Backing plate vs shoe size, how to tell?

[rumblefish360]

I'm putting together a 8-3/4 rear for the wife's '67 Cuda. It has the large bolt patten axles all ready, so that's a plus. It has 10 X 2-1/2 drums on it now. I have these mystery 11 inch backing plates. How wide of a shoe can I fit on it? Is it a matter of drum depth or is there a backing plate issue with the 11'inch drums?

 

[rumblefish360]

bump

 

[toolmanmike]

Drum depth.

 

[toolmanmike]

Here's a listing for a 1970 Dodge Monaco with a 440 just as a example. It has 11x3" shoes. Other applications and engine/brake options might be different. What did the backing plates come off of?

http://www.napaonline.com/Catalog/C...hoes-Front-Proformer/_/R-RTSTS336B_0319298368

 

[rumblefish360]

Unknown origin.

 

[72bluNblu]

It is NOT just a matter of drum depth. There was only one axle offset for BBP axles. 11" rear drums came in 3 varieties, 11x2", 11x2.5", and 11x3". Since the axle flange is in the exact same place for all of those, the backing plates are unique to each shoe width. So, you can't mix and match drums and shoes with 11" backing plates, you must use the drums and shoes that are correct for the backing plates.

Now, to measure the backing plates you want to set the backing plate flat on a bench. You'll need to hang the bottom 1/3 of the backing plate off the edge of the bench so that the mounts for the e-brake cables don't keep the backing plate from sitting flat. It isn't much, but they do change the measurement. Then, measure from the bench to the top of the backing plate through the center hole (for the axle) in the backing plate.

If you get ~1.75", you have 11x2.5" plates. If you get ~1.5", you have 11x2" plates. Those I know for sure, as I've measured them. I don't have a set of 11x3" backing plates, but the math would say you'd get ~2" measuring them as I described above. This is because half of the additional width is on the inside of the axle flange and the other half is on the outside to keep the axle flange in the same spot, as there was only one axle offset for BBP 8 3/4 axles! Make sense?

 

[toolmanmike]

It is NOT just a matter of drum depth. There was only one axle offset for BBP axles. 11" rear drums came in 3 varieties, 11x2", 11x2.5", and 11x3". Since the axle flange is in the exact same place for all of those, the backing plates are unique to each shoe width. So, you can't mix and match drums and shoes with 11" backing plates, you must use the drums and shoes that are correct for the backing plates.

Now, to measure the backing plates you want to set the backing plate flat on a bench. You'll need to hang the bottom 1/3 of the backing plate off the edge of the bench so that the mounts for the e-brake cables don't keep the backing plate from sitting flat. It isn't much, but they do change the measurement. Then, measure from the bench to the top of the backing plate through the center hole (for the axle) in the backing plate.

If you get ~1.75", you have 11x2.5" plates. If you get ~1.5", you have 11x2" plates. Those I know for sure, as I've measured them. I don't have a set of 11x3" backing plates, but the math would say you'd get ~2" measuring them as I described above. This is because half of the additional width is on the inside of the axle flange and the other half is on the outside to keep the axle flange in the same spot, as there was only one axle offset for BBP 8 3/4 axles! Make sense?

Dang, I follow you but I usually just measure the drum diameter and the drum depth. I must have been lucky.

 

[72bluNblu]

Dang, I follow you but I usually just measure the drum diameter and the drum depth. I must have been lucky.

If you have the drum that goes with the backing plate to measure the depth it's not a problem.

The problem comes in when you have a random set of 11" backing plates like rumble does, ie, you don't have the drums that came with the backing plates. If all you have is the backing plate you have to measure it because they're actually different for each of the 11" drum options, you can't just buy the drums and shoes you want because they may not fit that backing plate.

Here's a picture of the measurement I'm talking about. You can see the e brake cable mounts are hanging off the bench. The angle of the picture makes it difficult to tell, but the measurement is 1.75" for the 11x2.5" plate pictured. And yes, I know there's an oil spot on that shoe. :banghead:

 

[toolmanmike]

That makes sense! Thanks

 

[72bluNblu]

That makes sense! Thanks

No problem! :thumbup:

 

[nm9stheham]

Hey do you know there is an oil spot on one shoe? LOL

Very good info and thanks for sharing!

 

[rumblefish360]

72BnB, thanks! Makes sense, easy to understand. Just the information I needed.
The cream and cherry topping is the pictures so I know what goes where hardware wise.

LOL, would you have an 8-3/4 picture to hardware set up too?

 

[jamesrobert]

I'm putting together a 8-3/4 rear for the wife's '67 Cuda. It has the large bolt patten axles all ready, so that's a plus. It has 10 X 2-1/2 drums on it now. I have these mystery 11 inch backing plates. How wide of a shoe can I fit on it? Is it a matter of drum depth or is there a backing plate issue with the 11'inch drums?

lay backing plate on flat surface. make sure parking brake indent is not holding it up. might have to put parking brake over edge of table. plate must lay flat. now measure thru center to table. if it measures 1.75" =11x2.5" pad. 1.5" =11x2". 2.0" =11x3". these are for 11" backing plates

 

[Mopar92]

Genius. Thanks. I'm going through this now. Thanks.

 

[Moparmase]

If you have the drum that goes with the backing plate to measure the depth it's not a problem.

The problem comes in when you have a random set of 11" backing plates like rumble does, ie, you don't have the drums that came with the backing plates. If all you have is the backing plate you have to measure it because they're actually different for each of the 11" drum options, you can't just buy the drums and shoes you want because they may not fit that backing plate.

Here's a picture of the measurement I'm talking about. You can see the e brake cable mounts are hanging off the bench. The angle of the picture makes it difficult to tell, but the measurement is 1.75" for the 11x2.5" plate pictured. And yes, I know there's an oil spot on that shoe. :banghead:

View attachment 1714942228

Does this work for 8.25 backing plates as well?

 

[rbkt65]

Yes. The measurement for 10/11 x 2 1/2 inch backing plates is 1 3/4 inches. 1 x 1 3/4 shoes (stock "a" body rear brakes) are 1 1/2 inches. If you are building 10/11 x 2 1/2 backing plates, they will fit 8.25, 8 3/4(with big bolt pattern axles) 9.25 and Dana 60 with new ends. Example: look at the brake kits that are listed in the Brake section for sale, and they will fit all the above mentioned. Be careful as there are 11 x 2-inch plates out there that some parts are not avail to obtain.

 

[RustyRatRod]

This is what we're all trying to explain to that poorhouse guy in another thread, but he's as thick as the Hoover Dam. So I just gave up. You have to match up the axle offsets with the offsets on the backing plates. Not to mention the diameter of the shoes, drums and backing plates. There's a lot more to it than just bolting some parts together, and he'll find that out the hard way.

 

[72bluNblu]

This is what we're all trying to explain to that poorhouse guy in another thread, but he's as thick as the Hoover Dam. So I just gave up. You have to match up the axle offsets with the offsets on the backing plates. Not to mention the diameter of the shoes, drums and backing plates. There's a lot more to it than just bolting some parts together, and he'll find that out the hard way.

Uh, all BBP axles have the same flange offset. So, for BBP axles you can use any BBP brake set up regardless of what was on there originally- 10x2.5", 11x2.5", 11x3", and 11x2". The backing plate offset is different for the different width brakes, so, you can't run an 11x2" backing plate with an 11x2.5" drum.

But you can use an 11x2" brake set up on any BBP axle, be it 8 3/4, D60, 8.25 or BBP 7.25.

You can't use any of the BBP brakes if you have SBP axles, because the axle flange offset is different (not just because the bolt pattern is different!)

 

[RustyRatRod]

Uh, all BBP axles have the same flange offset. So, for BBP axles you can use any BBP brake set up regardless of what was on there originally- 10x2.5", 11x2.5", 11x3", and 11x2". The backing plate offset is different for the different width brakes, so, you can't run an 11x2" backing plate with an 11x2.5" drum.

But you can use an 11x2" brake set up on any BBP axle, be it 8 3/4, D60, 8.25 or BBP 7.25.

You can't use any of the BBP brakes if you have SBP axles, because the axle flange offset is different (not just because the bolt pattern is different!)

Well yeah, I was kinda lumpin um all together. I reckon that was need to know information. lol

 

[Moparmase]

Appreciate the info. I bought an 8.25 rear that only had backing plates so I’m having to buy new shoes and drums. I was hoping I could use the ones from by sbp 7.25 and just drill the drums for bbp, but the center hub is too small as well

 

[72bluNblu]

Appreciate the info. I bought an 8.25 rear that only had backing plates so I’m having to buy new shoes and drums. I was hoping I could use the ones from by sbp 7.25 and just drill the drums for bbp, but the center hub is too small as well

Nope. You need brakes from a car (or truck) with BBP axles. Drilling the pattern is the least of your concerns, the axle flange offset is different so the backing plate offset for the SBP brakes is wrong for the 8.25 and BBP axles. And yeah, center hub is different as well.