Bench Bleeding and Brake Bleeding Procedure.

[CheepComanche]

For the past couple days I have been struggling to get a firm pedal. I found different methods on how to correctly bleed the Comanche brakes and am not sure if it matters how its done exactly. What I'm more concerned about however is the fact that I got distracted while bleeding, let the MC get too low and sucked air in. Do I now need to Bench bleed it? Bench bleeding is something that doesn't really make any sense to me. I've never done it however most of my experience comes from the aircooled Volkswagen world where everything is as simple as it gets.

[eaglescout526]

My understanding of bench bleeding is to make sure you have a good unit that wont leak past the seals. Other than that I see no point other than to throw it in then bleed everything at once.

 

The order of bleeding is standard stuff. Start at the rear pass wheel(farthest from the master) then work your way up to the closest bleeder.

 

For the MJ specifically after all is bled is you open one of the front caliper bleeders, bleed allllll the fluid out to simulate a front brake failure and then you bleed the rears again to make sure that emergency bypass is bled and free of air. Then you bleed the fronts again. Tedious but how it has to be done. Grab a bottle and a hose the save the good fluid.

[75sv1]

       Well, I've had a different experience recently. I bought a MC for my 2010 Chevy Avalanche off of E-Bay. A Raybestos. I did bench bleed it. I had the ports capped, filled with fluid, then pumped the piston. Installed it. I used a brake bleeder unit I always use. Not good. My neighbor used an AUTEL scanner to active the ABS. Still, not good. Try, try, cry, cry. Well, Neighbor got me a unit from O'Rielly's, where he works. I read the instructs, bought a brake bleeding kit. I had one somewhere, but scattered to the 4 corners of the garage. 

        So, as per directions. Do not install the plugs. Fill the reservoir.  Let the fluid dribble or flow out the ports. Then cap the ports. This lubes the oring seals. I used the plugs that have the barbs for a flex tube. Routed the tubes to the reservoir.  Pushed on the piston, till no air bubbles.  I installed the MC. bleed it with my cheap $10 plastic brake bleeder. Brakes work OK. 

[gogmorgo]

Bench bleeding is done to prime the system. Both to make sure the seals get lubed and to make sure it actually pushes fluid when you push the pedal, to speed up bleeding the system when it’s installed. If you just assemble and tighten all the lines you’ll compress air in them and risk just pushing that air back and forth in the master until you wreck the dry seals. Even with bleed screws open, you might not get enough pressure out the bottom to make up for the amount of air you’re squeezing up top. 

“Bench” bleeding can also be done with everything installed in the vehicle, just by leaving the brake lines on the master cylinder loose and slowly pumping the pedal until they leak. Then you can tighten up the lines and move on to bleeding the full system. Just make sure to flush away the brake fluid dribbles with copious amounts of water or it will eat paint and the metal underneath will rust away. 

[gogmorgo]

13 hours ago, eaglescout526 said:

 

For the MJ specifically after all is bled is you open one of the front caliper bleeders, bleed allllll the fluid out to simulate a front brake failure and then you bleed the rears again to make sure that emergency bypass is bled and free of air. Then you bleed the fronts again. Tedious but how it has to be done. Grab a bottle and a hose the save the good fluid.

I’ve always done it by bleeding the bypass first. It’s how the procedure is always quoted from the manual.

But maybe the order doesn’t matter. Like with starting with the furthest away, the only reason is because that will push the most air out of the first bleeder and you’ll have clean bubble-free fluid to the other bleeders more quickly. But you can bleed in any order, you just might spend more time on average at each bleeder that way. 

[75sv1]

I like to do the longest first. The rear passenger. Then the rear driver. then the front passenger, then the front driver. I do not save the brake fluid. 

[CheepComanche]

Thanks for all the info. I got the pedal to where I think it should be, I'm just not very confident as I haven't ever done this process before. Again, my main concern was the fact that the MC sucked in air and I would have to bleed the entire system again. Being that the Comanches braking system is so much larger than I'm used to, I'm unsure of how long it takes to move air all the way to the back bleeders.  

[Pete M]

have you bled the emergency bypass line?

[CheepComanche]

18 minutes ago, Pete M said:

have you bled the emergency bypass line?

Yes, hopefully I did it right. I opened one of the front bleeders connected a line which I submerged in a bottle of brake fluid then bled the rear brakes. The brake light on the dash never came on but my guess is that the light just doesn't work anymore.

[Pete M]

that light needs to come on.  because after your done you'll need to make it go back off to confirm that all went back to normal. 

 

after you open a front line you sometimes need to stomp on the brake pedal HARD to get the shuttle to move. 

[fiatslug87]

From the ‘92 factory service manual:

Open the right front bleeder

Depress brake pedal and hold

Start engine, brake light should stay on after engine starts indicating bypass valve has moved (sensed front brake leak)

Turn off engine, leave bleeder open, release parking brake

Bleed left rear 

Bleed right rear

Bleed righ front (close bleeder when done)

Bleed left front

then repeat bleeding with right caliper closed