jon928se

I don't think they should look like this.



I haven't finished searching but I think this is my brake fluid leak.

I am also wondering if the seal could be letting air in when the MC pistons retracts ? and could explain my spongy brake pedal?

Thoughts ?

Mrmerlin

time to replace the master cylinder.
You will find that once you remove the tank the rubber grommet will have rust under it and it will leak.
Best bet is to take out the new grommets on the new MC and add some Dow Corning 111 to the grommets , this will assist in them not letting in water to cause the rust. also you might consider making some sort of cover for the MC cap this will help to prevent water dropping onto the tank.
Trying to keep the car from getting wet will also slow this from happening again

F451

Hey Jon,

I have a brand new set of those seals sitting in my garage that I won't be using. You're welcome to them for the price of shipping if you like (from Duvall, WA, USA, 98019).

But, as Stan suggested, I would go with a brand new mc if you're experiencing a mushy pedal. I just installed one in my S4.

Ed

Giovanni

That is how my master cylinder looked like before I replaced the seals. I replaced the seals in June and its been dry since then. See pics of old seals vs new seals.

Mrmerlin

what you wont see till you remove the seals is a rusty bore that the seals sit in, there isnt much of a way to fix the bore and if the inlet bore is rusted you can bet the MC bore is as well

F451

Hmm, those seals do not look like the the ones I have. I should go out and the garage and find them.

Regardless, I agree with Stan, I don't think the mc is too spendy from what I remember.

jon928se

they don't look like the seals I just removed either - they look like they should be cut in half to fit.

A new (RHD) MC from Roger is $550 - a bit more spendy than the LHD cylinder.

Now looking at options

Get the cylinder bored and sleeved - assuming that new seals can be had and are generic.

Buy a LHD cylinder and have the bosses for the RHD pipe connections machined to fit (The casting is the same for both cylinders) and the LHD connections fitted with plugs.

Fit a LHD cylinder and extend the pipework to fit. - In reality the rear circuit pipe can probably be bent to suit the front circuit pipe would need an extension piece.

Does anyone know if the MC has a stepped bore?

Lizard928

I do believe that the bore is stepped.
But at the same time, while the spot that this seal goes into might have some rust, I doubt the inner bore does. Esp if it has seen constant driving. If you have already installed the new seals and it isnt leaking then I would forget about it. I do agree with sealing the top. Use some rubber grease just along the top edge.

The problem with using a LHD MC in there is tightening and removing the hard lines will be a real bugger.

Mrmerlin

The MC bore will be rusted in the portion that the seals dont wipe, so if you dont push the pedal all the way down when your bleeding it then the seals should not get cut when they traverse the corroded portion of the bore..
The rubber seals that are pictured are being held together one of the originals against one of the new seals you can see the deformity from being in the MC feed bore.
Once again I will offer that MC is indeed corroded inside if the feed holes are

jon928se

Hi Stan

I'm pretty much resigned to either new or bored and sleeved cylinder. Although I have yet to get into the existing cylinder (The retaining clip is like a circlip with no holes so no obvious way of removing it) to check that the problem is rust/pitting.

For reference the bore is stepped - From the ATE website diameters are

Diameter 1/ Diameter 2 [mm] 23,81/20,64
equates to 15/16" and 13/16" - Porsche using imperial sized seals in 1990 ?

Mrmerlin

to remove the snap ring take a dremel and cut a slot into the edge where the snap ring sits its a PITA to do but thats about the only way i could get the one in my Euro out. , The bore was corroded past where the seals were running in my Euro MC and it was replaced

jon928se

Finally got the MC innards out - retaining clip came out relatively easily with a jewellers screwdriver to pry it out of the groove. Followed by the larger piston assy.

Then spent about 3 hours sealing off the reservoir port and making a fitting to connect air to the rear outlet port to blow out the rear piston - no dice - eventually discovered it is held in by a pin in the base of the reservoir port that just pulls out with fine pliers.

Dissasembled - the bore appears perfect not a sign of rust or pitting anywhere I can see and the seals also look virgin. I am tempted to clean and reassemble with new seals if I can get them readily here (Not holding my breath) The alternative is to buy a LHD MC and extend the pipework to fit.

jon928se

Some Pics

The complete piston assembly



A blurred pic of the bore - very difficult to get the camera to focus down the hole.



And finally - what I suspect may be the cause of the problem.


The greeny brown plastic donut thingy stays stationary in the pedal end of the MC and the pushrod moves through it. The scuff marks on the pushrod (It wasn't me Guv!) seem to be causing the piston to hang up on the plastic donut and not retract fully. This would cause the reservoir ports to be not uncovered thus the MC never gets completely full of fluid and would give a long pedal.

If I can't get new seals tommorow it's all going back together with the old seals and the scuff marks removed to see if it works.

Mrmerlin

So in addition to the top ports leaking you say the MC wont return to its stop?? If so there is a good chance that the seals are swollen . OR as you said the buggered portion on the inner pushrod could also be the cause.
Its great news that the bore isnt pitted but since there is this damage it also is cause for concern as a PO may have honed the bore since the piston is showing the cuts.
At this point how hard would it be to add extender lines to fit a MC from USA car.
I would figure that they would only need to be about 4 inches longer and the MC can still be bled from its tip

Mrmerlin

Jon, one other thing you should consider is to replace the clutch Blue line now is a good time to do this unless your planning on removing the clutch MC in the near future, I know Roger has the silicone blue hose and it will be easier to do now with the brake MC out of the way