chopper35nj Posted October 8, 2012 Share Posted October 8, 2012 Is there a secret to the Comanche's brakes? I have replaced the master cylinder, brake booster, ALL brake lines and rebuilt the metering valve (new O-rings). The weight sensing valve in the back was deleted by the previous owner so, that isn't an issue. I bench blead the master cylinder before I installed it. I have blead the brakes with 3, count 'em 3 differant methods. (1) reverse blead (2) one man bleader bottle (3) good old fashioned pump, pump, pump....hold crack the valve. Still, no pedal...at all, nada, nuthin............. I am no amature, I have litteraly blead and replaced hundreds of brake systems, it's what I did, I was a mechanic before becoming disabled 2 years ago. I know that this is the most rudimentary of hydrolic systems, no air.....good pedal, air.... poor pedal. I can't find a leak anywhere in the system. OH, one more thing, I started the engine to see if I could get any help from the booster again nothing, but! the engine races when I pump the pedal. In 25 years of turning wrenches I have never encountered anything like this.. It's gotta be somthin' stupid simple and I'm just too close to it. Help me out here PLEASE!!!!!! Thanx Eric Link to comment Share on other sites More sharing options...
Eagle Posted October 8, 2012 Share Posted October 8, 2012 Vacuum leak. Probably a bad booster. Dunno why you can't get a decent peddle with the engine off, though. The rear height sensing valve was removed by a previous owner? What outlet on the front metering block did he retain for the rear circuit, and how did he block off the unused port? The MJ originally had two separate lines from the front to the rear. One fed into the height sensing valve, for normal operation. The other was a bypass line that provided full brake power to the rear wheels if the front circuit failed. A lot of people eliminate the wrong line. Link to comment Share on other sites More sharing options...
chopper35nj Posted October 9, 2012 Author Share Posted October 9, 2012 I'm not getting bad peddle, getting none. Yes the height sensing valve was removed previously, the truck had no working brakes when I got it, that's why I replaced everything. The line on the bottom of the metering block is plugged with a brass plug, the rear line is now feading from the port on the front of the metering block. Any ideas? Thanx Eric Link to comment Share on other sites More sharing options...
Eagle Posted October 9, 2012 Share Posted October 9, 2012 Plugging the bottom outlet and using the "nose" outlet is correct. Only thing I can think of is that the new master cylinder may be defective. Link to comment Share on other sites More sharing options...
chopper35nj Posted October 9, 2012 Author Share Posted October 9, 2012 Wow, Ok I was thinking that port was wrong, You got me thinking when you asked wich was plugged and how, I went out and looked at my daughters XJ and the front is plugged and the bottom one is the one being used. Now I am really confused. lol Thanx Eric Link to comment Share on other sites More sharing options...
mountainman Posted October 9, 2012 Share Posted October 9, 2012 Are the rear shoes adjusted up to where they should be? also.. how much fluid do you get at each wheel when bleeding? May just be the new master is bad as was mentioned. Pretty rare deal but it happens. I like to open all the bleeders..and sit and just pump and pump and pump till all of them are squirting strong. Then i close the fronts and pump some more, then the rears. Then i move to standard bleed procedure. Is the master cyl rod adjusted properly? Hope you get it dialed. Link to comment Share on other sites More sharing options...
Eagle Posted October 9, 2012 Share Posted October 9, 2012 Wow, Ok I was thinking that port was wrong, You got me thinking when you asked wich was plugged and how, I went out and looked at my daughters XJ and the front is plugged and the bottom one is the one being used. Now I am really confused. lol Thanx Eric But the internals are different. The XJ "thingie" is a proportioning valve, with a spring and a plunger in it. The MJ "thingie" is nothing but a distribution block, with a shuttle valve to allow bypassing the rear height-sensing valve in the event of a front brake loss. Link to comment Share on other sites More sharing options...
chopper35nj Posted October 11, 2012 Author Share Posted October 11, 2012 OK, here go's....The master was indead bad, leaking at the rear seal, exchanged it (this is why I don't usualy buy parts from Advance) bench blead it rock hard- no air, installed it, blead the system, good pedal....skip forward 12 hours, no pedal...............WTF. Not a single leak that I can find. The rear shoes are adjusted propperly as I just replaced the parking brake cables and adjusted, adjusters are free and in good shape. I am begining to suspect the metering valve, I took it apart, cleaned it and replaced the O-rings on the shuttle valve. I fear it may be sticking or staying open/closed because the brakes are now inconsistant somtimes they're there, sometimes theyre' not, not real safe. When they are not and I try to pump them up the engine races (vac leak in booster? also reman from Advance), but if I do have pedal and step on the brake no racing so I "think" the booster is good (any thoughts?) When I do have pedal the rear brakes lock up with the slightest pressure. So, here's the question, since the load sensing valve has been removed and the rear wheels are locking up, should I go for the XJ metering valve with the proportioning valve? Seems to like a good idea to me, they are esentially the same vehicle after all. Thanx Eric Link to comment Share on other sites More sharing options...
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