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Ok, so I recently bought a 99 24 valve Cummins. When we purchased it, it needed front brakes rotors and calipers. Also, the rear axle seals were leaking so we change those and the rear drum brakes and drums.

When we got all done putting the brakes on front and back, we bled the system properly. When we took it out for a test drive, the brakes were extremely spongy and I could press them almost all the way down to the floor. After doing some research, we ended up replacing the master cylinder. That did not fix the issue, so we also replaced the hydro booster.

After bleeding both the power steering and the brake system, we took it out for another test run. At first we were sure we had fixed the problem. But after a few minutes of stopping and braking, the brakes started to get extremely hot and we lost breaking abilities. We got it back on the lift, and realized that the front calipers got stuck  in the open position , causing the brakes to rub. At this point, we don't know what to do. 

Any and all advice would be helpful at this point! I gave as much detail as possible but might of forgot something.

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1 minute ago, That Guy said:

Did you replace the front brake lines? Did you bench bleed the master before installing it?

Thanks for the reply!

Brake lines are what I WAS leaning towards on the next thing to replace, but I unscrewed the rear brake line on the master cylinder and then manually pushed the caliper cylinder in and got break fluid where I unscrewed it at. That leads me to believe that the break lines are still good. 

Yes, I did bench bleed MC according to directions that came with it. 

When I have both calipers off I can push one cylinder in and it pushes the other side out. BUT, I can not get BOTH cylinders to push in at the same time.

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1 minute ago, Caleb said:

When I have both calipers off I can push one cylinder in and it pushes the other side out. BUT, I can not get BOTH cylinders to push in at the same time.

 

That would be typical. They are on the same circuit and it is easier to push a cylinder out that to push it back into the master.

 

 

Put the calipers back on the rotors with pads. Pump the brakes a half dozen times. Crack the bleeder screws on the calipers, if any fluid shoots out with considerable flow, bad lines. If it just dribbles out like normal, lines are fine. The hoses will make a one way check valve with higher pressures and flow of fluid that would not be apparent with low pressure.

 

Also ensure the caliper slides are well greased.

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Thanks, I'll try that tomorrow and get back to you if it works.

On a side note, is there a chance that the aluminum box where the break lines and electrical wires go into bad? Could it possibly be clogged or anything? What is it and what does it do? ABS?

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6 minutes ago, Max Tune said:

I agree with guy, I suspect rubber brake lines deteriorated inside. I would replace them all. 

Again, like I said above, I unscrewed the brake line from the master cylinder, and manually pushed the cylinder IN at caliper. And I got fluid coming out of the line that goes into the master cylinder. Wouldn't this mean that the brake lines are clear going both directions? 

I'm guessing the problem is something very simple, I just need to figure it out. Is there possibly a fuse that could be causing this issue?

Edited by Caleb
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55 minutes ago, Caleb said:

Thanks, I'll try that tomorrow and get back to you if it works.

On a side note, is there a chance that the aluminum box where the break lines and electrical wires go into bad? Could it possibly be clogged or anything? What is it and what does it do? ABS?

 

 

Depends..... The one that is about an inch below the master is a sort of trouble indicator/proportioning valve. It has a little spool inside that moves back and forth according to brake flow, that spool can trip the :brake:light indicating an issue with the too much/little flow indicating a leak or something. 

 

It is known in the GM world (maybe here too) for sometimes being an absolute pain to get bled if air gets in it. (My chevy's brakes are a tiny bit spongy, I suspect that the valve in the issue, it will lock up all 4 wheels at 70 so I stopped caring)

 

PTDC0099.JPG.212f32ff14c27f9963824ae43e0051e2.JPG

 

 

If you have RWAL (rear wheel anti lock), you will have another valve thing below it that is the actuator. It is not know to be a bear to bleed. If you have the RWAL, you will also have another proportioning valve above the the rear axle on the driver side frame rail. If the linkage is gone, you likely won't get much fluid to the rears.  (Mine is gone, I tied it up with a wire as a stop gap measure)

fPZlcvU.jpg.d8311764eb3a0aba40d1c27cd2c001fd.jpg

 

 

Neither should be stopped up. I have never seen that happen before, but it is possible that they could stick, though, that is literally the absolute last two things I would replace.

 

 

23 minutes ago, Caleb said:

Again, like I said above, I unscrewed the brake line from the master cylinder, and manually pushed the cylinder IN at caliper. And I got fluid coming out of the line that goes into the master cylinder. Wouldn't this mean that the brake lines are clear going both directions? 

I'm guessing the problem is something very simple, I just need to figure it out. Is there possibly a fuse that could be causing this issue?

 

Not necessarily. you can put literally tons of pressure with a C-clamp, which is what most use to push in calipers. The residual pressure in the calipers could make the brakes drag with very little pressure. Just 20 psi residual would put over 60lbs of clamping force on the brake pads. Considering the system can operate at over 1000psi, 20psi isnt a lot.

Edited by That Guy
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Okay, after sleeping on it last night, I came up with an idea. After we had put the new Hydro booster on, we installed the master cylinder. the master cylinder was about half an inch from contacting the hydrobooster, so we just used the nuts to push it on there the rest of the way. Now that I think about the way we did that, I think the rod from the Hydro booster is keeping the master cylinder open.

If this is correct, why were we not able to push the master cylinder on completely? Or, is that correct?

Edited by Caleb
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The rod is an extension of the brake pedal. It should not prevent install. The master has a pretty heavy spring inside and should push the rod back out. Its not impossible, but you would have a very hard time getting any fluid out of a system that isn't allowing the fluid to return, or fill the cylinder in the master.

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11 hours ago, That Guy said:

The rod is an extension of the brake pedal. It should not prevent install. The master has a pretty heavy spring inside and should push the rod back out. Its not impossible, but you would have a very hard time getting any fluid out of a system that isn't allowing the fluid to return, or fill the cylinder in the master.

I have decided to replace the "new" hydrobooster. The auto parts store is going to take it back as defective. I had two issues with it that could lead back to my stuck calipers. 

#1 the brake pedal would hang down about 1/2 an inch when NOT being used, even when the truck is off.

#2 the rod from the hydrobooster stuck out about 3/8" to far causing me to force it on the master cylinder.

I believe that with the master cylinder being pushed in that small amount, it was enough to not allow fluid back into the master. This in turn caused the calipers to stick.

I'll give an update in a couple days once I receive new hydrobooster and install.

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After doing a Pirate Jack rebuild kit it not hard to rebuild a hydrobooster. Just make sure you have all the time you need and be ready for small parts to drop out too. Took me 3 hours from start to finish on the first one I did. 

 

As for caliper sticking this is because the piston are most likely too big. After time and brake usage the pistons get hot and cool so the brake fluid cakes on the piston making it grow a bit. This is what causes hung calipers. Then the pistons can be removed and cleaned. Then drop check them in the caliper. With all seal out the piston should fall to the bottom without being pushed. If not there is caked brake fluid yet on the piston. 

disassembled-caliper.jpg.319aac3b2ef01f8

 

I would suggest to make sure to change brake fluid every 30k miles. This is bad fluid and needed to be changed after 30k miles. The dark color is from the brake fluid absorbing moisture and starts to oxidize the metals and seals. hence the black tint or color to the fluid. 

used-brake-fluid.jpg.efe31bcd45de7dfed42

 

You should see nice amber color fluid nothing dark in the reservoir.

fresh-brake-fluid.jpg.97ccb5683a976f08cf

Edited by Mopar1973Man
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On 9/1/2020 at 7:39 AM, Caleb said:

Okay, after sleeping on it last night, I came up with an idea. After we had put the new Hydro booster on, we installed the master cylinder. the master cylinder was about half an inch from contacting the hydrobooster, so we just used the nuts to push it on there the rest of the way. Now that I think about the way we did that, I think the rod from the Hydro booster is keeping the master cylinder open.

 

This is very likely your problem.  There is a compensating port in the master cylinder that is immediately blocked on the forward stroke of the piston (stepping on the brake pedal).  This port allows for thermal expansion and contraction of the brake fluid in the brake lines, brake components, and the calipers.  It is operational only when the brake pedal is in the released position and the piston has completely returned.  The compensating port is normally blocked with about 1/8" of forward piston travel.

 

The photo below is a diagram of a generic brake master cylinder.  In this photo the compensating port is called the "inlet" port.

 

196408721_BrakeMasterCylinder.jpg.c62ca89d69ef7f5d83cd12ce08197482.jpg

 

On 8/31/2020 at 5:35 PM, Caleb said:

But after a few minutes of stopping and braking, the brakes started to get extremely hot and we lost breaking abilities

 

The symptoms that you described on your test drive match what would happen if the compensating port is blocked.  Thermal expansion of the brake fluid just from operating the brakes and trapped brake fluid equal dragging brakes.

 

-  John

Edited by Tractorman
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Thanks for the tips and diagram tractorman!

 

Another person stated that they very possibly make a second push rod that is aprox. 5/16 shorter, looking in to that and hoping that should fix the issue. Bty, I had used the old push rod assembly in the new hydrobooster.

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Thank you everyone one for the help!

 

Solution: the push rod between the master cylinder and hydrobooster ended up being 5/16 to long. I talked to a diesel mechanic in my area and they did confirmed that there ARE two different size push rods. This is due to OEM vs. Aftermarket setups. I ended up cutting my original rod down and rounding it off. 

AS OF THIS POINT... brakes are working as they should be. 

As for anyone who runs into to this problem in the future... be sure that when installing master cylinder, it goes on smoothly without any force. Failure to do so will result in the rod pushing the master cylinder in and locking up the brakes!

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On 9/1/2020 at 7:39 AM, Caleb said:

Okay, after sleeping on it last night, I came up with an idea....

 

Some times a good night's sleep does wonders.

 

Glad to hear you are back on the road.

 

- John

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