Rear brake restrictor things

Can't remember the technical name for these widgets but I rebuilt two on my clipper and I could have sworn there were rubber orings at the top of them? See pic one. I pulled one off my old Wolfsburg that's been sittings for years and there's nothing…..could have just rotted away but I don't know.

Reason for the question is I have two small brake fluid leaks from both these that I repaired. I'm thinking the o-ring is either not the right material, too big or they shouldn't be there at all. Can somebody clarify for me please.

brake bias valve see attachment o ring looks to big hard to be sure from the image

hard call look the same in full size image

tapered o ring perhaps

So i ended up pulling the other valve off my old wolfy sitting in the shop just out of curiosity to see what the second valve was like. From the outside you couldnt see any rubber oring but when i took the second valve apart there was actually an oring, but it seems to sit inside the recessed bit at the top of the valve (nut part). When installed it was actually inside the bigger cylinder (like you couldnt see the black oring at all. Also did a bit of homework too……. think the original orings looked like nitrile, so that what i replaced it with but think the size may have been wrong? Not sure…..i measured the one i took out of the wolfy and its much much smaller in comparion to the ones thats on my car. It old one measured in at 19mm OD with 17mm ID so i think that oring is designed to sit inside the cylinder and the top nut should be bottomed out? I ordered some fluorine o-rings yesterday to see if they hold up to the brake fluid better than the nitrile possibly and should fit inside the chamber of the cylinder when the nut is tightened up. 

https://classicparts.de/Bremskraftregler-am-Hauptbremszylinder-druckabhaengig-Golf-Cabrio-84-93-Scirocco-2-81-92-NICHT-FUeR-16V-Preis-pro-Stueck

shows an o-ring
533612151 for whole assembly, doesn't have the break down of individual parts tho.

Oh that's good to know Briano1234 I will check that out. I do know there are least another one or possibly two orings inside it if memory serves me correctly. Both smaller ones though. Both of mine are leaking for the top oring so I'm thinking they are either wrong material or wrong size and from looking at it I think they are wrong size and the top nut isn't screwed down enough. Will update when I get these new orings in tomorrow and see how that goes.

So just an update on this…..I ordered new fluorine oring 19mm OD and 17mm ID. They are the wrong size. The nut in the valve bottoms out before the o-ring comes in contact with the inner seat / shoulder of the proportioning valve body. So I re-measured the old oring from my Wolfsburg and it looks like it may have been 19mm OD and 16mm ID making the o-ring 1.5mm thick instead of the 1mm thick. So I ordered some new ones will see how they work out.  

In the meantime I was a raking thru my oring stockpile and found some 3/4" OD x 5/16" ID and 1/16" thick.



Put those on the car last night. When tightening the nut up the side of the o-ring blew out so slackened off and tightened up slowly and the o-ring eventually seated and the nut screws up nice and tight. So looks like these might work in a pinch as no leaks now but I still don't think that oring is correct. Once I get new one in I will try those also and see if they are a better fit. Will try to get dims of the inner orings also Incase somebody has this issue down the road.

Ok for anyone who is interested here are some pics of the internals of this beast. Still figuring out oring sizes but the small one looks to be 12mm OD x 9mm ID and 1.5mm thick.

Also there is a small delrin/plastic ball /plate inside the proportioning valve body that the brass piston pushes down on. It doesn't look like it comes out.

I usually spray brake cleaner holding my finger over the bottom,, then fill about 1/2 full cover the larger hole with my finger and shake the hades out of it, drain rinse repeat.

Hi, this is a brilliant thread, thanks for the photos. I might have to tackle this project soon…I've recently changed my front and rear brakes (front pads, rear drums, shoes, hardware and wheel cylinders) but my wheel cylinders keep leaking from the piston seals/boots (everything remains intact, just leaking). I've tried 2 new sets (17mm bore size), different brands, same issue on both wheels. I don't have a rear axle pressure regulator, but do have the 2 proportioning valves on the MC. I'm going to try 14.3mm cylinders to see if it makes a difference. I've bled the system multiple times, no bubbles in the lines. The brakes are hard when the engine is off, and super soft (too spongy) when the engine is running… The brake shoes are well centred, they aren't rubbing against the seals of the cylinder, same goes for the little pin connected to the handbrake via a spring. I didn't go near the MC, but I'm wondering if the new parts and new fluid + bleeding has done something to it or the valves, causing too much fluid/pressure going to the rear brakes. Any ideas?

Well, I had a car that had spongy brakes.
I replaced all the rubber bits from the hardline connection on the axle, then the two front hoses on each caliper with the Stainless Steel Jacketed ones.  New MC still spongy…

So I rebuilt the front calipers cleaned up the pistons and honed the Cylinders.

Dang me if that didn't cure the Sponginess, and I had bought rebuilt calipers for both cars as One of the bleeders broke in the thing and I was too lazy to drill it out.  

My other trick was to Wrap the Pleeder ports head to thread with white teflon tape and poked a hole for the bleed.  never had one ever rust seize on me again.

Did the Same to the other cabriolet and best 20 bucks I ever spent..IIRC it was 5 bucks back then per rebuild kit.