[Joshua Paul]

Looking to upgrade the drivetrain in my 72 Lemans. I currently have a low compression 455 with small cam, Th350 with hardened internals, and a 2.73 open differential. I want to swap out the heads to a set of 6X-4 and install a proper cam along the way. Here is what I "think" I want:
1. Keep the Th 350. We used to think that they were lighter and had less parasitic drag.
2. Install a 10 bolt 3.73 posi. I like they idea of the the 8.2 because of the bolt in axles. I have seen too many cars (back in the day) on the side of the road with an axle 30 yards behind them.
3. Install a Gear Vendors overdrive. I like the idea of having the 3.73 for the occasional Saturday night at the strip, but love having a freeway flyer that buries the the spedo!

So am I crazy? What are some thoughts?

[i82much]

you're not really having fun until you look back and see an axle 30 yards behind you!!!

[b-man]

Lots of different opinions on the 8.2 but I would not spend a dime upgrading one, almost all (except a few rare nodular housing units with 4-pinion posi) have weak gray iron housings. The ball bearing axle bearings usually trash the axle when the race spins on the axle after the bearings give up the ghost, they don’t take side loading (cornering forces) very well.

The ‘71-‘72 Buick/Olds 8.5 10-bolt has a nodular iron housing, bolt-in axles and superior tapered roller axle bearings. It’s almost as strong as a 12-bolt and shares the same pinion bearing.

I’d omit the Gear Vendors and swap to a 3.08 gear set, a healthy 455 has no problem pulling a tall gear. You’ll likely find with a 3.73 it won’t be easy to hook up in first gear. A 455 with 3.08s can run hard at the track and go plenty fast out on the highway.

[steve25]

Your gonna need a HD sprag in the TB350 once you up the cam in that 455.

['ol Pinion head]

8.5 A-body rear is best way to go. More pinion support than any of the different 8.2s, ton of parts availability, & in many ways superior to a even upgraded stock 12 bolts. My own opinion, & I've built tons of 8.5's & stock housing 12 bolts, until you start building off a new Moser 12 bolt housing, the stock 12 bolts have too many weak spots.

[PDC]

Even a mild cam with 6X-4 Heads on a 455 with headers and free-flowing exhaust will make so much torque everywhere on the tach between idle and 4500, you’d never run out of smiles on the street with 3.73s.

By the time you freshen up that TH350 and add the cost of the Gear Vendors unit plus the shortened driveshaft, you really are knocking on the door of the cost of a nicely built 4L80E - which offers a bit deeper OD gear (.75) than the GV unit (.78). Most would tell you that a mildly built 4L80E will be stronger and more reliable than the TH350 with the GV unit. You also might find that the 455 makes so much torque that 3.42s offer plenty of gear reduction from a dig and will let the OD gear do you a bigger favor on the freeway than 3.73s would. Just a thought from having been there and done that.

[Jay S]

With the broad power band and torque of a 455 combined with an automatic, cars work extremely well with 3.36s gears. For drag racing running a 455,, which make great average power, dropping down to a 3.73 often not offer much extra performance. 3.36s are also a decent cruising gear with a 275/60r15. I would start their, 2.73 are terrible off the line, 3.36 would really wake it up, even as is.

Our 71 T37 has a 3.36 8.2 10 bolt, just over 500HP 455, and a 4000 stall.

A friend talked to someone at Randy’s ring gear and pinion and asked about 8.2s and 8.5s. To his surprise, they told him that had not seen much difference between a 8.2 and 8.5 for strength, I think 400HP was mentioned. Next he called and asked Quick performance, they told him 400 HP for the 8.2”, and 500 HP for a similarly dress 8.5”. They both recommend running cover girdles. FWIW, I tend to agree more with Quick performance’s numbers.

Gear vendors does not make much sense to me. The cheapest, and quickest option (if you kept the 8.2) would be a 700R4 has a pretty low first gear (IRC..3.06?) That gear reduction is like running a 4.0 with a th350 in first gear, and gives you a big big overdrive to cruise with. Could drop down to a 3.55 to 3.73 also, which I would do if you went with a 8.5, and run c clip epilators. But my opinion is the 3.36 was the strongest gear set you could put in a 8.2, lower gears tend to deflect the pinion more and flex the case more. The lower the gears, the more likely you will break the 8.2.

[leeklm]

As long as we are throwing options out there... I have a stout TH400 with Coan low 1-2 gear set i might be willing to part with. This trans worked great in my 73 GTO with 3.08 gears. Your engine "thinks" it is seeing a ~3.42 rear in 1st and 2nd gear, but then a nice easy cruising 3.08 when shifting to 3rd.

I slightly modified the 8.5" diff in the 73 with a larger billet bearing cap on the ring side along with an Eaton posi, upgraded 28 spline axles, and a bearing cap support girdle. Had the car running low 11 second ET with a 600hp 461 and zero issues after several hundred drag runs. Note, I did eventually install 3.42 gears in that diff when it was turning its best ET.

As others have said, I would not attempt this with the 8.2 rear. I am not 100% certain on this, but pretty sure you can run c clip axles in most street classes? If yes, i would install Moser axles and new c clips in a chevy 8.5" corporate axle before attempting the same with a bolt in axle 8.2.

Sent from my SM-G965U using Tapatalk

[Jay S]

I think 11.0 et or quicker is when you are required to run c clip eliminators. It isn’t really enforced though until quicker than 10.0 when you would need a chassis certification. C clip eliminator is more of a want than need for 11.0 or slower.

Building a rear end gets to be pretty expensive. So it’s nice to start with the strongest thing you can find. 8.2 grey iron case your starting near the bottom for strength. But if your not using drag slicks, it is a doable place to start on a street build. Best not to get to much money wrapped up in an 8.2. Especially if your hiring the work done on it. Hiring it done, buy a complete 9” from quick performance and be done with it.

['ol Pinion head]

Not putting $$$$ in gray iron 8.2's, examined the pieces from quite a few that owners were determine to run w slicks & too much Torque loading,

Chevy 8.2 c-clip rers, early Buick & early Pontiac 8.2's , all lack pinion support. Later twin rib casting Pontiac 8.2's were marginally better, but still second string to the Nodular 8.2 Pontiacs which also have their limits eso in a heavier A-body.Buick had a few great ideas with their '68-70 late Buick 8.2. So did Olds w their best 67-68 Type "O"s.

None of the above various rears had the pinion support strength of the 8.5 A-body rear. How any rear is going to be torque loaded at launch, as well as the weight of the car is what I look at when preparing a platform to build. As far as 400 hp limit with an "8.2" & a 500 hp limit with an "8.5" one could state that concerning bone stock rear builds & not be far off. With well thought out upgrades, a 30 spline or 33 spline (spool) 8.5 can take a ton more abuse.

[Jay S]

The quick performance ratings of 400 HP for the 8.2, and 500HP for the 8.5 were for stock type builds, with an aftermarket carrier and a cover girdle. No other mods.

Randy’s ring gear and pinion really surprised me. They said the cover girdle make a big difference on the 8.2, and with the cover they were seeing similar breakage between the 8.5. Of course though there are a lot of 8.5’s around. I have a hard timing believing the 8.2 can come very close to a 8.5 in stock form. Maybe they are breaking spider gears on the carrier??

[b-man]

And…..no additional input from the original poster……lots of thoughtful advice given and nothing to say …..

[Goatracer1]

Maybe he is just overwhelmed by all the info. I'm with JayS and would use a 9" if the money is available. I bought one over 25 years ago when I got serious about racing and the only time it has been apart was to change ratios when I went to a taller slick. I also thought of an AOD trans but it still doesn't cure his weak rear end problem. My son used to race a highly modified 1987 Turbo Regal and the only thig he didn't break was the rear end.

[JLMounce]

Anything is possible as to why the OP never responded. But there’s good discussion here anyway.

I won’t comment on the rear end. Years ago I went straight to a Moser 12 bolt and never looked back.

On the gear vendor, I did extensive research on this unit prior to opting for a performance build on a 4l80e.

There’s almost nothing on paper or in reality that makes the gear vendor unit better. The units themselves are marginally less than a performance built transmission, they require much of the same amount of wiring work and while they are very strong themselves, are only as strong as the trans in front of them. In that case whatever savings you may have seen is eaten up on a trans build if you need more holding power.

Here’s the big kicker for me, the operation of the unit itself. It’s not really a set it and forget it type deal. It has an auto mode, but in that mode it’s always on and it makes ever gear in the trans much taller, killing your performance in situations where you don’t want to manually turn the thing on. In cases where you want to drive the car in a spirited manner and take advantage of its mid-gear reduction you literally have to shift, turn it on, turn it off, shift again, then turn it back on. Its operation appears, at least to me, to be rather annoying.

[Joshua Paul]

I sincerely apologize for such a tardy response. I got caught up in a another project and chasing a girl. One is a "modified small block" and the other is a 1984 Hydrostream 16' go fast boat

To the topic at hand. I think I like the idea of the 8.5. What do I need to search for as far as year and make? This is going into a 72 A-body. What kind of internals and money do you suggest? I currently want the stock look and parts swap. Years ago I was looking at a Moser 9" when I lived in the area. And the swap....yoke change...drive shaft?

I am currently thinking the 4L80E will come next year when budget allows. Insights on that swap?

I sincerely appreciate everyone's input and counter points from the beggining.

[Goatracer1]

When I bought my 9" it came ready to roll under my car. I didn't have to change anything. I rolled out the old one, rolled in the new, one bleed the brakes and I was done. The 8.5 sounds like a good choice but I don't see any good ones in my area.

[hurryinhoosier62]

The ‘73-‘77 “A” body 8.5” will be your best bet in fitting your ‘72 LeMans. The guys at Moser told me a properly built 8.5” cam handle 500 ft/lbs of torque easily, which is good since a mild 455 can generate in excess of 500 ft/lbs.

[Jay S]

As I recall a 73 to 77 A body will not fit in a 72 and earlier A body. I think the center control arms are taller, angled differently, and further apart, probably wider also. 73 to 77 A body are closer to fitting in B bodies than 72 and earlier A’s. I hope I am wrong, don’t think I am though.

The 8.5 that fits in an 72 and earlier A body was only made the later half of 1972. They are not easy to find. It takes some patients to locate one, they are usually bargains when you do find one though compared to buying a 12 bolt A body for 72 and earlier.

There was a 12 bolt out of a 71 Chevelle today on an online auction that brought $1025. That is pretty much the starting price for a 12 bolt A body rear end that needs everything.

[Half-Inch Stud]

Since you have a 455; Find a posi for your existing rear. And Swap to TH400. Done.

The idea of a Street 455 with anything over a 3.31:1, even a 3.23:1 is fraught with yuk on the highway. If ya must, then the 4L80 with the vacuum modulator kit allows manual-shift with switches on the shifter, no computer.

HEI in place of a points dizzy.

[mrmark1957]

Since you have the 455. put 6x-4 heads and a Summit 2801 cam in it. Since you have the TH-350, put the lower 1st and 2nd gear set in it along with the better sprag and a TransGo shift kit. Stock torque converter. Put a posi unit in your rear and keep the 2.73's. I have a car set up like this and it's a great all around combination.