Master Cylinders: Bench Bleed or just mount and bleed ?

I started bench bleeding them many years ago, but in a Mopar Action tech article, Rick suggested to skip the bench bleed and just do it all with everything bolted up. I trust him in most cases but wonder what his reasoning was on this. Any idea?
Maybe since the rest of the system needs to be bled anyway, the bench bleed portion is just a waste of time?

I bench bleed and only have to do minimal bleeding on the car.

I have always mounted the master cylinder in a vise and used an old pushrod to bench bleed the master which also can be accomplished by one person.The master can be bled on the car but now becomes a two person job.If you were working on a GM master cylinder which can be mounted on a severe angle the bench bleeding option is all you have.

I've done it both ways however when using DOT 3 and above I've found the actual bench bleeding works the best.

What reason did GM have for those crazy tilted booster/master cylinder positions??? I had 2 Camaros that were like that and i never knew anyone that knew the reason.

Dealership quick method. Mount it and fill. Have an assistant in the car. Put your thumbs over the outlet ports. Have the assistant push the pedal to the floor. Release your fingers while the pedal is down. Recover the ports and repeat 3-4 times until the pressure blows your thumbs off. It may be one port only at first. When either port builds pressure while the assistant is still holding the pedal down attach and tighten the line. Continue procedure for the other port. Now with both lines attached have the pedal pumped a few times and have your assistant hold it down. Now crack each line to relieve any trapped air. Repeat 2- times cracking the lines. If your installing a new master on a previously bled and functioning system there is no need to go any further. Rinse the spilled fluid with water as brake fluid is hydroscopic and will mix with the fluid. Blow it off with air, your done. If the system was compromised with air then wheel bleeding will be required.
Doug

If you're like me and want to deal with brake fluid a little as possible while around the car, bench bleed it.

I think either way works OK but for mess containment I like to bleed in a vise then cap the ports with a pair of brass inverted flare plugs from the Edelman cabinet at my parts house then move it over to & install it on the vehicle & bleed the corners if they ain't already bled out & if they are I wrap a towel around the lines under the MC & have a helper JUST push it till there is fluid at the brass cones in the MC ports then at that point connect the lines & hopefully nary a single bubble left at those two port/line junction(s). I put a block of wood under the pedal to limit the travel to the normal range & to give the helper a firm stopping point as I coordinate opening/closing the bleeders with his manning the pedal. If discs I like to have him pump vigorously for several strokes then I open a bleeder as he is on the 4th downstroke (perfect verbal timimg needed) as discs can be hard to bleed out & agitating the fluid helps greatly & on a toughie even removing the caliper & blocking the pistons & tilting it in my hand as he works the pedal. the bleeder dont always have to be at 12 0'clock but where the passage meets the caliper bore it must be & some times it ain't & the agitation helps overcome that

I have two steel lines that fit the outlets, bend them around to dump into the reservoir. Install M/C, put on bleed lines, put in fluid, slowly work pedal to "bench bleed", remove bleed lines one at a time, installing regular brakes lines and wheel bleed from there.

Bench Bleed. That's the only way!!

I wonder why Rick Ehrenberg suggested to skip the bench bleed...

It can be done easily either way,take your pick. It's not hard either way.

I have been doing the bench bleed in a table vise for years. I don't recall the last time I just bolted it on and did everything fully assembled.
I'm swapping from a power setup to a manual MC soon and was curious about why Rick seemed to buck the trend.

This is what I do and it works great every time.

I think it's easier and quicker to mount and bleed and skip the bench bleeding step. I use an old baking pan underneath the master cylinder to catch any brake fluid and to keep the mess to a minimum. After bleeding the air out of the master cylinder I attach both lines. Then crack one open slightly and use the line as a bleeder. Then do the same with the other line. Most times the system is then fully bled and I don't even need to bleed again at the wheel cylinders. The last master cylinder change I did on an early Dakota took no more than 15 minutes using this method. Pedal is hard as a rock.

You don't use a vise ?? That just sounds like hypocrisy to me.

Actually, I never understood why someone would want to bleed their master cyl in a vise on a bench and then take that leaky dripping thing over to the car and try to bolt it on, all while trying to prevent brake fluid from getting on the paint. I was always too lazy to do it the hard way too, so I always mounted mine on the car and went ahead and bled it the way you described above. On cars that have a master that is tilted, I just jacked the rear of the car up. Being lazy can contribute to working smarter instead of harder I always say.

If Rick e failed to mention the reasoning behind the skipping the bench bleeding then you do not need to follow that advice.

One thought on bench bleed is you can confirm a full stroke on the bench. On the car you can not ensure that the piston is fully releasing and reaching the bottom.

Bleed lines submerged back into the reservoir then extra steps to catch the dripping fluid during install. Followed by a 4 wheel bleed is the one garanteed method.

Not all m.c.'s are machined for the piston and seal to be pushed farther down the bore than they normally are when bolted onto the car. I have read tech bulletins warning of possible damage to seals when over stroking a master cyl. Down sides do exist in either situation.

If this was just a straight MC to another MC swap, I could see just doing a bench bleed and go. I have had the strange luck where the steel brake lines had fluid all the way to the threads and connecting the new MC requires almost NO bleeding to feel right.
This time I am changing to a different NON power setup. The steel lines from the MC to the distribution block need to be shorter and mine look a bit ugly too.

I think it had to do with getting the pedal ratio right. If you look at a manual brake GM car, the master cylinder is pretty much level. The power brake ones are tilted to get the back of the mc lower, so that the pushrod is lower on the brake pedal.

It seems the most significant advantage to bench bleeding is you can do it without any assistance. I'm used to working by myself so that's the method I prefer. Here's a kit to accommodate bench bleeding:
http://www.oreillyauto.com/site/c/detail/MTM0/13911/N0678.oap
Here's a video showing how it's done:
https://www.youtube.com/watch?v=kEPXgDGU6_0
No mess, no help needed.

Same here, plus I also save all the fittings and little flex hoses they give you with a new/reman master cylinder.

Just go n buy a Cardone Master Cyl.bench bleeder #10-5000MCB n GIT R DONE,I believe the GM master cyl.angle is for directing the energy from a collision upward so the pedal goes down away from the drivers legs.