, were standard rears did not have Safe-T-Track. Quite a few, have gone through replacing a sealed bearing axle or two, also bearings, races, seals. At least two of these '69 3.23's I rebuilt as 3.23 Safe-T-Tracks with nice used 4 pinion carriers out of '69 428 GP's.

Educated guess, is someone is confused. The only thing that could be conveyed as "medium duty" is the '69 4 pinion STT 3.23 GP rear due to the mixture of HD 4 pinion STT carrier and what amount to standard duty housing and axles.

I have a '69 GP rear 10-bolt 3.23 gear and posi. The carrier is a 4 pinion and the tubes are indented on the ends as previously stated. Whether or not the carrier is a two pinion or 4 pinion, they are made of the same material. The 4 pinion is what was the difference between heavy and medium duty, not the material like a nodular center section compared to a grey iron one.

AG, as far as "heavy duty" goes, would bet you have also noted that when Pontiac billed out a HD Safe-T-Track on an invoice it did so at at a higher price than regular Safe-T-Track. Only instances I've ever read with this higher charge is when a 3.90 or 4.33 HD Safe-T-Track rearend was optioned. Those instances were the only cases in an A Body or F- body that the rearend was built with the HD forged axles. The combination of forged axles, nodular iron 8.2 center housing, 4 pinion HD Safe-T-Track carrier, and either 3.90 or 4.33 gearing wiill be the only time one will see the designation HD Safe-T-Track in a vehicle with a Pontiac 8.2 rearend. Lacking all the attributes, the 8.2 Pontiac rear just isn't HD, one can call it standard duty, medium duty, or even light duty.

Your GP rear should have a 4 pinion carrier. the flat spots on the 69 GP housing tubes, am sure you have also seen them on '69 Firebird axle tubes as well.

of note to Mark's last post, I've yet to run a across a tapered bearing end housing in a factory assembled '69 A body housing built before July of '69. The extremely late (08A) Arlington '69 gold LeMans I parted many years ago, had its original sealed axle bearing rearend. From dealings with '69 Firebird guys, it seems to be Firebird housings got the tapered bearing hsgs a little earlier, and may be a good reason why master parts books use the confusing terminology early '69 and late '69 production when denoting the Pontiac 8.2 axles and ring & pinions.

Correct, but the question posed by the OP was about the carrier, not what constitutes a HD Safe-T-Track rear end.

I think all 4-pinion carriers are considered heavy duty while 2-pinions are medium. I do not think there is anything labeled as a "light-duty" limited slip carrier, rather the non-posi carriers are labeled "standard". Therefore, since ONLY 4-pins were used in nodular housings, all 4-pins are nodular and the 2.93-3.08-3.23 ratio GP while the 2-pins are the "grey iron" medium duty. However, I have seen a 55 gallon barrel of them fail regardless of being heavy duty or not over the years.

1969 GRAND PRIX TYPES OF AXLES:

1. Type axle: Regular Duty. Type Diff: Standard. Diff Carrier: Gray Iron. Axle Shafts: Cold extruded. Diff Asm. 2 Pinion Non-lock.

2. Type axle: Medium Duty. Type Diff: Standard. Diff Carrier: Gray Iron. Axle Shafts: Cold extruded. Diff Asm. 4 Pinion Non-lock.

3. Type axle: Medium Duty. Type Diff: Safe-T-Track. Diff Carrier: Gray Iron. Axle Shafts: Cold extruded. Diff Asm. 4 Pinion Lock.

4. Type axle: Heavy Duty. Type Diff: Safe-T-Track. Diff Carrier: Nodular Iron. Axle Shafts: Hot Forged. Diff Asm. 4-Pinion Lock.

The Grand Prix has two types of Safe-T-Track differentials - medium duty and heavy duty - -the usage dependning upon the engine - transmission combination and the axle ratio. The medium duty Safe-T-Track differential has four pinion gears and a gray iron carrier. Cold extruded axle shafts are used with the medium duty Safe-T-Track.
The heavy duty Safe-T-Track also has four pinion gears but the carrier is nodular iron. The heavy duty axle shafts are hot forged.

Important: Due to the material or manufacturing differences in the medium duty and heavy duty axle parts, they should NEVER be interchanged.

FWIW . . .

Just to get the nomenclature correct (per GM service manuals and MPCs), the "differential housing" is called the "carrier and tubes", while the differential (i.e. 2-pinion or 4-pinion) is called the differential "case". Most of the "cases" were serviced either as a bare case, or as a complete differential assembly.

OK, back to topic . . .

Roger -

All good info. One point -- I had two 69 Judges with a 3.55 HD STT (both RAIII M20), unless my memory is failing. Never had the axles out on either, so not sure if they were forged or not.

For those following along - the nodular housing has an "N" cast into the top of the "nose" of the housing. Right above the pinion seal. You can't see it from under the car, but you can feel it.

Cast axles are constant diameter and smooth surface. Forged axles are tapered and rough surface.

Took apart one 8.2 that had one cast and one forged axle; not sure how that happened, but would be interesting if it came like that from the factory.

Scott