Visit to Finland From US with C-2

[akema]

Looking good, Jack.

[Jack Panzica]

We are reworking a 78 Corvette Rear from 3:70 to 3:36 , plus tuning it.

Gary is doing the rebuild and here is a quote from him on bolts that attach the Ring gear.

"Here I countersunk the posi case ring gear holes. You see in picture#1 that the holes are square edged and the stock bolts work with that but not the ARP's. The ARP's have a larger radius under the head for more strength and have the shoulder on them like the old GM bolts did. Somewhere around 1977 they changed to the bolts that were in here before, shorter, no shoulder, and not loctited in place. Not good, many backed out in use sometimes within the factory warranty period. QC with the late 70's vettes wasn't as good as the earlier cars but that is probably the case with most lines of the period."

Stock bolts vs ARP's Stock on right

Before milling notice flat surface

Counter sink

Cut

Polish

Perfect fit

[Jack Panzica]

Gary is now assembling the posi unit after polishing.

Here is his commentary on the process.

Here I radiused the spider teeth to prepare to tune them. I used new solid steel clutches, new cross shaft, retainers, and washers. Next up the tuning process starts. Unlike a stock posi, where the spider lash is set between 002-008" and then the plates and springs are stuffed in there, I will set the posi up to a balanced, much more precise unit then any stock or rebuilt vette posi. where it is now I could just use the springs but it really works better to put the time and machine work in to tune them.


Pictures Parts laid out

Cross shaft and steel clutches

Radius Spider Teeth

Ready to Tune

Next series will be the tuning

Jack

[Jack Panzica]

Gary is now ready to tune the posi unit. Here is his explanation of the process.

"Here I started to tune the posi. While some think you just remove the springs and plates and bolt it together, there is much more to it. The process requires running in the new clutches to "seat" them. This will change the lash after about 50 rev's but I go at least 300 per side, CW & CCW. Then check it on the bench fixture and re-shim. The shims come in 005 increments so I grind them to within 001" to dial in the tune. The end result is a balance setup between both the Left & Right sides. The naysayers will tell you it will not work, yet Tom's has been building them like this for over 40 years for street, strip, and road race cars. You will have full posi action yet there won't be any hammering in the corners and there is less load on the clutches. All my vettes are setup like this and work great."


Video of process

Just click on picture for video

[Jack Panzica]

Continuing the rebuild, we are now preparing the case . It must be cleaned both inside and out. Here are comments from Gary on this procedure.

"Here I worked on the housing, cover and pinion yoke. I finished blasting them to bare iron. Now most places will just shoot a cheap top coat of paint and call it done. I never liked that since once the car is in use that paint isn't going to last as long as it should. So I blast the parts to bare iron. Then Etch them for 30 minutes, rinse, blow dry, flame dry, cool, POR15 and then when just right shoot the top coat to mix with the POR15 and harden together. I'm waiting for the POR15 to setup now to shoot the top coat. Then I'm going home to fire up my 72 vette for a weekend ride!
"

Blasting first

Etching

Flame Dry

POR 15 Base coat

Final Coat

Interior Case Prep Next

[Jack Panzica]

We are now installing the gears after countersinking bolt holes and using new bolts. Gary's comments:

"Once I had the posi were I wanted it, I stoned the back of the new USA 336 ring gear and the posi flange. Then I cleaned the new ARP's in Acetone, same with the RG holes. I use alignment studs to keep the ring gear in place since it is a press fit on the case OD. I use #271 red on the ARP bolts, torque them and then check for full seating of the bolt and the ring gear. I'll let the Loctite set up at least 24 hours before applying any load to them."


Clean Bolts in Acetone

Tom's US Gear 3:36 to replace 3:70

Stone surfaces

Alignment Bolts

Torque Bolts

Check Fit

All Set Up

[Jack Panzica]

We are now working the inside of the case prior to installing gears and posi unit. Gary's comments:

"Hi Jack
Here I final prepped the housing. You can see there in the ready pictures the inside didn't look so good after etching and rinsing. It was really only minor surface rust but I cleaned it up good with a wire wheel.
The holes were all chased. The pad holes were bottom tapped and countersunk, this means a bottom tap was used to cut new threads to the bottom of the holes. The factory used a starter or plug tap and the bottom threads don't always get a full tap. The bolt may not fully engage the threads so I know now the hole is fully threaded beyond the length of the bolt. The reason to countersink the holes is to cut the lead- in thread to prevent it from pulling when the bolt is torqued. The same process used on head bolt holes. All the oil passage were brush, washed, and blown clean with compressed air."


Rusting Before picture

Wire Bush

Chase holes

Radius Edges

Cleaning bores

Cleaned and ready to go

[Jack Panzica]

We are putting in a drain plug which will make changing oil a 5 minute job. Gary's comments:

"Here I tapped the drain plug hole and fit the plug. With new gears you will have to heat cycle them the first 10 drives you make. Drive 25-30 minutes, no racing, get the diff hot. Stop and let it cool at least 1 hour. At 500 miles you drain the oil and add fresh. With this drain plug it will be a 10 minute job, just jack up the RR of the car , pull the wheel off, put your drain pan under the plug, remove the fill plug with a long extension and 5/8" 8 pt socket and drain the oil. Clean off the fines on the plug, put a little #2 permatex on the plug and snug it up. Add posi additive and pump in Lucas 85-140 gear oil, should take just under 2 qts. Seal plug and install- done."


Tap hole

Fit Magnetic Plug

Installed

[Jack Panzica]

We are now installing the pinion bearing. Gary's comments:

"Here I installed the new USA Timken pinion races in the housing"

Checking work

[Jack Panzica]

I had removed the transmission last week to both adjust the linkage and to replace the rear seal and bearing. I did not want to take the case apart and in one of the recent posts, John Z mention a tool that would allow you to change the seal and rear bearing while the tranny was still in the car. I located the tool on E-bay and although my tranny is out of the car, I left the shift on to show it can be done .

My old slip yoke had 300,000 miles on it and it shows it.

My new slip yoke and balanced drive shaft

The tool to extract the rear bearing , with seal removed

Close up of tool

Rear Bearing , the tool slides in just like a yoke

I use a hose clamp to compress flanges of tool , edges grab bearing

Use wrench to extract bearing , bolt pushes on tail shaft , pulling bearing

Bearing pulled out

Can be done with tranny in car and not taken apart