ruddster84

First off, Hello!

I've been on the forum for a while but have never posted. Bought a '95 911 in July of 2017 and have proceeded to jump down the track rabbit hole


Anyway, I believe my brake master cylinder failed while bleeding the brakes before the final track weekend of the year (pretty happy it failed in the garage). I was bleeding the traditional way by having my gf press the brake pedal while I opened each bleeder, and on the final valve, the pedal was on the floor before I opened anything. I could not find any leaks, and there was no pressure at all. Starting the car did not help and a booster failure didn't really make sense to me the way it failed. So I have ordered a new MC and from what I can tell, I have an older ABS unit that used a MC with only 2 outlets, while the new part has 4. So my question is can I use the plugs that came in the new part? If not, does anyone know the thread size so I can buy a new plug? And lastly, is something like pipe dope recommended to seal the plug? I'm assuming a tapered thread but I want to make sure this is not a leak point for the brake system.

OEM LEFT, NEW TRW ON RIGHT

Thanks Everyone!
Bryan

AOW162435

pp000830

Unlike household plumbing brake systems are exposed to high preassure so plugs are sealed via tapered threads or seats. Nix the sealent idea generally. I have sealed a bleeder screw dust cover with acrylic nail polish to keep road moisture out.

ruddster84

absolutely on the pressure, which is why I was assuming they were tapered, or they could be british pipe threads which are straight. If not british, I'm not sure if they are metric or SAE. So that's why I was wondering if anyone had dealt with a this scenario when replacing a MC and what the solution was. Hoping the plugs that came in it can be used. They have a dog point on the end but it is not flared to seal like a flared fitting would be. I can post a pic of it when I get home if that helps

I don't believe so as I was adding fluid as I was bleeding, and I recall taking a pretty good amount out once I decided to remove the MC. It's unfortunately tricky to get the MC apart as the dowel that retains the second chamber is press fit and tapered...maybe I'll drill it out at some point just to have a look.

pp000830

Why would a master cylinder be supplied with plugs that can't be used?
If they were not intended to be used I would think the part would have been supplied with plastic disposable plugs.
You could always compare the plug threading to the threading on the brake lines that were detached from the original cylinder to verify size.
A question I would ask: Is the 4 port cylinder backward compatible to the two port application if the remaining ports are plugged?

A quick email to the cylinder maker should clear up any application questions you have.
Andy

Endoman

The plugs will be metric parallel sided with a conical seat (that's the seal). I feel that when you were bleeding initially your gf pressed the pedal full stroke with a valve open. A dual line sysyem if it develops a leak in one of the lines will shut off that line (via piston position in the master cylinder) so you don't loose all the fluid and still have brakes. It's best not to play with brakes unless you are fully familiar.

ruddster84

Not sure why they would be supplied with plugs that can't be used, possibly just for storage/shipping was my thought. I'd rather err on the side of caution rather than having a leak/air intake point.

I had that question as well about the 4 port. I asked my local Porsche service manager and he said it was the correct part and I would have to plug the two that I did not use. I also looked around at quite a few places and it seems all the cylinders with this PN have 4 ports.
I actually sent TRW (ZF Group) as well as ECS tuning messages before I posted, just have not heard back. I'll post whatever info they send.

Thanks for the info on the plugs. I can't recall if the end is conical or not, I'll check when I get home. That very well could be the case. When the problem occurred, I had not opened the valve at all though and the pedal went straight to the floor with almost no resistance. Can you explain further how the failure occurs if the pedal is depressed all the way to the floor? Also, by dual line do you mean a split system (front and rear in this case) or a system that would use all 4 ports and have some sort of redundancy or a line for each caliper?

Thanks for the responses

Peteinjp

KASH '95 993

Ruddster, where did we land with the 4 port MC? I think I have a failed MC as well and getting ready to order and replace, but all are 4 port units. I assume you ended up using the 2 ports you needed and locking down the other 2 plugs that came with MC? Thanks.