They do a lot for racing teams. So I let them pick the exact cycle details. I told them it was nodular iron. Temp was -300 for 24 hours, then room temp, then they warmed it for a while too. Temps were slowly decreased and increased by computer.
They do iron racing engine blocks and the cylinder bores wear 1/3 as much as normal. Gun barrels are more accurate since they heat up more evenly. Brake rotors wear less. etc. I tried cryo'd rotors before they really worked. well.

 

So cryo is the real deal, not just expensive voodoo snake oil?

 

I have heard stories of engines (race) that lost power after 6 road races ( cylinder wall wear) before and now they last 30+. They absolutely stopped my warping rotor problems on another race car. I can find no estimates on how much it would strengthen / toughen a posi or cast iron. But tool steel drill bits last 4-6 times as long. That's 600% !! So yeah it is definately not snake oil. It apparently has a large effect on rubbing wear items. I wish I could find someone to say the posi (or cast iron) is "x" % tougher. And I looked hard. But yeah for $100 I'll take what I can get, even if it is only 30% tougher. I have seen far too many cracked posi units in the last few months! They just like to crack in the same spot...over...and over...

 

Big day today! I assembled the posi. Followed Toms Posi tuning video. Made my own tool for rotating the housing. Fitted shims in succession, spun posi plates, then more shims. Finally it tightened up and stayed snug after spinning the plates. No slack at all in the spiders now. Larger shim set would not fit at all. Pretty difficult to turn without my handle. Well I did feel like I was trying to grab a greased pig! LOL


Spiders all have de-burred edges


Wide assortment of posi shims, from .010 to .050, all mic'd


Posi mounted on bad side yoke in vise. Too hard to turn this slippery thing by hand , so I made a turning tool.

GTR1999 recommended following Tom's posi tuning video. (Tom's Diffs)

 

Ok looks like I have not updated this in a week. But actually a lot has happened. My posi is now all 'Tuned" and completely assembled and ready to install. And I finally settled on a rear gear. I'll be using the 3.36 gears.


One issue with tuning the posi at home was that even though I had 52 different posi shims ! I still did not have the ones I needed. Mine all varied in .005 increments. And the final tune my posi liked needed at least one 0.0025 increment on each side. So I ran to my buddy with the machine shop, who is trying to retire, and he just sold his surface grinder last week. Hmm. so plan B was to call Gary and Toms Diffs. Gary was very busy so I ordered two .0275 shims from Toms. They took 10 days to get here from Idaho..... Patience....Breathe....Relax...

But they fit perfect. Now my posi is balance on both sides so the center pin is not snug at all, and yet it requires some considerable force to rotate the posi with your bare hands. Hint to self: Wipe off the very slippery smelly diff lube first!

The entire reason for going to all this trouble is not just to eliminate the center springs, but to get rid of all the lash in the 4 spiders to reduce the shock loading they see if they moved .010 before contact. I made a video to try to show you this.

It turns out this Posi Blueprinting procedure is very time consuming. But as Gary mentioned the majority of the labor intensive portions can be completed at home. I am doing this in a 2 car garage at home. My only special too is a 12 Ton Press from Harbor Freight. In fact this stuff is so time consuming Gary estimates in the 50 hour range for the entire diff. For me, I would say it is probably 2 or 3 times that. I have never done this before, so I had to learn how to do it (this forum) and then carefully check each step along the way. Fortunately I do not mind the hours, I rather enjoy doing it myself, and learning how to do it. Without Gary's advice and tuteledge I would not have the confidence and would probably mess it up. So now I can feel confident that my posi is not only properly rebuilt, but probably blue-printed during assembly better than any commercial shop/business would care to do it, unless you send it directly to Gary (GTR1999) himself.! If you are even going to think about trying all this yourself, I would suggest that it is far better to be OCD, and think like a machinist, and have a machine shop ready to back you up for jobs you can not complete at home.

Here is one example of what should be a brain-dead-simple item that turned into 2 hours of work. Inserting the small center bolt pin. Normally a what? a 15 sec job? Now ? HAH! It turned into machine work and an hour of select hand fitting. Here's the problem below:

Do you see the recessed lip at "B" ? That does not normally exist. It is now 0.175" deeper after a visit to my machine shop buddy. He had never even done this before and thought I was crazy asking for it, but Gary insisted, so we did. See how much of the cross pin "bolt" extends into the lower case now below the center pin? That is how deep it is after the machining. The hole in the case from the factory is that deep originally, but the pin only extended into the lower case by a pitiful .030" or so. Gary has seen many break in this area. So he recommends lowering the flange at "B" on a Bridgeport to get full bolt engagement. Milled .175" lower and we are all good to go right? No the threads also have to lengthened to match the bolt.

So after 30 min in the machine shop a couple weeks ago, when I got to assemble today, it should now be a 15 sec job correct? But NO, blue-printing is not that easy. Everything must be checked and double checked. My bolt DID NOT FIT !!! WT***!?!? There was .030" under the shoulder of the at "B" after it was tight! So what happened? I was using a different bolt! If you look closely at the bolt above you can see a certain amount of rubbing wear or fretting wear on the used bolt above. Since the center pin DOES NOT MOVE?ROTATE on the bolt I was surprised it had ANY wear. But it had a surprising amount. After all there is a lot of pressure here. I had 4 parts posi remember? so I checked all my bolts. They all had a lot of wear, one was even snapped, and only one looked brand new, that posi only had 1000 miles on it. So I chose that pin and naturally, due to Murphy's Law, it was .030" longer than the one I had taken to my machine shop, and thus caused my current dilemna. So my fix was to measure everything very carefully, grind just .020" off the tip of my bolt, so it would not bottom out, and add one more thread to the tapped hole so the threads would not bottom out, and not get any chips in my beautiful cleaned and assembled and heavily oiled posi. So 2 hours later, my 15 sec bolt install is done.

Did I mention blue-printing is very time consuming?

Anyway it's done now, and I am ready for the gear install, so I had to finally make up my mind about the trans 1st gear and rear gear. I had both 3.36 and 3.70 GM gears sitting on the table and waiting for me to make up my mind. I called Tremec and Silversport and a couple others, and finally picked the 3.36 gear and the 2.87 1st gear TKX 5 spd OD. So that big hurdle is over. Trans will be ordered on Mon.

Even my nice clean spotless used original GM gears needed a little bit of work to satisfy Gary's blue-printing guidelines. So I very carefully radiused the corners of all the teeth on the pinion and the main gear to remove any slight indentations from handling (but there were none) and to remove the sharp edges which could be a starting point for a future chip or crack. That work required a very steady hand and was a bit nerve wracking. I did not want to mar the wear surface of my 50 year old pristine gears!

Look closely and you can see both the radiused edges and the original dates. These gears were spotless even though the posi housing had a 1 inch crack in it. Go figure.

Non C3 News:
Now I need to take the rest of the day off from the Corvette and go visit my brand new grandson who was born in NYC last Tuesday. Yes that officially makes me a grandpop for the first time! Woo Hoo!

 

Congrats,and kudos to you for taking that on yourself. I wasn’t brave enough to do it. Kudos also to Gary for helping you along. May it live a long and happy life. 😀

 

I forgot I hadn't updated this diff build thread in a while.

Last month I got bogged down in ARP bolts that were too long.
https://www.corvetteforum.com/forums...roubles-2.html

Well those were select fit and the ring gear is now torqued and loctited on:

Each ARP bolt was selectively ground to correct length for each of the 10 spots


GM OEM bolt on left, my .060" shorter ARP, and stock ARP ring gear bolt


Torqued, loctited and done

Yesterday's issue:
I have two C3 diff rebuild bearing sets, and the front pinion gear bearing is different in each and both are Timkens.???
Close examination shows they have different roller bearing angles.
I will use the ones that match my OEM NDH bearings, and I have one set of those dremeled out loose to a slip fit for setup use.
The NDH bearings say 88048 and so do the one set of Timkens.
The other set does "fit" but it has a different race angle and is no NP966883. No idea why it is in a C3 rebuild kit?!?!

 

I have no idea on the bearing issue but I'm glad to see you're back at it.

 

Today's fitting:
GTR recommends a 1.5 thou rock of the two caps.
Well I did not have any rock.
In fact I could spin one race by fingertip after torqueing! Not good.
The bore was not exactly round, the caps seem to have "arched" a little bit.

The main caps grabbed the bearing on the side only. Even when installed and torqued down the bore was 1.5 thou too tall, and the caps did not rock.

So after a couple hours of careful filing, and 6-8 test fittings for each main cap, I finally achieved Gary's recommended 1.5 thou cap rock. Would not want those races to spin!

Kitchen Aluminum foil is .0012" thick


.0015" brass shim stock worked better. A .002" feeler gauge would not fit.

Next step is fitting the posi and doing the ring gear pattern. My best friend of 45 years, my engine builder and machinist, passed away from Covid a couple weeks ago.
So I no longer have his backup. So hopefully with Gary's and all your help I can get thru this. Don't forget I have never done this before.

 

Sorry to hear about your buddy Leigh. Covid is a nasty bitch.

Gary will certainly have your back on this build. Wish I could help but I cheated. I sent mine to Gary and let him do it.

DC

 

Hi Lee
Just saw your latest pic's- 0015 is max, 001 is where I like them but that is subjective to the feeler gage and the builder, if 002 doesn't fit you're ok as once the cap is parallel it will be 0005"

Very, very sorry to hear your buddy died. Covid is still around and many seem to forget it.

 

So timken used to be a customer of mine years ago. They told me about 10-12 years back that they have a company based out of Japan make just about all their automotive products and they now focus on the industrial stuff....

 

Today's project:
I made a few tools for the press. Old bearing shells, ground undersize with a dremel until they were a slip fit.
Then I pressed on the carrier bearings.

Bearing press tools / 2-3 old bearing races


Bearings assembled. Ready for install.

As usual I would have been in big trouble later without GTRs excellent on-line documentation. I checked the bearing install with a shim gauge and found one was a little loose. .001" gap on one side only.

.001" gap on one side.

A couple more quick squeezes on the press and the gap dissapeared. If not for GTRs photos for guidance I would not have known to even check for this.
The carrier housing now sits .025" proud of the carrier bearing on both sides, all the way around. The old bearing shells worked perfect!

Next up carrier install and spin test!

 

Installed the carrier without the pinion and torqued it down. No binding. Spun great!

Re-installed pinion:

These are the tools I used to torque down the pinion flange. Adapter plate found on ebay.


No crush collar. Old GM pinion bearings dremeled for a slip fit. Pinion tightened until 15-18 in-lbs. 80 in-lb beam wrench from E-Bay, reads every 1 or 2 in-lbs.



Dialing in the side shims for a reasonable backlash reading. Just setting it up. Realized no caps in this pic.

 

Ok first pattern test!

Here is my old belt setup to load the yoke when I turn the pinion. No welding required, used old yoke/halfshaft


Pattern is too deep and too far to toe. At least my pattern checking setup worked and I got a easily read pattern!

Here is my Gary suggested checklist:

Guess I'll go take this whole thing apart and see what kind of thinner pinion shims I have! Sure glad the bearings are a slip-fit at this stage.

 

Lee,
Couple of thoughts
1- mount the indicator behind the ring gear to get it out of the way and work from the RH side when checking the lash.
2- mix your paste to the consistency of mayonnaise and apply a fair amount of drag on the pinion. I made a tool I bolt into the yoke but a leather belt on the yoke will work. Use a long wrench on the RG bolt, I made one of these too.
3- You have the white paste, FORD uses that, I have used it too but like the yellow better. You can get a tube from your chevy dealer if you want.
4- You are setting up original gears, keep the original shim that came with them since that is where they are seated. The pattern you show is the Drive side, go by the Coast side when setting up used gears. Do not expect to get a text book pattern with used gears. If the Coast is equal between the root and crown and probably full you're good. The Drive shows low, you would have to go to about a 025 shim to bring it up but that is with new gears not uneven worn gears. GM gears for the vette usually are 028-032

Here is a 66 370 gear set I built and ran at 007 lash. 029 original shim, gears are quiet

 

Gary I am so glad you checked in!
Yes these are used gears and that is the original shim.
I only showed the drive because I thought it was the most important.
The coast pattern did not come out as clean but does look more centered.
I will re paste and post more tommorrow:

This was the coast side that goes with the prior post.

 

You can see the coast pattern is equal between the root and crown and center on the tooth. I would keep the lash 6-8 and use that shim. If there is no gear clash rotating it then you're set.

 

I'll get more pics tomorrow, today didn't work out.
Thanks so much Gary!

Gary is the greatest isn't he guys?
Freely helping us with his expertise.
I could not do this without his mentoring.

But with expert guidance, and an occasional look over my "shoulder", it isn't that ?!?! hard.
Just very ... time consuming.

And I least I am somewhat more confidant it is built correctly (or well) versus just dropping it off at an unknown shop and getting who-knows-what kind of quality.