Am replacing M/Cyl tonight, just want to know if there are any tips like lubricating the cylinder first, gentle pressure on the pedal when bleeding etc.

Seems I probably totalled it when manually bleeding the system, so want to avoid anything like that).

...you can prevent fluid loss from the Master Cylinder, when reconnecting the car's brake lines by following these steps:

1) Mount the MC to the booster with Bleeder Hoses/Lines still in place.

2) Improvise a prop to hold the brake pedal depressed about an inch and a half (1.5"). This will prevent fluid loss when removing bleeder lines.

3) Reconnect the main brake lines, but leave slightly loose to do a final pedal bleed, as Cliff Pope suggests below, while tightening the connections.

A complete system bleeding is probably in order, since the results of the previous one are somewhat questionable.
--
Bruce Young,
'93 940-NA (current), '80 GLE V8 (Sold), '86 240dl, '85 244 ti, '83 245t
'76 244 (R.I.P at 255k), 73 142 (98K), '71 144 (ex circle track car)
Used '70 144 from '78 to '92, New 144 from '67 to '78, Used '62 122 from '63 to '67

You need to bench bleed the mc before attaching the brake lines to it. You can purchase kets to do this or if you have old brake lines laying around you can cut and bend them to work.

Attach the master cylinder to the booster. Run a line from each of the two ports on the mc back into the reservoir. Fill reservoir with Dot 4 brake fluid. Castrol LMA is my choice. Make SURE that the ends of the lines from the ports are BELOW the fluid level. Gently press the brake pedal repeatedly. You will see air bubbles exiting the ends of the lines in the reservoir. Continue until no bubbles are seen.

Carefully remove the bleeder lines (one at a time if possible) and screw the proper brake lines in. Use rags to prevent brake fluid coming in contact with painted surfaces, wipe up immediately any that gets on the paint.

To be safe I would bleed the system, but sometimes people claim it is not necessary if it was properly bleed prior to swapping out the mc.

Randy

Bleed it like this!
Two short steel lines from FCP or almost any other parts place. I actually mounted it on the car when I bled it and had someone else pump the pedal. Took 5 minutes, entire replacement time 10 minutes, plus about another 1/2 hour bleeding the VERY small amount of air from the system. Keep as much fluid in the lines as you can when you remove them- a small rubber cap such as on your bleeder screws will cover the line ends nicely.
--
Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

The current owner of this car (88 244GL, 148K) reports that she's let other people drive it and "they can't believe how great the brakes are". I'll take that as a compliment. :)
--
Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

To be safe I would bleed the system, but sometimes people claim it is not necessary if it was properly bleed prior to swapping out the mc.

When you take the hydraulic lines apart at the MC, you introduce air into the lines downstream of the MC and therefore will need to bleed the brakes whether they were done previously or not.

Bleeding a new MC is not as touchy as bleeding an old one, since there's no corrosion in the cylinder. If you're manually bleeding (i.e., pumping the pedal), you can feel free to pump it to the floor as you go along. Pumping to the floor is what ruins old MCs.

Disconnecting the brake lines at the MC doesn't have to introduce air. When you undo them avoid 'twanging' them so flicking fluid out. Undo them slowly and carefully, and plug the ends.
When you come to refit them, check fluid is still visible brimming to the end of the pipes, and inject a bit more to top up if not - old syringe useful here.

I have replaced 3 MCs on different cars, and never had to do any bleeding other than the bench bleeding of the MC itself.

How did you bleed/flush the first time around?
I am thinking of bleeding/flushing with IPD's brake bleed tool (22USD) and would like to avaoid damaging or totalling my master cylinder ! Can learn from your experience...

In the FAQ it says that the reservoir should be removed and cleaned with brake fluid and put back in, filled up with barke fluid, before you start the bleed/flush procedure with the brake bleed tool.

You said you did it manually, do you mean without a pressure brake bleed tool? Maybe it is worth buying this 22 dollar piece of equipment to bleed/flush. I read a recent post that said it works very nicely and makes it a one man job.

Thanks in advance for sharing your experience, giving me more details and letting me know what to avoid, not do when bleeding/flushing so that I will not total my master cylinder.
--
'89 244DL M47 158K miles

If you are careful about bench bleeding you can with luck swap a mc without needing to bleed the rest of the system. You can tell if it has worked because you get a solid pedal not a spongy one.
Having bench bled it I connect up the pipes but leave the unions loose. press the pedal very gently, so that any air bubbles out of the leaking joint and doesn't get forced down the pipes. Then tighten fully.
This doesn't change the old fluid of course, but you can do separately by bleeding out the old and pouring in new.

Another reason for being gentle on the pedal is so as not to set off the 'octopus' uneven pressure switch.