So I am a big fan of the rear discs....my question is this. Is it worth it to try and find a rear end with the disc setup or just stay with the drums? Ive been doing some reading and it seems as though the OEM calipers are NLA.....

 

...as are the rear DRUMS for the SA RX7 I believe

NLA calipers prob still means rebuilds or aftermarket units could be found. Or just rebuild the existing ones. Mazda makes (or did) a caliper kit with all the seals and rubber bits.
So - your Q, is it worth having rear discs? I swapped in a GSL 12A rear disc axle into my 80 RX7, mostly because I found the idea have having to manually adjust the rear drums on occasion a drag. I believe the FB rear drums are self-adjusting? So it depends which RX7 you have.
FWIW the rear discs don't stop the car any better, and unless you are a serious track star, any fade-advantages of discs vs drums will probably never be noted. Do bear in mind you DO get an LSD with the rear disc set up, FWIW.

Stu A
80GS
Rear Discs
AZ

 

Not just calipers, you're looking for a whole rear axle housing and parking brake cables. They're a little harder to find nowadays.
If you can find one the amount of rust may tell you how rebuildable they are.

 

Thanks guys.

My car is a 85 with the drum brake axle. The car does have a 13b swap but the idea of getting a LSD is now enticing. I'll have to see whats available close but as you guys know parts for these cars are getting rare.

Does the Rear disk cars use the same proportioning valve and MC as the non?

 

The LSD can go in the drum brake rear ends. There's a small axle (81-83) and a big axle (84-85) LSD. Both are rather illusive, although the earlier one is more difficult to track down. I haven't been actively searching, but I've only seen one small axle LSD pop up in the last couple years. You however would need the large axle version, which is a little more common to find.

Based on Rock Auto, it appears that the master cylinders are different for disk vs non-disk. Hopefully someone else can confirm that. I'm not sure about the distribution block.


This was a good reminder that I need to swap to FB drums, at the least. SA drums are not worth the price or headache as 7aull touched on...

 

If you want an LSD, there are later Mazda torsen and Kaaz aftermarket ones available for 84-85 axles.
They're over $1000 which would have been crazy years ago when you could find our cars in scrapyards.

 

Both the MC and the Prop.Valve are different between disc and drum cars. MC is easy (just order from RockAuto, Mazdatrix, NAPA, etc.) but the prop valve you'll need to hunt for. I think the drum prop valve sends less fluid to the rear, so the rear discs might not get a full squeeze. You can also get an aftermarket prop valve and experiment with adjusting that.

 

Thats what I figured. Thanks for the confirmation.

 

Again - FWIW - when I dropped my small-axle LSD rear in my 80 SA, no other brake components were needed except a custom (by that I mean aftermarket-made) soft-line line adapter at the axle to allow the coarse thread FB line on the axle mate to the finer-threaded (I may have this reversed as to which line is coarser) SA hard line, and use of the rear E-brake lines that come with the axle. MCs and all other hardware remained original SA components-

Stu A
80GS
AZ

 

I didn’t change anything on my SA when I did a disk brake conversion and the brakes worked fine on my car. The car work fine on the road and track.

 

There is no benefit to the swap unless you are a hard core racer and only because certain drums are NLA and the adjustments . There are test showing the drums on a stock SA had better stoping distance than ALL the disks except the slotted disks on the GSL SE , those stopped a few feet better.
Some one here said his adjusted drums could lock at highway speeds and I called bullshit until a few weeks ago. A moron blew a red light and I slammed my brakes and they did indeed lock . Little bastard drums worked.

 

I've got a drum rear end too, I was thinking about a disc rear swap but probably will keep the drums and just look for a third member to swap in with a higher gear ratio and LSD. I'm thinking the 4.44 B2600 front diff with a Miata Torsen unit. Sure it's not going to be cheap but I can take time and find the right pieces and build it out of the car, then just swap it in and have a spare in case something blows up. Still probably going to be cheaper than buying a KAAZ and R&P kit and building my existing diff, or hunting down a GSL/SE factory rear end and driving a 14mpg truck to pick it up.

 

Rear calipers are NLA aftermarket. The pistons have been discontinued by the piston manufacturers so they have nothing to rebuild calipers with.

I have a small hoard but I would really prefer to un-swap my '81 for the drum brakes it should have. The handbrake holds the car much better and the pedal feel is better.

My '84 uses rear calipers from a late model VW so that's all good for now. Except FRONT calipers for RX-7s are NLA...

 

There are plenty of rebuild parts for Drums. , certain SA drums are NLA and the drums are non compatable with the backing plate , so all you need is a 80 backing plate and you are good to go

 

Thanks for all the info guys.

My main reason for bringing this topic up was with the increasing difficulty in finding 13" tires i was planning ahead for when I upgrade the wheels and rear discs look a lot better through the wheels than the drums do (my opinion) so wanted to see if upgrading to rear discs was an upgrade or downgrade!

 

For parts availability, 80 + drums are the best.
Calipers are straight-up NLA but rebuild kits are readily available.

 

81+ is the best, you don't want 80 either. Mazda went through three different drum brake designs during the 1979-1980 model years and all of them are darn near impossible to find.

 

The design changes all end with the first batch of the 80s don't they? I spent a while researching the drum designs based on the forum post you guys had made, there were some inaccuracies but for the most part, the information was pretty accurate.
The 79-80 has three drum designs and TWO backing plate designs.
The original backing plate only works with the original drums, 75% of SA's use this damn design, and we are screwed.
Drum ver 2 and 3 worths with a backing plate over 2 ONLY, these drums are available online. some 79's got the 2nd backing plate, the 80 got the same backing plate but about 30-50% through the run they got a new drum design, that still works with SOME 79's if you have the revised plate.

TLRD there are two backing plates, and unless you have an early 79 with the lipped backing plate, the drums are available online for both the 79 and 80 because they both use the same backing plate revision , that plate is not compatible with early drums. The 80 is pretty solid because that year only ever saw the 2nd backing plate.

but to make **** simple, 80+ is good.

 

I admittedly have not looked into it in a while, but I'm very curious where you are finding the drums for the 1980 model as I cannot track them down for a reasonable price (if at all). In '81 the backing plate changed again for the addition of the star adjuster so all SA drum parts are incompatible with FB backing plates, drums, shoes, etc.

I've been planning for some time now to utilize some of my FB backing plates and swap everything over, as I haven't been able to find new '80 drums and mine are over the wear limit. But if these drums do exist (and not for $300 a pop like I've seen in the past), I'd consider sticking with the SA stuff. Granted it would be really nice to have a star adjuster and ditch the square head adjusters regardless, and I have the parts so... Just need the motivation to pull the axles and replace the bearings.

 

Yeah, interested in where 79 drums are available.are you talking used or new> and how do I know which drums I would need for a 79? from the backing plate style? or the drum style and how would we tell the difference?

 

I'm a magic man .
894026251A is the drums used on vin _______578961+

BUT
vin 554325+ uses the same backing plate so Im guessing they are compatable due to the fact they share a backing plate and the shoes are the exact same .

Just look up the part number .

A way i find parts is finding a part even if discontinued and they normaly have a list of oem parts they replace , these OEM parts are compatable with our cars because that replacement part replaces OUR part along with the other brand cars , Just shoot those OEM numbers into google and you will be suprised what you end up finding .

 

cool, thanks. where do you find the OEM part numbers? are they in the FSM?

 

In the parts cataloge. I post the part number above as well , the other two Drums are NLA.

 

Pretty sure I have all my 1980 brakes in a bucket in my attic if it would help and you want me to look. Axles with all that stuff still attached too. LMK if I can help.

 

I'm showing 8940-26-251A as a drum that fits the 1985. So you're saying this will fit a 1980?