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Brake Proportioning Valve Rebuild...

Old 12-08-18, 10:20 AM
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Brake Proportioning Valve Rebuild...

Hey guys.

I am trying to see if anyone has experience with the innards of the OEM brake proportioning valve.

I am swapping my GS drum brake car to GSL/GSL-SE rear end and already have a new GSL/-SE master cylinder.

I have a rear disc GSL prop. valve and took it apart to clean it up.

Everything looks good with the exception of the seal on the needle valve (anodized aluminum). The pics below kinda shows how there is a tiny chunk missing from it.

There are no rebuild kits available. The seal looks to be identical to the seal in teh early Miata prop. valves. I was thinking of buying a new Mazda OEM Miata valve to steal it from.

Another option is the installation of a Wilwood prop valve which is adjustable, but works different than the OEM component. There are some writeups on installing these on Rx7's and Miatas. Another option is to just retain my stock GS prop valve, many people report that it works just fine with the rear discs....



Good reference thread:
https://www.rx7club.com/1st-generati...alves-1018317/
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Old 12-10-18, 11:39 AM
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FWIW I pulled mine apart once and it had some similar little issue

seal and chunk out of it do not belong in the same sentence.

not trying to be a smartass, cause this is probably one of those things you know the answer on just want confirmation.

I bought another used on with brake booster and all pretty cheap. their a dime a dozen.

thanks for the heads up on adjustable..didn't know it was an option
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Old 12-12-18, 05:55 AM
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Yup for sure don't want to just install this thing and run it..

I found this a little bit hard to find. I don't see them come up for sale often. That why a new OEM Miata valve may offer up its useful parts for a rebuild.

Going an installing a drop in Wilwood adjustable is a cheaper alternative but I need to do more research to understand what the differences between the OEM Prop valve are. The OEM valve has the front and rear circuit reference eachother.

The Wilwood unit is just for the rear circuit and all it will do is decrease pressure across the entire brake pressure range.
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Old 12-12-18, 10:36 AM
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consider all the brake line cutting and flaring in there as well

I've found this useful for parts Car-Part.com--Used Auto Parts Market

search for the brake booster, as it's usually ittached i think
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Old 12-12-18, 11:43 AM
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I will be selling my brake booster, but not sure if its in any better condition. 85 GSL
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Old 01-12-19, 07:58 AM
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Here is a bit more information.

Credit to these Miata forums:
https://forum.miata.net/vb/showthread.php?t=474070

The innards of the Miata valve look similar to that of the FB unit, and these Miata valves are available on eBay in decent condition.

I may get one and take it apart to see if it can serve to rebuild the FB prop valve.

Basically us FB guys are stuck with 35+ year old soft seals and no direct rebuild components.

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Old 01-13-19, 12:49 PM
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Bears saying; Always be cautious with "similar" where brake components are concerned. Manufacturers don't change stuff unless the change had some kind of impact - it's cheaper for them to just keep making the same thing unless there's a reason to change.
When dealing with non-cosmetic parts, sometimes the change is for manufacturing cost reduction, and sometimes its performance related.
Be sure you understand the what and why of the change.

Experimenting on brakes on a street car is sub-optimal.
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Old 01-13-19, 02:30 PM
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Other then the thread pitch which we know is different, I wonder if the whole Miata unit can be used as is with just adding some adapter to correct the pitch?
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Old 01-13-19, 04:54 PM
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I am planning on just using the tiny rubber seal that goes on the small dia of the aluminum piston (Just above the (R) in the above photo). That is of course if it measures to be the same as the seal in our FB units.

The Miata prop valve most likely has a different curve compared to the FB valve (GS and GSL/-SE). Would lead to improper brake bias.

Trying to be careful with the GSL rear end swap on my GS an use the proper GSL/-SE prop valve.

Other alternative is to take my GS prop valve apart and swap the seal to the GSl/-SE unit...
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