63 diff inspection

[Gary R.]

On another thread I was speaking of how the 63-79 posi cases are now obsolete and ended up talking about a 63. Well as fate will have it, a local guy brought in an original 63 diff today that he hear a loud bang out of while driving his 340hp roadster. I was hoping it was worked on in the past and upgraded but as soon as I pulled the cover I saw the dreaded Dana posi. You can see how these are different then the Eaton posi's. The case, springs,plates, spiders, and clutches are all different and for a lack of a better word- junk.






While turning it I saw the ring gear had a LOT of lash and the gear and posi case had different movement.You can see when I got the case out it was the 2-piece design! Yup cracked it in half after years of use.




The original side yokes are prefect after 50 years. NO wear on them at all, .200" from the face to snap rings. These are better then ANY new or rebuilt yoke on the market today.Anyway since we were talking about this subject the other day I figured some of you would like to see what I was talking about.See ya

[Gary R.]

Re: 63 diff inspection

I do have a question here. There was a tag on one of the cover bolts- below the fill plug - never saw one before, anyone have an idea what it is for? Alignment guage??

[Bob J.]

Re: 63 diff inspection

Gary,
I think the tag you show tells the rear end ratio depending on how its cut or if its cut. They were used on pre 63 models as well.

BTW..I hope you save the useable parts from those exploded 63-64 Dana posi units...........I frequently need misc parts from one! Bob

[Gary R.]

Re: 63 diff inspection

Hi BobWell that would be something new I learned as for the tag. I have build plenty of 63's but this is the first one of these I saw.I usually return the posi cases to owners so I don't have much stock for these Dana's, you still use them??

[Bob J.]

Re: 63 diff inspection

Gary, I think this print is accurate in showing what ratio each tag is.
Yes, I use Dana posi units in my 63s regardless how superior the later Eaton posi units are.
I like originality more than most. Bob
100_2201.jpg

[Gary R.]

Re: 63 diff inspection

Bob, The tag is the 370 ratio and exactly what this is. Thank you for sharing that, based on what I saw no one was ever into this diff before. You also the first guy I know who wants to stick with the original DANA, I'll give you credit for that. Have you ever broken a case?

[Bob R.]

Re: 63 diff inspection

I have the original 3:08 tag on my 63 diff. I never knew how the tag identified the ratio.
Thanks for the lesson.

[Bob J.]

Re: 63 diff inspection

Bob, You also the first guy I know who wants to stick with the original DANA, I'll give you credit for that. Have you ever broken a case?

Gary, I've rebuilt a few that were cracked in the window but I never exploded one like your picture.
I stocked up when Dana cases were dropped by GM, just like you did with the Eatons. Bob

[Joe L.]

Re: 63 diff inspection

Gary------


I doubt that GM abandoned the Dana-manufactured units and switched to Eaton because the Dana worked just as well!

[Duke W.]

Re: 63 diff inspection

Maybe you can help clear up my confusion.

Is that broken Positraction unit the same one illustrated in the 1963 Corvette Shop Manual Fig. 78 on page 4-30?

I always thought it was manufactured by Borg Warner.

What was the sequence and years of the two or three Positraction cases used up to the mid/late seventies.

For reference the drive pinion on my SWC snapped in two - right at the section change - at about 2.5 years/30K miles. I got some consideration from GM. They paid for the parts, and I paid for the labor, but I don't think they replaced the Positraction case - just the ring and pinion.

Fast forward to circa 1977. I rebuilt the axle myself due to "clunking" from excess differential pinon backlash/yoke end play caused by worn clutches and a pinion seal leak. The Positraction case was definitely not the type shown in the 1963 Shop Manual. Magnaflux inspection revealed a small crack at the case window, so I bought a complete, assembled Positraction case from Chevrolet service parts, and when I finished setting up the axle with proper ring and pinion backlash, yoke end play was a little less than .010" on both sides.

I don't recall checking differential gear backlash, but final yoke end play was a little less than .010" on both sides, so I decided not to take it apart and reshim the case to reduce yoke end play, which would also reduce differential gear backlash.

The Chevrolet Power Manual recommended less than .005" for racing, but I figured mine was tight enough for road use.

So what did I pull out in 1977 and what did I replace it with from Chevrolet service parts at that time?

Duke

Duke

[Joe L.]

Re: 63 diff inspection

Maybe you can help clear up my confusion.

Is that broken Positraction unit the same one illustrated in the 1963 Corvette Shop Manual Fig. 78 on page 4-30?

I always thought it was manufactured by Borg Warner.

What was the sequence and years of the two or three Positraction cases used up to the mid/late seventies.

For reference the drive pinion on my SWC snapped in two - right at the section change - at about 2.5 years/30K miles. I got some consideration from GM. They paid for the parts, and I paid for the labor, but I don't think they replaced the Positraction case - just the ring and pinion.

Fast forward to circa 1977. I rebuilt the axle myself due to "clunking" from excess differential pinon backlash/yoke end play caused by worn clutches and a pinion seal leak. The Positraction case was definitely not the type shown in the 1963 Shop Manual. Magnaflux inspection revealed a small crack at the case window, so I bought a complete, assembled Positraction case from Chevrolet service parts, and when I finished setting up the axle with proper ring and pinion backlash, yoke end play was a little less than .010" on both sides.

I don't recall checking differential gear backlash, but final yoke end play was a little less than .010" on both sides, so I decided not to take it apart and reshim the case to reduce yoke end play, which would also reduce differential gear backlash.

The Chevrolet Power Manual recommended less than .005" for racing, but I figured mine was tight enough for road use.

So what did I pull out in 1977 and what did I replace it with from Chevrolet service parts at that time?

Duke

Duke

Duke------

The 63-64 posi differential assemblies were manufactured by Dana (as were the earlier C1 posi's). I've seen them described as Borg-Warner-manufactured (in fact, I may even have slipped a time or two) but they were manufactured by Dana.

In 1977 the only unit you could have gotten from GM was an Eaton. The last Dana posi unit was discontinued by GM in July, 1969 and replaced by the Eaton. When SERVICING a car originally equipped with a Dana with an Eaton, the complete posi unit must be replaced; internal parts are not interchangeable. Some internal parts for the Dana were available from GM after 1969 but not the complete Dana units.

[Gary R.]

Re: 63 diff inspection

Duke, The 63-64 posi were Dana and as mentioned weren't too good. The 65's got what I refer to as the first design posi noted by the 1" square window and 10-18 spiders. These were not too good either because the casting had parallel seams and often cracked. I find about 80% of them cracked when I open the 65-68 diff's. The 69-79 was the 2nd design Eaton with what I call the "tear drop window" the casting seam in these is a staggered tooth type and they are less prone to cracking like the first design cases. The 69 & 70 posi used 10-18 spiders and the solid steel clutches used since '65. 71-79 got the better 10-17 spiders but in a effort to resolve posi chatter the slotted clutches, I refer to as snow flakes, were used and failed to resolve the problem. Under hard use the snowflake clutches break apart. The first design posi also used brass thrust washers which didn't wear well, the later ones used steel thrust washers. Nearly every Eaton posi case I have worked on, from 65-79, new bare and new loaded cases have shallow depth engagement of the cross shaft bolt. I machine the pads on everyone I work on to give the cross shaft better support as I have seen them break the casting or the bolt. The pinon gears used on the 63 into 65's were a 17 spline, sharp edge pinion that used a small crush sleeve, what I refer to as the wedding band crush sleeve. These are also prone to shearing in half as you experienced and I have posted pictures of. I do not reuse these gear sets if I see them in a diff, they are not worth the risk. Mid 65-79 and the after market use a tapered shaft 30 spline pinion which resolved the breakage issue. The bottom line, there was not a perfect differential built in any one year between '63-82. I didn't mention the 80-82' but they were also Dana's and the worse of the lot. Issues with broken bearing caps, soft cross shafts, and posi case issues are typical, I won't work on them, converting to an iron diff is the better option.

[Wayne M.]

Re: 63 diff inspection

..... The pinon gears used on the 63 into 65's were a 17 spline, sharp edge pinion that used a small crush sleeve, what I refer to as the wedding band crush sleeve. These are also prone to shearing in half as you experienced and I have posted pictures of. I do not reuse these gear sets if I see them in a diff, they are not worth the risk. Mid 65-79 and the aftermarket use a tapered shaft 30 spline pinion which resolved the breakage issue. .....

Gary -- there was an intermediate design (during 1965 MY, maybe a bit beyond) that used the stepped pinion shaft with the "wedding band" crush sleeve [love that term, BTW], yet had the 30-spline of the later years.



c

[Gary R.]

Re: 63 diff inspection

Hi Wayne. Yes that is correct I had a couple of those in this year in fact and installed new gears in them.

[Joe L.]

Re: 63 diff inspection

Gary -- there was an intermediate design (during 1965 MY, maybe a bit beyond) that used the stepped pinion shaft with the "wedding band" crush sleeve [love that term, BTW], yet had the 30-spline of the later years.



c

Wayne------

The GM #3817864 was used from 1963 to sometime during the 1966 model year. Just when, I do not know.