LoneStar23

Anyone have a source for the above other than a salvage yard? The usual parts suppliers don't seem to have one. Need it for a 1985. Thanks.

Seniorchief

(https://www.ebay.com/itm/16543585686...waAjNlEALw_wcB)

LoneStar23

Thanks Senior Chief. I snagged that one.

Maxwedge

iTrader: (1)

Note - the disc brake cars (GSL & GSL-SE) use a different prop valve than the drum brake cars (GS & S).

LoneStar23

^ ^ ^ Right... and I think the one on eBay will not work on my GS. The hunt continues...

Seniorchief

Will an 83 RX7 proportioning valve work?

Maxwedge

iTrader: (1)

When I swapped from rear drums to discs (GSL-SE brakes all-around) I found out on this forum that rear disc cars use a different prop-valve than rear drum cars. It takes a different pressure to operate the little cheel cylinders in a drum system than the big pistons in a disc system.

Now most guys don't know or care about this and just keep the stock drup prop valve. And most of those guys say that the brakes work just fine. But I'm taking my time on this build and I wanted to be particular, so I got a prop valve off an SE that was being parted out. And everything feels fine.

I would imagine ANY disc car's PV would work fine. I'm not an expert though like many others here. I just remember reading a post from a trusted member, that pointed out the 2 different PV's used on FB's (depending on disc vs drum).

rwatson5651

iTrader: (5)

One difference is that the drum valve maintains a small amount of pressure on the rears (Called residual pressure) to keep the wheel cylinders from collapsing from the force of the springs that hold the shoes in place. This is not needed with the disc brakes and I figure could result in causing unnecessary engagement of the rear pads. Also it is likely to cause problems with the rear to front balance.

tommyeflight89

iTrader: (4)

And to be sure you can always take it apart and check the colour of the anodized aluminum piston. There is a detailed post here that has pics of the various colours vs car model. Also a good chance to check the internal condition, there are two rubber seals inside.

j_tso

iTrader: (2)

Mazda must have tweaked something out for 1983, proportioning valve FA07-43-900 is listed for both drum and disk cars for '81 and '82, but it changed to FA48-43-900 for '83.
If there was a pressure issue, why not designate that prop valve for older cars as well?

Maxwedge

iTrader: (1)

Tommy, are you talking about the brake master cylinder? We're talking about the proportioning valve... the "splitter" that sends one line to the rear and two to the front brakes.

7aull

iTrader: (2)

Have an SA with FB (81-83, not sure which year) LSD rear end, and original Prop Valve. Would LOVE to source new/correct one!

Stu A
80GS
Rear LSD/Discs
AZ

tommyeflight89

iTrader: (4)

Yes we're talking same thing. The large hex cap on the valve will unscrew and an anodized aluminum piston and steel spring are behind it. The seals I was mentioning are shown in his pics. The hex cap seals with a copper crush washer.

The first used prop valve I bought, naturally I just had to take apart since I wanted to clean it up anyway. That's where I found a torn seal. I am quite sure that the early Miata prop valve uses the exact same seals but cannot find Mazda documentation to confirm that. Then we can rebuild our 40year old prop valve with new seals. Maybe J9fd3s knows?!

And be sure to install the associated master cylinder that corresponds to the front/rear caliper type. I am running 84/85 GSL rear end in my 82 GS and have installed the 84/85 prop valve with 84/85 (rear disc) master.

Ah I found Glazedhams write up with lots of info:

https://www.rx7club.com/1st-generati...alves-1018317/

j9fd3s

iTrader: (3)

i don't! Mazda seems to only sell the valves assembled. that being said they all kind of look the same, so you could probably try FC or early Miata ones.

there is also this, in case you wanted the rabbit hole in the rabbit hole... https://forum.miata.net/vb/showthrea...ht=brake+boost

j9fd3s

iTrader: (3)

further reading,

https://www.rx7club.com/race-car-tec...-valve-945620/

and https://www.rx7club.com/race-car-tec...-valve-931953/

swbtm

iTrader: (2)

+1 for the 94/95 Miata brake proportioning valve and brake booster. I’m going to be using that. 82transam installed one too with an aftermarket adjustable valve in place of the stock one. Works well from what I understand. I’ll eventually find it when it’s rolling again.