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I am restoring a 70 L46 and have gotten to the stage where I need to rebuild the rear end. The engine build I'm considering will make around 450 HP and I am using the stock Muncie. Can I just do a basic rebuild, or are there some upgrades I should consider at that power level? Thanks.
Search this forum and also Digitalcorvettes for posts by Gary Ramadei (GTR1999). Gary is the most knowledgeable person on the 63-79 differentials. I did a lot of research on the topic and a lot of the knowledge was obtained by reading Gary’s articles.
450 HP/450 lb-ft is about the limit for a unit that can be built using mostly stock components but you’d be advised to seek out a 3rd generation Eaton posi unit as it is beefier than what you have (2nd gen). You want to have solid steel clutch plates, the 17 tooth spiders (yours has 18 tooth if original) and “tune” the posi (look at the Tom’s Differentials YouTube video). Your axles may or may not be excessively worn so that is another area to examine closely.
That said, you can upgrade the unit with stronger axles (30 spline vs the stock 17), a steel bearing cap (on the left side), cryo treating the parts, REM polishing, and so on. The ultimate is converting to a 12 bolt R&P but now you are into 2nd mortgage territory.
Gary is great to deal with and has a long history of providing information and guidance. He’ll likely jump in on this thread as he is a Tech Contributor.
This was mine the day I began the assembly process a couple years ago.
Yes, I have seen some of Gary's posts. I think one of them may have mentioned that 450hp was fairly close to the limit of stock as you say, which led me to thinking about upgrades. Thanks for the ideas.
Reliability, What are you doing? Cruising to the Saturday moring car show? Running an autocross or occasional drag strip? Slicks will destroy that rear end on a heavily modded engine. But if you are just spinning your tires, it probably wont hurt it. Hook it up, and then you will find your weakest link. I too installed a Toms 12 bolt conversion. Its good stuff. But do you need it?
I had mine done by Jim at Vtec when he had a stash of US made gears. Jim claims with stock tires they will hold up to 500hp. He’s been at it a long time so I will take his word for it.
I would suggest Gary Ramadei. He just finished my trailing arms and Super 10. Attention to detail and documentation are second to none. You would not be disappointed.
Reliability, What are you doing? Cruising to the Saturday moring car show? Running an autocross or occasional drag strip? Slicks will destroy that rear end on a heavily modded engine. But if you are just spinning your tires, it probably wont hurt it. Hook it up, and then you will find your weakest link. I too installed a Toms 12 bolt conversion. Its good stuff. But do you need it?
No racing, just street driving. Maybe some of it spirited when I find myself out away from traffic but not up to racing-level abuse. I going to run slightly wider than stock tires, so no super-traction to shock the drivetrain.
With a manual, larger tires, i would probably upgrade some low hanging fruit for durability.
i do not know what would break first but curious in order what that would be frm others.
cost no object? Upgrade all..while there…ratio change?
i would think with a manual and stock..you could break something too
Yeah, figuring out what to do with the transmission is next. I was trying to investigate whether a stronger gearset was available a few months ago, then got sidetracked with other projects. Now I can't remember what I had found. Getting old sucks.
I have been trying to figure out a simple way to make the gearbox handle more power reliably. A buddy at a transmission shop suggested that I get a set of straight cut gears like they used in the high horsepower Corvettes in the late sixties. The straight gears are still available so it is the easiest and least expensive option. The bevel cut gears have a tendency to push to one side when power is high. This is why the straight cut gears make sense as long as you don't mind the noise they make.
One of the best things I ever did to my C3 was replace the shifter with a Hurst Shifter. We had overhauled the factory shifter to get it working and it worked like new. The difference in the Hurst was amazing as the distances are shorter and the gear pattern is nice and tight. It makes it easier to drive fast with the Hurst. I installed mine on a lift in a couple hours and have loved that swap ever since. A very worthwhile upgrade.
I'm definitely going with the Hurst. I had read about the straighter cut gears. I think that was the main difference between the M22 "Rock Crusher" and the others. There is an Italian company manufacturing a high quality set. There were others too, but I think they were considered inferior to the Italian set. But IIRC, the Italian set was unavailable at the time. Can't remember if that was a temporary Covid-related shortage, or they had quit making them.
69L88 in post #2 had some very worthwhile upgrades at your power level.
I will add one important one:
Examine the posi unit very carefully for cracks! I found 3 cracked ones before I found a good one!
Past that:
Polish the sharp edges off the posi case, to prevent future cracks, it is definately one of the weakest links. Completely polish it if you like, in/out, it's only labor!
The later 3rd gen Eaton posi is preferred, and stronger, per Gary
Throw your weak 17T18T spiders away and get some stronger 18T 17T ones. ( I still have a couple of good used sets) OOPS got that backwards!
You may have solid steel posi discs. If so measure them they may not be worn too badly and be reuseable. Or buy new ones. If you have snowflakes throw them away. ( I have some good used solid posi discs too I dissected 5 posi units to get 2 good ones)
Tune the posi by eliminating the springs, and shimming the spiders. See Toms Diffs video. It eliminates a LOT of shock on the spiders. You'll see what I mean when you do it.
Use solid spicer u-joints, not the grease fitting ones.
Setup the ring & pinion clearances carefully as normal.
Don't do 5000 rpm clutch drops, use slicks, or do crazy smokey burnouts. If you hit a bump doing a burnout, or get axle hop while it's hooking up, something might let go.
That should be enough, and it doesn't cost that much. It's mostly labor.
That's basically what Gary advised/coached me to do, except I added a Cryo'd posi carrier. But I do have 550TQ and a 454. You should be good.
Gary usually comments on these threads. But that should get you started.
On the Muncie just rebuild it well and you should be good to go. I autocrossed my wide ratio muncie for 27 years with very sticky non-street tires and an LT-1 and it was fine. I would have worried more if I had a BB.
Last edited by leigh1322; Dec 12, 2022 at 10:19 PM.
Put a polyuerathane front pinion snubber on it if you plan on driving it hard.
You do not want axle hop at your HP level.
Interpon has a video which shows how much a rubber pinion snubber moves, with a stock L82.
I'm definitely going with the Hurst. I had read about the straighter cut gears. I think that was the main difference between the M22 "Rock Crusher" and the others. There is an Italian company manufacturing a high quality set. There were others too, but I think they were considered inferior to the Italian set. But IIRC, the Italian set was unavailable at the time. Can't remember if that was a temporary Covid-related shortage, or they had quit making them.
I've got a buddy selling a real nice Richmond 5 speed that came out of a Vette. They are NON-O/D....so 5th is 1 to 1. You stick with stock 3.08/3.36 or whatever rear gears. They have a real steep 1st gear (3.29) and 4th is underdrive..so it's like having 4.10's in 4th...and then click to 5th and cruise. They fit in same spot as a Muncie. His has the shifter and output yoke you'll need to bolt it all in.
I ran one in my car for years with a 427 and for a good while with the 540 and loved it.
Let me know if interested and I'll put you in touch. It's located just an hour or so south of Dallas.
Rear end rebuild recommendations
