Question about backing plates

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slotto

slotto

Bolt Turner
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My brother in law dropped off an 8.75" rear, axles and 3.55 gears. He said these came from a truck. I was planning to replace my stock /6 rear with this but they do not have backing plates or drums. I went to the local parts store and stocked up on shoes and a new spring kit. Also had the drums resurfaced. I pulled down the stock rear with 9" drums, and was going to use that setup. Soon after I quickly realized that the bolt pattern on the backing plates was not going to fit on the 8.75 rear. :banghead:

My question is what size brakes are supposed to go on the 8.75 rear?
Here;s a pic of the gasket for the backing plate:
http://s1239.photobucket.com/user/slotto1/media/scamp/05Jun14/IMAG0910.jpg.html

My short term plan is to clean up the stock rear and put on the new brakes then use that until I can get the $ together for the correct setup for the beefier rear as I'm gonna need backing plates, shoes, springs and drums.

Thanks in advance
steve
 
Did you have the stock 9" drums turned and buy shoes and hardware for them?
Or did you spend your money on the 8 3/4 parts, wasn't sure if you got any brake parts
with the axle to rebuild?
 
The rear my brother in law dropped off has no backing plates. It's just the housing, the gears and 2 sbp axles.

The car came with a /6 and small rear.
I sorta put the cart before the horse and bought all the hardware and got the 9" drums turned in hopes of transferring it all to the 8.75 rear. After I got all my parts together, I pulled the stock /6 rear and I noticed that the backing plates on the /6 rear has 4 bolts and the 8.75 rear requires a backing plate with 5 holes.

Is there a backing plate I can use for a 8.75 rear using a sbp axle for 9" brakes that has 5 holes?
Or would it be easier to try and return everything I bought and upgrade to the 10" drum setup for bbp?

sorry for all the confusion, I'm new to all this.
thanks,
Steve
 
They will not work. Every 10" brake 8 1/4 backing plate will work.

You do realize that the truck rear end is way too wide for an A-body. You will need to have the housing cut down, spring perches moved and different axles to use it.
 
Uh oh. I did a rough measurement for the distance between the holes in the perches and compared that to the nubs on the leaf springs and it was fairly close.

I have much to learn...
 
http://s1239.photobucket.com/user/slotto1/media/scamp/16Aug14/IMAG1079.jpg.html
I went ahead and replaced the 9" setup on my 7.25 rear
I'll run the stock setup above 'til I can afford backing plates, shoes, springs, wheel cylinders and drums for the 8.75.

It turns out the 8.75 rear I have is from a car. The perches line up with my leaf springs so this means either an A or B body.
The center section was from a truck and this mates perfectly with the rear housing.

http://s1239.photobucket.com/user/slotto1/media/scamp/23Aug14/IMAG1096.jpg.html
Today I cleaned up and painted and installed the center section, a new gasket and the adjustable pinion snubber.

I'm setting these aside for later until I can get the appropriate backing plates. Most likely 10".
Thanks for your help guys.
 
If the perches line up, its an A-body rear end unless the perches were moved. Same with the SBP axles. They only came on A-bodies.

Here's the bad news. If you're going to use the SBP axles, you MUST find backing plates that are for SBP drums. Nothing else will fit. BBP drums have a different offset on the backing plate, and can't be used with SBP axles. So even if you find a set of 10" backing plates, you have to be sure they're for SBP drums. That also severely limits your ability to find rear drums, as I believe there's only one or two places left that sell SBP drums.

I don't know about the SBP 7.25" backing plate, but I know that the BBP 7.25" backing plates are the same as for a BBP 8 3/4, you just have to drill out the 5th hole. The other 4 bolts line up. But that may be different on the SBP 7.25", because they don't actually swap parts with a BBP 7.25".
 
cant he redrill the axles and problem solved?or find some stock lbp axles,i would think these would be cheap and plentifull
 
jdsduster said:
cant he redrill the axles and problem solved?or find some stock lbp axles,i would think these would be cheap and plentifull
Click to expand...

No, you can't just re-drill the axles. The offset of the axle flange is different between the SBP and BBP axles, so the offset on the backing plates is different. If you mix and match between SBP axles and BBP backing plates the drums aren't centered over the shoes. I forget which combo leads to which, but in one case the drums bottom out on the backing plates, and in the other they're about a 1/4" short. The two incorrect combo's would be BBP axles with SBP backing plates or SBP axles with BBP backing plates. Either way it doesn't work. If you re-drill SBP axles, you have to use SBP brakes and re-drill the drums too.

Stock LBP axles don't exist for A-body 8 3/4's. The 8 3/4's were phased out for the A-body when they went to BBP, so the only way to get A-body BBP 8 3/4 axles is to either buy aftermarket, or have a set of truck or C body axles cut down and re-splined. The later BBP A-bodies came with either 7.25" or 8.25" rear axles, and those rear axles are not interchangeable with the 8 3/4.
 
The drums I have for the 7.25 rear are 9" SBP. My plan was to drill out the 5th hole and use the backing plates on my 8.75 but I've read on other forums that there would be offset problems. That's why I decided to just use what I have until I can get the parts that I need. My plan is to put a 318 in the car. I should be ok with the 7.25 rear as long as I don't stand on it.

Lots of good info there 72, Thanks!
 
72bluNblu said:
If the perches line up, its an A-body rear end unless the perches were moved. Same with the SBP axles. They only came on A-bodies.

Here's the bad news. If you're going to use the SBP axles, you MUST find backing plates that are for SBP drums. Nothing else will fit. BBP drums have a different offset on the backing plate, and can't be used with SBP axles. So even if you find a set of 10" backing plates, you have to be sure they're for SBP drums. That also severely limits your ability to find rear drums, as I believe there's only one or two places left that sell SBP drums.

I don't know about the SBP 7.25" backing plate, but I know that the BBP 7.25" backing plates are the same as for a BBP 8 3/4, you just have to drill out the 5th hole. The other 4 bolts line up. But that may be different on the SBP 7.25", because they don't actually swap parts with a BBP 7.25".
Click to expand...

Wish the previous owner of my Dart would have read this. He swapped to BBP and 10 inch drums and they bottomed out on the backing plates. His solution was to add spacers behind the axle flanges to get drums to clear.:wack:
 
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