No adjusting slot on drum backing plate - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ZEKE68 · 08-05-2018, 09:35 PM

My rear drum brake backing plates don't have a slot in them for adjusting the brakes. Is this the norm for our trucks? I have had other vehicles that I had to back off the brakes through the slot to get the drum off. Hate to have a drum stuck and have no slot.

**LockDoc** · 08-05-2018, 09:48 PM

Quote:

Originally Posted by ZEKE68

My rear drum brake backing plates don't have a slot in them for adjusting the brakes. Is this the norm for our trucks? I have had other vehicles that I had to back off the brakes through the slot to get the drum off. Hate to have a drum stuck and have no slot.

The knockout on these trucks is on the front of the drum (outside) instead of the rear backing plate. They are not punched very well and are a bear to knock out. It would be easier to take the drum off and drill them out....

LockDoc

**Steeveedee** · 08-05-2018, 09:53 PM

Yup.

ZEKE68 · 08-05-2018, 09:55 PM

Will check that out, Thanks LockDoc

ZEKE68 · 08-05-2018, 10:08 PM

Just looked at the drums ( which I had off ), and there is not even a hint of a punch out. These are likely replacement drums. I was thinking of putting a hole in the backing plate that would fit one of those rubber plugs they sell.

**LockDoc** · 08-05-2018, 10:14 PM

Quote:

Originally Posted by ZEKE68

Just looked at the drums ( which I had off ), and there is not even a hint of a punch out. These are likely replacement drums. I was thinking of putting a hole in the backing plate that would fit one of those rubber plugs they sell.

I have never tried it but it should work. Let us know if you run into any problems with that.

LockDoc

**Stocker** · 08-05-2018, 11:34 PM

Quote:

Originally Posted by ZEKE68

Just looked at the drums ( which I had off ), and there is not even a hint of a punch out. These are likely replacement drums. I was thinking of putting a hole in the backing plate that would fit one of those rubber plugs they sell.

My K20 still has original drums, also with no hint of a knockout. Finally drilled holes in the backing plates and put in rubber plugs a number of years ago. Works great!

**Steeveedee** · 08-05-2018, 11:36 PM

Weird. I've punched literally hundreds of those knockouts out of drums and backing plates (trucks and cars). I guess the new stuff from Chinee isn't provided with that feature?

**FL71C10** · 08-06-2018, 12:06 AM

I just bought new drums for my 71 and they dont have knockouts. I'd be interested to see how you cut the holes in the backing plates. Drill holes on each side and then file out the middle?

toolboxchev · 08-06-2018, 12:48 AM

Quote:

Originally Posted by Steeveedee

Weird. I've punched literally hundreds of those knockouts out of drums and backing plates (trucks and cars). I guess the new stuff from Chinee isn't provided with that feature?

Its called "Value Added Processing" another words you guessed it they cheapened up the parts by removing a critical step in the casting.

Value added What?

panhead59 · 08-06-2018, 07:26 AM

Stocker says his original drums has no slots, so there's more to the story than cheap and/or replacement drums. So my first ? Would be to stocker- how do u confirm your drums are original ? Stamped part # maybe. Facts first
.

ZEKE68 · 08-06-2018, 08:49 AM

Think I would drill two or three holes, and then dremel them out.

**Stocker** · 08-06-2018, 09:42 AM

Quote:

Originally Posted by panhead59

Stocker says his original drums has no slots, so there's more to the story than cheap and/or replacement drums. So my first ? Would be to stocker- how do u confirm your drums are original ? Stamped part # maybe. Facts first
.

I have owned the truck since 1977 when it was 5 years old with about 50K miles. Pretty sure everything on the truck was factory original at that point, except the saddle tanks and rear bumper. If the drums had been changed before I got it, they would probably not be the same as whatever is available these days.

littlehopper · 08-06-2018, 12:59 PM

I have a low mile 68 that has the knockouts outlined on drums. With under 40k , I am confident they are originals. Maybe later ones don’t have the markings for knockout.

57Suburb · 08-06-2018, 04:11 PM

Don't blast me for mentioning this, but don't our trucks have a self-adjusting rear drum brake set-up. A few 10 mph reverse blasts, then lock up the brakes is supposed to adjust the rears drums. Might be why we see so many back plates with no holes?

**FL71C10** · 08-06-2018, 04:40 PM

The problem is when you want to take the drums off, it is nice to be able to back off a little bit on the adjuster to free up the drum.

**Stocker** · 08-06-2018, 07:41 PM

Quote:

Originally Posted by FL71C10

The problem is when you want to take the drums off, it is nice to be able to back off a little bit on the adjuster to free up the drum.

Yes, especially if the drums have worn enough that there's a ridge catching the shoes and preventing drum removal.

Also, those adjusters operate in a nasty environment and may not work anymore. With luck, they can be cleaned & lubed and continue doing their job.

68panelman · 08-07-2018, 08:04 AM

Quote:

Originally Posted by 57Suburb

Don't blast me for mentioning this, but don't our trucks have a self-adjusting rear drum brake set-up. A few 10 mph reverse blasts, then lock up the brakes is supposed to adjust the rears drums. Might be why we see so many back plates with no holes?

No blasting here, you are 100% correct.

ZEKE68 · 08-18-2018, 09:54 PM

Cut in brake adjusting slots in my rear drum backing plates to fit the rubber plugs I bought. This is so I can adjust the brakes initially, or back them off if I need to take the drum off, and it won't come off.

**Steeveedee** · 08-18-2018, 10:14 PM

And you only have to do it once. It's worth all the sweat.

08-05-2018, 09:35 PM	#1
ZEKE68 Registered User Join Date: Jul 2012 Location: Space Coast, Florida Posts: 403	No adjusting slot on drum backing plate My rear drum brake backing plates don't have a slot in them for adjusting the brakes. Is this the norm for our trucks? I have had other vehicles that I had to back off the brakes through the slot to get the drum off. Hate to have a drum stuck and have no slot. __________________ 1968 SWB Step Side, Big Block, 4L80E , Running!

08-05-2018, 09:53 PM	#3
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,723	Re: No adjusting slot on drum backing plate Yup. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

08-05-2018, 09:55 PM	#4
ZEKE68 Registered User Join Date: Jul 2012 Location: Space Coast, Florida Posts: 403	Re: No adjusting slot on drum backing plate Will check that out, Thanks LockDoc __________________ 1968 SWB Step Side, Big Block, 4L80E , Running!

08-05-2018, 10:08 PM	#5
ZEKE68 Registered User Join Date: Jul 2012 Location: Space Coast, Florida Posts: 403	Re: No adjusting slot on drum backing plate Just looked at the drums ( which I had off ), and there is not even a hint of a punch out. These are likely replacement drums. I was thinking of putting a hole in the backing plate that would fit one of those rubber plugs they sell. __________________ 1968 SWB Step Side, Big Block, 4L80E , Running!

08-05-2018, 11:36 PM	#8
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,723	Re: No adjusting slot on drum backing plate Weird. I've punched literally hundreds of those knockouts out of drums and backing plates (trucks and cars). I guess the new stuff from Chinee isn't provided with that feature? __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

08-06-2018, 12:06 AM	#9
FL71C10 Senior Member Join Date: Jun 2010 Location: Orlando, Florida Posts: 2,509	Re: No adjusting slot on drum backing plate I just bought new drums for my 71 and they dont have knockouts. I'd be interested to see how you cut the holes in the backing plates. Drill holes on each side and then file out the middle? __________________ 71 Chevy C10 Shortbed Stepside. LT1 with 4l60E. Just got back from painter, in assembly now.

08-06-2018, 07:26 AM	#11
panhead59 Registered User Join Date: Feb 2012 Location: Vinton, Va. Posts: 493	Re: No adjusting slot on drum backing plate Stocker says his original drums has no slots, so there's more to the story than cheap and/or replacement drums. So my first ? Would be to stocker- how do u confirm your drums are original ? Stamped part # maybe. Facts first . __________________ "You are not forgotten" USMC 75-79 (Aviation Ordnance Tech- F-4 Phantom) 1959 H-D Panhead. Owned since 1978. Currently with son in Lawton, OK. 1968 Chevy Custom SWB pick up. Fleetside. Lowered 4/6. Totally refurbished. 1966 Pontiac GTO. 4 speed. Saved original 389. Now has slightly built 455 engine. 355 rear gears. Very fun to drive !

08-06-2018, 08:49 AM	#12
ZEKE68 Registered User Join Date: Jul 2012 Location: Space Coast, Florida Posts: 403	Re: No adjusting slot on drum backing plate Think I would drill two or three holes, and then dremel them out. __________________ 1968 SWB Step Side, Big Block, 4L80E , Running!

08-06-2018, 12:59 PM	#14
littlehopper Registered User Join Date: Mar 2017 Location: Port Murray, NJ Posts: 147	Re: No adjusting slot on drum backing plate I have a low mile 68 that has the knockouts outlined on drums. With under 40k , I am confident they are originals. Maybe later ones don’t have the markings for knockout.

08-06-2018, 04:11 PM	#15
57Suburb Registered User Join Date: Apr 2014 Location: Southern Iowa Posts: 310	Re: No adjusting slot on drum backing plate Don't blast me for mentioning this, but don't our trucks have a self-adjusting rear drum brake set-up. A few 10 mph reverse blasts, then lock up the brakes is supposed to adjust the rears drums. Might be why we see so many back plates with no holes? __________________ 1972 C30 Grain Hauler, 350/400 1967 1500 GMC Stepside SWB, In Transformation Process 1967 RS/SS Camaro 350/TKO600

08-06-2018, 04:40 PM	#16
FL71C10 Senior Member Join Date: Jun 2010 Location: Orlando, Florida Posts: 2,509	Re: No adjusting slot on drum backing plate The problem is when you want to take the drums off, it is nice to be able to back off a little bit on the adjuster to free up the drum. __________________ 71 Chevy C10 Shortbed Stepside. LT1 with 4l60E. Just got back from painter, in assembly now.

08-18-2018, 09:54 PM	#19
ZEKE68 Registered User Join Date: Jul 2012 Location: Space Coast, Florida Posts: 403	Re: No adjusting slot on drum backing plate Cut in brake adjusting slots in my rear drum backing plates to fit the rubber plugs I bought. This is so I can adjust the brakes initially, or back them off if I need to take the drum off, and it won't come off. Attached Images __________________ 1968 SWB Step Side, Big Block, 4L80E , Running!

08-18-2018, 10:14 PM	#20
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,723	Re: No adjusting slot on drum backing plate And you only have to do it once. It's worth all the sweat. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA



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