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Thread: brakes giving me fits

  1. #1
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    Default brakes giving me fits

    so basic info: im trying to finish up my 94 YJ build and the brakes are not cooperating

    I have a dual diaphragm booster and master from a grand cherokee I think, bought an adjustable proportioning valve and plumbed it all in to the chevy metric calipers that are on the axles., yes the calipers are installed

    correctly all is well, no leaks etc. I have held and bled and bled these things to include bench bleeding the master a few times but I cannot for the life of me get a good pedal

    got it better when the jeep is off, but when its running the pedal is very soft still. I will say that I have a sneaking suspicion that there's still air in there somewhere but I have no clue how to

    get it out, pedal has gotten a bit better but i think I cycled 3-4 bottles of fluid through the last time I bled so I doubt its in the lines.

    any tricks you fine folks can help me with?

    offending vehicle...looks really cool sitting in the garage
    3BDC3685-0EA4-495A-8106-31B0248BC3E5.jpg
    Last edited by redneckboarder12; 02-27-2021 at 06:36 AM.
    jon
    some parts to build a YJ buggy
    "look at life through the windshield not the rear view"

  2. #2
    Rubicon's Avatar
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    Question

    Brand new booster?
    ABS or non?
    Are you running stainless steel braided brake lines or rubber?
    Did you bench bleed the calipers? Did you start with the caliper pistons all the way in?
    Is the master cylinder reservoir at the highest point?
    If so, are you leaving the reservoir cap off overnight so any air bubbles and/or cavitation in the fluid can escape/float upwards to get out?
    How are you bleeding? Reverse, vacuum, pushing from reservoir with adapter, jar method by yourself, or old school manual method with help from a friend?
    Traction, articulation, and gearing make a good off-road rig. Just a tall lift, big mud tires, winch, and a light bar simply do not.
    Why buy a Wrangler if you don't take the top and doors off?
    ~Shawn(the correct spelling ;)

  3. #3
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    Quote Originally Posted by Rubicon View Post
    Brand new booster?
    ABS or non?
    Are you running stainless steel braided brake lines or rubber?
    Did you bench bleed the calipers? Did you start with the caliper pistons all the way in?
    Is the master cylinder reservoir at the highest point?
    If so, are you leaving the reservoir cap off overnight so any air bubbles and/or cavitation in the fluid can escape/float upwards to get out?
    How are you bleeding? Reverse, vacuum, pushing from reservoir with adapter, jar method by yourself, or old school manual method with help from a friend?
    no abs

    brand new booster and master

    ive bench bled calipers exactly 0 times in my life and have had the same amount of issues

    resivoir is highest

    left cap off for like a week and it did improve

    doing the ol have a buddy press and i open/close bleeders
    jon
    some parts to build a YJ buggy
    "look at life through the windshield not the rear view"

  4. #4
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    Default

    I didnít think YJs went fast enough to need brakes? Just let off the gas and it comes to a stop?
    Paul (FSHJNKY)

  5. #5
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    Question

    Quote Originally Posted by redneckboarder12 View Post
    no abs
    brand new booster and master
    ive bench bled calipers exactly 0 times in my life and have had the same amount of issues
    resivoir is highest
    left cap off for like a week and it did improve
    doing the ol have a buddy press and i open/close bleeders
    The push and the buddy method are my preferred choices, so you should be good there Jon.

    I have seen some stubborn air pockets behind the pistons of some calipers. And you did state that they were Chevy, so there you go :p

    Swelling rubber soft/flex lines?
    Any weird rises in the hard lines that drop back down, or unnecessary loops?
    Maybe a faulty/defective booster and/or master? Do you have the correct rod length to actuate the master properly?
    Traction, articulation, and gearing make a good off-road rig. Just a tall lift, big mud tires, winch, and a light bar simply do not.
    Why buy a Wrangler if you don't take the top and doors off?
    ~Shawn(the correct spelling ;)

  6. #6
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    Default

    Quote Originally Posted by Rubicon View Post
    The push and the buddy method are my preferred choices, so you should be good there Jon.

    I have seen some stubborn air pockets behind the pistons of some calipers. And you did state that they were Chevy, so there you go :pA Chevy must mean it works the first time...

    Swelling rubber soft/flex lines?
    Any weird rises in the hard lines that drop back down, or unnecessary loops?
    Maybe a faulty/defective booster and/or master?
    Do you have the correct rod length to actuate the master properly? This check that measurement
    ...
    An armed society is a polite society.

  7. #7
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    Quote Originally Posted by FSHJNKY View Post
    I didnít think YJs went fast enough to need brakes? Just let off the gas and it comes to a stop?
    This one has a 5.3LS... itís kinda quick

    Iíll see if I can get measurements for the pushrod. I have a buddy dropping off a vacuum bleeder tomorrow so Iíll see if that helps...
    jon
    some parts to build a YJ buggy
    "look at life through the windshield not the rear view"

  8. #8
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    Didn't know it was a swapped engine job.are you drawing good vacuum from the ls engine,would a hydro-boost system be better?
    An armed society is a polite society.

  9. #9
    cda's Avatar
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    Quote Originally Posted by agent smith View Post
    Didn't know it was a swapped engine job.are you drawing good vacuum from the ls engine,would a hydro-boost system be better?
    5.3 should have plenty of vac for a regular booster.

    if there's a chance the calipers have air trapped in them you can always pull them and shove a block of wood in and orient the bleeder absolutely up. Otherwise I'd agree with the rod length line of questioning, that's a solid place to double check.

  10. #10
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    Default

    Sounds like the caliper volume is much larger than the master. Also a common problem with swapping front calipers to a rear position. With the stock XJ boater and master WJ fronts and 8.8 rears the brakes are one of my favorite things when driving it. WAY better than my 2006 Tacoma.

    Itís a balancing act with volume and is easy to get out of hand with.
    Last edited by Mach2NH; 03-03-2021 at 08:19 AM.
    97 Jeep XJ Trussed/gusseted D30,Ford 8.8,locked F/R with Moly shafts and 4.56s,Stock 4.0 with a NVG241OR Rock-trac,5.5" long arm, full under armor, OBA, 35x12.5-15.

    NEA

  11. #11

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    Quote Originally Posted by cda View Post
    5.3 should have plenty of vac for a regular booster.

    if there's a chance the calipers have air trapped in them you can always pull them and shove a block of wood in and orient the bleeder absolutely up. Otherwise I'd agree with the rod length line of questioning, that's a solid place to double check.
    Too add to this, the GM calipers can be mounted on either side. A left will fit the right and a right will fit the left.
    The only issue is the bleeders will be at the top if on the correct side and not at the top if mounted on the wrong side. If DIY/aftermarket caliper brackets were added maybe they don't hold the caliper in a position where the bleeder is high enough to be effective?? In that case the block 'O wood trick would get that last bit of air out.

  12. #12
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    Quote Originally Posted by Rubicon View Post
    The push and the buddy method are my preferred choices, so you should be good there Jon.

    I have seen some stubborn air pockets behind the pistons of some calipers. And you did state that they were Chevy, so there you go :p

    Swelling rubber soft/flex lines?
    Any weird rises in the hard lines that drop back down, or unnecessary loops?
    Maybe a faulty/defective booster and/or master? Do you have the correct rod length to actuate the master properly?

    This might be the ticket! The bleeders on the rear calipers arenít at the top of the ďplaneĒ if you will... they are higher than the banjo bolts but if Iím remembering correctly they are below the top of the piston.... I will update with findings!
    jon
    some parts to build a YJ buggy
    "look at life through the windshield not the rear view"

  13. #13
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    Default

    well the pedal is still a bit soft and the prop valve needs to be adjusted but she stops pretty damn good

    now onto the next problems: power steering seems to be caveating pretty bad, was bled properly, no leaks on suction side that I can find, all fittings are nice and snug, happens in 2 and 4 wd, seems to be worse when locked in 4wd (as per usual) im thinking the pump might just be bad from sitting for so long without oil.

    also the speedo only reads up to about 20 mph. vss from 4l60 to LS computer/autometer speedo, thats a problem ill have somebody who knows the wiring/engine swap stuff MUCH better than myself
    jon
    some parts to build a YJ buggy
    "look at life through the windshield not the rear view"

  14. #14
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    Lightbulb

    Ya pump or reservoir not large enough(capacity wise), which could also cause cavitation.

    As for the speedo, there has got to be a programmer to fix that?
    Traction, articulation, and gearing make a good off-road rig. Just a tall lift, big mud tires, winch, and a light bar simply do not.
    Why buy a Wrangler if you don't take the top and doors off?
    ~Shawn(the correct spelling ;)

  15. #15
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    Quote Originally Posted by Rubicon View Post
    Ya pump or reservoir not large enough(capacity wise), which could also cause cavitation.

    As for the speedo, there has got to be a programmer to fix that?
    Reservoir is plenty big enough, gonna see if adding a bit of fluid shuts it up first

    Yea idk about the speedo, wonít even dive into that myself, Iím sure josh and Erik can sort it out
    jon
    some parts to build a YJ buggy
    "look at life through the windshield not the rear view"

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