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Rear backing plate question for 1948 GMC 3/4 ton
#1316890 Sun Jul 07 2019 05:59 PM
Joined: Jun 2019
Posts: 50
R
RyanC Offline OP
'Bolter
I just searched through the forum and couldn't find what I was looking for. I'm pretty sure I'd like to change the backing plates on my 48 GMC 3/4 ton pickup with the HO52 Eaton axle. First question is can a change just the backing plates, or do I have to change both the plates and drums? What years will actually fit this axle and what are the best ones to choose from. Mostly making this change for easy access to parts. Current shoes are the 12 x 2 huck style brake shoes.

Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1316986 Mon Jul 08 2019 02:37 PM
Joined: Nov 2005
Posts: 6,008
3
3B Offline
'Bolter
Hy RyanC, welcome, I am not sure how long the mounting flange for the backing plate remained the same, but the basic rear axle housing was used up into the mid sixties. There were changes in the brakes as you appear to be aware of and once again I'm not sure what else has to be changed when you change your backing plates to something else. Hubs may also have to be changed as the brake drum mounting flange on the hubs may be in a different position. The largest drums fourteen inch are almost impossible to find, in 1960 and later the largest drums are thirteen inch and parts are more readily available. It would appear that a lot more research is necessary before attempting a change, hope that helps.

Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1317009 Mon Jul 08 2019 07:32 PM
Joined: May 2005
Posts: 9,176
G
.
There as been mention of such an easy swap to later brakes, more info and pictures would be helpful in the long run.
Start here https://www.stovebolt.com/ubbthread...vy-3600-rear-end-options.html#Post971515

Some brake info and mounting dimensions here amongst the axle swap info.
https://www.stovebolt.com/ubbthread.../14-bolt-axle-swap-info.html#Post1249600


1951 GMC 250 in the Project Journals [stovebolt.com]
1948 Chevrolet 6400 [stovebolt.com] - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup [stovebolt.com]
---All pictures [picasaweb.google.com]---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-
Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1317100 Tue Jul 09 2019 04:11 PM
Joined: Jun 2019
Posts: 50
R
RyanC Offline OP
'Bolter
Looks like I may have enough data here to finally start looking for parts, any idea as to what I will need as far as any specialty tools to remove the hubs? There's a couple different types of axle nut sockets and I don't know what the newer, vs. the older vehicles take.

Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1317167 Wed Jul 10 2019 02:16 AM
Joined: May 2005
Posts: 9,176
G
.
I have one axle nut socket and have taken a lot of these Eaton and 14 bolt axles apart.Pretty sure it fits both. A 6 pin axle nut socket sold at a discount auto parts store for front spindle nut on 4wd.


1951 GMC 250 in the Project Journals [stovebolt.com]
1948 Chevrolet 6400 [stovebolt.com] - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup [stovebolt.com]
---All pictures [picasaweb.google.com]---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-
Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1317383 Thu Jul 11 2019 05:32 PM
Joined: Jun 2019
Posts: 50
R
RyanC Offline OP
'Bolter
So in doing a little more research anyone here been able to figure out if the 53 to 59 12 x 2" Bendix backing plates are a direct bolt on with no modification? I would think that because they are the same size they should still work with my original drums unless there is some kind of depth change with the flanges on the drums. Any input on that here?

Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1317438 Fri Jul 12 2019 01:05 AM
Joined: May 2005
Posts: 9,176
G
.
Check parts book to see if drums are the same between applications, of if later part number supersedes previous.
http://chevy.oldcarmanualproject.com/parts/1929_54/index.htm


1951 GMC 250 in the Project Journals [stovebolt.com]
1948 Chevrolet 6400 [stovebolt.com] - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup [stovebolt.com]
---All pictures [picasaweb.google.com]---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-
Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1319773 Tue Jul 30 2019 03:37 AM
Joined: Jun 2019
Posts: 50
R
RyanC Offline OP
'Bolter
So I may have run into a snag here, I have the replacement backing plates, but now I think I may have a drum problem. For sure my originals will not work. There are drums available on Rockauto for the rear with an 8 lug but the height doesn't seem right. Drum height appears to he right around 4.75" to 4.80". If I measure from the plate to the top of the flange on the hub I have only 3.75". Where do I gain that inch, is it on the flange for the drum on the hub?

Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1319787 Tue Jul 30 2019 11:22 AM
Joined: May 2005
Posts: 9,176
G
.
You may need drums that are used with the backing plates you have.
But even then the hubs might be different...

Compare measurements from backing plate flange on the axle to drum mounting surface on the hub. Between both applications. Keep in mind that some drums mount inside hubs and some outside and methods are not usually interchangeable on the same hub.


1951 GMC 250 in the Project Journals [stovebolt.com]
1948 Chevrolet 6400 [stovebolt.com] - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup [stovebolt.com]
---All pictures [picasaweb.google.com]---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-
Re: Rear backing plate question for 1948 GMC 3/4 ton
RyanC #1320012 Thu Aug 01 2019 03:45 AM
Joined: Jun 2019
Posts: 50
R
RyanC Offline OP
'Bolter
So I think I may have found the solution to my problem. Using the stock drums or the drums that mate to the backing plates are not an option. The depth is just not there, however I got to thinking there were other vehicles that were an 8 lug. So I looked at drums for a 58 to 65 Ford F-250 and they are much shallower. These drums have a height of 3.92 inches and are for the 12" x 2" brake size. However there may be one small issue of centering the drum, the center measures at 4.75" and the stud holes are for a 9/16 stud. If the height is good, what is the best way to center this?

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