GreasemonkeySC Posted June 4, 2018 Share Posted June 4, 2018 I just picked up this 92 MJ 4.0 5spd SB 2wd from a meth head hillbilly a week ago. Of course he lied extensively about what had been fixed. Thankfully I didn't pay much, and there's no rust on it! I'm a retired auto tech, but totally new to MJ's. I have 3 wranglers in the driveway, and I got the MJ to become my daily driver! Brakes are the important issue to deal with first. So here we go... While driving I randomly start to feel resistance against the drivetrain, then can smell the hot brakes. It's evenly across the front brakes, no rear interaction that I can tell. Let it cool, and can drive on for a few miles, or hours, it's random. The previous owner apparently had an issue as well because upon inspection it has a shiney new set of rotors, pads, calipers, hoses, and master cylinder. I removed the calipers to check them, and they collapsed easily, pushed fluid back to the master cylinder resivoir with no issue. Fluid is all clean & clear, though I bled the system anyway, and filled with fresh fluid. Any ideas? My mode door in the HVAC air box is stuck on defrost. I'm fairly sure it's going to be the vacuum actuator, as the vacuum lines aren't showing any leaks. I'm not sure where the mode actuator is located. I always like to test the part before I just think I have it narrowed down. I've seen stuff get down in an air box and jam up the doors. Techs have cost customers big $$$ only to find a $.25 Bic pen holding a blend, or mode door from moving! I've searched online, but I get mixed results. If someone could point me to the mode door actuator..... Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 4, 2018 Share Posted June 4, 2018 I once had intermittent front brake drag and squealing that was caused by reversed caliper pads. 91-92 2WD's w. the combo rotor hub/disk use an inboard and outboard pad that are easy to install backwards. I know - I did it. HVAC sticking on defrost is usually caused by a cracked vacuum line up near the right front bulkhead where the hard plastic vacuum line passes through to the vacuum canister. The vacuum canister (round ball or football) is located behind the right front bumper. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 4, 2018 Author Share Posted June 4, 2018 I once had intermittent front brake drag and squealing that was caused by reversed caliper pads. 91-92 2WD's w. the combo rotor hub/disk use an inboard and outboard pad that are easy to install backwards. I know - I did it. HVAC sticking on defrost is usually caused by a cracked vacuum line up near the right front bulkhead where the hard plastic vacuum line passes through to the vacuum canister. The vacuum canister (round ball or football) is located behind the right front bumper. I noticed the pads right off. The set I just installed are slightly different inboard & outboard. You can't get an outboard pad on the inner mount. It won't fit.The vacuum system checks out, no leaks. I'm just not familiar with an MJ, so I was wanting some directions to the location of the mode actuator. I've seen them rusted in place, or disconnected if someone has been tinkering previously. I want to put hands on the actuator, and test it directly before I order a replacement. Link to comment Share on other sites More sharing options...
Jeep Driver Posted June 4, 2018 Share Posted June 4, 2018 Check the slides for the brake pads they will wear in an indention get stuck there and not relax The way to fix is fill with weld Link to comment Share on other sites More sharing options...
DesertRat1991 Posted June 4, 2018 Share Posted June 4, 2018 16 minutes ago, GreasemonkeySC said: The vacuum system checks out, no leaks. I'm just not familiar with an MJ, so I was wanting some directions to the location of the mode actuator. I've seen them rusted in place, or disconnected if someone has been tinkering previously. I want to put hands on the actuator, and test it directly before I order a replacement. The problem you describe is almost always a vacuum leak. I wonder how you verified that the vac system was sound? The HVAC check valves prevent leaks in the HVAC vac lines from compromising engine vacuum. Did you inspect every inch of the line in the diagram below? I would also recommend pulling out the blimp and inspecting all sides for cracks. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 4, 2018 Share Posted June 4, 2018 43 minutes ago, GreasemonkeySC said: I noticed the pads right off. The set I just installed are slightly different inboard & outboard. You can't get an outboard pad on the inner mount. It won't fit. Yes you can. Quite easily in fact depending on the manufacturer. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 4, 2018 Author Share Posted June 4, 2018 Check the slides for the brake pads they will wear in an indention get stuck there and not relax The way to fix is fill with weld Checked those while I was replacing pads. No issue there. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 4, 2018 Author Share Posted June 4, 2018 Yes you can. Quite easily in fact depending on the manufacturer. No, you miss understood.The pads I just put on are manufactured with the design that can not be improperly placed on the inboard & outboard.So that's not the issue. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 4, 2018 Share Posted June 4, 2018 3 minutes ago, GreasemonkeySC said: No, you miss understood. The pads I just put on are manufactured with the design that can not be improperly placed on the inboard & outboard. So that's not the issue. Interesting. What pads did you use? Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 4, 2018 Author Share Posted June 4, 2018 The problem you describe is almost always a vacuum leak. I wonder how you verified that the vac system was sound? The HVAC check valves prevent leaks in the HVAC vac lines from compromising engine vacuum. Did you inspect every inch of the line in the diagram below? I would also recommend pulling out the blimp and inspecting all sides for cracks. I removed the line before & after the check valves, capped the intake end, and tested the system with a gauge & vacuum pump. Then tested the system with the truck running to verify that it was getting sufficient inches of mercury to operate properly.Like I said. I'm a retired auto tech. I have tools, and basic knowledge of vehicles, but not MJ's in specific. I'm waiting on brown Santa to bring my FSM, but until then I thought I might get lucky and find out that there's some querk to the brake problem, and find a definite location on the mode actuator so I can test it directly. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 4, 2018 Author Share Posted June 4, 2018 Interesting. What pads did you use? My son brought me brake best pads. I asked for cheap pads... So while diagnosing & repairing this problem I'm not destroying good pads. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 4, 2018 Share Posted June 4, 2018 Just now, GreasemonkeySC said: 5 minutes ago, HOrnbrod said: Interesting. What pads did you use? My son brought me brake best pads. I asked for cheap pads... So while diagnosing & repairing this problem I'm not destroying good pads. The best brake pads? They must have been Mopar then. Or maybe Brembo. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 4, 2018 Author Share Posted June 4, 2018 The best brake pads? They must have been Mopar then. Or maybe Brembo. They came from oreilly.Brake Best Select brand. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 4, 2018 Share Posted June 4, 2018 1 hour ago, GreasemonkeySC said: They came from oreilly. Brake Best Select brand. Ah - okay. When I had that mounting problem years ago I used the mid-range Wagner pads from Oreilly's. You could mount those either way. I don't see them anymore on their site; they were about the same cost and their house brand. I got rid of them later and went with some ceramics from Autozone. Those pads could only mount up the correct way. I really like them; no noise and no dust. Link to comment Share on other sites More sharing options...
Eagle Posted June 4, 2018 Share Posted June 4, 2018 6 hours ago, Jeep Driver said: Check the slides for the brake pads they will wear in an indention get stuck there and not relax The way to fix is fill with weld ^^^ Agree Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 7, 2018 Author Share Posted June 7, 2018 Update:::Brake issue is repaired.A friend ask if I had a pedal free play adjustment. While checking if there was an adjustment, I noticed there was no free play in the pedal. I found the brake switch causing the issue.The previous owner had apparently bent the bracket where the brake switch attached. It was depressing the pedal only a fraction of an inch. It was apparently enough to move fluid, and as the brake calipers heated the fluid expanded, causing the pressure to increase.I bent the bracket back to its proper position, and no more excess brake drag. Link to comment Share on other sites More sharing options...
coolwind57 Posted June 7, 2018 Share Posted June 7, 2018 On 6/4/2018 at 12:50 PM, Jeep Driver said: Check the slides for the brake pads they will wear in an indention get stuck there and not relax The way to fix is fill with weld On 6/4/2018 at 7:20 PM, Eagle said: ^^^ Agree I had heard about this before but I am struggling to picture it. The "U" channels on the tops and bottoms of each pad assembly slide across it's mating "rail" on the Jeep. Its this rail that wears down or something? Tried to find a pic here on the site with no success. If my description is accurate, then would that make only the inboard pad assembly the one sticking? Though rare, I have experienced this issue on occasion. I lubricated my rail with some anti-seize and I just replace my front brake hoses two days ago, so I'm still waiting to see if that took care of it. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 8, 2018 Author Share Posted June 8, 2018 I had heard about this before but I am struggling to picture it. The "U" channels on the tops and bottoms of each pad assembly slide across it's mating "rail" on the Jeep. Its this rail that wears down or something? Tried to find a pic here on the site with no success. If my description is accurate, then would that make only the inboard pad assembly the one sticking? Though rare, I have experienced this issue on occasion. I lubricated my rail with some anti-seize and I just replace my front brake hoses two days ago, so I'm still waiting to see if that took care of it. Found a pic.Yes it's usually the inboard side that wears because the majority of stress & motion is on the inboard pad from the caliper piston.I've had to fix my TJ twice in 135k. Link to comment Share on other sites More sharing options...
Eagle Posted June 8, 2018 Share Posted June 8, 2018 One other possibility. If the previous owner got the wrong calipers, they may be hanging up. There were some changes within the MJ years, and you can't mix and match from one year to another without knowing what parts work with what other parts. This is what I came up with for the book I started to write. It's copyrighted, so please do not give out copies of it beyond this forum. Quote In general, the parts to be concerned with in keeping the front brakes compatible are the steering knuckles, the hub/bearing assemblies, the rotors, and the calipers. (There is a more complete enumeration of the interrelationship of these parts in Chapter 6, Axles.) Only two steering knuckle designs were used: 1984 through 1989, and 1990 through 2001. Left and right side knuckles are different part numbers within each group. Three different hub/bearing units were used. The hub/bearing units are the same for both sides of the vehicle. The different years for hub/bearing assemblies were: 1984 through 1989; 1990 through mid-1999 (composite rotors); and late-1999 through 2001 (cast rotors). Three rotor types were used: 1984 through 1989; 1990 through mid-1999 (composite); and late-1999 through 2001 (cast). Only two caliper types were used: 1984 through 1989, and 1990 through 2001. Left and right side calipers are different part numbers within each group. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted June 10, 2018 Author Share Posted June 10, 2018 One other possibility. If the previous owner got the wrong calipers, they may be hanging up. There were some changes within the MJ years, and you can't mix and match from one year to another without knowing what parts work with what other parts. This is what I came up with for the book I started to write. It's copyrighted, so please do not give out copies of it beyond this forum. In general, the parts to be concerned with in keeping the front brakes compatible are the steering knuckles, the hub/bearing assemblies, the rotors, and the calipers. (There is a more complete enumeration of the interrelationship of these parts in Chapter 6, Axles.) Only two steering knuckle designs were used: 1984 through 1989, and 1990 through 2001. Left and right side knuckles are different part numbers within each group. Three different hub/bearing units were used. The hub/bearing units are the same for both sides of the vehicle. The different years for hub/bearing assemblies were: 1984 through 1989; 1990 through mid-1999 (composite rotors); and late-1999 through 2001 (cast rotors). Three rotor types were used: 1984 through 1989; 1990 through mid-1999 (composite); and late-1999 through 2001 (cast). Only two caliper types were used: 1984 through 1989, and 1990 through 2001. Left and right side calipers are different part numbers within each group. Was that for my issue, or in reply to "coolwind" ?My issue is fixed! Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted July 19, 2018 Author Share Posted July 19, 2018 So I still got the issue, and here's what I found. Link to comment Share on other sites More sharing options...
MJCARENA Posted July 19, 2018 Share Posted July 19, 2018 Looks like your missing the bushing and clip. Kind of scary if the rod pops out the brake pedal arm. Maybe the master is bad, even though you say it looks new. (could be a low quality rebuilt unit). The piston assembly not returning all the way and blocking the fluid return hole. Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted July 19, 2018 Author Share Posted July 19, 2018 Looks like your missing the bushing and clip. Kind of scary if the rod pops out the brake pedal arm. Maybe the master is bad, even though you say it looks new. (could be a low quality rebuilt unit). The piston assembly not returning all the way and blocking the fluid return hole. I removed the clip so I could see to make the video, and there is no bushing that goes there. It's suppose to fit snug. Link to comment Share on other sites More sharing options...
zomeizter Posted July 19, 2018 Share Posted July 19, 2018 For some reason I cannot watch your video, I only hear sound. I went through a situation like yours and it was resolved by adjusting the push rod in between the MC and vacuum booster, check it out... Link to comment Share on other sites More sharing options...
GreasemonkeySC Posted July 19, 2018 Author Share Posted July 19, 2018 For some reason I cannot watch your video, I only hear sound. I went through a situation like yours and it was resolved by adjusting the push rod in between the MC and vacuum booster, check it out... Here's a pic.The push rod has a gap of 1\8" to the pedal stud. I looked at the export model bushing, but it's paper thin, not nearly enough to fill the gap. Link to comment Share on other sites More sharing options...
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