Rear Drum Differences
 

There's going to be a lot of questions out of me while I figure out my 70 CST.

I pulled the drums off of the rear in order to be able to move the truck around easier. It has been a LOT of years since I've worked on drum brakes, since my first car anyway. I knew I had to loosen the adjuster in order to get the drums off. The drivers side had a slot in the face of the drum!?! I expected the slot to be in the backing plate. Maybe that is a Ford thing. Anywho, I got the drum off. On the passengers side is where things are different. There is no slot in the face of the drum and no slot in the backing plate. However, I was able to get the drum off. The drum on the passengers side is heavier than on the drivers side. I figure that is because of how worn the drivers side drum is worn.

It appears that there should be a slot in the face of the drum or the rear axle has been changed. What is correct for our truck? The one on the left is the drivers side and very worn, the one on the right was on the passengers side. Thanks for any help.

Re: Rear Drum Differences
 

Some vehicles had the adjustment slot on the backing plate, not the drum. I cannot remmeber if I ever have run across that on our year trucks. On one of my older trucks, I drilled the replacement drum and made my own slot. I use to see drums that had the marking for a punchout for it, but it was not in all the replacement style drums.

Re: Rear Drum Differences
 

Original 1970 smooth drums had the punch-out on the face of the drum, so the one on the left is a factory issued part. The one on the right is an aftermarket replacement.


Original GM part number for the non-finned 11"x2" rear drum for 1964-70 GM 6 lug pickups/Blazers is 3846271 in the 6/71 parts book.


There is an anti-chatter spring on the outer circumference that was originally installed on them to reduce noise.

https://67-72chevytrucks.com/vboard/...1&d=1736382866

Spring is GM 3694290

32 3/4" free length

https://i.ebayimg.com/images/g/9mAAA...C/s-l1600.webp