1963 17 spline to 30 spline questions, is this such a unique diff?

[Jeremy 63]

Hey all Chevy fans,

For the past few months i have been recieving much information regarding my diff. The truck is a 1963 Chevy LWB C-10 2WD 1/2 Ton. The diff in question has the following markings:

GM4 - 12 Bolt
3.73 ring gear & pinion
Diff Date: F133 = June 13, 1963
Diff Nr:*3838227*N
Spline: 17
Pressed on backing plates, not bolted on (with 4 bolts).*

From the information that has been gathered, many people, along with companies have told us that purchasing 30 spline replacement axles for this rear end will be virtually impossible due to Chevy only making this rear end from 63 to 64.

I know we have to stay with 3.73 gear and pinion because of the housing.
I would like to change from the 17 spline axles to the 30 spline.
Since the rear is completely disassembled, I am also wanting to change to a posi track or locker rear end (nobody makes a posi or locker for 17 spline axles). I also need all the bearings and seals, plus a new 3.73 ring and pinion set.*

Is it possible to find 30 spline axles for this unique differential?

Any help would be greatly appreciated.
Thank you in advance.

Jeremy Franklin
Posted via Mobile Device

[lucifer]

I took my 17 spline side gears out ...replaced them with 30 spline side gears and ordered 30 spline axles. ( same as 1965-66 trucks) They are actually available off the shelf from Summit Racing, Jegs and Moser axles.
Moser # A30 65GMTK

[Jeremy 63]

Hey lucifer,
Thank you for the quick up-date. Was your diff also from 63'? I am so confused at the moment and so worried about ordering 30 spline axles for this diff because we have received so much confusing info.
Talk to one company, and when they find out it is a 63' diff with 17 spline axles and pressed on backing plates they take a step back and say "sorry, we can't help you, due to the bearing journals being something like 1.873 (don't exactly know).
Another company says, "it would be murder for a company to produce a batch of 30 spline axles that where only made for about 1 1/2 years (63-64). Sorry, can't help you".
Talk to another company, and their opinion is "well Mr. Franklin, you have three options, 1st. You can build you diff back to stock, custom make the shafts or buy a new/used diff with 30 spline in it".
We have called many custom axle makers and their reply is, "the bearing journals are too big".
We can't believe there is not a company out there that can't supply us with 2 new 30 spline axle shafts. This diff can't be so difficult, can it?
Someone please help us!!!!!!!
Thanks!
Posted via Mobile Device

[1963c-10]

I was going to say that I thought Sumit had them...lucifer beat me to it.

[lucifer]

Originally Posted by Jeremy 63

Hey lucifer,
Thank you for the quick up-date. Was your diff also from 63'? I am so confused at the moment and so worried about ordering 30 spline axles for this diff because we have received so much confusing info.
Talk to one company, and when they find out it is a 63' diff with 17 spline axles and pressed on backing plates they take a step back and say "sorry, we can't help you, due to the bearing journals being something like 1.873 (don't exactly know).
Another company says, "it would be murder for a company to produce a batch of 30 spline axles that where only made for about 1 1/2 years (63-64). Sorry, can't help you".
Talk to another company, and their opinion is "well Mr. Franklin, you have three options, 1st. You can build you diff back to stock, custom make the shafts or buy a new/used diff with 30 spline in it".
We have called many custom axle makers and their reply is, "the bearing journals are too big".
We can't believe there is not a company out there that can't supply us with 2 new 30 spline axle shafts. This diff can't be so difficult, can it?
Someone please help us!!!!!!!
Thanks!
Posted via Mobile Device

My truck was an early 1964 and I had no issues. Can't answer the larger bearing question. Might be safer to get a whole rear end?

[Jeremy 63]

So lucifer, yours was an early 64 with 17 spline and pressed on backing plates?
If so, then that would match what I have been told about this diff only being made from 63 through 64.
They must be the same, or?
Posted via Mobile Device

[lucifer]

Yes it was. I changed the pressed on backing plates because I went to four wheel discs.

[Captainfab]

To my knowledge the only thing unique about your differential is the pressed on backing plates, which all '63's had. There should not be an issue with converting your housing with 30 spline axles and a posi unit to match. Also you don't have to stay with 3.73 gears either. You just have to purchase the correct series posi carrier for the gears you want to run. There are 2 carriers for the truck 12 bolt. The 3 series if for the 3.42 gears and higher (lower numerically) and the 4 series carrier for the 3.73 and lower (higher numerically) gears. The GM truck 12 bolt housings are all basically the same from '63-'82......most parts will interchange.

[Jeremy 63]

Thanks for the info guys.
Captainfab, is it possible to put 3.42 gears in the GM4 that had 3.73 gears? Did I understand you right.
Also, if I order the same axle shafts as the other gentleman, they will work in my diff?
Again, thank you all for the help.
Posted via Mobile Device

[Jeremy 63]

Also guys, why are some sites advertising axle for "63" with a length of 30.50 and other sites are advertising lengths of 31 5/16 in.
Which one would be correct for the above mentioned axle.
Lucifer, Moser is 30 1/2, whereas Accuautoparts axles for 63 are 31 5/16.
What do I do?
Posted via Mobile Device

[Captainfab]

Yes you can put 3.42 gears in your 12 bolt housing. In fact this is what I did on my '66 Suburban. The housing itslef has nothing to do with what gears you can install. You just need the correct carrier for the gears you want to use. Since you are planning on a locker or posi carries, you just need to be sure to purchase the correct one for the gears.

As for the lengths of the axle shafts, the 30.5" are correct. I am not familar with Accuautoparts, but I am familar with Moser. Moser knows differentials, that's what they do. While I have not switched axles in a '63 12 bolt, I don't see why you could not use the typical axle that everyone else uses on their trucks. I will do a little checking and let you know.

Originally Posted by Jeremy 63

Thanks for the info guys.
Captainfab, is it possible to put 3.42 gears in the GM4 that had 3.73 gears? Did I understand you right.
Also, if I order the same axle shafts as the other gentleman, they will work in my diff?
Again, thank you all for the help.
Posted via Mobile Device

Originally Posted by Jeremy 63

Also guys, why are some sites advertising axle for "63" with a length of 30.50 and other sites are advertising lengths of 31 5/16 in.
Which one would be correct for the above mentioned axle.
Lucifer, Moser is 30 1/2, whereas Accuautoparts axles for 63 are 31 5/16.
What do I do?
Posted via Mobile Device

[Jeremy 63]

Good morning Captainfab,
Thank you for the info. I will wait for your further info response, and then make a final decision and then purchase what you recommend.
As stated before, I would need everything for the rear end, master kit, carrier, ring and pinion, axles, everything to match. Also at the lowest price possible, we still have to get the parts shipped overseas.
Again, many thanks in advance.
Jeremy
Posted via Mobile Device

[Jeremy 63]

Sorry, also all seals and bearings too
Posted via Mobile Device

[Heater63]

Jeremy,
You didn't say (or I missed it)..do you want to go to 5 lug axles?
I have a the same rear end, and rebuilt it with 30 spline 5 lug axles from Early Classic. They have a kit including bearings and seals for $340 US; I stayed with the 3:73 as I am running an overdrive tranny and it is perfect gearing for that. I used a Detroit Tru Trac posi...it is helical gear, no clutches to wear out. I bought the posi from Summit or JEGS. CaptainFab is correct and a great help if you need to change your ratio.

the '63 press on brake backing plates result in you having no easy rear disc kits available..you will have to stay with drums ( I did), or cut the plates off and weld on a flange to mount disc caliper.

good luck.

[Captainfab]

I didn't have much time today, but I did a little searching. I checked on O'Reilly's site, and they list the axle/wheel bearings as '60-'63, and another part number for '64 and up. I think the inclusion of '63 with the '60-'62 is a mistake, as the '60-'62's used the Eaton HO32, and not the 12 bolt as used in '63. It is my belief that the '63 12 bolt should use the same axle/wheel bearings as any truck 12 bolt differential. It's been 30+ years since I've rebuilt a '63 12 bolt, so I don't remember for certain. I do still have that differential, but it will be a couple days before I can pull a wheel and verify the axle/wheel bearing.

It sounds as though Heater63 used a kit for his axle conversion, which may be an alternative for you Jeremy.

I will check my '63 12 bolt and get back to you.

[Jeremy 63]

Hey guys,
Again, thank you greatly for all the help and advise. So, all in all, replacement axles for the 63 rear end should be 30.5 inches in lenght, and any master kit, posi carrier, ring and pinion kit, seals and bearing, shims, everything, can be purchased from any distributed, as long as it is for a 12 bolt!?
I am staying with the 6 lug, drum brakes due to the pressed on backing plates.

Again, I hope to hear from you all soon. This networking has been a great info source, and I appreciate the time and effort you all have put into this question.

Best regards,
Jeremy
Posted via Mobile Device

[Captainfab]

You can still switch to the 5 lug wheel bolt pattern. You will just need to use the '71 to about '75 narrow brake drums.

[Jeremy 63]

Good morning Captianfab,
Ok good info, but I will be staying with the 6 lug rear and original drums. Already ordered them, they are on airfreight today underway to Germany (ordered them 3 monthes ago)

My main concern are the axles, bearings and seals. I am planning on changing the carrier to a posi, 30 spline. Will buy a new 3.73 ring and pinion.
The only worry are these 17 spline axles. I am scared of buying the wrong lenght axles.
When I measured the axles, I measured from the back of the flange to the tip of the C-clip and had a measurement of 77.9 cm (I don't have a standard measuring tape, all I have is metric here). 77.9 cm is 30.5 inches, so I don't see why the 65' axles won't work. Also my worry is the bearings. The axles are semi-floating, and the shims are 2.1 mm.

Have you been able to pull a tire off and check your early 64' axles and bearing?
This problem is driving me crazy. Summit sent me an email back stating that:

(Hi Jeremy,

Thank you for your email.

I wasn't able to find the parts you requested. I don't know of a way to modify or upgrade the rear end, I don't think the parts your looking for are made. )

Captainfab, what do I do. I want to keep the rear end, due to it being original. All I want to do is simply change to a posi with 30 spline. This has turned into a nightmare!
Some say the 65' axles will work (30 spline, 30.5 lenght) no problem. Others say there is no way.
Please help.

Jermy
Posted via Mobile Device

[Heater63]

Jeremy,
call Early Classic Enterprises. Here is a direct quote off of their website
'63-'69 6 LUG with 30 SPLINES:

1963-'69 6-Lug Replacement Axle Shafts (Pair)
The 6-Lug Replacement Axles are a direct replacement for your factory '63-'69 (30 Spline)6-lug set up. These precision machined parts are American-made.$309

Perhaps that is a mistake, but it says 30 spline axles for '63-69. They have been great to me over the phone, I suggest you call and talk to them.

If that fails, I would think someone can easily make you the axles you need as simply as re-drilling a 5 lug axle for 6 lugs.

good luck,
Heater

[Captainfab]

I will check my '63 either tomorrow or Sunday, and see what size the bearings are.

[bama63]

check here http://www.showmetheparts.com/timken/ it shows part number 6408 as the correct bearing click on that number then the attributes button and timken shows 63-74 and 75-86 all use the same bearing hope this helps

[6flee3]

I heard the 63 12 bolt was an early style only in the 63's with the 17 spline axles, that they went to the 30 spline in 64. I found 17 spline on my 63, 3.73 gears, I changed the carrier to a Eaton 3.08 posi, 30 spline axels and pinion, stayed with the six lugs, stock wheels and the dog dish caps, 350/350 with 3.08 gears ... love it.
Also have a 61 ... has a wierd rear end, has a removable punkin in the front and also a removable cover in the rear, havent counted the bolts yet so don't know if 10 or 12 bolt ... needs to be replaced. Having trouble finding a bolt in replacement because of the 60-62 frame is different. Trying to save money as it is my beater, 350/700r ... fast, loud and fun to drive.

[Captainfab]

Okay, I pulled apart my '63 12 bolt today. That was good news for me as well. Just as I suspected, and as others above said, the axle/wheel bearings are the same as the '64 and up 12 bolts. They use the 6408 bearings, so the '63 is not an oddball, axle/wheel bearing wise. Since I built this rear end back in 1980, I didn't remember that I had installed 30 spline axles. All this time, I thought there were 17 spline axles in it. Also I confirmed the length of the axles are 30.5" as I previously said.

[Imperial Kustom]

All truck 12 bolt guts (gears, bearings, seals) are interchangeable for all years with the exception of axles. The 30.5" are correct for '63.

[Rannos]

I recently upgraded the rear end in my 64 to moser axles and a mini spool. Replaced axle bearings and seals while I was there. Mooser will make any axle you want/need. Length, spline or diameter. I know this from having trouble finding a mini spool to fit my axles or axles to fit my spool. One thing I did find is not all manufacturers use the same spline. Moser uses the same spline as gm, ford or dodge and richmond uses their own spline that wont mate with anything else. I tried 3 different spools to fit my axles and finally got Summit and a rep from Moser on the phone at the same time and the Moser rep explained this and sent me the right mini spool for free by next day air so I could get my truck together that had sat on stands for 3 weeks over the mix up.