Nickshu

Someone posted this on the GT3 forum...if you have a Non-PSM car you can buy the Boxster line that goes from the rear M/C port to the ABS unit and avoid needing to use an adapter. The Boxster line is the same as the 996 Non-PSM line but is M12 for the rear port instead of M10 so it eliminates the need for an adapter. Does not work for PSM (Please Save Me - LOL-) cars.

Here's the post: https://rennlist.com/forums/996-gt2-...l#post15301049

The part number for this line is 996 355 313 04. I ordered one and installed on my non-PSM GT3 without any issues.

246GTSA

Hi guys, for anyone looking to do this upgrade, there seems to be a world wide shortage of the TRW MN166 Master Cylinder!
I have tried all the usual online suppliers and there is zero stock!
Any ideas where I could maybe try?

Nickshu

Take the hit and buy from Porsche for $500+ appears to be the only option currently. I tried to buy one on Ebay only to be messaged by the seller that they were sorry they forgot to take the auction down b/c there is no stock left on the TRW part. Bummer.

GVA-SFO

By the way, I confirm that is is easy to find a M12 bubble nuts built for 4.6mm tube.
(The M12 bubble nuts that we have on our cars are set on 5.8mm tubes.)

So, if you can get the OEM brake line that goes from the rear outlet of the master cylinder to the PSM booster pump, then : by cutting the bubble at one end (loosing only about 1/4 of an inch), and replacing the M10 bubble nut of the master cylinder side nut by a m12 nut (built for 4.6mm tube), and rebuilding the bubble, ..then you will have a tube assembly that will let you forget about the need an adapter !

Or, we have two solutions : adapter or re-building a taylor made tube with an M12 bubble nut at one end and the M10 at the other end !

GVA-SFO

Install done : such an INCREDIBLE improvement.

Would like to thank you Nickshu, the info in your post made the install easy.

Now, I have the feeling that I have real good brake.

tekkie

246GTSA

Help!!
I fitted the MC (PMN166) and the ABS and PSM lights along with error 4460 came on.
I refitted the original MC and the warnings went away.
All this was done at Porsche and was correctly bled using PIWIS and the valve behind the headlight.
I then replaced the brake switch with 2 original Porsche switches and 2 Facet switches, still the ABS/PSM lights come on.
I also fitted a new Mass Airflow Sensor, lights still come on.
Upon further research I found that no one has reported a successful installation on a Carrera 4/Turbo, whereby the lights do not come on.
Does anybody know of this being done successfully on a Carrera 4/Turbo?

DGI

Im assuming my '99 would be a direct swap as well?

Really looking forward to doing this swap since I'll be replacing my brake lines with some stainless braided lines... cant wait to feel the difference.

Edit: Anyone know where the TRW part is in stock? cant find it anywhere. Pelican shows it instock but when you add to cart it redirects

TexSquirrel

I looked a couple of months back and gave up.
Hoping they'll show up sometime and I'll grab one.
Let me know if you find a stash somewhere.

Splitting Atoms

Is it the GT3 master cylinder you are talking about? Are they NLA?

TexSquirrel

No one had the TRW version in stock.
Porsche had them, but they're a lot more expensive.

Nickshu

I believe you can buy them from Porsche, just can't currently get the TRW version (exact same thing just not in a Porsche box). Of course double the price from Porsche.

GVA-SFO

Yes, I have the exact same problem. I changed the brake switch and cleared the 4460 error, (that came up in intermittent ways). Too early to say if problem solved or not yet, ..but still, thinking about the overall situation :

Whoa, I'm impressed, in and out MC, ..this is a lot of purging !
I'm curious : How much time the local Porsche dealer is charging you to do a complete "Piwis purging" ?

About this specific problem, I think the source is the sync between the "brake on" signal (sensor is the brake switch, a 20 bucks part) and the pressure sensor (I think located in the ABS pump assembly, ..that is a multi thousand bucks part). It looks (to me ?) like in the ECU logic, if the pressure sensor is up to a threshold level before (too early) the brake on signal, the ECU do trigger the error 4460. It is probably also the same, ..if the opposite situation happen. I never seen the ECU code, but this looks to be logical steps ! (Remember (joke), the ECU code is quite "sophisticate" : It can even check that a car has open "hood", steering wheel not moving for a certain time, etc.. to then decide to change some fuel intake quantity, thinking that these conditions are like that someone may be putting a probe in the exhaust pipe )

Back to serious:
I think it is a question of adjustment and timing sync between the switch action and pressure (level/threshold) detection.

I'm not sure at 100% yet if the switch should be "longer" or "shorter", ..but I guess, as with the new MC, the pressure building up "faster" (or "earlier"), the switch seems to tend to send "brake on" signal "too late" and have the ECU "thinking" that there is a pressure problem (pressure up before brake switch on ???), ..or : the switch (if my logic is correct ??) is "too long" and should be shorter.

Still, the brake feeling with this type of MC is absolutely great (so much better than the OEM feeling). Worse to investigate further in order to find a solution that is technically correct.

(We are talking about a 20 bucks parts, that is "relatively easy" to excahnge (beside the non comfy mode, that requires to put our head, ..where we normally put our feet !!!)
Can even use the previous ("old switch"), shorting it a bit and retest !

Well, one thing seems to be quite clear on your experience : in your case, it is not a problem of "The" pressure sensor !

jpurban

I spent years on this issue and never found a work around. The OEM master cylinder has a special bypass circuit in it that is required for the PSM system to function. I think it is a bypass that allows the PSM system to build pressure when the brake pedal is not applied. With an incompatible MC, you can not pass the PSM readiness test (because no pressure builds at the sensor) that occurs each time the car starts and first exceeds about 30 mph. When that happens, the 4460 error is set.

I had to go back to the stock MC to fix the issue. So, you have a choice... Great brake feel with an incompatible MC or a PSM/ABS system that works. Since I drove my car for years without PSM, I would probably vote for the better braking if doing it again (but I spent $500 on the stock MC). You don't "need" PSM/ABS, though many like the sense of security it provides. Of course, don't expect to sell your car without working PSM/ABS...

If someone can find a compatible MC with a larger piston, that would be ideal. Anyone have a contact at TRW? We want a 27mm piston with a bypass (or without one -- I'm not sure -- basically same as 99635591050, but larger piston)...

GVA-SFO

Thanks a lot for your post @jpurban, VERY interesting.

Have you been able to understand what is the "special bypass circuit" that you mention as present in the OEM MC (and not in the TRW PMN166) ?

Did you tried to contact TRW in order to get some deeper explanations ?

(Looking at TRW, I just learnt that in 2015, ZF (German transmissions Co) did acquired TRW !)