Effing Continued Effing Brake Effing Issues

[NC Tom]

Well over a month now dealing with this garbage and I have another question. What is typical break pedal travel?

 

Replaced: MC, Booster, Calipers, Cylinders, Front Pads, Line in the back. The system has been bled several times.

Pedal started out good this morning with little travel before engaging, but this afternoon it's drops quickly to 1-2" from the floor. It does stop, but I am assuming that the extended travel is NOT normal.

 

Please help! I've lost countless hours, 1K in cash, my wife and my dog are giving me the "stink eye", and I have a rash on my . . . never mind.

[Limeyjeeper]

Bleeding a Comanche brake system is one of the most infuriating things you can do, Keep bleeding. If you have no leaks, (including a booster vacuum leak) it has to be air in the system. Passenger rear first, then driver rear, passenger front, driver front. Keep doing it until the pedal hardens. I have had Comanches where it took many attempts to get the pedal firm. Just is what it is.

[eaglescout526]

How new are your front rubber lines? The older they get, the less pressure they can handle. 

[Pete M]

47 minutes ago, Limeyjeeper said:

Bleeding a Comanche brake system is one of the most infuriating things you can do, Keep bleeding. If you have no leaks, (including a booster vacuum leak) it has to be air in the system. Passenger rear first, then driver rear, passenger front, driver front. Keep doing it until the pedal hardens. I have had Comanches where it took many attempts to get the pedal firm. Just is what it is.

 

that's only half the bleeding procedure for an MJ.  getting that emergency line bleed can be a real pain.

[howeitsdone]

Adjusting the rear shoes was key for me. Once those were tightened, it became a lot better. I didn't know there was a Comanche procedure for the bleeding though. I bled clockwise from the driver. I pumped the pedal a few times and then applied hard pressure while someone bled at the wheel. Probably took 4 or 5 times average per wheel. When I got to the passenger rear it took a few more, like 8-10 times because we were also adjusting the shoes and the pedal still wasn't quite right.

Still travels a bit to stop and I'm not going to lock up the wheels no matter how hard I press, but they work fine.

[cruiser54]

Adjust the rear shoes for sure. 

[watchamakalit]

Always start bleeding at the furthest point from the master cylinder.  If you still have a rear proportioning valve on the rear diff, the only way you will successfully bleed the system is to follow the MJ specific procedure.  Any other method will result in trapped air in the system. 

[Eagle]

5 hours ago, watchamakalit said:

Always start bleeding at the furthest point from the master cylinder.  If you still have a rear proportioning valve on the rear diff, the only way you will successfully bleed the system is to follow the MJ specific procedure.  Any other method will result in trapped air in the system. 

 

No matter how many times this is repeated -- people still don't want to believe it.

[gogmorgo]

Because it hasn’t been mentioned yet, the MJ-specific procedure on a factory system is to open one of the front bleeders and leave it open while bleeding the rear, then closing the front bleeder, bleeding the rear again, then bleeding the front.

This simulates a front brake failure, shuttling the valve and sending fluid through the prop valve bypass to bleed it out. If the bypass isn’t bled out, you’ll just compress any air bubbles in it instead of building pressure in the main system. The second rear bleed with the front bleeder closed then bleeds out the regular service pathway through the proportioning valve.

 

 

Something else to watch is to make sure the linkage on the rear axle is hooked up correctly. The rod hooked to the diff cover should be vertical, the bar on the valve should be pointed just above horizontal. I don’t know how or why, but they do sometimes over-centre, or the rod goes missing, and your brakes will be horrific with the valve pointed straight down and dangling. If ride height has been changed, the length of the vertical rod needs changed the same amount. It’s also reasonable to tie the bar in position and leave it disconnected from the axle, although then you won’t benefit from the load sensitive proportioning, not really a huge concern if you’re not hauling heavy loads.

[youngfred]

3 hours ago, gogmorgo said:

Because it hasn’t been mentioned yet, the MJ-specific procedure on a factory system is to open one of the front bleeders and leave it open while bleeding the rear, then closing the front bleeder, bleeding the rear again, then bleeding the front.

This simulates a front brake failure, shuttling the valve and sending fluid through the prop valve bypass to bleed it out. If the bypass isn’t bled out, you’ll just compress any air bubbles in it instead of building pressure in the main system. The second rear bleed with the front bleeder closed then bleeds out the regular service pathway through the proportioning valve.

 

 

Something else to watch is to make sure the linkage on the rear axle is hooked up correctly. The rod hooked to the diff cover should be vertical, the bar on the valve should be pointed just above horizontal. I don’t know how or why, but they do sometimes over-centre, or the rod goes missing, and your brakes will be horrific with the valve pointed straight down and dangling. If ride height has been changed, the length of the vertical rod needs changed the same amount. It’s also reasonable to tie the bar in position and leave it disconnected from the axle, although then you won’t benefit from the load sensitive proportioning, not really a huge concern if you’re not hauling heavy loads.

...

 

 

 

The e-brake Light on the Dash should come *ON while

bleeding the rear and then go OFF, when AFTER

bleeding the front, correct ?

 

*(with key ON)

 

 

youngfred

[Eagle]

29 minutes ago, youngfred said:

The e-brake Light on the Dash should come *ON while

bleeding the rear and then go OFF when bleeding

the front, correct ?

 

 

Probably not. The warning light comes on when you open a front bleeder to simulate a front brake failure, and it usually stays on throughout the rest of the bleeding procedure. Once you have finished bleeding, you have to stomp on the brake peddle a couple/few times to reset the shuttle valve and turn off the light.

[youngfred]

3 minutes ago, Eagle said:

 

Probably not. The warning light comes on when you open a front bleeder to simulate a front brake failure, and it usually stays on throughout the rest of the bleeding procedure. Once you have finished bleeding, you have to stomp on the brake peddle a couple/few times to reset the shuttle valve and turn off the light.

...

 

 

'Stomp' - is useful,

sometimes.

 

 

youngfred

[zomeizter]

16 hours ago, youngfred said:

...

 

 

'Stomp' - is useful,

sometimes.

 

 

youngfred

If you don't "stomp" correctly the light shall remain on...

[Eagle]

These images may help explain how the MJ rear brake emergency bypass circuit works.

 

Normal operation:

 

 

Bypass operation:

[NC Tom]

Thanks for all the information. It's at a shop now. They are struggling as well. This is truly unbelievable!

[Eagle]

51 minutes ago, NC Tom said:

Thanks for all the information. It's at a shop now. They are struggling as well. This is truly unbelievable!

 

Do they know how to bleed the rear bypass circuit? If they don't follow the procedure, they'll never get a solid peddle.

[NC Tom]

1 hour ago, Eagle said:

 

Do they know how to bleed the rear bypass circuit? If they don't follow the procedure, they'll never get a solid peddle.

 

Not sure, so I sent it to them just in case. It's hard talking to a mechanic with a lot of experience. They get kind-of belligerent if they think you're trying to tell them their business.