Bench bleeding master cylinder twice?

9 LIVES

9 LIVES

Demolition Expert
Thought I could tackle putting new rubber brake hoses on the front of my 95 3500 and a new master cylinder :doh:

I ran into a few issues. First I bench bled the master in a vise just using the two plastic plugs that came with the master cylinder and a wooden dowel. With each push the master cylinder would push fluid past the plastic plugs and im assuming this wasn't completing the task of bench bleeding? The master cylinder did get rock hard to the point where I couldn't push it in anymore so would that be considered done? Even though fluid was leaking out of the plugs? I did try putting o-rings on the plugs but that didn't help seal them off.

I put the master cylinder on the truck and started to bleed each wheel with no luck. Still the pedal goes nearly to the floor after bleeding each wheel an average of 10-12 times.

Could it be a bad master cylinder? It was a new not reman from advance auto.

Can you RE-bleed a master cylinder after it's already been done once? I'm assuming you can't because the piston is so hard to push in that I don't see myself making any progress with that.

I do plan to take the old master cylinder to NAPA and getting some brake lines to screw into the master for easier future bleeding the lines back into the reservoir.
 
Another question is if you improperly bench bleed a master cylinder then install on the truck, what negative affect does that have? Just more then normal air in the lines? Does this ruin the master cylinder? I was reading somewhere else online that if you improperly bench bleed the master cylinder that it MIGHT not ever function properly.
 
The only way to bench blead a master cyl is to have the plastic fittings that have clear hoses on them and loop them back into the fluid reservoir and pump until to air bubbles are present.

It locked up because the outlets were capped, if I understand what your saying, you just pumped it up with the plastic block off plugs? No damage would have been done if so. I think your just not bleeding them out correctly.
 
With my wife in the truck I have her pump 3 times on the pedal on the 4th pump she holds and I open the bleeder valve. Once it squirts off for a second or two I close it off and tell her to let off and repeat. I start at the driver's front side then passenger front. Lastly I do the rear.

So far I've gone through 3+ quarts of fluid. I top it off after I do each wheel.

The master cylinder didn't come with anything to bleed it other then two plastic plugs.
 
Blessing procedure sounds correct, I always start at the furthest back pass side wheel and move in from there.

No way you did damage with just a wooden dowel rod by hand.
 
As long as she's keeping her foot to the floor on the 4th pump, until you've shut the bleader off.
 
Yes she is keeping her foot to the floor on the last pump. She's well versed with this technique as she's been my front seat bleeding partner for 12+ years lol
 
Bleed them while the engine is running and hydro boost or vacume is helping her push them to the floor.
 
It's driveable after bleeding but coming to a stop the pedal falls below the level of where the throttle pedal rests. Mushy would best describe it.
 
jasonc said:
Blessing procedure sounds correct, I always start at the furthest back pass side wheel and move in from there.

No way you did damage with just a wooden dowel rod by hand.
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Agreed. We were tought is school to start at farthest point and work your way to the master cylinder.

Not saying it is but just something to check. The other day had a truck in the shop buddy couldn't get his brakes bled to save his life. And numerous people looking at it. I had helped him bleed them twice not paying any attention really. Finally after me getting frustrated from not being able to get a nice pedal(bled 100s of vehicles manually). I decided to look It over. He had I installed the new front calipers upside down, with the bleeder on the bottom.

I really felt just as stupid because I had helped bleed them twice without relay paying it any attention.
 
^^^^ I did the same recently. Was in a rush in between rain fall trying to get the truck together and didn’t even think. Bought a new master cylinder since the old one went dry after the truck sat for almost two years and got the same pedal to the floor smoosh feeling. Looked at the rear calipers and sure enough bleeders were on top.
 
Some of the firmest brake petals I’ve felt are when I gravity bleed the brake system. Open the rears and hook a small piece of hose to each blender and drain into an coffee can. Once I known all new fluid is present in the line, all air removed, find a helper to bleed via pedal and bleeder at the wheel. A few pumps and we are in business. Repeat for the fronts.

This has saved me lots of time instead of forcing the air out. It does help to install a caliper with the breather at the top.
 
Bleed the lines at the master, have your wife do the same deal of pumping X times and you crack them open on the X’th time.

Drum brakes? Are they adjusted correctly?
 
I haven't tried to adjust the drum brakes. Everything was normal just a few weeks ago until coming to a stop at the red light the truck wouldn't stop and I had to pump the brakes. I'm assuming to adjust the drums it's much like a trailer? Jack the rear off the ground and free spin the tires until they start to scrub then back off the clicker a few notches?
 
Make sure bleeder screw on the calipers are pointing upwards or on the top, Like Jones Runner said I also have seen the issue of the calipers upside down.
 
Well fortunately on the drums I can't change where the bleeders go. Both front calipers are on top.

Is it possible to get a bad master cylinder from the parts store? It's new not a re-man but I know in the past when I did buy remans I had similar issues and it would sometimes take multiple master cylinders before I got a good one.
 
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