9in rear drum rakes; do 7 1/4 and 8 3/4 interchange???

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604

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Well while doing my suspension up grade tonight I noticed my 8 3/4 on my early dart as the big 10in brakes while I have the 9in up front. I know not good. Can any one tell me if the backing plates and all off of a 7 1/4 will fit an 8 3/4?? That would be nice then I could just swap them out. Other wise I will be looking for a set of 9in 8 3/4 brakes! Thanks!!!!!!
 
I think 10" rears are the smallest that the 8.75 came with. Also 10" isn't big, I have a set of 11x2.5 for my brakes. That said, I'm going rear disc.

If you use an adjustable Prop valve, you can still use the 10" rear brakes and not be rear bias.
 
I don't believe they made 9" brakes for the 8 3/4's, just the 10's. And A-body 10" rear drums were different than everything else, they were 10x1.75". Everything else came with 10x2.5" rear drums, or the "big" rear drums which were 11x2.5".

I also don't think the 9" drums will swap over to the 8 3/4 for several reasons. But, even if you could figure it out I believe you'd need new axles anyway, since the length of the A-body 8 3/4 axles is different, the backing plates used a different offset (also true of trying to put 10x2.5" or 11x2.5" drums on an A-body 8 3/4, need new axles).

Either get an adjustable proportioning valve, or ditch the 9" fronts. They were sub-par even back then. If you're trying to stay SBP, I'm sure you could find someone with a set of 10" front drums they'd be willing to get rid of, lots of folks swap to disks and drop even the 10" drums.
 
Thanks!
Sucks I just put all new front brakes on it. New drums, hubs bearings, wheel cylinders, pads, and NOS grease caps.

Can I switch to the 10in front drums with out changing the spindles???


72bluNblu said:
I don't believe they made 9" brakes for the 8 3/4's, just the 10's. And A-body 10" rear drums were different than everything else, they were 10x1.75". Everything else came with 10x2.5" rear drums, or the "big" rear drums which were 11x2.5".

I also don't think the 9" drums will swap over to the 8 3/4 for several reasons. But, even if you could figure it out I believe you'd need new axles anyway, since the length of the A-body 8 3/4 axles is different, the backing plates used a different offset (also true of trying to put 10x2.5" or 11x2.5" drums on an A-body 8 3/4, need new axles).

Either get an adjustable proportioning valve, or ditch the 9" fronts. They were sub-par even back then. If you're trying to stay SBP, I'm sure you could find someone with a set of 10" front drums they'd be willing to get rid of, lots of folks swap to disks and drop even the 10" drums.
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I believe you can save the spindles and just swap to the 10" backing plates, but not positive about that. I have a few sets of the 10" fronts, and spindles too if you needed them. Of course, a switch to the K-H discs would be a much better upgrade, but also much more $$. Let me know if you're interested in a 10" setup and I'll put a set together for you!!

To answer your question, no 8 3/4 ever came with anything less than 10" brakes. As a matter of fact, the smallest brakes you could get on any 8 3/4" is in fact the 10x1 3/4" that the A-body cars had. That is also the only size available for an A-body 8 3/4" as they were all SPB axles and all the same size brakes for every year they were available!! There are 2 different style drums however, the flanged "Canadian" drums and the non-flanged style. Hope all this helps, Geof
 
Yes! I would be interested in a set of your 10in fronts!

And thanks for the info!

cosgig said:
I believe you can save the spindles and just swap to the 10" backing plates, but not positive about that. I have a few sets of the 10" fronts, and spindles too if you needed them. Of course, a switch to the K-H discs would be a much better upgrade, but also much more $$. Let me know if you're interested in a 10" setup and I'll put a set together for you!!

To answer your question, no 8 3/4 ever came with anything less than 10" brakes. As a matter of fact, the smallest brakes you could get on any 8 3/4" is in fact the 10x1 3/4" that the A-body cars had. That is also the only size available for an A-body 8 3/4" as they were all SPB axles and all the same size brakes for every year they were available!! There are 2 different style drums however, the flanged "Canadian" drums and the non-flanged style. Hope all this helps, Geof
Click to expand...
 
Guys, I don't know what was done, but I bought my 69 GTS well used and altered back in 1980. it has 9" brakes on the 8.75 rear. I have had it stored and am just now beginning to work on driving it. it has the 10" fronts which will go away for a 73-76 disc swap. I will need new rear axles for the 4.5 BBP and am in need of ideas and advice on brakes. to use something like Diplomat brakes from an 8.25 rear do I order the stock machined axles in 4.5 or do I need to specify a special axle length or bearing surface to fit the backing plate depth? thanks, paul
 
When you swap out the front 10in drums I will take them off of your hands! LOL

gtsport said:
Guys, I don't know what was done, but I bought my 69 GTS well used and altered back in 1980. it has 9" brakes on the 8.75 rear. I have had it stored and am just now beginning to work on driving it. it has the 10" fronts which will go away for a 73-76 disc swap. I will need new rear axles for the 4.5 BBP and am in need of ideas and advice on brakes. to use something like Diplomat brakes from an 8.25 rear do I order the stock machined axles in 4.5 or do I need to specify a special axle length or bearing surface to fit the backing plate depth? thanks, paul
Click to expand...
 
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