Brake line woes Really need ideas

[KYMJ]

Busted through a brake line yesterday making a panic stop. Replaced lines yesterday. CANNOT get my pedal back. Bled brakes mutiple times including the procedure for the load sensing thingie posted by Eagle. Replaced M/C, something seemed amiss with it. But, still the same. I'm at a loss, any suggestions?

[KYMJ]

Do you bleed the by-pass at the tee or the dist. block? I bled it at the rear. This really has me stumped.

[KYMJ]

Only thing I can figure out is the piston is stuck in the distibution valve. I'm just pissin' in the wind and deader than a doornail. Don't reckon I can bypass it with the piston stuck or unstick it? The new line going to the rear sensing valve screams bloody murder when you pump up the brakes. I can honestly say I've never seen anything like this and I'm absolutely stumped. Valve not available so I'll have have to find a used one.

[Eagle]

Only thing I can figure out is the piston is stuck in the distibution valve.

If it is, the brake warning light will be on. Is it?

 

The new line going to the rear sensing valve screams bloody murder when you pump up the brakes.

Translation?

[maddzz1]

Have you checked the wheel cylinders?

[KYMJ]

Brake warning light is not on. It works however when thr parking brake is on. According to your bleed instructions: open a caliper bleeder apply brakes-light should come on. Never did.

 

The line literally squeels loudly when pumping on the brakes during bleeding. Had me stumped until I held the line and it muffled the noise somewhat.

 

I checked the wheel cylinders.

 

I replaced the M/C, because it leaked afterr bench bleeding, don't remember one doing that. Also when checking fluid after bleeding, there is a mini gusher in the front resevoir and it fills back up a little. So, I thought It might have blown the seals, evidently not. Still the same.

 

Something happened other than blowing a hole in the steel line, but I haven't a clue. I know the lines aren't crossed, I did one at a time. The only reason I did both is because of them running behind the tank.

 

 

Details of failure. Light turns yellow as I approach. I slam on brakes to catch the red light. Pedal goes to floor. I coast through light, luckily as it turns red. Consider getting tow truck. Short distance to home, luckily back road, no cars and emergency brake working now, so I decide to nurse it home. Go slow enough that engine brakeing, minimal hyd braking gets me home. Get ride to Oreillys and bring home enough steel line and rented flaring tool to replace brake lines. Atempt to bleed brakes like I've done many times on both my Comanches(never used the FSM procedure you posted). Never get a "pedal". I've gone through 3 qts of fluid. Finally give up.

[Eagle]

Which line blew out? If you replaced the lines to the rear, it sounds like that's what you think blew out. You should have still had a slightly low pedal, but about 70 percent braking, because the fronts should have still worked, and they do most of the work. I drove my red MJ on front brakes only for more than 6 months until I figured out what was going on with the dual lines to the rear (and that in addition to a line I had also blown out the rear height sensing valve). Heck, if your height sensing valve works correctly and you don't have a load, you are essentially driving on front brakes only all the time.

 

So if you had NO brakes after something blew -- you blew more than just one line to the rear.

[KYMJ]

The one I found the hole on was the line going to the sensing valve. It had the bigger nut that I had to cut the new line and double flare. The other one goes to the "tee". Pretty sure that was the only one leaking, But as soon as I saw how the lines were routed I was going to replace them both, (that is my usual habit) before I had to replace the other in the future.

 

The pedal bottomed out after the blowout, and still does. I want to say I had maybe 20%(if that) braking on the way home.

 

The best thing I can think of now is to plug the front outlet of the dist. block and run the other line I replaced, which would be the one connected to the bottom hole front of Dist.block, to the rubber line to the rear brakes. Thats from my searching today, believe me, my head is spinning. Is that the procedure for bypassing the load sensing valve? I've got to start somewhere. I have no spare vehicles anymore.

 

Edit: I know the line blew 1. Fluid in vicinity of hole in line.

2. I found the hole. 3. I can find no evidence of other leaks.

so, I know that for sure, just not what happened after that.

[Eagle]

The best thing I can think of now is to plug the front outlet of the dist. block and run the other line I replaced, which would be the one connected to the bottom hole front of Dist.block, to the rubber line to the rear brakes. Thats from my searching today, believe me, my head is spinning. Is that the procedure for bypassing the load sensing valve? I've got to start somewhere. I have no spare vehicles anymore.

I would second eliminating the height sensing valve. Mine exploded in a panic stop just like yours.

 

However, you have the wrong outlet. Plug the forward outlet on the bottom on the metering block, run the hard line from the front ("nose") outlet directly to the rear flex hose.

[KYMJ]

Gotcha. Thanks. Thats what I'll be doing tommorow, provided I can find a plug in this town. I don't like the idea of not having the bypass feature, but I need to start somewhere eliminating stuff.

[Eagle]

Gotcha. Thanks. Thats what I'll be doing tommorow, provided I can find a plug in this town. I don't like the idea of not having the bypass feature, but I need to start somewhere eliminating stuff.

You don't understand how the brakes work. That rear height sensing valve reduces the amount of braking to the rear wheels when the back is not loaded. As load drops the bed down, the valve opens up and allows more braking force to the rear wheels. The most it can possibly allow is 100% of what would be available if the valve weren't there.

 

And that's exactly what you get when you eliminate the height sensing valve. You get the maximum possible braking to the rear wheels at all times.

 

The safety redundancy in the brakes is the separate front and rear circuits. If your front brakes fail, you (theoretically) still have the rears. If the rear brakes fail, you theoretically still have the fronts. But if the fronts failed when the truck wasn't loaded, with the rear heightsensing valve reducing most of the braking to the rear you would have essentially no brakes -- which is why they built in the bypass. If you eliminate the height sensing valve, you have the same condition as a bypass condition if your front brakes fail.

 

The plug you need is a 1/2" SAE fine thread bolt, the shortest one you can find. I cut mine down enough that with a gob of RTV on the end and a 1/2" O-ring under the head, the O-ring and the RTV both seat at the same time so I have a double seal. The actual length of thread I had left was about 3/8" IIRC, but that's approximate.

[KYMJ]

Well, I've bypassed the valve in the rear, and I seem to have some pedal. I have to route another line to the rubber line that satisfys me and bleed the brakes. I'm not feeling too well at the moment and it will have to wait a little while.

 

Hopefully, I'll report back that all is well and be thanking you Eagle. Evindently I had a failure of the valve during the stop. Wish I had a dollar for every time you posted about the load sensing valve I turned up while searching, ha ha.

[KYMJ]

I'm back on the road thankfully. I had pedal again after installing the last line and I had to do some bleeding. Drove for a short distance and I don't think I'll have a problem with the rears locking up. I was prepared to order an adjustable prop valve, but I'll wait awhile. I only got it to lock up 1 time and it was really an effort. I appreciate the help Eagle. I'm still clueless about this thing and what could have gone wrong. Maybe I'll find a breakdown of the guts of this load sensing valve to help me understand. :cheers: