I understand.
I have work waiting that 5 years ago would be done by now.
no rush. we aren't going anywhere.

 

When the differential housing breaks in the fashion as presented the ring gear is no longer supported accurately by both carrier bearings in alignment, so the relationship of it to the pinion gear is lost, sometimes to a greater sum causing obvious damage of the two, to something less that may not be so visible but still makes them junk, or even they may be salvageable; but even if they might look O.K., unless the budget really won't permit their replacement, this being the highest load relationship present in the differential, it would be advised to just toss 'em.

Also, just a comment on the subject of "super-tuning" the diff.:

De-burring and even polishing the differential housing casting (and the gears too!) isn't something new, as such preparation processes have been practiced for over a century at this point in the automotive mechanical component world and the intention is valid; but be aware that such as is being presented here for the most part is intended and has had its' best results in applications of longer duration fatigue failure instances, not necessarily so effective (though every little bit does help!) in the instances singular or even low cycle instances of significant over-loading where the item is just not capable in it's basic design element, where failure is inevitable, and just breaks in half like an egg shell.

So here in this conversation this means that for some, in the environment as they utilize their vehicle, the effectiveness of this will range from: minimal value (for those whom baby their car; the wife 'always' rides along!) as long as you didn't receive a "nearly" defective part out of the box; to very effective (those whom are operating on the limit, but not much beyond, of the capability of the component); to no really great benefit for those with significant horsepower (the guy's got drag slicks and wheelie bars, that actually are needed!) as the part still breaks in half just the same. So where are you?

As for "setting-up" the gear lash clearances between the pinion and side gearing, this is out-lined with "proper" values by the manufacture of the component and if not followed in the re-building process this is just called plain sloppy work; though often in the performance world we will purposefully "modify" this intent often because we understand that the environment that the customer intends to subject the component to is not as identified as "typical" as was that of the manufactures' intent. Yes, setting (shimming in some cases) these gears with the intention of reduced back-lash is/has been popularly practiced (for more than one reason), and advised particularly in abusive environments, but for example note (as nothing is free!) that generally this causes the gear set to generate higher temperatures in operation. This is not such a problem here, as these are generally of intermittent operation, but just understand that there are often consequences when changing things from the intentional norm. Also setting the gears "tightly" (though not actually crowded, as that would be a "no-no"!) but for example, realize that as the clutch-pack wears (posi-unit) the side gears move away in the setup, so if your so intent on it being "tight", you'll need to periodically service the unit either re-shimming or installing new clutch-packs (and re-setting clearances appropriately).

Just food for thought,
Scott.

 

Pulled the rear out today and this is what I’ve got…
Plan on replacing everything with new

 

wow, no half measures there.
that baby broke.

 

These cars were not built, nor designed, for drag racing style abuse. Just a simple fact. All those who feel that beating a car is what makes it fun should be looking at Chevelles, Novas, etc.

 

If you had a better oil filter in there it would have caught all those little metal particles and might have lasted a bit longer.
LOL

 

On a serious note, check the housing really good and if it’s damaged, just replace the whole unit.

 

Wow, that's a good old fashion grenaded rear end, doesn't get any better than that.

 

Spyder gears laying on the bottom is not a good sign.

 

Sorry about that Mike.

Based on what I saw, when I found 4 cracked used posi housings in a row, I will bet you had a crack in there for a long time. I don't think you abuse it, but that doesn't mean nobody never did in it's 50 year life. If the posi was cracked eventually even smooth full torque roll-ons of a BB could do 'er in. As I recall you have street gears too. Like 336 or so. That's only a 7.4 or maybe a 8.4 in 1st gear and IIRC you have the milder L68 427. Mine had a crack with the same gear setup and a low HP 72 454.

My buddy George just pretzeled both his driveshafts at Atco drags. He has a slightly warmer ZZ427, but it's not wild. He does have though a TKO 600 with 411s so 11.8 torque multiplication in 1st gear. He only ran it twice, and it didn't go past 13.0, so he didn't beat on it too hard, but he did warm the tires up, and the Nitto 555 285-40-18s must have gripped pretty well, and he wound up with a vibration. Both stock halfshafts had twisted some, like 30 degrees or so. Fortunately they didn't completely let go.

There is nothing in a Vette IRS that you can't break with a BB!

 

Thats what I call Metal Salad. It's not uncommon, I see it a lot in fact. Almost always from abuse- hard launches, burn outs, hard power shifts. There was a reason Eaton revised the posi case 3 times between 1965-1972.

All the internals are junk, don't trust the ring or pinion, possibly the axles but they have to be checked. The housing typically is reusable. If you don't see a hard impact mark on the inside of the housing or cover they are good. I have seen some cracked from hard impacting but not a lot.

You have several options now. Time and money are usually the factors in a decision. Lack of understanding the weak areas and what is commonly sold today are passed over many times and sometimes that will come back to haunt you.

1-Trash that diff and replace it with another used one. You can find them for sale as there were a lot of them made. Most on the market today are out of a car for a reason, usually not a good one. Market value is $300-$400 for an as- is out of the car diff. Some think they have gold and want a lot more for worn out junk, so you have to know what to look for.

2- Buy one outright. You can find them on ebay or from rebuilders. Keep in mind many places don't rebuild them, they just resell what they buy from someone else. Prices can vary a lot, but figure about $1200 give or take, depending on any core charge- which yours won't qualify for. I don't recommend this course, but it will be faster and less expensive than building a better, custom diff. Again, you need to know the weak areas in these and how they are put together. I could type several pages on that alone but will just say, this is not what I would do.

3- Build it yourself. I have coached people worldwide on this and posted 100's of pictures of how to build them the best way possible. Some here have followed and had success. It takes time and patience and while the process is pretty much the same, everyone presents their own issues. I am working on a 64 now with an odd ball issue I have never seen before. There is no one for me to call, I have to resolve it on my own. That is what you will have to do as well. You will need good tools, engine stand, and measuring tools. I use a mill, lathe, and surface grinder to build my diff's, boxes, and TA's. NOTE- I will be happy to answer any questions but some people take it too far, calling me daily for instructions over days or even weeks. Most of the time they buy parts from someone else, which is their right. They should be calling those who supplied them with the parts in that case.

4- Find a local shop that knows how to build these beyond what the textbook says. Any competent Diff shop can usually build a textbook diff. If that is what you want to go from point A to point B, no abuse, no detail work, etc, then that might be your best option. Finding a place that knows them through the year ranges with the different issues and knows how to improve them over stock may be a different story. Be careful of the lying conman out there, who will tell you everything you want to hear, offer a cheap rate, take 50% down and then you never hear from him again.

A quality shop- no matter what the specialty today is almost always booked out months in advance. They are not the cheapest, fastest, but usually the best out there in their business. For example, engine shops here that are good are out 6-12 months if not more, yet some shops offer 2-3 week lead times for less. Think that is good? This is not new, not a result of Covid, it's been going on for decades. Some of the biggest crooks in the business were/are auto machine shops.

5- New posi case. Another option, use your housing and buy a new posi and gear set. For posi's you have Eaton, Yukon, and Auburn cone type. You can also machine fit 12 bolt or Trutrac but I don't think you need to go there. For gears you have Richmond, Motive, and Yukon. There are some other brands but it is unknown if they make thier own gears or more likely rebox one of the three list. They are all imported today. No more usa made posi cases, ring and pinion sets, but USA Timken are still available. Posi's come loaded with powder metal spiders and fiber clutches. Not what I would use first choice but will work in a street car. I like the Eaton over the others. Eatons run about $700 now, Yukons can be had from $400-$800, Auburn and never use but were less than Eatons. I never use a new loaded Eaton out of the box. I always take them apart and rebuild them to the way I want them. If you don't do that I would still take them apart and check the set up. Once those spring packs are out you may find loose set up or tight tight setup. The springs keep constant tension on the clutches, and they smudge away at every turn. They are quiet though.

Good luck. Choose wisely, and you're done probably for the time you own the car. Choose by price, availability, or false claims and you will revisit this again.

Now I have to go figure out how to correct the oddball issue I am working on.

 

Assumptions are great. I pulled off a light and rolled into it a little more than your grandpa would, no where near full throttle when it blew. Wasn’t a flat foot drag style launch. I even backed off a little when it started to spin a little but it still blew. Gee, if your going to put a 427 with tri-power in a car you’d think the rear would be able to take that. It’s 55 years old with an unknown history before it became mine and the law of averages caught up with it. I don’t drive my cars like I’m trying to break them, hell why would I do that? I’m the guy who’ll be repairing it. But I will say I didn’t buy a Vette to drive it like it was a Prius.
When all is said and done it’ll be as strong or stronger that the factory built it when it hits the road again.

 

Option 5 is the only one I’ve been considering. I’m 62 and not thinking about doing the diff myself. I’ve built engines and can do pretty much anything there is to do with a car, truck boat or bike but I don’t do transmissions or especially differentials. I see those as something that takes years of experience to get right and experimenting on my own will be costly in the learning process. Nope this is for the pros to do. Have a shop by me that offered to rebuild a posi unit in a rear they have on a shelf. Are they capable of doing it right ? Good chance they are, but here I am again taking a chance with another 50+ year old unit with probable abuse. Is it likely that there are fractures hidden inside waiting to grenade again, I’m thinking the odds of that are good.
It’s going to be new. I also agree on the Eaton posi units. There appears to be 2 made for the Vette , which ever is stronger will be the one that goes in.
I was considering a good used set of the 3.36 gears as with the way the early gears were cut the run quieter than the ones made today. If theres any question of that being a gamble it’ll be new gears as well and I’ll live with the hum.
Did want to give you a call to pick your brain. Wished we lived closer.

 

I did not mean that you abused the car.....but many people do. Guys brag about it here on this forum. And I get accused of being too easy on my C3 Corvette. So....it was not meant to be a direct attack on you, it was meant to further the point that C3 Corvettes were not designed to be drag racers,......and if you choose to treat them that way, things will break.

I have talked to Gary Ramadei many times, and he has built the differential for my 69 Big Block. He makes it clear that these stock components were never made to handle the big power many people apply to them. ITs just a fact.

The best thing you could do is get Gary Ramadei (GTR1999) to build you a differential. Every other option will most likely be lesser quality. He has been doing this for many years,....and is one of the remaining guys who really know how to do it right. Others think they do....maybe some do.....but I would never risk it.

 

Like I said in an earlier post, I’ve used a professional, well known differential builder near me for numerous builds.
The last was a 4x4 I built and they did a wonderful job.on both differentials.
When I was looking to build my Corvette I planned to go back to the guys I’d used for years, Why not!
I knew nothing about Gary Ramadei, except he was a guy on the forum who everyone talked about as the go to guy for Corvette differentials.
I emailed Gary a couple times with questions about what made a Corvette different from any other GM car’s differential.
Pages and pages later I discovered this guy is the go to guy.
Gary didn’t discourage me from going to my local pro’s and as a matter of fact encouraged me to talk with them in more detail.
I did and after asking them the specific questions Gary told me to ask them about, I found they had little knowledge about Corvette differentials.
A short time later I contracted with Gary to build my rear differential and I couldn’t be happier.
My opinion only, but I wouldn’t let anyone but Gary build me another Corvette differential.
At the very least, email Gary, talk to him and then decide if your old go to guys should be building you a new Corvette differential.

 

X2

Gary mentored me thru building my own.

And I must have been an OK student because he inspected my work and said my diff would be much stronger than any stock rebuild at any of the diff rebuilders or corvette suppliers.

I still spent $800-900 or so. And countless hours, maybe 100-150 or so.

 

I just bought an entire brand new unit from Yukon. Fit great works great. 700 including tax. Think I got it from zip, can't remember. Still have old original one but it had a cracked thrust washer and it was 200 bucks for a washer. So I decided to spend 500 more for a new one. Keep other for a spare and hope to find a cheap washer one day. Lol