Will 8 1/4 backing plates work on the 8 3/4?
An accurate 8 3/4" rear axle width list
- Thread starter 72bluNblu
- Start date
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That I don’t know.
metalbender58
Active Member
I want to thank everyone for their input. I was able to pick up some BBP 10 x 2.5 backing plates, drums and shoes that are like new, and the shock plates for my 8.75 housing at Mopars in the Park over the weekend.
jpl572103
Well-Known Member
I have a question about Dr. Diff axles. I just ordered a set for stock A body housing length. I chose the BBP so am I to assume that I should have my housing narrowed to 51.5? Nevermind, I just realized that is for 7.25 and 8.25. The 8.25 through me off. I need my housing narrowed to 52 5/8. What a great place for info!! Thanks.
If I remember correctly there are 2 options for big bolt pattern axles.
1. Axles for using stock abody small bolt pattern backing plates and drums (slotted to fit big bolt pattern). Using a stock small bolt pattern housing width will result in a stock small bolt pattern flange to flange overall width.
2. Axles for using big bolt pattern backing plates and drums (already at 4.5" big bolt pattern). Using these axles with a stock width small bolt pattern housing will result in a slightly wider overall axle flange to axle flange width. Wider than the stock abody small bolt pattern rear end. I can't remember how much wider off the top of my head right now.
The reason for this is the drum backing plate offset is different between small and big bolt pattern rear ends. This makes the distance between the bearing and the axle flange longer on the big bolt pattern rear ends. Also If I remember correctly the register on the axle for the drun is a smaller diameter on the small bolt pattern axles.
I think you can narrow the housing and shorten the spline end of the axles by the offset amount and end up with the same overall axle flange to axle flange width as the stock small bolt pattern 8 3/4" rear ends. I think Dr. Diff offers the axles both ways.
If this isn't right please say so.
jpl572103
Well-Known Member
Which drums and backing plates did you order?
jpl572103
Well-Known Member
I am using the 11 inch that came from the housing.
Is this a housing that already has big bolt pattern axles that you are having narrowed?
jpl572103
Well-Known Member
Yes. B body
jpl572103
Well-Known Member
I probably will have to put disc on the front. Currently have the 9 inch drum. Not sure how the brakes will do. Most likely they will continue to stop fine if not better with the larger rear shoes.
If dr. diff knows your plans he would have sent you axles with offset to match your backing plates.
Be aware your overall width drum to drum will be a little wider than a factory stock small bolt pattern abody 8 3/4.
If you're having your housing narrowed you can correct for that if you want to. If I remember correctly there was plenty of spline length on the axles so cutting them wasn't an issue.
I didn't correct when I did my drum rear because I already had an abody housing. I did on my rear disc brake rear end because it started as a b-body housing that was already being narrowed anyway.
Hope this makes sense.
I only bring this up because you are asking for wheel offsets for your dart. If the person you ask has a factory small bolt pattern 8 3/4" rear keep in mind your's will be a little wider than their's.
jpl572103
Well-Known Member
Great info. The older gentleman who is doing the work says he’s done hundreds over the years. The axles ordered with the doctor is for a stock 52 5/8 housing The axles will be LBP. Not sure how much further they stick out or in verses my current 7 1/4. I’ll learn more along the way.
jpl572103
Well-Known Member
I did get the housing narrowed, assembled it on stands and then took it apart until I'm ready to install. Then I can take measurements for the rear wheels.
@72bluNblu I’ve got another one if you want to add it to the list. 1967 sbp 7.25 is 57 1/2” drum to drum. I’d imagine 67-72 is the same (if not all the sbp 7.25”) I’ve got a 63 Dart and 72 valiant that I can measure as well to see if those are the same.
OK I've read through this entire thread and I notice that the 60-64 8.75" Axles are left out does anyone know what the width of a 63 Newport 4D sedan Axle is I'm setting one up and I cant find any information on this axle it is an 8.75" axle with a 741 case if anyone can help please do so
Powerflite
Well-Known Member
There are 3 different 8 1/4 rear axles. The first one was used from 1937 to 1961. The second from 1962 to 1965, and the third from 1970-up. I assume you are talking about the last one. Yes, the backing plates from the Gen3 8 1/4 will interchange with the 8 3/4.
Unfortunately, I don't know the width of the '63-'64 Chrysler. But here is more information for you:
'57-'61 All except Imperial, '62 Chrysler, '62-'63 Dodge 880: 60.625" Drum to Drum, 45.5" perch to perch (close enough to 46" to interchange)
An 8 3/4 was also used in 1956, but it is completely different and won't interchange with '57-up.
I’m not an expert on 8 1/4’s but I know not everything from the 90’s/00’s Jeep and Dakota 8.25’s are a direct swap. The Jeep Liberty disks can be used on the 8.25’s but require some custom work to be used on an 8 3/4 (Ehrenberg did an article on this, there are better options for the 8 3/4). I think the carrier bearings are different from the 70’s 8.25’s. Not sure about axle spline counts etc.
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