Calling All Eaton Rear End Guru's

[roger0080]

I need some info on the Eaton rear end brake drums from those who have them.
Trying to upgrade my brakes.

I am all confused when looking at the GM parts book and online parts sites (www.rockauto.com, www.federal-mogul.com (AKA wagner) etc) as to what would interchange on which axle and what is ACTUALLY on the axle.

From What I can tell (Eatons ONLY; not talking about Dana's):
67-72 C20 2WD Eatons have 11-5/32x2-1/2" shoes
67-70 K20 4WD Eatons have 12x2" shoes with 1/2" studs
71 C20 2WD Eatons have 11-5/32x2-1/2" shoes with 9/16" studs
71 K20 4WD Eatons have 12x2-1/2" shoes with 9/16 studs
72 C20 2WD Eatons have 11-5/32x2-1/2" shoes with 9/16" studs
72 K20 4WD Eatons have 11-5/32x2-1/2" shoes with 9/16" studs

Q: GM parts book lists the hubs as different between 67-70 & 71/72 so I suppose
that means 1/2" and 9/16" studs respectively in those years?

Q: According to the GM parts book, all 67-72 4WD 3/4Tons have the same backing plate. How does a 11-5/32" drum fit on a 12" backing plate?

Q: Whats the difference in the drums between a 71/72 C20 and a 72 K20 drum ?
Books say these are all 11-5/32" drums yet give 2 numbers for 71/72 C20 & 72 K20 drums and 2 different prices:
71/72 C20 drum $110.00 non-finned
72 K20 drum $55.00 finned;
waaaay cheaper! (www.rockauto.com); I thought the finned cools better (and would be more money)

Now here is my delema:
I have a 71 K20 Eaton with the oddball 12x2-1/2" drums, 9/16 studs (fronts are 9/16")
I have a 69/70 K20 Eaton with a NoSpin in it, but it has the 12x2" drums with 1/2" studs.

Here is what I am thinking to keep the 71 with 9/16 studs:
1. Take the 3rd member NoSpin out of the 69 and put in the 71 Eaton. No problem.
2. Get a set of backing plates off a 71 or 72 C20 and replace the 71 Eatons with these
3. Buy new C20 11-5/32x2-3/4" drums.
4. bolt it alltogther
5. Could I then use the 72 K20 finned drum instead?

If anyone outhere has these parts disassembled and lying around in their garage and sheds and could look and measure for me I would really appreciate or anyones knowledge of this.

-Roger
PS I don't at this time want to convert it to disc brakes; As long as I stay in the 71/72 years I should be able to swap around???
__________________

[Robert1970C20rstbukt]

67-70 - 1/2" studs
71-72 - 9/16" studs

They made the lip of the drum bigger to fit over the backing plate, at least that's how they are on my 70.

All Eaton rears had smooth drums, no finned ones.

Here's some info out of the 69-70 GM truck parts book:

Ser. 20 (4/WD)............3754300 $23.75 rear

Ser. 20 (Conv.)
(exc. leaf type spring,
L.P. Gas, 396)..............3857752 $22.35 rear

Ser. 20 w/Dana axle......2458493 $23.25 rear(motor wheel 86516-A)



I couldn't find any measurements for brake drums in that book.

[4x4Poet]

I don't see why you couldn't make the swap. Just check if the wheel cylinder bolt holes are symmetrical or asymmetrical to get what you want. Shouldn't matter if you are replacing the wheel cyls anyway.

BTW, my '71 K20 burb's H052 has 12"x2" brakes. Originally had smooth drums.

My '72 K20 pickup's H052 has 11"x2.5" brakes that may not be original to the axle or the truck, but I was recently able to purchase finned drums thru Carquest that were made in USA or Canada, forget which. IIRC, they were ~$62 each, but no shipping, obviously.

[roger0080]

See my reply over on this post:
http://www.67-72chevytrucks.com/vboa...=172827&page=2