cudamark
Well-Known Member
No, not true. All '73-6 A bodies have the large upper ball joint regardless of which brakes it has.
Disc question
- Thread starter DusterOnaDime
- Start date
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cudamark
Well-Known Member
They went from 9" drum brakes on some low level A-bodies to 10" drum brakes as that service bulletin shows, but, the upper ball joints, lower ball joints, wheel bearings, and spindles stayed the same from the beginning of the model year. Just the hub and drum assembly and the backing plate assembly changed. And NOTHING from a '72 and earlier was used except the bolt pattern. This was all changed right at the model year changeover Aug 1st.
doug 371
Well-Known Member
Yes he edited his original post from saying it was a 72
We’ve had this conversation before. What you’re suggesting makes no sense from an engineering or production standpoint, because some of those parts would have needed to have been produced for only a 3 month run.
Never mind that there’s a long, fairly well documented history of Ma Mopar running the previous model years parts until they ran out if they weren’t specifically cosmetic model year changes. Hell my August built ‘72 Challenger has a whole bunch of “1971 only” original parts on it.
Still, if you want to show me a 9” hub and drum assembly that uses large wheel bearings I’m game. Or even a 10x2.25” drum assembly with large wheel bearings. Until then I’m going with logic, documented past practice and the TSB.
***Edit***
Corrected 10" drum dimensions to front drum dimensions
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cudamark
Well-Known Member
First of all, they didn't make a 10 X 1.75 front hub and drum assembly, but that's beside the point of this discussion. As I've mentioned before, there are no before and after dates in any factory manual showing different drum brake spindles used in a '73 A-body. So, only one spindle (3402739) means only one ball joint and one set of bearings. The '71-2 9" front hub and drum is a 3580702 made by Budd and uses the small bearings (A1 and A4). the '73 9" hub and drum is a 33699574 and uses the big bearings (A2 and A17). I know this form owning two of those early '73 A-bodies with 9" front brakes. At the time I parted them out (both rubber floor mat cars with totally rusted out floors) 35 +- years ago, they were both virgins. Nothing had been messed with. At that time, there were still quite a few of them running around here as daily drivers, and those front hub and drum assemblies were gold, as most people weren't looking to convert those cars to disc at that time. Those drums were the first thing sold off those cars. It was a surprise to me when I first encountered them too. After all my research, I discovered how unique they were and that even though they were 9' brakes, all the other attaching parts were the same as the 10" drum and disc brakes. That came in handy when I sold a later disc brake setup off say a '73-4 E-body or later F body to someone putting them in an A-body and needed the upper control arms. The service bulletin I've seen posted only mentions going from 9" to 10" in December, not that they changed from the '72 and earlier parts to '73-up parts. It wouldn't be the first time that Mopar designed and made a part only to change their mind and make something different a short time later. A case in point is the early vs late '66 Barracuda grille emblem. They tooled up to make a V emblem to fit the new grille that year only to decide a couple of months later to make the fish version. There are other examples, but, this diatribe is getting long enough. In closing, just look at all the factory '73 manuals and even aftermarket ones for bearings and ball joints. You will see only one listing for both on a '73 model.
I used the '73 disk brake setup with pin-type calipers and 11.81" rotors from a '78 Cordoba. These were the reinforced rotors like Cop Rotors. Use the longer caliper bracket with the larger rotors and all is well. The brakes are fantastic compared to the KH 4-Piston original brakes, which were good, but not great. I also did a real disk brake conversion using Liberty brakes and instructions from Mopar Action. These are also a very good conversion. One panic stop when I wasn't paying attention to lights and the car locked up all 4 wheels and stopped straight. Brand new BFG's did the rest of the work.
I highly recommend the big diameter rotors with no power booster. Feal is supreme.
I highly recommend the big diameter rotors with no power booster. Feal is supreme.
BillGrissom
Well-Known Member
Just to clarify, OP mentioned "control arms" above. Only the upper control arm varied. The lower control arm was the same for disk or drum, and I recall for all years 1963-76. Except some lower control arms have a bracket to attach a sway-bar link (optional) and I recall that bracket varied between early-A and 1973+ A, probably because the later have a wider engine bay (+1"?).
cudamark
Well-Known Member
Just to add to your post Bill, '62 A-bodies used the same lower control arm too. Also, there are actually 3 versions of the sway bar type. The '65-6, the '67-72, and the 73-6. The '65-6 will interchange with the '67-72, they just have a slight appearance difference with an extra built-in washer on the lower part of the "eye" where the strut links attach. For the purist, there are also appearance differences in the later years too. The welded-in plate for the bumper changed over the years. Some went full width across, and others were a bit narrower. To save a few cents cost and a tiny bit of weight I suppose?
Sorry, I know this and just typed the dimensions for the rear drum because it comes up more often. I fixed it to read 10x2.25" like it should have been.
Quite frankly, I'm tired of this. There are enough errors in the parts manuals and discrepancies from production (especially early production for a given model year) that they don't prove much of anything when it comes to special cases.
The '73 parts manual shows NO 10x2.25" drums or hubs at all. It does have a part number for your magical 9x2.5" drums that use large bearings. But there are a handful of other members that claim their early production year '73's still had small upper ball joints.
So who to believe? Beats me. By your account all drum equipped '73's before 11/1/72 (per the TSB) would have to be 9" drum cars, because there is no part number listed for a 10x2.25" drum/hub with large bearings. So no 10" drum '73's before November (ish) per the TSB if that's true. And of course, never a small upper ball joint UCA.
And of course that makes all the other members that have claimed in the past that their early model year drum brake '73's had small upper ball joints are wrong. Truly, I have no reason to believe them or you, since either could easily be misremembering something that happened decades ago.
With Ma Mopars history of reusing parts, well, it could be anything. Because I wouldn't bet a penny that small ball joint spindles and UCA's never left the factory on a model year '73 car.
Bottom line is, check which ball joints you have before you do a disk brake swap so you know if you need new UCA's. Goes for everybody really, because you can find just about anything on a 50+ year old car and just because it's really old doesn't mean it's original.
As for the magical 9x2.5" drum hubs with large bearings, well, I'll believe it when I SEE it. Not before.
junkyardhero
Well-Known Member
this is the biggest takeaway.
just cuz it's there doesn't mean it's original or that it's right.
anything can happen in 50+ years.
michiganpat
Well-Known Member
case in point, when I ordered parts for my disc brake swap, the inner wheel seal I ordered was correct for the year of car (even cross references the same as the F body part), BUT the replacement discs that were "correct" and listed for a 1976 duster were actually machined to use a larger diameter inner wheel bearing seal that I think happened in the early 80's-- the part number needed cross referenced to a mid 80's 5th avenue....
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