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So I have been doing a lot of deburring, cleaning and painting on the case. As well as reading and research. Hours of dremel tool sanding / smoothing - inside and out.
Primed and painted. Eastwood chassis primer and cast grey topcoat.
I found some measurements for the oem side yokes and mine seem to have almost no wear at .188-.190" So maybe they are the better hardened ones? In 1972? I can tell the original diff was never apart at 90k miles. They are BB units with caps.
I would love to find a place to test them for hardness and/or heat treat them. I would rather go for a few more $ to be sure they are good. Anyone have any sources here?
So here is my HD BB diff plan: (Just a little short of a Super-10)
A full complete polishing of the eaton posi case. I'll do what ever it takes to do it right here. It's just time. I don't mind.
ARP RG bolts seem like a no-brainer.
So does the deeper set pin bolt.
As long as my gears and 10-17 spiders have no marks/cracks can I assume they are good to go?
Posi will be tuned, I'll build the tools I need.
Hex socket cap bolt upgrade.
Just for a little extra insurance I feel like a left steel cap would help. My best friend has one of the best one man race engine engine machine shops in the metro area. So that one is easy for me/him.
I feel like the solid pinion spacer is another mod I could do here in my home garage and just put in the time to dial it in. I bought a small press just for this project. I am inclined to do it for the ease of changing the front seal when/if it leaks alone!
Three inch GM halfshafts calculate to be 20% stronger. Sounds like another easy upgrade.
Spicer u-joints/timken bearings/ all top shelf components.
I may try to set the pinion pattern myself, or not, but my buddy has already offered, and he has done 100s.
I am familiar with cryo treating, and the posi may benefit quite a bit, so if I had a source here I may send that out as well.
I am probably going a little overboard on mods, for my intended street use, but for a few hundred $ here and there, I think of it as peace of mind insurance. I really do not want to ever take the diff out again, or take the remaining step to 31 spline yokes/axles. That's big money. And I have no intention of putting slicks on it, just sticky street tires. If something "gives" I would like it to be tires or outer axles, things that are easier to get at.
So what do you guys think of my plan?
Got any sources for me for hardness testing/heat treating/cryo?
Have you done any polishing of the posi case yet (not the diff housing) ?
I have an OEM open unit that I'd like to install a lunchbox locker into and may spiff it up some. (non vette)
Not yet. That's next. But I found a lot of good threads on this site. Search for posi tuning, diff polishing, diff, super-10, and especially GTR1999. I have downloaded/read hundreds of pages of this stuff. Lots of great ideas/pics.
I built my 69 diff mostly along the the same lines.
See my previous reply. Lots of hours researching, watching Tom’s tuning video, reading Gary’s and Tracdogg’s posts. Take your time and document what you do so if you start going down a rabbit hole, you can review what you’ve done.
I built my 69 diff mostly along the the same lines.
See my previous reply. Lots of hours researching, watching Tom’s tuning video, reading Gary’s and Tracdogg’s posts. Take your time document what you do so if you start going down a rabbit hole, you can review what you’ve done.
So here is my HD BB diff plan: (Just a little short of a Super-10)- A real Super 10 or one from the knockoff artist- big difference in builds, honesty, and integrity. What many don't know is I came up with this build and the name super10. As with any quality product there is always someone trying to copy it and sell them for less and that is just not possible when greed is more important than quality.
A full complete polishing of the eaton posi case. I'll do what ever it takes to do it right here. It's just time. I don't mind.
This is very doable at home with some emery wheels, mini belt sander, grinding wheels and time. It takes me about 3 hours and cleaning up just the windows is not a fully blended, radiused, and polished posi case.
ARP RG bolts seem like a no-brainer.
The best RG bolts on the market, cheap builds use plain full thread grade 8 bolts- no comparison at all.I use ARP RG bolts on every RG I install
So does the deeper set pin bolt.
Simple process to give more support through the cross shaft into the case I do it on every posi I build. Should be done on a mill.
As long as my gears and 10-17 spiders have no marks/cracks can I assume they are good to go?
Yes
Posi will be tuned, I'll build the tools I need.
This is more involved then leaving the springs out, Follow TOM'S video closely. A correctly tuned posi has no lash and is balanced between sides. Figure about 800 rev's CW & CCW
Hex socket cap bolt upgrade.Super easy $5 upgrade
Just for a little extra insurance I feel like a left steel cap would help. My best friend has one of the best one man race engine engine machine shops in the metro area. So that one is easy for me/him. Steel caps have been around for years and work well once properly setup for 001 rock. Since the posi wants to pull out the LH side and dig into the RH side under drive load the steel cap is only needed on the LH side. Those that claim otherwise are uninformed or were sold a bad bill of goods. These are for hard launches, if you are not going to drag race they are not needed.
I feel like the solid pinion spacer is another mod I could do here in my home garage and just put in the time to dial it in. I bought a small press just for this project. I am inclined to do it for the ease of changing the front seal when/if it leaks alone! If you need a steel cap you need a solid sleeve as they both provide increased load protection. Solid sleeves have to be machine fit- no questions. The common solid sleeve kit comes with shims and are about as close as the shim kits for rear bearings- no where close. Surface grinder is required for this operation. Again if not drag racing then it's not needed. Some of the knock off super10's didn't have them either. Kind of like using a cast pinion yoke in place of a billet yoke as the build was designed for but not letting your customer know about it.
Three inch GM halfshafts calculate to be 20% stronger. Sounds like another easy upgrade.
2.5 or 3" GM will work in this application. Tom's 3.5 are the strongest shaft tubes but the weak link is the u-joint, they all use 1350's and that would be the point of failure most of the time which will take out the shaft yoke - regardless of tube size. GM shaft tubes are thicker then the aftermarket ones that come balanced.
Spicer u-joints/timken bearings/ all top shelf components. Good choices, include the full complement axle bearings.
I may try to set the pinion pattern myself, or not, but my buddy has already offered, and he has done 100s. you are going this far why not set the pattern? The principle is the same as any differential. The gear set machining and lapping will dictate the final pattern. Text book is centered in all 4 axis but that rarely happens. I used to be able to tell the lot that US Gear gears were machined in because they all setup the same way. Some were centered, others were center to toe, others center to heel. There is only so much adjustment in them as well. Again the shims supplied in the kits today are not too good. You may find you need to double them up. I grind shims to size to get to where I want. Kit shims used to come in 002 increments but that stopped a year or two ago. I haven't used kit shims since.
I am familiar with cryo treating, and the posi may benefit quite a bit, so if I had a source here I may send that out as well. cryo is good option. It is done in a batch, so you should send as many parts as you can. Prices are around $300-$500 depending on where you go. I do not recommend shops so please don't ask who I use. There should be plenty to pick from if you decide to do this. Most times you don't get any paperwork but the place I use sends a cert with each batch, that is a sign of a good business but you pay for it. Any good machine tool guy, machinist, toolmaker knows you do all your machine work prior to hardening, with final grinding after. Some found out the hard way about this in the past. I am sure you machinist knows this but you may want to confirm if you cryo parts.
I am probably going a little overboard on mods, for my intended street use, but for a few hundred $ here and there, I think of it as peace of mind insurance. I really do not want to ever take the diff out again, or take the remaining step to 31 spline yokes/axles. That's big money. And I have no intention of putting slicks on it, just sticky street tires. If something "gives" I would like it to be tires or outer axles, things that are easier to get at. Use governs cost. No sense in spending money you don't have to, ie RH steel caps. Sticky street tires can break parts, Inner axles can be upgraded to 30 spline but the spiders are not as good as Tom had made. There are good and no so good on the market today. 31 spline axles are the outer axles, they are worth the money for hard use as stock axles will shear at the base of the threads about 500hp with some abuse. Later 70's stock axle spline twist more then earlier.
So what do you guys think of my plan? So that's what I think, go for it. You won't learn any younger that's for sure. I don't post as much as I once did so I won't say I will offer future advice but I may not get the time to. By the time my day ends, calls made and paperwork done - I don't want to spend a lot of time online. Good luck.
Got any sources for me for hardness testing/heat treating/cryo?
My thoughts in red above for whatever it is worth. Some may agree, disagree, or just don't know as much as they think they do. As with any trade it takes a lot of time to see various things that come up with any type of build. The housings and posi cases were machined to various levels of tolerance and QC wasn't always good. I read on different forums where a guy builds one well and is an expert which may be true if everyone was the same. Same for setting up rear bearings and steering boxes,
You are the best when it comes to these things. Your pics and Bmans pics of your Super 10 build are what gave me the confidence and know-how to do this. So I'll do just what you recommended,
So no LH steel cap for me, but I will do the polishing and cryo.
yup, it's junk. You have 3 options
1- source another 72 - 79 posi
2- source a NOS GM bare case- expect to pay $600 for one now. I have a couple of them from the few dozen I bought when GM closed them out but I'm holding on to them
3- buy a loaded Eaton which you can use with their internals or use just the case with the better internals. You better check the case either way some are coming through from China with poor machine work inside.
# 1 is your best option
How is this for a crack. This goes back a few years, it was a fresh rebuild with -0- miles from a place in Tx. Luckily I was asked to check it before installing in the car- this was about 1000 miles or less from imploding.
Bad castings I think, or just a "weak" spot. Unfortunately I have seen several of Gary's and others examples and this seems to be a very common location for cracks.
How is this for a crack. This goes back a few years, it was a fresh rebuild with -0- miles from a place in Tx. Luckily I was asked to check it before installing in the car- this was about 1000 miles or less from imploding.
And there's no such thing as repairing something like that? It couldn't be welded?
Is that due to a bad casting or typical stress damage? How did someone miss this doing a rebuild?
Last edited by brassplyer; Jan 23, 2021 at 06:42 PM.
There is no repairing this. Some will try and drill a hole at the end of a crack and weld it. That might work for some applications but not a posi case. A crack, whether an 1/8" long or 2" long like the one in my picture is a crack and the posi is junk. That diff was never installed and run, it was brought to me for an inspection after being purchased as a complete rebuilt unit. There is no way the rebuilder didn't know the posi was cracked. My opinion is they simply wanted to take the guys money and by the time the diff imploded it would be the owners fault and they could blame him for abusing it- probably try to sell him another one. There is an automotive machine shop near me that operates like that and has taken guys for years. The old saying you get what you pay for applies here. If you think you can get a custom engine, trans, differential or any other unit that needs to be rebuilt for a catalog price, think again. When profit is more important then quality bad things happen.
Well I am truly awed by the friendships I have developed on this forum!
I was actually very depressed when I discovered that expensive crack on friday night. The issues I find just keep on coming! Will it never end?
So many of you have come forward with helpful leads and offers of assistance that it has really given me a new outlook on this hobby.
I only wish that we could all get together and I could buy all of you a beer! (Maybe someday)
I currently have more leads than I could possibly follow up on, and I am indebted to all of you!
The problems will eventually end, and I will someday get this build done. Just like Covid. I got my first Vaccine shot this week. So I feel like life just may get back to "normal" someday after all!
it was brought to me for an inspection after being purchased as a complete rebuilt unit. There is no way the rebuilder didn't know the posi was cracked. My opinion is they simply wanted to take the guys money and by the time the diff imploded it would be the owners fault and they could blame him for abusing it- probably try to sell him another one. There is an automotive machine shop near me that operates like that and has taken guys for years.
That's just real lowlife crap - straight-up theft. What was their previous line of work - scamming the elderly on driveway re-topping? Running out the door with charity donation boxes from store counters?
Do you know if the guy got any satisfaction from them like a refund? If someone pulled something like that I wouldn't want anything they touched in my car.
