I've never heard of bench bleeding the M/C before so I've been reading old posts. I found the following explanation. Is this acurate for a new M/C and booster? Do I pump the plunger to the booster or do I have to take the M/C off the booster? Thanks all

"If you're installing a new master cylinder you need to "bench bleed" it. This is a very simple thing to do but is often overlooked by novices. All you do is clamp the cylinder in a suitable holder(vise) connect 2 short lines to each of the outputs with the other end sticking in the cylinder fluid chamber. Fill the chamber, then using short strokes on the plunger, pumping the air bubbles out of the cylinder and back into the fluid chamber. Keep pumping until you see no more bubbles(sometimes it takes a while). A clear line makes it easier to see your progress. Leave the bleeder lines attached or use plugs to minimize fluid loss and install the cylinder. Quickly hook up the brake lines(to minimize fluid loss). Now do a normal bleed, you should be OK. Remember, whenever you "open up" your lines you should bleed the system. "

I guess you could do it either way. However, it seems like it would be easier to handle the master cylinder only.

Yes, do just the m/c. You can buy a bench bleed kit at your local auto parts store for around 4 bucks. Use a blundt tool like a phillips head screwdriver and depress plunger with short stokes (about 3/4") to bleed the air.

OK I'll take the M/C off, bolt the booster on the firewall, bench bleed it and put it back on the booster.
More question on bleeding: I'm using a later model prop valve that has a rubber plunger? on the end of it. What's that for? Does it come into play during bleeding? I now have a Mighty-Vac and will use it for the first time. Do I still do the brakes in the shortest to longest sequence?

You don't do anything with the metering valve plunger. If you were to pressure bleed it, you would have to override it with a little tool. Other bleeding methods require nothing to be done with it.

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my NEW webpage at: http://www.geocities.com/compuboy007/

Do you have to bench bleed it ?????

I just replaced my entire brake system with a BAER set-up and all new lines. Since my current rims wont fit with the BAER calipers, I havent put the rotors or calipers on yet. Its also going to the body shop and I was worried they would get overspray and alot of dust on my new set-up, so I left the nice stuff off for now.

I mounted the master and connected all of the new lines.

Once the car comes back from the body shop, I was planning on putting on the calipers and rotors, and then suction bleeding the entire system with the minivac pump.

I know it will take awhile to get the air out, but it will be alot cleaner than trying to connect lines with brake fluid running everywhere on my freshly painted engine bay etc..

Winch, Silver is right, you have to depress the metering valve only when pressure bleeding. You'll have no trouble suction bleeding. Also, I was told by a (kinda butcher) mechanic, it doesn't matter where you start on the car bleeding.

DRJDVM, I've had friends tell me I was crazy with bench bleeding. They've installed many master cyl's without doing it. I just always have done it. (Old anal roundy round racing days makes me) You can do it on the car but it can get messy. You can set the lid on the m/c to avoid splash over. I suggest lots of rags and depress the brake pedal very slowly with short strokes. And definately use a bench bleed kit with the lines.

I just found some instructions that came with the unit. They provide 2 plastic fittings that go in the M/C outlets and are used for bench bleeding. Maybe they have real small holes in them to allow the air to escape? Anyway it says how to do it about like everyone has said and then you are supposed to leave the plugs in until ready to hook the lines up. I guess if you're all ready to go and do it quickly it won't make too big a mess.

There are no holes in the plugs. The air gets pushed out of the holes in the fluid reservior. I helped a friend install a new MC recently on his car and his MC came with these plugs. The instructions said it was a new way to bench bleed. I guess the little hoses aren't needed.

I just had to do that on my car you are supossed to put plugs in and with M/C sitting level short rapid pumps some how this is better than the old way? but it did work

Short, rapid pumps won't do it properly; what you're trying to accomplish with bench-bleeding is to get rid of all the trapped air in the primary and secondary piston/seal cavities in the bore, which is very difficult to remove with the normal bleeding process. When bench-bleeding (which is essential with a new or rebuilt master cylinder), it's important that you make full travel strokes to drive the air out of the cavities - short strokes will leave some air trapped and give you a soft pedal no matter how much you bleed the whole system.

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JohnZ
CRG
'69 Z28 Fathom Green

The reason I say short strokes is because you can bottom the piston within the bore and dislodge the internal seal. Just make sure you use slow strokes and don't jam it in. Man, after writing this, I think I'll go and see what my wife is up ta. http://www.camaros.net/forum/biggrin.gif

The instructions say slow strokes of about 3/4 inch. I guess that's a short stroke. I'm wondering how you know you've got all the air out with the plugs method. I like the idea of the clear tubes. I might still go that route.

I'm following this post carefully since I am about to replace my master cylinder. Mine (Bendix) came with the plastic plugs and the instructions read the same as above - short strokes until no more air bubbles. This will me my first bench bleed (didn't know to do it before now) and I am trying to learn as much as possible before hand.

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Dave
'69 Z11 Pace Car, 350/4 speed, manual top, console w/gauges, tilt rosewood wheel, AM radio

I may have misled you on the rapid part they explained it to me as making the smaller air bubles will work there way out better by not using long slow strokes and they stressed the M/C must be level I have never done it like this before but it worked well and didnt lose a drop of fluidand no messing with return lines to res.