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Lemondrop;7877354 They also use o-rings inside and the 1983 valve I had (the ports were rotted so I could not use it) had square seals in the same positions.[/QUOTE said:
A round o-ring takes on a square shape after years of sitting inside the bore. It wouldn't hurt to try square cut ones:

McMaster-Carr
 

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Ah, old thread!

Pretty sure my block has been on the car a couple years now, so far so good.

I went so far as to get the plug connected and run into the cabin, but I wanted to tie it into the E-brake handle, but I converted to a T5 and my exhaust was in the way of e-brake part that connects to the new crossmember. Crap, I need a new exhaust... but now I want duals... well that wont work, I still have the "single" rear brake hose location, but that's OK I need to rebuild the rear and put a 3.25 in it (anyone else ever have this problem???), but I can't stop there, the springs are sagging, so lets pull the whole rear and rebuild it...

So, all of this so I can have a working idiot light for my brakes and ebrake! I have a 3 day weekend coming up, I hope to get the rear rehung this weekend.
 

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Rehashing this old thread

Has anyone else had problems with these things? I'm wondering if the two I got came from a poorly machined batch. They also use o-rings inside and the 1983 valve I had (the ports were rotted so I could not use it) had square seals in the same positions.
I suspect that - like anyything else these day - there 'things' are probably made by multiple manufacturers. Buy cheap on Fleabay and get what you pay for.

A round o-ring takes on a square shape after years of sitting inside the bore. It wouldn't hurt to try square cut ones:

McMaster-Carr
It certainly could hurt. A lot.

Use the proper o-ring (round cross-section) for the application. If you dont know the exact proper o-ring (and I dont) then get help finding them (Ford dealer, etc) or replace the entire unit. Those o-ring sizes inside your hydraulic braking system and the last thing you want to guess at or 'redesign'.

Paul
 

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I suspect that - like anyything else these day - there 'things' are probably made by multiple manufacturers. Buy cheap on Fleabay and get what you pay for.



It certainly could hurt. A lot.

Use the proper o-ring (round cross-section) for the application. If you dont know the exact proper o-ring (and I dont) then get help finding them (Ford dealer, etc) or replace the entire unit. Those o-ring sizes inside your hydraulic braking system and the last thing you want to guess at or 'redesign'.

Paul
By square O-ring I meant the rebuild kits I've seen have a square cut o-ring in them, the repop unit I got does not. It is a MBM unit, which from what I can tell is the only manufacturer of these turds. When I opened it the first time, the o-ring was sideways and pinched, like they assembled it by tossing the parts into the hole and then threading the end fitting on, damn to the position of the guts......they will sort themselves out. Finding a NOS and or Ford original is pretty hard to come by since from the info I gathered said Ford stopped producing them somewhere around 10 years ago.

I had a 1983 Mustang prop valve, which had the square seals and I could have rebuilt but corrosion wiped out the seats for the brake tube flares and thus I had to buy this crap-ball. I'm lining up a junkyard visit this weekend to check a 1984 mustang to see if it still has the valve and if it is good (Aluminum block that corrodes). The 82-85.5 or so valves are supposed to be a dead-ringer for the 67/68-? Mustang valves. The 79-81 valves will work but something is different about the bias or residual pressure, I can't remember. Mid 86 into 87 they blocked off one of the ports and split it elsewhere down the line but supposedly changed the bias again when they changed the valve.

The o-ring(s) on the repop unit that are causing the problem is on the shuttle valve that activates the brake warning light and shuts off the circuit that has low pressure. I think the o-ring is leaking from the rear circuit, into the center section where the switch is at. That is why I may just plug the switch port as my 64.5 does not use a brake warning light as it never had one (so the switch is just sitting there with nothing attached). I'm thinking the second seal on the other end of the shuttle/spool valve will keep the front and rear sides still separated and allow me to have brakes on this thing until I can find a good used piece and rebuild it.

Frustrating as I'm real close to being able to start the car up and drive it for the first time since I got it in 2003. It is not finished yet, I still have to sand/paint the thing and assemble the interior but I need it to run/drive/stop to move it up and down my driveway to do the bodywork.
 

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A round o-ring takes on a square shape after years of sitting inside the bore. It wouldn't hurt to try square cut ones:

McMaster-Carr
There's something else to consider: the rubber compound used. EPDM is compatible with brake fluid. Many other compounds are not.

Square rings are actually old technology. I provide newer-style x-rings in the rebuild kits I make because they provide a better seal than the square rings (two sealing surfaces vs. one).
 

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There's something else to consider: the rubber compound used. EPDM is compatible with brake fluid. Many other compounds are not.

Square rings are actually old technology. I provide newer-style x-rings in the rebuild kits I make because they provide a better seal than the square rings (two sealing surfaces vs. one).[/Q]
X-rings would be square rings with a half moon cut into each one of the flats right? Because that is what the rebuild kits I've seen have. I just call them square, unless it is a larger flat square ring, which I call square cut seals.
 

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There's something else to consider: the rubber compound used. EPDM is compatible with brake fluid. Many other compounds are not.

Square rings are actually old technology. I provide newer-style x-rings in the rebuild kits I make because they provide a better seal than the square rings (two sealing surfaces vs. one).
These are not round cross-section o-rings?:


Paul
 
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