76 breaks problem

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Hello everyone. I finally had a chance to take some pictures. If they aren't correct let me know. I have the drum in my possession.

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10x2.5 drums, 5x4.5 bolt pattern?

Regarding what rear it is I was wrong here. The photo of the rear pan made it look oval but looking closer I can't see the upper pass side of the cover so it as @junkyardhero noted probably is a 7 1/4.
 
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Dana67Dart said:
You have an 8 1/4 with 10x2.5 drums, 5x4.5 bolt pattern
Click to expand...
i don't think so. that looks 7.25 to me

cover isn't round enough, the axles look different than the one i have sitting here.

FlqbPwdl.jpg
 
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slant6dart76 has an 8-1/4, as is junkyardhero post 28. Just count the 10 bolt (5 below in post 26). A 7-1/4 has 9 bolts.

Oops. Just noticed that 7-1/4 also has 5 bolts on the lower half, and we can't see the upper half in post 26, so agree slant6dart76 has a 7-1/4 rear-end.
 
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I don't know what some of you are lookin at, but the rear end in post #26 is a 7.25 plain as day.
 
BillGrissom said:
slant6dart76 has an 8-1/4, as is junkyardhero post 28. Just count the 10 bolt (5 below in post 26). A 7-1/4 has 9 bolts.
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i think it's forced perspective or a bad angle, or some of y'all either ain't got your nails dirty in awhile or need to book a visit with the eye doc.

that's a 7.25 in slant6dart76's car
 
measure the axle tubes or space between the U bolt legs, 2.5" it's a 7.25, 3", it's an 8.25

cover shape of the 7.25 changed in the early 80's, and the tubes grew to 3" in M bodies, AND the cover changed to more angular with 10 bolts, but it still necked down to 2.5" at the center casting.
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never seen a 3.31 ratio tag on a mopar before, but have seen that ratio in fords. I was wondering it someone swapped a ford 7.5" out of a grenada into it, because the axle tag looks more like a ford tag.....can't see real well in the pics, what's the actual measurement of the center register? IIRC fords are 2.75, mopars are 2.81, so a ford wheel typically won't fit on a mopar.
 
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Something I misses...


(but thanks michiganpat for the note about 7 1/4 cover and tube change in the later years)

The 8 1/4 uses internal C clips no bearing retainer (From Ebay)
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Older 7 1/4 use traditional bearing retainer (from OP)
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michiganpat said:
I was wondering it someone swapped a ford 7.5" out of a Grenada into it,
Click to expand...

(also very interesting about your 3.31 note)

in looking at this site it looks like all the ford photos do not have a drain plug on any of their rear covers

Bad Shoe Productions How To Video Series - Ford Transmissions & Rears
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Just noticed something else...

on 68 and older backing plates there are no tabs to either side of the wheel cylinder. The OPs backing plates also do not have the tabs. Could this rear be a 7 1/4 from a B, C, E or truck? Did any 7 1/4 have 1/2 inch wheel studs in 68 and older?

Ebay
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OP
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I love a good mystery!
 
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Thank you all for your time. I hope you are all having fun with this puzzle.
So far I gather this:
10"x 2.5" rear drum
4.5" bolt circle
7 1/4 rear axle
1/2 studs

So what drums am I looking for?
Mechanic says my drums and shoes are 10" 1 3/4.
If I understand correctly the ones Dana67dart showed on his picture wouldn't have fit because of the 4.5" bolt circle correct?
Here are the options I think I have and feel free to give me your opinions.
1.- figure out how to find the replacement drums. (Pain in the rear)
2.- find backing plates that match the "correct drum"
3.- disc conversation (not original and less fun)
 
A 4th option is to install a Ford 8.8 rear-end. That is mostly done by drag racers and not needed for a slant-six. It gives disk brakes. Not trivial since one side must be shortened by cutting and re-welding, then using a shorter-side axle on that now-shortened side. Several posts with photos. Label it so it won't similarly confuse next-guy.
 
slant6dart76 said:
Thank you all for your time. I hope you are all having fun with this puzzle.
So far I gather this:
10"x 2.5" rear drum
4.5" bolt circle
7 1/4 rear axle
1/2 studs

So what drums am I looking for?
Mechanic says my drums and shoes are 10" 1 3/4.
If I understand correctly the ones Dana67dart showed on his picture wouldn't have fit because of the 4.5" bolt circle correct?
Here are the options I think I have and feel free to give me your opinions.
1.- figure out how to find the replacement drums. (Pain in the rear)
2.- find backing plates that match the "correct drum"
3.- disc conversation (not original and less fun)
Click to expand...
as far as large bolt A body 10" rear brakes, I've only seen 10x2.5". a YJ wrangler from 87-89 has a dana 35 with 5x4.5" bolt circle and 10x1.75" brake drums--they are finned, not smooth. I wonder if you can just pick up those drums and use them

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I have a theory...

The backing plates are 68 and older B,C body 10x2.5?
The hardware and the backing plates match pre 69 parts
The rear seems to be a 76 7 1/4 with 1/2 inch studs, 5x4.5 bolt pattern and the large center register.

Dr Frankenstein would be proud

Evidence...

Car is a 76 /6 which got 7 1/4 but with BBP
Mechanic states the old shoes are 10x1.75 simple measurement. A lot of difference between 1.75 and 2.5 I doubt he mis-measured


67-68 10x1.75 backing plate (8 3/4)
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OPs backing plate
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69 - 76 Automatic adjuster cable
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OPs automatic adjuster cable (pre 69)

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10x1.75 69 up backing plate (8 3/4), the spacing is tiny
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7 1/4 is deeper
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OPs backing plate, the spacing is huge compared to 1.75 (8 3/4), easily 1/2 of an inch more

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So my theory...

The backing plates MIGHT be correct for 10x2.5 brakes only a test fit or some measurements will know for sure.
(edit: well that theory is proved wrong, backing plates and shoes are 10x1.75)
The backing plates and hardware came off a 68 and older rear
(edit: I still hold that theory)
Somewhere along the way someone put 10x1.75 shoes on (how they fit is a mystery to me, The shoes being narrower would not interfere so in theory it could work)
(edit: proved wrong again!)


I believe the OP needs to go to a local auto parts store and buy 10x2.5 rear drums for a 76 Dart /6 rather then ordering them. Taking the old drum that fits the hub and the studs and the backing plate along for size.

This can also be done to determine what drum the backing plate fit

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michiganpat said:
as far as large bolt A body 10" rear brakes, I've only seen 10x2.5". a YJ wrangler from 87-89 has a dana 35 with 5x4.5" bolt circle and 10x1.75" brake drums--they are finned, not smooth. I wonder if you can just pick up those drums and use them
Click to expand...


The 2 highlighted seem to spec correctly for your car. DO NOT QUOTE ME. you need to compare what's on it now assuming they fit correctly and how the replacement fits.

BUT all your parts should be for YOUR car. The backing plate ASSUMING it is 10x2.5 will work fine with 68 and older hardware OR 76 hardware you just cant mix and match
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slant6dart76 said:
If I understand correctly the ones Dana67dart showed on his picture wouldn't have fit because of the 4.5" bolt circle correct?
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Correct. They are for A body 10x1.75 SBP

slant6dart76 said:
Mechanic says my drums and shoes are 10" 1 3/4.
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I take him at his word BUT if you have 1.75 shoes AND drums on your backing plates there would be a 3/4 gap between the backing plate and the drum.

the drum braking surface should be maybe 1/4 inch wider than the shoes. So a drum for 1.75 wide shoes might have a machined surface of 2 to 2.25

A 2.5 drum might be 2.75-2.95, So you can measure the same distance on your old drums and see what they really are.

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slant6dart76 said:
Here are the options I think I have and feel free to give me your opinions.
1.- figure out how to find the replacement drums. (Pain in the rear)
2.- find backing plates that match the "correct drum"
3.- disc conversation (not original and less fun)
Click to expand...

  1. Not really a pain several options have been shown. GOING into a store will make your life much easier.
  2. You could get real 76 7 1/4 BBP backing plates AND the correct drums, BUT you don't know if your backing plates will work with correct 76 drums THEY MIGHT!
  3. While not the most difficult thing in the world... you think you have issues now!
 
Well Now I'm stumped and I agree with your mechanic that those drums are for 10x1.75
slant6dart76 said:
This is what my current (shot) drums look like with the 10" 1 3/4 shoes. In case this helps
Click to expand...
any chance you could get a photo or 10 of the drum on the axle
 
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Dana67Dart said:
Well Now I'm stumped and I agree with your mechanic that those drums are for 10x1.75

any chance you could get a photo or 10 of the drum on the axle
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I will try and go by the mechanic shop today before hw goes home for the weekend and take more pictures and count the bolts on the cover.
 
slant6dart76 said:
I will try and go by the mechanic shop today before hw goes home for the weekend and take more pictures and count the bolts on the cover
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If you can get under there and clean the housing and cover, there will be numbers cast into the housing somewhere.

Also details of the breather, older 7 1/4 had a cover that sticks up slightly on the axle tube (not like the vent bolt that holds the brake distribution on 8 3/4" rears.) many times they are covers in dirt and grease so not easy to see

But please put the drum on the axle flange and take a photo from the rear showing the backing plate and the drum and how they engage each other
 
Dana67Dart said:
If you can get under there and clean the housing and cover, there will be numbers cast into the housing somewhere.

Also details of the breather, older 7 1/4 had a cover that sticks up slightly on the axle tube (not like the vent bolt that holds the brake distribution on 8 3/4" rears.) many times they are covers in dirt and grease so not easy to see

But please put the drum on the axle flange and take a photo from the rear showing the backing plate and the drum and how they engage each other
Click to expand...
Apologies for the delay. The car being at the shop is a pain.
So I counted and there are 9 bolts on the housing cover. I did my best with the pictures. As for numbers i couldn't find anything under there other than the tag with the numbers on the picture.

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