The problem

As we are progressing through this build series we hit another small speedbump that we thought that we could share a little bit more detail on.

If you haven’t read the entries on the rear axle rebuild you may want to check out Part 1 and Part 2.  We also did a post focusing specifically on the rear brakes.  This is an addendum to that post.

The research

After we had already started on the re-assembly we ordered some of the final parts needed to finish off the rear axle.  The rear brake drums were part of this.  When we received the new drums we knew right away that something was wrong, they were way to big.  So we started to backtrack and see where things went wrong.  After doing some research and scouring some of the familiar forums we found that in about 1979 GM changed the 12 bolt truck rear axles and put larger brakes on them.  Up until this point they used 2″ wide shoes and drums. After they had 2-3/4″ shoes and drums.  The axle housing, and axle shaft length stayed the same, but they changed the backing plates to accommodate the wider brakes.  One thing we found throughout this is that it is not that difficult to upgrade an axle with 2″ brakes to an axle with 2-3/4″ brakes.  And it just so happens, we had the parts laying around to make the upgrade.

We have done a short video of some of the differences between the older and newer styles.  Here we will try to describe what we found and also add some pictures to hopefully provide some better detail.

You can see in the photo above the center section of the backing plate on the right sits up a bit taller than the one on the left.  This allows for the backing plate to sit back onto the axle a bit further  and make room for the larger brake shoes and drums, while keeping the axle housing and shaft length the same.

The stud bolts pictured above are also different lengths. The longer bolt on the left is for the larger brakes.

The difference between the 2″ and 2-3/4″ shoes.

The 2-3/4″ drums are about 11-1/8″. Technically speaking I think they are actually 11-5/32″ if memory serves, but anyways they are just a bit bigger than the 2″ drums.

The 2″ wide drums are 11″ in diameter.

The width difference between the two different sizes of drums.

The solution

There were two options as we saw it. 1) Try and send the larger drums back, and get the right ones (2″ wide drums) or 2) Find parts and keep the new drums in order to upgrade the brakes on out axle rebuild.  Since we had another axle available that had the right backing plates for the larger brakes, we decided to use those.  This will upgrade the brakes a bit, and while not as good as a disc brake conversion, will provide a bit more stopping power.

So we kind of decided to go a different direction, not only parts but in coloring as well.  The truck has always been planned to be orange and black from the start.  Its been cold enough here lately that painting in our drafty shop probably would not turn out well and with the dry time would take longer than we wanted so we decided to powder coat the backing plates instead.  This a Chevy Orange from Prismatic Powders.  We also did the differential cover the same color.

We used the same 3/8″ bolts and nuts as we did on the other backing plates previously.

The picture above is with all the brake parts assembled, and we remembered the guide plate, yay us.  Now for the axle.  Don’t forget to put some oil on the seal before inserting the axle shaft.  Also be careful not to tear or damage the seal when inserting the axle shaft into the housing.

We have installed new lug bolts and nuts on both axles.

The conclusion

And after all that we finally have success.  Everything seems to fit, and all the spacings seem to be good.  This one was a learning experience for both of us.  In the end I think we ended up with a good solid rear end that will work fine for what we have planned and everything has been gone through top to bottom.  We ended up having a good long discussion on open carriers, limited slips, lockers, spools and the like during the course of this axle rebuild.  We looked at some limited slips but just didn’t think it would make it in the budget so passed on this for now.  A rear disc brake upgrade fell into the same category.  These are all things that could be done later on once the truck is rolling and Dylan has a chance to drive it for a bit and decide if that is something he wants to spend his money on or just leave it as is.  For now the rear axle is done and will be set aside until we get all the work done on the frame and then we can get it holding up the frame with a new 4″ lift.

Keep watching for new posts as we progress through this massive undertaking.  Here is the finished product.