cudak888
Well-Known Member
Here's the deal (and a bit more on why a brake question is in the driveline forum):
Car data: 1968 Plymouth Satellite w/factory original 8.75 housing, 10" drum brakes, and (since swapped) original 2.76:1 open diff in 741 case.
A few weeks ago, I swapped the 2.76:1 diff in my Satellite to a 3:23. The 3.23 is also an open diff, but a 742 case.
When performing the swap, I had to re-adjust the right hand axle bearing inboard to maintain proper end play. No biggie, but the odd part was that after installing the 3.23, I had to readjust the axle endplay until the adjuster sat about 4mm deeper than previously - the curve of the adjuster already started to disappear in the threaded shaft. But it worked fine in the end, so what business did I have to complain, right?
Well, I had to find some way to get the problem to rear its head.
The 10" rear drums on the car were beat, so I figured it was an opportune time to install a pair of factory 11" Budd rear drums. Today, I did the deed, yanking the 10's off and fitting the Budd 11" drums, backing plates, and hardware (like a glove!):
Everything went well until I reinstalled the right-side drum. To my surprise, the lip of the backing plate rubbed on the corresponding channel in the drum. The rubbing was so light that it left no witness marks from spinning it by hand, so I buttoned up the assembly, dropped the car back down on the ground, and went for a drive.
These extremely light witness marks were the result, along with the off-and-on scraping sound of metal on metal, like a brake shoe that just wore out enough to expose its first rivet. This scraping sound was especially prominent when the car's weight was loaded on its right side (that is, when making left-hand turns):
I initially considered whether the drum was warped, but swapping the left drum with the right resulted in exactly the same symptoms. Then I considered whether the backing plate might be warped, but I've venture to say one would expect much more drastic (and consistent) witness marks if so.
I also know I have the end play itself adjusted correctly based on factory specifications, so slop couldn't really be a factor. And if it were, it would affect the left drum's position too.
This said, I'm rather convinced this isn't really a problem with the drum or the backing plate (they were a matched set from the same donor car, I believe), but some kind of funkiness going on with the 3.23's thrust block.
EDIT: I just read up on the wider thrust blocks on the pre-'64 8.75 standard center sections. Couldn't be that. Would have required an axle swap to start with, and the center section is definitely a post-'63 #2070741 unit.
However, I'm at a loss to what could be causing this - unless the 3.23 is missing something internally, or that the 742 case expects a longer axle to be used. And this is what brings me to you fellows, because I'm at a loss to explain it.
Let me know if you have any ideas.
-Kurt
Car data: 1968 Plymouth Satellite w/factory original 8.75 housing, 10" drum brakes, and (since swapped) original 2.76:1 open diff in 741 case.
A few weeks ago, I swapped the 2.76:1 diff in my Satellite to a 3:23. The 3.23 is also an open diff, but a 742 case.
When performing the swap, I had to re-adjust the right hand axle bearing inboard to maintain proper end play. No biggie, but the odd part was that after installing the 3.23, I had to readjust the axle endplay until the adjuster sat about 4mm deeper than previously - the curve of the adjuster already started to disappear in the threaded shaft. But it worked fine in the end, so what business did I have to complain, right?
Well, I had to find some way to get the problem to rear its head.
The 10" rear drums on the car were beat, so I figured it was an opportune time to install a pair of factory 11" Budd rear drums. Today, I did the deed, yanking the 10's off and fitting the Budd 11" drums, backing plates, and hardware (like a glove!):
Everything went well until I reinstalled the right-side drum. To my surprise, the lip of the backing plate rubbed on the corresponding channel in the drum. The rubbing was so light that it left no witness marks from spinning it by hand, so I buttoned up the assembly, dropped the car back down on the ground, and went for a drive.
These extremely light witness marks were the result, along with the off-and-on scraping sound of metal on metal, like a brake shoe that just wore out enough to expose its first rivet. This scraping sound was especially prominent when the car's weight was loaded on its right side (that is, when making left-hand turns):
I initially considered whether the drum was warped, but swapping the left drum with the right resulted in exactly the same symptoms. Then I considered whether the backing plate might be warped, but I've venture to say one would expect much more drastic (and consistent) witness marks if so.
I also know I have the end play itself adjusted correctly based on factory specifications, so slop couldn't really be a factor. And if it were, it would affect the left drum's position too.
This said, I'm rather convinced this isn't really a problem with the drum or the backing plate (they were a matched set from the same donor car, I believe), but some kind of funkiness going on with the 3.23's thrust block.
EDIT: I just read up on the wider thrust blocks on the pre-'64 8.75 standard center sections. Couldn't be that. Would have required an axle swap to start with, and the center section is definitely a post-'63 #2070741 unit.
However, I'm at a loss to what could be causing this - unless the 3.23 is missing something internally, or that the 742 case expects a longer axle to be used. And this is what brings me to you fellows, because I'm at a loss to explain it.
Let me know if you have any ideas.
-Kurt
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. There's a neighbor not far from me with a perfectly restored, numbers matching '67 Camaro Z-28 which has been a FLAWLESSLY restored, primered shell for 20 years now. I'm not really a Camaro guy, but I'd sure pick it up in a heartbeat if he offered it to me. Also has a '67 convertible in the same condition and a '64 Nova. Wouldn't kick a single one of those out of bed...
