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Yet another brake issue

chris85

chris85

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Alright, my brake issues all started with my rear brakes not bleeding, and we found the need for the bleeding tool on the prop valve. Then, the MC still would barely bleed bc it seemed that it just wouldn’t push enough fluid. Now, I have a 99 3500 MC and the brakes bled great, they do well on the road but they can’t hold the truck on a steep grade. My driveway is pretty steep and it will just roll down with the brake pedal slammed.

I remember when bench bleeding this MC the piston seemed to travel further than the others. When holding the brakes the pedal does not hit the floor but it does feel like it hits a hard stop. Not spongy feeling.

This is all new lines, a basically gutted disc/disc prop valve, new MC.
 
Are you sure you have all the air out of the system? What front/rear brakes calipers are you running?
 
I believe they’re JB6 calipers. I feel pretty confident that we got all the air out. Numerous cycles of bench bleeding the MC and several at the calipers. For once we didn’t have any issues bleeding.
 
Try bleeding it on the driveway first with the nose up then with it down. I've had air bubbles trapped to where it took forever to finally bleed them.

One trick I learned was, with the nose of the truck pointed up, push pedal down slowly but hard, block it so it stays down (block of wood to the seat worked well) then go around and tap on all brake lines. After 1/2 hour let off the brakes quickly. Do this a few times. If you have trapped air bubbles it can work them up to the mc and burp them out.

Also, on the later model mc's didn't they swap the front and rear brake line placement? If so did you swap them?
 
ChrisPerry said:
Try bleeding it on the driveway first with the nose up then with it down. I've had air bubbles trapped to where it took forever to finally bleed them.

One trick I learned was, with the nose of the truck pointed up, push pedal down slowly but hard, block it so it stays down (block of wood to the seat worked well) then go around and tap on all brake lines. After 1/2 hour let off the brakes quickly. Do this a few times. If you have trapped air bubbles it can work them up to the mc and burp them out.

Also, on the later model mc's didn't they swap the front and rear brake line placement? If so did you swap them?
Click to expand...

Yeah the ports are reversed. Still the same thread sizes though so you can’t really mess up putting the wrong line on the wrong port.
 
I like using speed bleeders to bleed my brake systems, but of course a power bleeder is the ultimate. Bleeding brakes the old fashion way of pumping the peddle just seems to add air back into the system when trying to hold the brakes down while closing the bleeder valve.
 
1-ton said:
I like using speed bleeders to bleed my brake systems, but of course a power bleeder is the ultimate. Bleeding brakes the old fashion way of pumping the peddle just seems to add air back into the system when trying to hold the brakes down while closing the bleeder valve.
Click to expand...
I just open up all bleeders and leave it for 30 minutes, I come back and check the fluid level top off and leave it another 30 minutes.
Works every time.
I do put a clear hose on the bleeder and run it down to a container
 
I often end up being the official "pedal pumper" at my friends shop when I visit him--he does a ton of brake line replacements and other brake work that requires them to be bled after the work is done..

Very few times has bleeding the brakes the "old fashioned way" failed for him...the few times it did was when he had to replace every brake line on a vehicle including those going to the anti-lock brake module and master cylinder..it seems once the anti-lock module's hydraulic circuit gets completely empty from a failed brake line,then the vehicle gets driven that way awhile,it gets very difficult to eradicate all the air..
 
I hadn't thought of that before, @chris85 do you have any anti-lock stuff on the truck?
 
imiceman44 said:
I just open up all bleeders and leave it for 30 minutes, I come back and check the fluid level top off and leave it another 30 minutes.
Works every time.
I do put a clear hose on the bleeder and run it down to a container
Click to expand...

Same here, I've had good luck "gravity" bleeding brakes that wouldn't bleed properly any other way. Run a clear tube (1/4" ID/3/8" OD) into a container. I just topped off fluid (full) in MC then left checked every hour. This method was suggested to me by a friend who had similar problems before. YMMV. Just a thought.

Also, I did until fluid ran clear to be sure to flush old brake fluid out of system. Siphoned some of old fluid out of MC then refilled with new fluid. Have to be careful not to siphon so much out of MC to loose prime inside MC!

You Tube has a lot of videos on this. Chris Fix actually has a good video showing this.

Good luck!
 
Since I'm alone 99% of the time working on my truck,I rigged up a vacuum brake bleeder that uses the engine's vacuum to bleed brakes..
Its nothing more than a jar with an air tight lid,a few pieces of brake tubing secured thru the lid and enough vinyl tubing to reach the farthest bleeder...
It works slick...except on my diesel pickup,the diesel has no vacuum...so I must use another gas powered vehicle to supply the vacuum or do it the "hard way" by pushing the pedal down,then block it in the down position with a board between the seat and brake pedal,go close the bleeder,pump it up again,hold it down--repeat as needed..
Gravity bleeding has worked for me often also..
 
Did you purchase an BRAND NEW M/C? I once put a rebuilt M/C on my '67 K30. Ended up replacing three times under warranty. Finally purchased a brand new unit (only $10 more) and no problems. Several mechanics explained to me the bore that the piston moves in wears and the rebuilt units simply get new seals and allow the piston to "cock" in the bore causing failure to hold fluid pressure. Mine happened while driving, would suddenly have no brakes. New M/C fixed problem. May not be your issue but I learned NEVER buy re-manufactured brake components, EVER! Good luck with your fix.
 
trukman1 said:
Did you purchase an BRAND NEW M/C? I once put a rebuilt M/C on my '67 K30. Ended up replacing three times under warranty. Finally purchased a brand new unit (only $10 more) and no problems. Several mechanics explained to me the bore that the piston moves in wears and the rebuilt units simply get new seals and allow the piston to "cock" in the bore causing failure to hold fluid pressure. Mine happened while driving, would suddenly have no brakes. New M/C fixed problem. May not be your issue but I learned NEVER buy re-manufactured brake components, EVER! Good luck with your fix.
Click to expand...

the one I just put in was a new AC Delco. It seems to have fixed the problem. I had tried this same bore MC before, can’t remember if it was new or rebuilt, but the threads for the brake lines were all jacked up. I could never get it to bench bleed and it leaked when it was on truck.
 
trukman1 said:
Did you purchase an BRAND NEW M/C? I once put a rebuilt M/C on my '67 K30. Ended up replacing three times under warranty. Finally purchased a brand new unit (only $10 more) and no problems. Several mechanics explained to me the bore that the piston moves in wears and the rebuilt units simply get new seals and allow the piston to "cock" in the bore causing failure to hold fluid pressure. Mine happened while driving, would suddenly have no brakes. New M/C fixed problem. May not be your issue but I learned NEVER buy re-manufactured brake components, EVER! Good luck with your fix.
Click to expand...
I try getting new everything now that I know they cost the same or a few bucks more yet they last 5 times more
 
Only "good" rebuilt master cylinders are the ones that were sleeved,but nowadays its cheaper to have a new one cast in China...
I had many rebuilt master cylinders get returned either right after purchase due to not being able to hold a pedal or stay bled in the past during my parts counterman days..
 
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