[78MayanW87]

Originally Posted by Skip Fix

All of the 78 codes start with a "2" for all body series. For posis 2PS -2.41, 2PT-2.56, 2PW 3.08, 2PX 3.23, 2 PY 3.42
Third letter identifies manufacturer G=Chevrolet Then day built of the model year(342), then shift-2

Thanks!!! This is super helpful. I guess the last piece is deciphering the “4PP”. Any idea what that belongs to?

[johnta1]

4PP is for a 1979 TA with 3.23 gears.

[78MayanW87]

So...upon further inspection, it appears that the carrier was involved in an explosion at some point in time. If you look at the attached pic, you will see where the teeth from one of the gears has cut into the carrier. The carrier was obviously reused when it was rebuilt as the cuts should have impacted the edges of the clutch plates but those show no signs of damage. From the research that I have done, it seems that a 2.56 carrier will not support any lower gears without a spacer (don't know what this spacer is or where it goes) as well as longer bolts (assuming these are ring gear bolts?). I know that some of you have weighed in on my other "Engine Built Recommendation" thread and know that I am building up my 400 to ~400 hp and am planning on upgrading my rear gears anyway. My plan is to go with 3.42 gears. So now my question to the rear end experts is: should I just go with a whole new carrier and if so, do you have a particular name you like or is the "spacer and bolt" upgrade to the existing carrier simple enough? As always, thanks in advance for the time and suggestions. Lee

[78w72]

Originally Posted by 78MayanW87

So...upon further inspection, it appears that the carrier was involved in an explosion at some point in time. If you look at the attached pic, you will see where the teeth from one of the gears has cut into the carrier. The carrier was obviously reused when it was rebuilt as the cuts should have impacted the edges of the clutch plates but those show no signs of damage. From the research that I have done, it seems that a 2.56 carrier will not support any lower gears without a spacer (don't know what this spacer is or where it goes) as well as longer bolts (assuming these are ring gear bolts?). I know that some of you have weighed in on my other "Engine Built Recommendation" thread and know that I am building up my 400 to ~400 hp and am planning on upgrading my rear gears anyway. My plan is to go with 3.42 gears. So now my question to the rear end experts is: should I just go with a whole new carrier and if so, do you have a particular name you like or is the "spacer and bolt" upgrade to the existing carrier simple enough? As always, thanks in advance for the time and suggestions. Lee

the spacers are ok for low power builds but i wouldnt want to invest the money using one with 400+hp. i used one back in the 90's converting a 2.56 to a 3.90 behind a mild 455 with 6x4 heads, besides being horrible to drive above ~45-50mph, the spacer bolts would loosen up & eventually stripped a few of the bolts out, this was assembled by a professional driveline shop too. i beat on & street raced this car almost daily so im sure the abuse had a lot to do with it but the fact is those spacers arent a good idea for higher power/torque if you plan to use it.

best option would be to find a good complete GM rear end or center section with 3.42 or even 3.23 for a good all around ratio. or look into the eaton posi units, i have a 30 spline one in a 2nd gen 10 bolt with yukon brand 3.23 gears & moser forged street axles, so far has been great on a 500+ 467 stroker engine & lots of low 11sec drag strip runs on M/T drag radials.

[Singleton]

Originally Posted by 78MayanW87

Ok any insight into the origin of the ring and pinion and what it may have come out of? Looks like it is a super common gear set but I didn't know if the code would give away any answers.

Date code on the pinion is 11/74, so likely the entire carrier and gears came from a 1975 GM model vehicle produced in nov-dec 1974, and later swapped into the '79 housing replacing the original 3.23 unit

[78MayanW87]

After some research, I think that I am going to go with Quick Performance's: GM 8.5" 10 BOLT / EATON DETROIT TRUETRAC POSI / GEARS / BEARING KIT / PACKAGE with 3.42:1 gears. I would still appreciate any input that you all have. Thoughts? Lee

[Skip Fix]

Correct 2.41 and 2.56 same carrier. I used an Eaton 28 spline in the 78 with stock axles and ran low 11s and even a few 10s. It and the 81 have an Eaton 30 spline with aftermarket axles.

My first hot rod a 64 409 Impala 4 speed ripped all the ring gear bolts out of a pumpkin that had a spacer plate and 4.11s. I did not know that potential. Next pumpkin had "thick" 4.56s in it.

[jd0n88]

78Mayan - I just received the same kit from Quick Performance except 3.08 gears. I was disappointed to see the pinion and carrier bearings are Koyo brand made in Japan. When I called QP they told me the bearings would be Timken brand made in US. The ring and pinion gears are made in China, the Eaton Truetrac is made in Taiwan. I plan to install the parts myself over the next few weeks.

[78MayanW87]

I wanted to follow up here... I ended up ordering the Quick Performance Eaton TrueTrac kit with QP 3.42 gears. I contacted QP and ordered over the phone rather than through the website and explained that I was specifically requesting Timken bearings rather than Koyo. I also requested a pinion set up bearing. QP was great to deal with and I received my package within about three days. Upon inspecting the contents of the package; however, what I had received was Koyo bearings, a "setup" bearing that hadn't been machined for set up and a Yukon Dura-Trac diff. The QP ring and pinion were correct, so there is that. I double checked the order that was in the package and it matched precisely with my phone order. Not sure what happened during the packaging process. I called QP and explained what I had received and they were suitably embarrassed. They reassured me that they would take care of this and apologized profusely. Within about three days I received another package with all the correct parts along with a packaging label to return the wrong parts. So, all in all, it wasn't the smoothest of transactions, but they were great to deal with and made things right as quickly as they possibly could. I would definitely do business with them again and wouldn't hesitate to recommend others to do so. Got everything set up with a perfect gear mesh pattern, pinion preload, ring/pinion backlash and combined ring/pinion preload. It took a bit of time but in the end, I was very happy with the set up. Just waiting on the Wilwood rear disc conversion kit to arrive to finish this up. I appreciate the input from all of you to help get me here. Lee

[Skip Fix]

Which rear disc kit?

[78MayanW87]

Originally Posted by Skip Fix

Which rear disc kit?

Wilwood Forged Dyanalite Rear Parking Brake Kit 140-7141-D