12 bolt rear issues

[609thomasm]

In the pics attached are two 12 bolt rears out of 67/72 trucks. (both coil spring). Notice the difference in the distance from the axle flange to the wheel cylinder. One is about a 1/2 inch greater. My issue is that when installing the brake drum on the one with the greater distance the brake shoe does not get completely covered by the drum. The shoe surface of the drum doesn't make it all the way back. Drums and shoes are 11" X 2". You can see in the pics that the extra distance is due to where the flange is attached to the axle tube, one welded on further from end of tube than the other. Trying to figure this out so I can use the rear with the greater distance but need to know if there were different drum or other options for the brakes. The backing plates and axles from both seem to be the same. Thanks for any input.

[tjc]

is it possible that 1 has the wrong axle.

[Redneck Rydes]

Some years from 67-72 used different length axles,my 1970 has a one year only axle,or someone has put in 5 bolt axles in a 6 bolt housing,can't do that

[StingRay]

Looks like 70 1/2 - 87 axles in a 67-early 70 housing.

[68Gold/white]

Originally Posted by StingRay

Looks like 70 1/2 - 87 axles in a 67-early 70 housing.

Exactly what's wrong!!!

[BigBird05]

It looks like the axle housing is sticking out from the backing plate farther in the first picture.

[A1971Blazer]

agreed....wrong axle shaft
the lip on the drum should go back almost flush with the back of the backing plate

[609thomasm]

How do we identify a six bolt housing between a 5 bolt housing?

[Andy4639]

Originally Posted by 609thomasm

In the pics attached are two 12 bolt rears out of 67/72 trucks. (both coil spring). Notice the difference in the distance from the axle flange to the wheel cylinder. One is about a 1/2 inch greater. My issue is that when installing the brake drum on the one with the greater distance the brake shoe does not get completely covered by the drum. The shoe surface of the drum doesn't make it all the way back. Drums and shoes are 11" X 2". You can see in the pics that the extra distance is due to where the flange is attached to the axle tube, one welded on further from end of tube than the other. Trying to figure this out so I can use the rear with the greater distance but need to know if there were different drum or other options for the brakes. The backing plates and axles from both seem to be the same. Thanks for any input.

What drum was on it before? 71-72 axles are longer than the earlier ones.

[609thomasm]

when i bought truck it was like this. (drum not riding completely on all of shoe). On both units the axles and backing plates are the same. What appears to be the only difference is where the flange that the backing plate bolts to is located on tube in a different location. As far as 5 bolt axles and 6 Bolt axles go, did any 2 wheel drive trucks have 6 bolt axles. Assuming these are both 2 wheel drive due to coil springs

[Andy4639]

Everything was 6 bolts until 71. 71 the 2 wheel drives went to 5 on 5.
4x4 stayed 6 bolts.
I not 100% sure about anything before 71but I know 71 & 72 model rear ends are longer than any other rear end from backing plate to plate.

[68 TT]

For reference can you measure both housings from end of axle tube to end of axle tube and from the outboard side of the backing plate mounting surface to the other backing plate mounting surface.

Also measure the length of the axles.

This way we can compare the dimensions to known examples of original parts to help you figure out what is going on and figure out what parts go together.

I know there are wider finned 6-lug drums from the HD brake option that may belong on the housing with the larger offset backing plate mounts.

The square body housings used different offset backing plates to switch between the LD 2" drums and the wider shoe HD brake option versions instead of changing the rear end housing but their 6-lug 4x4 HD brake drums might work for you.

[gmc684x4]

I will agree with earlier post that its a longer axle from a 71 to 79 12 bolt did carry on into the 80s but only in certain models of trucks

Do you know how to remove the axles ?

Remove diff cover wipe down the carrier I use a high quality 6 point wrench I want to say 5/16 and use a plumbers torch to heat up the cross shaft bolt to help lossen it from the red loctite it probably has on the threads
It is a small bolt i use heat because if you break it it can be extremely difficult to remove and not damage your carrier

Remove the cross shaft then you can push in one axle remove c clip then do the same to the other side

Then you can compare the two in length one will be longer then the other

Square body brakes are 11.16 x 2 3/4 wide and will use a different backing plate then a 11 x 2

63 to early 70 12 bolt axles are 30 3/4 inches long
Late 70 to 82 12 bolts are 31.312 inches long

[Bigdav160]

Doesn't look like an axle problem to me. It appears the axle tube/backing plates are made fo wider drum and shoes.

[mikelcobb0@gmail.com]

I have a carrier with axels that might solve your problem.

[gmc684x4]

Hc should have 3.73 gears with a posi 67 to 69

my money says wrong axle
even a quick dirty measurement from back of flange to axle housing i would say from the pics one is close to 1\2 longer then the other

[StingRay]

!970 housings could be early or late being narrow or wide. I've seen both so be careful trying to identify a 6 lug housing. 1970's can fool you.

[garyd1961]

Is one of them for heavy duty brakes? I had 70 suburban with heavy duty brakes, still have the rear end out of it.

[Mike_The_Grad]

HD brakes used wider drums and shoes. You can use the rear end as an "upgrade" for bigger brakes. But you gotta get the right size parts. (drums,shoes, and I think the wheel cylinders might even be different.) Early Classic Enterprise used to sell the HD Drum Brake overhaul kit for these years. But they went out of business recently. seriously was one of the best vendors around for parts. Quality, customer service, all the stuff that counts when your looking for replacement parts. I want to say service vehicles like tow trucks, ambulances, school buses, and emergency vehicles usually had the HD brake option. Also the HD shoes are 2 3/4" wide now that I remember. That would account for the extra 1/2" you measured on the one rearend.

['68OrangeSunshine]

Mike's right. I found I had the bigger brake drums/shoes on my '71 GMC Jimmy 4x4.
The drums on my '67 C/10 stepside were 11 x 2. The outside rim of the light truck drum is smooth. The bigger drums are deeper and have ridges, cooling fins, almost, around the circumference. They stop a hell of a lot better, too.

[lousyflyer]

I say wrong axle for the housing. The clue for me is the shiny area that the axle bearing rides on which is protruding from the shorter axle housing. If that axle was original to that housing, there would be no shiny surface exposed past the outside of the seal. It also makes me wonder what surface the bearing is actually riding on now. If its not fully riding on a machined area it will drastically shorten the service life of the rear end, possibly contaminating it with metal particles.

If the narrower rear end appeals to you or better suits your wheel/tire combination, a set of new five lug axles of the proper length are available.

[HotWheelsFan]

2nd picture appears to have a different axle in the housing than original. It appears to show the wear spot on the axle itself made from oil seal. Thus it sticks out from the housing farther.

This would indicate the axle came from another housing.

[garyd1961]

I believe all axles have play in and out like that. I'll bet on heaven duty brakes.
Wish I had kept the spindles off the 70 suburban, I would put heavy duty drum brakes all around on my 70 C10.

Well I may have spoken too soon. Just went out to the shop and the rear I have appears to be standard brakes. I'm sure it had heavy duty brakes on the front because one of my friends who is pretty much an expert on these trucks pointed it out to me one day. Could a 1970 suburban come with HD brakes on the front and standard on the rear? Maybe someone swapped rear ends in the suburban before I got it.

['68OrangeSunshine]

Originally Posted by garyd1961

I believe all axles have play in and out like that. I'll bet on heaven duty brakes.
Wish I had kept the spindles off the 70 suburban, I would put heavy duty drum brakes all around on my 70 C10.

Well I may have spoken too soon. Just went out to the shop and the rear I have appears to be standard brakes. I'm sure it had heavy duty brakes on the front because one of my friends who is pretty much an expert on these trucks pointed it out to me one day. Could a 1970 suburban come with HD brakes on the front and standard on the rear? Maybe someone swapped rear ends in the suburban before I got it.

Is it 4WD? My 1967 K/10 Suburban had different p/n drums on the front, to allow for the diameter of the protruding locking hubs. They were all 2'' x 11''. The front drums were a lot more expensive -- being 1967-68 -only pieces. The rear drums were the same that my '68 C/10 Stepside has all-around. That Sub stopped like a gravel truck going down hill. More like choose your impact target, if some Zoomer cut in front of your stop-zone.

My '71 Jimmy has front disc brakes and finned HD drums rear.

You may have a PO switch. Usually, HD drums would be in rear, if different.

[609thomasm]

Thanks for all the input. We found drums that will work. Local NAPA counter person did some major research and found drums listed by the dimensions and it wound up being a 73 drum that worked out. WMS to WMS is the same on both rears. Backing plate to Backing plate is a different measurement. Mystery not solved but drum issue resolved. Thanks again.