I was pressure bleeding my new master cylinder that I installed and I had an issue.. I bought a pressure bleeder and I hooked it up, pumped it a few times, and didn't see any pressure build up on the gauge. So i pumped some more and still no pressure on the gauge. I'm wondering what the hell is going on, then all of a sudden brake fluid starts coming out of the reservoir level sensors and the gromits that hold the reservoir to the master. Apparently there was pressure seeing as I was able to release the air from the tank using the relief valve. Have I damaged the master and should I replace it again? I've read you shouldn't exceed 20psi and I may have exceeded this but unsure seeing as the gauge is apparently not working... I have a1985 w123 300d.

If you didn’t send fluid into the brake booster, the master cylinder should be fine. It sees far more than 20psi at the business end. You might have to unhook the master cylinder and slide it forward to check that the back end is dry.

You might need new reservoir seals.

Sixto
98 E320s sedan and wagon
02 C320 wagon

The reason they say 20# Max is because of what happened to you....

Exchange the bleeder for one that works and don't exceed 5 PSI when bleeding .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I bled my ‘83 SD at 20psi without leaks.

Agree, though, that you don’t need to go that high, at least with a non-ABS system.

Sixto
98 E320s sedan and wagon
02 C320 wagon

No damage.

Try this as a first step, without any pressure bleeder. Connect a tube from font left wheel bleeder valve so that it feeds back into the reservoir. Open the bleeder valve. Fill the reservoir with new fluid. Pump the brake pedal until no more air bubbles appear from the hose. This is called "bench bleeding" because it used to be customary to first fill up the MC on the bench, using a short section of brake line, to pump the brake fluid around in a circle so that the MC was primed up and ready for install.

This is also a great way to bleed out air from the entire system, you just need a long enough tube to reach all four wheels (air hose tubing for fish tanks works great and is cheap from Wal-mart). However, it won't push new fluid out to each wheel without a lot of messing around, so a pressure bleeder is much nicer for that job.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

If the 123 uses the same master as a 126,your grommets are old and cracked. They used to be available for not much money.

Your bleeder not registering pressure is a separate issue probably with the gauge. I don't even have a gauge on my home made bleeder. Just pump it up some and pull the trigger. No problem yet.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

I'm guessing your grommets busted causing a lack of pressure before you realized it.

No your master cylinder isn't damaged

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.