DivinDriver

iTrader: (15)

Sorry, another picky detail question - - but this one's important!

According to the FSM, the SA's whent thru 3 different brake drum designs, and 2 different brake back plates, for the rear drum brakes:

Drums: (by VIN #)
500001-554324 8871-26-251B
554325-578960 8872-26-251A
578961-end of run 8940-26-251A

Back Plates (Rt):
500001-554324 8569-26-280D
554325-end of run 8531-26-280D

Problem is, I don't know for certain which ones I have, thanks to a rear-end swap, followed by and axle/bearing/backplate/drum swap, done around 10 years ago... and for which I have no record of the "donor" car's VIN. (My original rear was a late number - 597799)

I know the parts I have are SA parts, because they have the manual-adjust shoe mounts (no star wheel, solid spreader bar) and that places them in SA-only territory.

Here's what I do have; Pix of the assembled backplate, and the drum:




I know that one of the variations involved the "double lip" around the edge of the backplate, there's a groove around hte edge of the drum that the inner lip meshes with. At least one drum and backplate type does not have this inner lip... but I don't recall which one.

Any one of you SA folk out there than can help sort this out for me?

Luckily, shoes and cylinders are universal, but eventually, the drums will wear out. And I don't like not knowing what I've got.

7aull

iTrader: (2)

DD -
well, I got curious and checked all FOUR Factory Parts catalogues I have (2 diff books, 2 diff Fische) and, with the exception of drums for SN 54,xxxx+ NONE appear to be interchangeable - the parts books code them for backward and forward compatibility and all the rest are "blank" = not compatible
Which does you no good I realize - I was just surprised at this lack off interchange - or apparent lack, any way...
Sorry no good news here unless we can start talking folks into popping drums off and submitting pix and VINs??
Stu Aull
80GS
Alaska

DivinDriver

iTrader: (15)

Thanks, Stu. I appreciate the effort.

Looking at the VIN numbers, it seems that the key is that the earliest drums have to match the earliest backplate. All the other assemblies that either of these parts interact with don't vary across the same VIN numbers, and the two later drums seem to fit the same (later) backplate. I suspect the "no interchange" between the last two drum designs was a forced-upgrade-in-pairs, rather than a fitment issue, since nothing else in the assembly changed across the same VINs.

So, the simpler question is: Do I have Early (prior to 554325) or Late (554326-on) backplates?

If these are the Late backplates, then I have the ones that were original to my car, and I can match the drums to my VIN.

If these are 'Early' backplates, then these are the backplates that came with the replacement rear end, and I have to use the earliest drums.

I'm pretty sure I remember when I did the original swap, that the drums I did NOT use, did NOT have the double rim. I noticed it when I tried to put the wrong drums on. And I've only ever had the two rearends, so it's an "either/or" issue.

So, if anyone with known-original rear parts can confirm if their backplates have the double rim or the single rim, and knowing their VIN, I would be set.

DivinDriver

iTrader: (15)

Another clue, but i don't know what it means:

The 80 FSM has a photo of the brake drum in it... it's non-split rim:



The 554325/554325 VIN split reflects cars produced before/after april of 1979... but I've no way of telling when the PHOTO was taken.

djessence

Thats a good pic of a drum brake.

7aull

iTrader: (2)

DD FWIW April 79 was commencement of _80_ production...
Stu Aull
80GS
Alaska

DivinDriver

iTrader: (15)

That's helpful, actually. Expains why a number of parts changes happen around that serial number.

I note that the drum brakes shown in the 1985 FSM have split, not solid, rims.

I'm betting this means that the 78's and 79's had solid rim drums until April 79, then with the 80 model year, they went to split-rim design, and used it from that point forward even though other mods were made.

Cant see them changing once, and then changing back.

Which means that most likely I still have my late-series 1980 backing plates and drums, and the solid rims that came on the replacement rear-end I installed, and which were later trashed, were from the earlier build.

grandgarson

If it's helpful I'll take some pics when I take the drums off of my 80. I don't know when I'll be doing that, but it will most likely be soon. I need to get in there and make sure everything is setup right since my e-brake has become almost useless and a few months back when I redid the rear brakes it worked great.

DivinDriver

iTrader: (15)

Sure; if you haven't swapped your diff or axle plates, your pics (or even just your IDing you have solid or split rims on the drums) and your VIN, would lock it up. Thanks!

vipergts_3

iTrader: (9)

here is a couple pics of 85 brake hardware and the drum.

DivinDriver

iTrader: (15)

Well, that for-sure solves it: The "split" rim drum is the latter design, and seems to have been used on all models except the '78s and '79s.

Thanks for the follow-through!

j9fd3s

iTrader: (3)

i found an old bulletin.

SA22C-554404 4/79 build got the new grooved drums

non grooved was part number 8871-26-251B

grooved is 8872-26-251

DivinDriver

iTrader: (15)

Nice! Thanks for the definitive answer.

j9fd3s

iTrader: (3)

As an Update,

the early part, used from SA22C-500001 to SA22C-554324, is 8871-26-251C. it has no groove on the inside, and is NLA from Mazda

the current late part is 8940-26-251A used from SA22C-554325 or April 1st 1979 to the end of the SA/ series 1 production. it IS available still. has a groove on the inside.
it starts from 8872-26-251A and the supersedes forward

the FB/1981+/S2 and later cars use an FA01-26-251

DGRX780

This is a super helpful discussion, thank you!

Unfortunately for my SA 1980, the drum 8940-26-251A is no longer available. I haven't even been able to find available aftermarket versions either (Centric 12345008, Raybestos 9526R, Dynamic Friction 36580008) - not sure if temporary supply chain issues or perminent...

Would the FB/1981+ drum FA01-26-251 fit a stock 1980 with a late model VIN SA22C-554325+? I need new drums and am getting desperate.

Ckforker

The SAs haven't been made in a while. I can't imagine the FBs would fit, but hopefully someone with more knowledge chimes in.

KansasCityREPU

iTrader: (9)

I've been looking for four years using those same part numbers.

I might have to switch to a 1984 drum rear end I have on my parts car.

j9fd3s

iTrader: (3)

i show an AC Delco 18B272, they don't list the split, so who knows
Bendix PDR0647, and a Carquest YH140647 also

t_g_farrell

iTrader: (1)

Based on rockauto data, it looks like in 1/81 the drums changed to the newer style without the outer lip flange which is unique to the SA drums. So you would need to get the rear drum brake backing plate from an 81-85 rearend post 1/81 to use the drums that are in stock. of course this would mean popping out the axle and changing the bearings to get the newer backing plate on, if it bolts up ok still.

Frogman

The question, the centric brand drums say to 3/79 . ( i need an answer on this)
I have a SA that is 536XXX and falls within the first batch ( there are three drum batches ).

Ok i did some digging around, the only drum brakes available for the SA are the Raybestos and centric ones, you can find them if you look hard enough online, the Raybestos ones only fit the 2nd batch of drum brakes, it is not explicitly said but they fit the 1980 GLC as well, and the GLC shares the drum brake umber with the 2nd batch of SA drums.

Benjamin4456

Figured I would just share that a listing for some Raybestos 9526R drums just popped up on eBay six days ago (just saw it myself an hour ago). Typing the part number in eBay search brings them right to the top. Listing says they fit all 79 and 80 but in reality they are only for the split drum design.

Can't vouch for the seller but I just snagged a couple myself and figure others might be looking as well (I've been searching for a couple years now). Only eight left if stock is accurate. Same seller also has 10 of the 81-85 drums.

Cheers!

Frogman

Do these fit the early 79's or the newer ones ?

Benjamin4456

These would be for the later ones, or the third revision I believe. So late 79 into 80 if I understand correctly.

Frogman

its the second revision , should be compatible with the original backing plate .

Benjamin4456

Sorry yes, second revision/third version. Got my wording mixed up.