Power brakes bench bleeding.

[GH85Carrera]

Once again I need the help from the bran trust.

My 1986 El Camino went 370,000 miles before the power brake booster started leaking air and needed to be replaced. I looked at the procedure and decided I really did not want to fight that fight, and went to the checkbook method of car repair.

Of course I am a "while you are in there" type and it seems insane to not replace the master cylinder with 372,000 miles while replacing the booster.

They got it replaced, but they did not properly bench bleed the master cylinder so I have a soft pedal. Then the virus hit, and they seem to have very limited hours if they are even still open, now I can't get in touch with them at all. One reason I almost always do the work myself.

So, I need to bench bleed my master cylinder. I really really don't want to have remove the thing to put in in my vice, and from what I can see, bench bleeding is using some short temporary brake lines to come out of the side of the master cylinder, and just feed right back to the reservoir, pump the brakes and get the trapped air in the master cylinder out.

I have tried to bleed the lines three times, first with a vacuum system, once with pressure at the master cylinder, and once with just pumping the pedal. The lines are free of air, it has to be the master cylinder.

So, the question is can I bench bleed while the master cylinder is already in place? I know I have to remove the brake lines going to the brakes, and I will be making a mess, but if I get a bench bleed kit can I leave the master cylinder in place?

[GH85Carrera]

Here is the kit I found that looks like it will work for my application.

https://www.amazon.com/dp/B076HSBM24/ref=cm_sw_em_r_mt_dp_OMD.FbTD3XA8F

Not a major investment.

[Bob Kontak]

Originally Posted by GH85Carrera

So, the question is can I bench bleed while the master cylinder is already in place? I know I have to remove the brake lines going to the brakes, and I will be making a mess, but if I get a bench bleed kit can I leave the master cylinder in place?

I have cracked the lines to the master and had a friend do the old fashion up, down routine on the pedal to remove air from the master cylinder while I worked the line wrench.

Mostly when someone has sucked in air vs installing a new master.

[GH85Carrera]

Originally Posted by Bob Kontak

I have cracked the lines to the master and had a friend do the old fashion up, down routine on the pedal to remove air from the master cylinder while I worked the line wrench.

Mostly when someone has sucked in air vs installing a new master.

So you just bled the master cylinder directly?

[Bob Kontak]

Originally Posted by GH85Carrera

So you just bled the master cylinder directly?

Yes, but I do not know if this is as thorough as bench bleeding. I have definitely improved pedal feel doing this.

You will hear and see the air come out on the down stroke.

[fastfredracing]

You can just bleed it conventionally at this point . If you have air in the system , it will find its way to the bleeders.
You can also disconnect the lines from the master all together, and " bench bleed " with it on the car .
I think the bench bleed , just makes it easier to get started pushing fluid and air . I have had models , where a bench bleed was not really possible, and still got a great pedal the old fashioned way .
Lucky its just an old elky. No abs....

[nota]

I bought a car a guy did not bench bleed for cheap and redid the M/C in the car
used the kit lines that came with the M/C to get the air out of the M/C
then the bottle gravity bleed to get the air out of the system/lines
it is important to remove ALL the old brake fluid as it is hygroscopic [(of a substance) tending to absorb moisture from the air.] and will cause rust in the system and steam can cause the same problems as air in the system once the brakes get hot

garage queens need the brake fluid bled out every year or three

[Bob Kontak]

Originally Posted by nota

.........used the kit lines that came with the M/C to get the air out of the M/C

My compliments to the cost accountant who had input into the length of those bench bleeding lines they supply with a new M/C. They are always very short.

[fastfredracing]

Originally Posted by Bob Kontak

My compliments to the cost accountant who had input into the length of those bench bleeding lines they supply with a new M/C. They are always very short.

He deserves a raise , I have noticed that a lot of master cylinders, are no longer even coming with those lines . I always saved the old ones when I was done, and have hundreds of them in the same container as my pheonix injector ( pressure bleed tool) .
Good luck Glen, Id just go around and bleed the whole shebang 2-3 times, and report back . Make sure to adjust your rear brakes also . That will have a large impact on how good of a pedal you get