C2 Rear End Help

[Jeff B.]

My 1964 posi differential has a couple of things that have me confused. First, it uses a short crush sleeve instead of the longer sleeve that came with the 63-79 rebuild kit. I'm thinking the ring/pinion must be aftermarket. Also, the posi carrier and clutch pack don't look like expected.

There are several numbers on the carrier: C-32324, A large "24", 30 and PAT2966076.

The diff housing has the numbers 3818758-N, GM4 and B84.

The cover has the number 3830303 and GM2

Any experts out there know what I'm dealing with?

[Timothy B.]

Re: C2 Rear End Help

Jeff,

I am not a expert but the cover and housing are correct for your 64. The date B-8-4 indicated February 8, 1964 cast. The cover 3830303 is correct for 63-4 and early 65 cars.

I remember something about the crush sleeve being shorter on the 63-4 and early 65 rears, I think it changed with the fine spline pinion in 1965. The early posi units are Dana and that changed to Eaton but I am not sure the time frame, others will know. If your pinion gear is course spline it is probably original.

Many people change/upgrade to the fine spline 65-up gears and that is all that's available on the market but I used original gears and have no problems to report.

[John H.]

Re: C2 Rear End Help

There are several numbers on the carrier: C-32324, A large "24", 30 and PAT2966076.

Jeff -

That's the original Dana posi unit - most were field-replaced with Eaton units when they failed. Doubt if a "'63-'79 rebuild kit" would have any Dana parts in it - they haven't been available for years.

[Jeff B.]

Re: C2 Rear End Help

Thanks for the replies. This confirms what I suspected. With the clutch disks and baskets in bad shape and no replacement parts being made, it looks like the only solution is be to replace the entire posi unit with a new Eaton unit. Anyone want an old 64 Dana Posi really cheap?

[Joe L.]

Re: C2 Rear End Help

My 1964 posi differential has a couple of things that have me confused. First, it uses a short crush sleeve instead of the longer sleeve that came with the 63-79 rebuild kit. I'm thinking the ring/pinion must be aftermarket. Also, the posi carrier and clutch pack don't look like expected.

There are several numbers on the carrier: C-32324, A large "24", 30 and PAT2966076.

The diff housing has the numbers 3818758-N, GM4 and B84.

The cover has the number 3830303 and GM2

Any experts out there know what I'm dealing with?

Jeff-----


The 1963-65 differential unit used the short spacer ("crush sleeve"). Regardless of whether you change the posi unit to an Eaton, if you continue to use the original housing and R&P gear set, you will need to continue to use the short spacer. It was 0.625" in length (prior to installation). This spacer was of GM #3817864, but it's GM-discontinued. Likely available, though, from sources like Tom's Differential or Randy's Ring and Pinion.

The 1966-68 spacer was GM #3885939 which was replaced in 1969 by GM #3954483. It was 1.445" in length (prior to installation). It's also GM-discontinued.

A photo of the 3817864 and 3954483 appears below.

[Jeff B.]

Re: C2 Rear End Help

Thanks for the detailed information, it clearly answers the last of my differential questions. I thought the R&P was original but I could not reconcile that with the short spacer. So it appears that the entire rear end was completely original, which makes sense for the 48k original miles. Is there any use in trying to repair the original Dana carrier? I would just need the clutch pack.

[Joe L.]

Re: C2 Rear End Help

Thanks for the detailed information, it clearly answers the last of my differential questions. I thought the R&P was original but I could not reconcile that with the short spacer. So it appears that the entire rear end was completely original, which makes sense for the 48k original miles. Is there any use in trying to repair the original Dana carrier? I would just need the clutch pack.

Jeff-----


For many years there were no parts available to repair the Dana posi unit. However, I think there may be now. You might check with the sources I mentioned in my last post. Also, Gary Ramadei who frequents this board, should be able to provide better advice than I on this matter.

[Harry S.]

Re: C2 Rear End Help

Jeff, I have a unit that also needs to be rebuilt, maybe between the two we could build one good one. But, it may go from together to apart very quickly. Send me an email and I'll send you a picture of the mess I have.

[William V.]

Re: C2 Rear End Help

Jeff



Good Luck

BV

[Wayne M.]

Re: C2 Rear End Help

The 1963-65 differential unit used the short spacer ("crush sleeve"). Regardless of whether you change the posi unit to an Eaton, if you continue to use the original housing and R&P gear set, you will need to continue to use the short spacer. It was 0.625" in length (prior to installation). This spacer was of GM #3817864, but it's GM-discontinued. Likely available, though, from sources like Tom's Differential or Randy's Ring and Pinion.

The 1966-68 spacer was GM #3885939 which was replaced in 1969 by GM #3954483. It was 1.445" in length (prior to installation). It's also GM-discontinued..

Here's anther pic showing short sleeve and a "stepped" June '65 dated pinion (right) alongside a tapered '66 dated pinion on left. Both are fine-splined, unlike '64 and earlier coarse (14-splines ?).

[Joe L.]

Re: C2 Rear End Help

Jeff



Good Luck

BV

Bill-----


I don't think the 66+ ring and pinion will work in a 63-65 carrier. I'm not 100% sure about that, but that's what I seem to recall.

[Joe R.]

Re: C2 Rear End Help

Jeff,

There are other issues with the Dana rear end other than parts. The springs for the Dana are very strong and require a special tool to compress them when rebuilding the rear Dana posi. Don't know of anyone that has that tool but it's probably out there somewhere.

Most of the rebuilders for Corvette rear ends (Ikerds for example) will not touch the Dana rears but will supply used parts and replace everything in a Dana housing with Eaton parts.

JR

[Gary R.]

Re: C2 Rear End Help

Wayne's pictures show exactly what you have. You have a few options, replacing the Dana unit should be done as they were weak and as mentioned most are gone by now.

The current loaded Eaton posi is an option but not one I'd recommend. They come with weak spiders,less clutches, and huge springs. The clutches are fiber coated and these have failed in HD use. The cases are pretty good though.

You can buy a used 65-79 posi case or complete differential and see if the spiders are still good. If you want to maintain the casting date and code then you'll want to re-use your carrier and cover.

If you're looking for a used posi look for the better 69-79 castings,the 65-68 are prone to cracking more then the later units. I always install new clutches so I don't care which ones are in the case. The 71-79 clutches are also junk,prone to breaking under load.

another thing you're going to find if you haven't your typical vendor rebuild kit is not setup for the 63-68 carriers. The early carriers used single thin shims, (.070-090" range) the later carriers used cast shims ground to size. The kits come with stackable thin shims for the 69-79's but no thin shims for the early diff's. I have them here and grind them to size to setup the backlash.I'm doing a 66 now in fact and spent some time on the surface grinder today.

I suggest you look up my threads on Digitalcorvettes or vettemod. They have plenty of pictures to help you and offer some mods you can do to beef up these diff's. I just built a 12 bolt setup for a 650hp '66, there's no way a stock vette IRS will hold up once you get over 500hp and put your foot in it a lot.

Good luck.

Gary